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Basic Principles of Aboveground GRE Piping System

Written by Anup Kumar Dey in Engineering Materials,Pipeline,Piping Design Basics,Piping Interface,Piping Stress Basics

Glass Reinforced Epoxy Piping or GRE pipes are becoming a popular choice in the piping and pipeline industry due to their many advantages. The present article aims to give some basic principles and cares to be considered at the moment of the draft design of an aboveground GRE pipeline.

GRE pipe and GRP pipe differ in the used resin during bonding the glass fiber. GRE pipe used Epoxy Resin while GRP pipe used Isophthalic Resin. The designer should evaluate if a deeper stress and strain analysis is required for the pipeline, for the supports, and for other bearing structures connected to the pipeline.

Apart from special cases, GRE pipes should be always connected to the bearing structures by means of saddles, made of steel or concrete or of other materials (GRE itself for instance), in order to distribute the loads on a length and on an angle that is able to minimize the stress concentration on the pipe/support contact points.

In nearly all aboveground applications tensile resistant couplings should be used.

Only in the case of well-supported pipelines for non-pressure applications, a non-tensile-resistant system can be used. The forces close to elbows or other singular points such as valves, reducers, or tees, can become relevant.

GRE/GRP Pressure Class Selection

The selection of the GRE pressure class has to be made according to the following loads:

The stress in the hoop direction due to the internal pressure is calculated as shown in Fig. 1:

Hoop Stress and Axial Stress for a GRP Piping System
Fig. 1: Calculation of Hoop Stress and Axial Stress for a GRP Piping System
  • In GRE pipes it is important to always check the axial stress due to internal pressure since the material is anisotropic and the difference of strength in the hoop and axial direction is relevant.
  • The sum of stresses due to the above loads, calculated in the hoop and axial direction, has to be lower than the allowable stresses, defined for each pipe class or by a specific job.
  • Approximate values for allowable stresses for a common filament wound pipe for above-ground use are 50 Mpa in the hoop direction and 30 MPa in the axial direction.
  • The high working temperature could reduce the allowable stress in the GRP pipe and consequently reduce the pressure class.
  • The Code (AWWA M45) generally considers a 40% tolerance in the allowable stresses in case of transient surge pressure based on the increased strength of fiberglass pipes for rapid strain rates.

Both the following equations (Fig. 2) have to be calculated:

Equations to calculate stresses
Fig. 2: Equations to calculate stresses

Vacuum Design for GRE pipes

The AWWA M45 standards admit a safety factor for vacuum conditions between 1.3 and 3.

For different pressure classes and the same standard pipe (55° filament winding), the approximate relation between pressure class, stiffness, and vacuum resistance is resumed in the following table (Fig. 3).

Vacuum resistance with respect to pressure class and pipe stiffness
Fig. 3: Table showing Vacuum resistance with respect to pressure class and pipe stiffness

For low-pressure pipes with a vacuum, a convenient solution can be either to provide stiffening ribs or a sandwich pipe wall structure with a mortared core.

Thermal Expansion Coefficient of GRE Pipes

The approximate axial coefficient of thermal expansion (α) for a GRP pipe made by filament winding with a winding angle of 55°is:

α = 1.8×10−5  m/m °C

For different GRP pipe classes (with mortar core) or for different winding angles, please consult the GRP Vendor.

The total expansion (or contraction) of a pipe length ( L ) is calculated as:

ΔL =α ⋅ L ⋅ ΔT

ΔT is the temperature gradient (positive or negative) with reference to the installation temperature T0.

The thermal expansion coefficient of GRP has the same magnitude as the steel coefficient (α=1.2× 10-5 °C-1), whilst thermal end loads for restrained expansion are significantly lower since the axial E-modulus of GRP (Ea) is around 1/20th of steels.

The loads applied to expansion joints and to bearing structures are hence considerably lower in GRP pipelines.

Thermal End Loads for GRE pipes

The thermal end load (F) due to constrained expansion is calculated as shown in Fig. 4:

Calculation of end loads for GRP piping for constrained expansion
Fig. 4: Calculation of end loads for GRP piping for constrained expansion

and ID is the internal (nominal) diameter.

The thermal end load due to constrained expansion could be too big for both the stress arising in the pipe and for the load that the bearing structures have to support.

Considering the pipe itself, its elastic stability has to be checked. The pipe’s elastic stability depends on the pipe section, on the E-modulus, and on the span between axial guide supports which is the length of free deflection.

The allowable compressive end load due to instability (Pcr) is calculated as shown in Fig. 5:

Calculation of End load due to Instability
Fig. 5: Calculation of End load due to Instability

When the end loads are too big, they should be reduced by providing the system with anchor points and expansion joints, or better, by operating on the pipeline’s geometry and on the support placement in order to let the line expand where it is not dangerous. Expansion loops can be added to the system where it is possible.

The second solution is preferable since the involved loads and thrusts are much lower than in a similar steel pipeline.

Selection of Anchor Points in GRE Pipeline

Pipe Anchors have to be placed in such a way that pipeline expansions are forced in predetermined directions, in order to balance loads and displacements on the different expansion devices, and to minimize displacements close to dangerous locations, for example in weak branch connections or in connections that are not allowed to move.

Use of Directional Changes or Offsets in GRE Piping

Changes of direction in a pipeline can be used to partially absorb the line’s elongation, when close to an elbow; a branch that is free to expand is available, as shown in the following figure (Fig. 6):

Effect of Direction Changes
Fig. 6: Effect of Direction Changes

The “available bending strength” is considered the remaining strength, after that, all of the other stresses on the pipe have been removed, such as the stresses due to internal pressure.

Clearly, any term of the equation can be obtained once all of the other terms are known, for instance, the length ΔL that can be absorbed can be found when the length of the leg that is available is H.

Expansion Loops for Long GRE Pipelines

“U” expansion loops are provided for long straight pipeline runs, as shown in the figure (Fig. 7) below:

Expansion loop in GRP piping system
Fig. 7: Expansion loop in GRP piping system

The recommended spacing between axial guide supports close to the expansion loop is also shown in the drawing. Other supports shall be spaced following other calculations (beam load).

Use of Expansion Joints in GRE Piping Systems

Various kinds of standard expansion joints can be used. Low-stiffness expansion joints are preferable since they develop a low reaction in correspondence with relatively big displacements. GRE pipes expand more than steel pipes but have much lower thrusts.

Using stiff expansion joints would reduce the stresses in the pipe only by a little

We suggest rubber joints with one or more waves, possibly with limiting travel devices, with an activation load lower than the  Pcr load, and with a working travel equal to the total expansion.

Support Span for GRE Pipes

Horizontal pipes should be supported according to the spacing suggested by the support spacing data or according to a specific project.

A pipe support span is defined as the distance between two consecutive pipe supports or anchoring devices.

The maximum support span/spacing length for every pipe size and class is suggested by the Technical Department of GRP Vendor for standard pipes or according to a specific project.

The span length is limited by the following considerations:

  1. the maximum axial strain must not exceed the allowable value;
  2. the mid-span deflection has to be smaller than 1/300th of the span length and anyway not exceed 15 mm which is the minimum value.

If factor (b) is the determinant factor, then the distance between supports must not be changed by reducing the working pressure.

Often the spacing between the supports is set by other reasons, for instance, joint spacing or existing bearing structures. Normally the 6-meter half-length span is the maximum that is used, even for large-diameter pipe, for which a theoretical longer span could be used. The maximum support span in meters is shown in the following table (Fig. 8), for different pipe sizes and pressure classes:

typical support span for a specific project
Fig. 8: Table showing the typical support span for a specific project

The maximum span has to be evaluated for a continuous span length when the joint can transmit axial loads.

GRE Piping Support Design Rules

The following are suggested basic rules for design and for the positioning of supports, anchors, and guides.

Loads with linear and punctiform contacts have to be avoided, therefore curved supports that bear at least 120 degrees of the bottom part of the pipe and that have maximum bearing stress of 600 kPa have to be used. Unprotected pipes are not allowed to press against roller supports or flat supports. Do not bear any pipe directly against ridges or other points of the support’s surface. Protective sleeves have to be used in these cases.

To protect pipes against external abrasion between the pipe and the steel collar, a PVC saddle (Fig. 9) or a protective rubber layer has to be positioned in between. The PVC saddle is necessary when free axial sliding of the pipe must be permitted (axial guides).

Valves and other heavy equipment must be supported independently in both horizontal and vertical directions.

The pipe clamps must fit firmly but must not transfer excessive force to the pipe wall. This could result in deformations and excessive wall stresses

Vertical runs have to be supported as shown in Fig. 9. Excessive loading in vertical runs has to be avoided. It is preferable to design a “pipe in compression” than a“ pipe in tension”. If the “pipe in tension” method cannot be avoided, take care to limit the tensile loading below the maximum tensile rate recommended for the pipe. The guiding collars will have to be installed by using the same space intervals used for horizontal supports.

PVC saddle and Vertical Supports
Fig. 9: Figure showing a typical arrangement of PVC saddle and Vertical Supports

Anchoring Points in GRE Piping Installations

An anchoring point must efficiently restrain the movement of the pipe against all of the applied forces. Anchors can be installed in both horizontal and vertical directions. Pipe anchors divide a pipe system into two sections and must be attached to some structure that is capable of withstanding the applied forces. In some cases pumps, tanks, and other similar equipment function as anchors.

However, most installations require additional anchors where pipe sizes change or where fiberglass pipes join another material or a product from another manufacturer. Additional anchors are usually located on valves, pipeline changes of direction, and major branch connections.

It is a good practice to anchor long, straight runs of aboveground piping at intervals of approximately 90 m.

In any case, the correct positioning of anchor points has to be decided only after a detailed stress analysis.

The pipe must be able to expand radially within the pipe clamps.

To secure the pipe to the clamp it is suggested to apply a GRP lamination (as shown in Fig. 10 below) on each side of the clamp. If the movement of the pipe has to be restrained only in one direction, it is sufficient to apply only one overlay ring of GRP in the opposite position.

GRP lamination in pipe anchors
Fig. 10: Figure showing GRP lamination in pipe anchors

FAQs for GRE Piping Systems

What is GRE piping?

GRE stands for Glass Reinforced Epoxy. It is a composite material used for manufacturing pipes and fittings. GRE piping systems are known for their corrosion resistance and durability.

What are the advantages of using GRE piping systems?

GRE piping systems offer several advantages, including excellent corrosion resistance, high strength-to-weight ratio, low maintenance requirements, high hydraulic efficiency, and a long service life. They are also lightweight and easy to install.

Where are GRE piping systems commonly used?

GRE piping systems are used in a wide range of industries, including chemical processing, offshore oil and gas, plant piping, oil and gas flowlines, water treatment, power generation, downhole tubing and casing, irrigation, and desalination plants.

How does GRE piping compare to other materials like steel or PVC?

GRE piping is corrosion-resistant, making it an excellent choice for environments with corrosive substances. It is lighter than steel, making installation easier, and it doesn’t require painting or coating. PVC is also corrosion-resistant but may not be suitable for high-temperature applications or certain chemical environments.

What is the temperature and pressure rating of GRE piping systems?

The temperature and pressure ratings of GRE piping systems can vary depending on the specific material and design. Generally, they can handle temperatures up to 250°F (121°C) and pressures up to 1500 psi (10,342 kPa).

Can GRE piping systems be used for underground applications?

Yes, GRE piping systems can be used for underground applications. They are resistant to soil corrosion and can be designed to meet the specific requirements of buried installations.

Are GRE piping systems environmentally friendly?

GRE piping systems are considered environmentally friendly because they are corrosion-resistant, reducing the risk of leaks and spills that can harm the environment. Additionally, they have a long service life, reducing the need for frequent replacements.

How are GRE pipes joined together?

GRE pipes are typically joined using adhesive bonding or flange connections. Adhesive bonding involves using epoxy resin to bond pipe sections together, creating a strong and leak-proof joint. Flange connections are used for larger pipe sizes and provide a more mechanical connection.

What maintenance is required for GRE piping systems?

GRE piping systems require minimal maintenance. Regular inspections for signs of damage or wear are recommended. In most cases, maintenance involves cleaning and visual inspections.

Can GRE piping systems be customized for specific applications?

Yes, GRE piping systems can be customized to meet the specific requirements of different applications. They can be designed to handle various chemical fluids, temperatures, pressures, and sizes.

Are GRE piping systems cost-effective?

While GRE piping systems have a higher initial cost compared to some materials, their long service life, low maintenance requirements, and corrosion resistance can make them cost-effective over the long term.

Are there any limitations to using GRE piping systems?

GRE piping systems are not suitable for extremely high-temperature applications or applications where fire resistance is critical. It’s important to consult the manufacturer to ensure the system meets the specific needs of the project.

What are the Design Codes for GRE Piping Systems?

Design codes and standards for GRE (Glass Reinforced Epoxy) piping systems may vary depending on the specific application and location of the project. The most widely used GRE piping codes are:

  • ISO-14692
  • NORSOK M-710
  • DNV GL RP-F112
  • AWWA M45

Few more related Resources for you..

HYDROSTATIC FIELD TEST of GRP / GRE lines
Stress Analysis of GRP / GRE / FRP piping system using Caesar II
A short article on GRP Pipe for beginners
Stress Analysis of GRP / GRE / FRP Piping using START-PROF

Piping Design Considerations for Vertical Columns or Tall Towers (Column Piping)

Written by Anup Kumar Dey in Piping Design Basics

Vertical Columns or Fractionating Towers are frequently used in the process units for fractionation and stripping. They are cylindrical in shape and their axis is vertical to the grade. This article will provide guidelines for piping design considerations from such columns or towers.

What is Fractionation?

Fractionation is the process of separating a mixture of different miscible liquids by vaporizing the mix and condensing the constituents at their individual boiling points. The process of distillation has evolved during the century from the Batch shell still process to the Continuous shell still process to the present Fractional distillation process.

Principle of operation of Fractionating tower

Fractionation is the process of separating a mixture by vaporizing the mix and condensing the constituents at their individual boiling points. Higher boiling point liquids will condense first, followed by lower boiling point products. This is achieved in the fractionating tower by creating zones of different temperatures along the length of the tower, the lowest at the top and the highest at the bottom. As the vapors rise along the column, they lose heat and condense at their respective boiling points. Column internal trays / packed beds, accumulators, and draw-offs help in this function.

What are Trays in a Vertical Column?

Trays are stamped plates of steel with unidirectional valves attached to them. They allow the passage of vapor in the upward direction only. They are placed all along the length of the tower. The valve lifts when the vapor force on the bottom of the valve exceeds the liquid force on top of it. As the vapors push the valves and pass through the liquid, vapors with higher condensation points lose heat and condense. The excess liquid on the tray flows down to the lower tray via a downcomer. Lighter boiling fractions in this liquid are vaporized on the lower tray by the heat of the upward-traveling vapors. Vaporization and condensation take place all along the length of the tower. Draw-offs at appropriate locations allow the removal of desired products from the column.

What are Packed Beds in a Vertical Column

These are beds of metal rings, packed along the length of the column. They function similarly to trays. Rising vapor passing through the metal rings comes in contact with liquid flowing down the column. The down-flowing liquid is heated by the upward-flowing vapor similar to trayed columns.

Design Considerations for Vertical Columns Piping Layout

Column Piping Layout: Locating the column

The piping designer should economize piping interconnections between the column and its adjacent pieces of equipment (pumps, condensers, heaters, reboilers, etc.) when locating the column. The following documents are needed to locate the column on the plot plan.

  • P&ID
  • Process Vessel Sketch
  • Plot plan
  • Piping & Plant Layout Specification

The column is located on the plot plan as per the process sequence dictated by the P&ID. Small columns can be placed on stand-alone structures. Large columns need a civil foundation of their own. In plants where the related equipment is housed, they are placed adjacent to the building or structure. Columns are best located on either side of the pipe rack, serviced by auxiliary roads for maintenance access. Vessel transportation, erection, and other constructibility issues should also be looked into while finalizing the location of the vessel. Adequate space must be provided around the column for operator movement and maintenance access. Locating close to an access road to reduce maintenance efforts. Interdistances between adjacent pieces of equipment are fixed as per Table 5 of Piping & Plant Layout Specification. The Bottom Tan Line elevation is fixed by the P&ID. The same may be increased to facilitate piping and equipment layout in consultation with the Process group.

After the column has been located on the plot plan, the following jobs are carried out.

  • Column elevation review and support selection
  • Tray orientation
  • Nozzle orientation
  • Platform and access requirement
  • Support cleat location detailing
  • Lifting lugs and earthling lugs location planning
  • Finalizing Vessel Name Plate location

Column Piping: Column elevation review and support selection

The Bottom Tan Line elevation fixed by the P&ID is the minimum elevation required for NPSH of the bottom pumps. This may be increased in consultation with Process Group for the following.

  • Operator Access – Proper headroom clearance should be available for safe operator access to the column.
  • Maintenance Access– Proper maintenance access clearance should be available for the safe movement of maintenance equipment around the column.
  • Minimum clearance as per piping layout
  • Bottom nozzle size – The bottom nozzles are connected to the bottom head with a straight pipe piece and a 90(elbow. This lowers the clearance available below the bottom of the elbow
  • Bottom head details (elliptical, hemispherical, etc.) The hemispherical head has a depth twice as compared to the elliptical (2:1) This will change the centerline elevation of the bottom nozzle and consequently the clearance under the elbow.
  • Vertical thermosyphon reboiler connections -The Reboiler bonnet removal area dictates the minimum tan line elevation of the column when the reboiler is attached to the column.

Column Piping: Supporting Arrangement of Vertical Column

Columns are generally supported by the following methods

  • Skirt Supported with a foundation on grade – most preferred. Skirts are straight for short columns and flared for tall ones.
  • Ring girder supported – On tabletop (when the bottom nozzle needs to be accessed)
  • Skirt supported – On the tabletop
  • The choice of support may fix the column elevation for some layouts.
Image of a Typical Vertical Column
Fig. 1: Image of a Typical Vertical Column

Tray orientation on Column Piping

The following documents are required for orienting the trays.

  • Vessel Process sketch & Tray data (No. Of pass, downcomer area, tray spacing, etc)
  • P&ID
  • Plot plan
  • Plant Layout Specification

Vertical Column Piping: Tray nomenclature

  • Odd and Even trays – Trays are numbered from the top of the column to the bottom. Trays with odd numbers 1,3,5 are the odd trays and those with even numbers 2,4,6, are the even trays.
  • Number of Passes – Trays can be One-pass, Two-pass, Three-pass, or Four-pass depending on column diameter.
  • Active Area (Bubbling area) – Area of the tray, which allows vapor to pass thru it
  • Downcomer area – The area allows excess liquid on one tray to flow down to the tray below it.
  • Tray spacing – Interdistance between adjacent trays.
  • Chimney tray – It is a solid plate with a central chimney section and is provided at the draw-off sections of the column.

Column Piping Layout: Tray orientation considerations

The main items influencing tray orientation are

  • Feed nozzle orientation
  • Reboiler location
  • Access Manholes

Feed nozzles are large in diameter and their orientation is fixed by the piping layout. The feed nozzle may have one or multiple external connections with different internal configurations for the following:

  • One nozzle with two orientations
  • Two nozzles with two orientations
  • One nozzle with multiple orientations

It is of utmost importance that the feed nozzle is parallel to the tray downcomer. The reboiler location is fixed on the plot plan. Now, as the reboiler draw-off nozzle is mostly located on the same side as the reboiler to minimize piping run, the draw-off orientation is established. The reboiler returns the nozzle to be parallel to the tray downcomer. For the bottom draw-off nozzle arrangement, tray orientation remains unaffected. Access Manholes on the cylindrical section are best located towards areas of direct maintenance access and opposite pipe racks. Thus their location may dictate the orientation of the trays.

Vertical Column Nozzle orientation

The following documents are required for orienting the nozzles.

  • Process vessel sketch
  • Level co-ordination diagram
  • P&ID
  • Plant layout specification
  • Nozzle summary
  • Insulation requirements
  • Plot plan

General considerations for locating nozzles in Column Piping

Generally, the following nozzles are present on all columns.

  • Feed Inlet
  • Bottoms Outlet
  • Drain
  • Vapor Outlet
  • Vent
  • Reboiler Draw off
  • Reboiler Return
  • Product Draw off
  • Reflux
  • Instrument Nozzles
  • Steams Out Nozzle
  • Access Manholes

Orienting the nozzles

While orienting these nozzles the following points are to be considered.

  • The feed inlet is to be placed parallel to the downcomer tray as discussed in tray orientation. The orientation of the feed inlet is in the sector towards the pipe rack from which the feed piping is coming. Proper support and flexibility should be available to route the piping.
  • Bottoms Outlet will be on the bottom head, best located on the center of the head. This is of gooseneck type for vessels with skirt-type support and the nozzle flange has to be brought outside the skirt. A separate drain nozzle at the bottom head but a tapped nozzle on the bottom outlet is most preferred. Orientation is generally chosen to minimize piping to the bottom pump keeping the line flexible enough from a stress point of view.
  • The vapor outlet, PSV connections, and Vent will be on the top head of the column. The vapor outlet is best located in the center of the head, though it may have to be shifted based on some layout considerations as explained. A large diameter makes the location of the vapor nozzle critical. The nozzle may have to be offset from the center of the column so that, after two elbows, the piping travels down the column at a practically supportable distance from the column.
  • The reboiler draw-off nozzle is mostly located on the same side as the reboiler to minimize piping run, thus the draw-off orientation is established. For the bottom draw-off nozzle arrangement, the best-suited orientation as per the piping layout may be chosen.
  • The re-boiler return nozzle is to be parallel to the tray downcomer as discussed in tray orientation.
  • Reflux nozzles are to be oriented for proper and even flow of refluxed liquid on the bubbling area. This can be achieved by internal distributor piping.
  • Level Instrument nozzles should be oriented as close to any inlet nozzle as possible to avoid the effects of turbulence. When baffles are provided this consideration is relaxed.
  • Pressure tapping for vapor pressure should be oriented in the bubbling area of the tray above it.
  • Temperature tapping for liquid temperature measurement should be oriented in the downcomer area. They are best oriented perpendicular to the tray downcomer. When multiple temperature elements are required, they are best placed at the same orientation but at different elevations. Care must be taken to ensure that the internal projection of the temperature element does not hit the downcomer. The nozzle should be made hillside if the probe length cannot be accommodated in the radial direction.
  • Inaccessible Instrument nozzles to be oriented near ladders (location of ladder and Instrument nozzles to be decided concurrently)
  • Steam-out connection should preferably be hillside type on the cylindrical shell so that swirling action is generated inside the vessel. This will ensure faster steam out of the column. These should be placed as close to the bottom tangent line as possible.
    • Access manholes can be located at the following places, depending on the type of access required in the column.
    • On the top of the column. (In this case, the vent can be located on the blind flange of the access manhole.)
    • On the cylindrical portion of the column (radially or hillside), this is the most preferred location. The orientation of the manhole should be such that the manhole faces the maintenance access area. This is to be in conjunction with tray orientation. Manhole entry should be directly in a bubbling area and never in the downcomer area. Internal piping should not block the access area of a manhole.

It should be verified that the davit swing area of the manhole cover does not obstruct the movement of maintenance personnel and does not hit any instruments or instrument nozzle connections. The centerline of the manhole should be between 600mm to 1000mm (ideally 760mm) from the top of the service elevation of the vessel.

  • A Gooseneck nozzle for a Vapor outlet should be considered when the piping layout is fixed and requires an elbow immediately at the nozzle. This can be a flanged type, thus acting as a manhole also for big nozzle diameters. Flange-type nozzles have the added advantage that their orientation can be changed even after the delivery of the vessel at the site.
  • Skirt access manholes are to be oriented for easy access.
  • Skirt vents are to be oriented in such a manner so that they do not come at the same location as the access ladder.

Nozzle standouts

Nozzles on the top of the column should have their flange a minimum of 180mm and a maximum of 1000mm from the TOG of the access platform. Nozzle standouts on the shell are calculated on the clearance requirement for maintenance access to nuts on the back of the flange. Due consideration is to be given to vessel insulation when calculating the standout. This standout will be confirmed by mechanical so that the nozzle passes the mechanical requirements.

Preparing the Nozzle Orientation Document

This document should show the plan, and if required, the elevation of the vessel with the location of nozzles on the same. Nozzle orientation is to be from plant north and taken clockwise. Dimensioning should show the radial distance of the vessel flange from the vessel center. A nozzle summary table indicating the Nozzle number, service, size, rating, flange face, elevation from the bottom tan line, and stand out from the vessel center is to be included in the drawing. For nozzles on the vessel heads, the F/F stand out from the bottom or top tan line should be given. In lieu of elevation from the bottom tan line.

Miscellaneous Data to be included in Nozzle Orientation Document

Lifting Lugs

Generally, columns can be lifted with two lugs welded below the top tan line. A tailing lug is to be provided near the bottom of the skirt for tailing operation. The preferred locations should be marked on the nozzle orientation drawing.

Earthing Lugs

Two earthing lugs, ideally 180° apart should be provided on the lower portion of the skirt. The same should be marked on the nozzle orientation drawing.

Name Plate

The nameplate should be located at a prominent location and marked on the nozzle orientation drawing. Care should be taken that the nameplate projects outside the vessel insulation.

Vessel Insulation Clips

Indicate that insulation clips/rods are required for holding the vessel insulating bands.

Platforms and Access Ladders

Platforms are required for the following purposes

  • Operational access to valves and instruments etc.
  • Maintenance access to manholes.
  • Mid landings (when the elevation difference between two platforms exceeds 9m)

Calculating the TOG elevation

The platform on the top head of the column

TOG elevation from the top of column head = Insulation thickness + 50mm clearance + Platform member depth (assume 200mm minimum) + 30mm grating. Round off to the next higher multiple of 10.

Platforms on the cylindrical portion of the column

  • Nozzles – Platform to be 500mm (minimum) below the bottom of the flange of the nozzle.
  • Instruments (LT/LG) and their standpipes – Platform to be 200mm below the lowest process drain on any of these items.
  • Access manholes – The platform is to be ideally 750 mm below the centerline of the manhole. The acceptable range is 600mm to 1500mm below the centerline of the manhole.
  • Mid-landing platforms are to be provided when the elevation difference between two platform levels exceeds 9m. The mid-landing is to be ideally evenly placed between the two platforms.
  • Two platforms being serviced by a single ladder should ideally have an elevation difference of 600mm between them.
  • The platform elevations (TOG) should be rounded off to the nearest multiple of 10.

Platform sizing

The platform on the top head of the column

This platform should be rectangular. It should cover all the nozzles, instruments davits, etc. that need access for operations and maintenance. Ideally, a space of 750mm should be provided around 3 sides of a nozzle. This may be lowered at the discretion of the piping lead. Side entry access to the platform should be the first preference when deciding the exact shape of the platform. Orienting the platform axis along the ladder orientation and providing an extended landing point may achieve this.

Platforms on the cylindrical portion of the column

Determining the Orientation angles

  • This platform should be circular. Its orientation extent should cover all the nozzles, instruments davits, etc. that need access for operations and maintenance. The platform should extend beyond the centerline of the manhole by a minimum of 1 manhole diameter.
  • A free landing space of 750mm is to be provided for access ladders.
  • Ideally, a space of 750mm should be provided around the sides of a nozzle. This may, however, be lowered to 600mm at the discretion of the piping lead.

Determining the width

  • The inner radius of the platform should clear the column insulation by 50mm.
  • Platform width is dictated by operator access requirements. The following considerations are to be taken care of when deciding the width.
  • The minimum platform width is to be 750mm(free of all obstructions).
  • The width of the manhole platform is to be a minimum of 900mm.
  • Platforms may be locally extended width-wise at regions where vertical pipes pierce the platform, maintaining 750mm clear space from the insulation of piping to the handrail of the platform.
  • When controls are located on the platform, the width of the platform is to be 900mm plus the width of the controls.

Platform bracket orientation

Platform support brackets are to be oriented so that they clear the vertical piping traveling down the column, through the platform. Support bracings for platforms at all elevations should be maintained the same as far as possible.

Column Piping
Fig. 2: Sample Column Piping Example

Access ladder

  • Access ladders are to be vertical. They should have a clear climbing space of 680mm. Toe clearance from the centerline of the ladder rung to any obstruction to be 230mm. Special care is to be taken for vessel stiffeners.
  • A cage is to be provided for all ladders at an elevation of 2300mm and above. Side entry ladders are the first preference.
  • The ladder is to be oriented so that it can also be utilized for access to instrument connections that are inaccessible from the working level.
  • Inclined ladders are permissible on inclined portions of the skirt and column. The angle is limited to 150 from vertical.

Preparing the Platform Input Document

Platform and Access ladder input is transmitted to Civil via a platform input drawing.

Platforms on the top head of the column

This should clearly indicate the TOG elevation from bottom T/L, dimensions of the platform, and its location w.r.t. The vessel centerlines. Grating cutout requirements (indicating size, shape, and location), required swing direction of the self-closing gate, and davit location need to be marked on the same drawing. Any pipe supports intended to be taken from the platform should be marked.

Platforms on the cylindrical portion of the column

This should clearly indicate the TOG elevation from bottom T/L; the dimensions of the platform (orientation angles and width), and its outer radius from the vessel axis. Grating cutout requirements (indicating size, shape, and orientation), required the swing direction of the self-closing gate. Any pipe supports intended to be taken from the platform should be marked.  Orientations of access ladders should be marked on the respective platform elevation plans.

Orienting piping on the face of the column

It is imperative that the orientations, arrangement, and standouts of various piping traveling down the face of the column are calculated keeping in mind the following points.

Large diameter columns

  • Piping has to be arranged in the order of the elevation and orientation of the nozzles.
  • The piping of these columns can travel down the column radially, with independent supports.
  • The clear minimum space between the pipe and shell is to be 300 mm excluding any insulation.
  • The pipe with insulation should clear the stiffening ring and its insulation.
  • The minimum orientation angle between two adjacent pipes should be calculated to clear the support bracket of one pipe hitting the insulation cladding of the adjacent pipe.
  • Support points of adjacent piping should be offset to save space between them. as the support brackets will have to be oriented so that there is no clash between the cleats of the supports or between the support members and bracings.

Small diameter columns

  • Piping has to be arranged in the order of the elevation and orientation of the nozzles.
  • Small-diameter columns have an inherent problem of supporting and guiding each line independently due to the small circumference available for the piping. After the first rest support near the nozzle, the pipes should be oriented as though they are traveling down a vertical pipe rack.
  • The clear minimum space between the back of the pipe or shoe and shell is to be 600mm. On the vertical run, minimum spacing requirements have to be followed.

Supporting Piping from Vertical Columns

Piping should be supported from the vessel or its platform when it is difficult to construct civil support from grade or adjacent structures at the required location. Vessel support may also be taken to take advantage of lower differential thermal growth between vessel and piping, as compared to piping and civil support. A judicious selection of support locations can eliminate the requirement for springs.

Thumb rules for supporting piping from columns

  • Small loads can be transferred directly to the platform members. These include rest, one-way stop, two-way stop, or hold-down supports and the piping layout should be done accordingly.
  • Large loads should be transferred to the vessel shell and the piping layout should be done such that the platform members do not interfere with these independent supports.
  • The first piping support is Rest support and it should be as close to the equipment nozzle as possible. The second and subsequent supports are guides and they are to be located as per the allowable piping spans available in the tables. For tall columns, another rest support may be needed. This is done by providing spring support which will take care of the differential expansion of the vessel and piping.
  • Piping support should not cause any hindrance to the movement of personnel.
  • Vessel growth should be considered to check the clash of piping support with any adjacent piping or structure.

Types of supports for Column Piping

Supports welded to piping

Horizontal trunnions welded to the pipe take the vertical load of the pipe. They are generally used in pairs, set apart at 180°. Their axis is perpendicular to a line drawn from the center of the column to the center of the pipe at the location of support. Trunnion lengths should be adequate enough so that their ends project 50 mm from the outer edge of the support bracket member Shoes are provided for guidance purposes and to prevent insulation cladding from hitting the support bracket member. Adequate shoe length is to be taken for differential movement of pipe and vessel.

Supports welded to the vessel

Support brackets( non-braced and braced ) and Guide brackets( non-braced and braced ) are the most common support arrangements for vertical piping.

Calculating the minimum dimensions of support members

Load bearing supports

Trunnions or springs transfer load to these supports. Minimum clear inside dimensions are calculated so that the insulation cladding is 50 mm away from the inside of the structural member or support plate of the spring.

Guide supports

The bare pipe is guided directly by the guide bracket. Shoes are provided in pairs,180° apart, for lines with insulation. These can be single pairs or double pairs depending upon the type of guiding required at that particular location. The guide gap required by stress is to be added to the end-to-end-to-end dimensions of bare pipe or pipe with shoes.

Preparing the Civil Pipe Support (CPS) Input Document

CPS input is transmitted to Civil and Mechanical via a CPS input drawing. A sketch clearly indicating the TOS, dimensions, and CPS location with respect to the vessel centerline needs to be drawn. Any requirement for additional support plates for springs or trunnions is to be indicated. A summary table indicating the CPS number, TOS, stress file number, and corresponding node number from the Nozzle cleat load information chart needs to be created. The Nozzle cleat load information chart indicates the various loads acting at the support location under various conditions. It is to be attached along with the CPS input document.

Few more Resources for you..

Stress Analysis of Column piping system using Caesar II
Piping Design and Layout Considerations
Piping Materials Basics
Piping Stress Analysis

Pipe Support Span (Spacing) | Pipe Support Spacing (Span) Chart/Table

Written by Anup Kumar Dey in Piping Stress Basics,Piping Supports

Pipe support spans play a crucial role in maintaining the longevity, efficiency, and safety of aboveground piping and pipeline systems. Pipe support span is also known as pipe support spacing. A proper pipe support span not only reduces the pipe supporting problems but also adequately supports pipes at regular intervals to reduce failures associated with improper supporting. In this comprehensive guide, we will discuss the intricacies of pipe support spans, covering design considerations, factors on which it depends, best practices, and pipe support spacing charts based on different codes and standards.

A. What is a Pipe Support Span?

Pipe Support Span is defined as the optimum distance between two consecutive pipe supports to avoid excessive stress, sagging, bending, vibration, or failure of the piping or pipeline system in extreme cases. It ensures that the piping system remains securely in place throughout operation. Adequate pipe support spacing is synonymous with

  • Structural Integrity
  • Reduced Maintenance
  • Safety
  • Operational Efficiency

We all know that while routing aboveground piping or pipeline from one part or equipment to another we have to support the pipe at some definite spans. A properly designed pipe support span helps the piping design personnel to support pipes at regular spacings, thus reducing his work for unnecessary calculations. Pipe Support Span is also known as Pipe Support Spacing. Refer to Fig. 1 which defines the pipe support span for a pipeline system.

B. Factors on Which Pipe Support Span Depends

Various factors influence the pipe support span. In the following section, we will discuss 11 such important criteria that dictate the Pipe support spacing.

1. Pipe Material:

Pipe Support spacing varies with pipe material, For non-metallic pipes, the support span is lower than metallic pipes of the same size. Even Stainless Steel pipes have lower pipe support spacing as compared to Carbon steel pipes.

2. Nominal Diameter of Pipe & Schedule:

With the increase in pipe diameter and schedule, the pipe support span increases. That is the reason you will find that a 10-inch pipe has more support span as compared to a 4-inch pipe support spacing.

3. Type of Fluid Service:

Piping support span varies with fluid service; Pipes carrying liquid service have less support span as compared to pipes carrying gaseous fluids. This means with an increase in the density of the flow medium pipe support spacing decreases.

4. Type and Thickness of Insulation Material:

With an increase in thickness and density of the pipe insulation material, pipe support spacing reduces. An increase in insulation density and thickness imposes more load on the parent pipe which needs to be supported by increasing the number of supports which means the pipe support span reduces.

5. Piping Configuration (Straight pipe and Pipe with elbows):

Pipe support spacing is dependent on the piping routing or geometry. A straight pipe has more support span as compared to pipes with directional changes. Because of this reason, to find out the span for piping including elbows, the straight pipe span is multiplied by a factor as shown in Fig. 2.

6. Locations of Valves and Rigid Bodies:

The presence of rigid bodies in a piping or pipeline system reduces the pipe support span. It is a general engineering practice to provide at least one support near rigid bodies like valves (Preferably to provide support on both sides of the valve).

7. Structural Availability for Supporting:

Available structures are normally used for supporting the pipe. So, the pipe span chart may be reduced in those places. Also, an increase in the number of supports distributes the piping loads on supports and increases the piping stiffness. So, if a structure is available, pipe supports are usually taken from those structures.

8. Vibrating or Pulsating lines:

For vibrating or pulsating lines pipe support span is reduced to avoid vibration tendency and to increase the natural frequency of the piping system. A reduction in pipe support spacing increases the system rigidity which reduces the tendency of pipe vibration.

9. Fluid Temperature:

With an increase in fluid temperature as the pipe material’s allowable stress value reduces, the pipe is supported in a nearby position, thus reducing the pipe support spacing.

10. Equipment Connection

Sometimes, the Pipe support span is determined considering various equipment connections that have the potential for vibration transfer from the equipment like reciprocating compressors and reciprocating pumps. For these pipes, the supporting span is reduced from the standard pipe support spacing.

11. Flow Induced Vibration Criteria

For lines with the flow-induced vibration susceptibility as high, the pipe support span is reduced to increase the natural frequency of the piping system so that the tendency of FIV failure is reduced.

Figure showing pipe support span
Fig. 1: Figure showing pipe support span

C. Deciding Pipe Support Span

Pipe Support Span Length Depends On-

  • Bending Stress
  • Deflection
  • Indentation
  • Allowable Loads
  • Vibration Possibility and Natural Frequency of the piping system

1. Bending Stress

Bending is caused mainly due to two reasons:

  • Uniform Weight Load
  • Concentrated Weight Load

1.1 Uniform Weight Load

  • Own Weight Of Pipe
  • Insulation Weight
  • Weight of Fluid During operation
  • Weight of hydrostatic fluid During Hydro Test

1.2 Concentrated Load

2. Deflection

Deflection (Δ) is defined as a relative displacement of the point from its original position.

  • The basic piping practice is to limit pipe deflection between supports to 1” or 1/2 the nominal pipe diameter, whichever is smaller.
  • The most important reason for limiting deflection is to make the pipe stiff enough, that is, of high enough natural frequency, to avoid a large amplitude response under any slight perturbing force. As a rough rule, for average piping, a natural frequency of 4 cycles per second will be found satisfactory. The natural frequency can be calculated by
Natural Frequency

3. Indentation

Indentation

Where,

  • t=corroded Thickness of pipe Wall(mm)
  • S=0.67Sh(N/mm^2)
  • R=Radius of pipe (mm)
  • d=Bearing Length(mm)
  • b=Bearing width(mm)

4. Allowable Load at Support

Allowable Load

Where,

  • Pa=Allowable Load at the Support point
  • t=effective local thickness (pipe wall +Reinforced Pad If Any)
  • R=outer radius of Pipe
  • b=Bearing length of pipe (along the axis) on the support structure

IF THE ACTUAL LOAD AT SUPPORT IS GREATER THAN THE ALLOWABLE LOAD GIVEN BY THE ABOVE FORMULA, A REINFORCEMENT PAD WILL BE REQUIRED.

5. Vibration Possibility

The support span for vibration-prone lines is reduced to make the system stiffer such that the pipe does not easily vibrate. The natural frequency of the system is usually maintained above 4 Hz as mentioned in clause C.2 above.

D. Pipe Support Span Chart

A pipe support span chart is a table or diagram that provides information on the maximum allowable span for different types of piping and support configurations. The span is the distance between two points where a pipe is supported, such as at two adjacent pipe hangers.

The purpose of a pipe support span chart is to help engineers and designers ensure that piping systems are properly supported to prevent sagging, bending, or other types of stress that could cause damage or failure. By referring to the span chart, designers can select the appropriate type and spacing of supports for a given piping configuration, based on the materials used, the size and weight of the pipes, the fluid being transported, and other factors.

Pipe support span charts may also include information on the recommended type of support for different piping materials, such as steel, copper, or plastic, as well as information on recommended hanger spacing, temperature limits, and other design considerations. Proper use of a pipe support span chart can help ensure that piping systems are safe, reliable, and long-lasting.

Normally project-specific Support Span is provided in tabular format for straight pipes that are known as a “Pipe Support Span Chart”. But for elbows or turns, the span is to be reduced by a factor as shown in the attached figure (Fig. 2). Readymade support spans for specific pipe diameters and thicknesses are available in the MSS code. For the Shell group of companies, the support span is provided in DEP in tabular format.

Factor to reduce support span depending on layout.
Fig. 2: Factor to reduce support span depending on layout.

1. Pipe Support Spacing Chart for Steel Piping as per MSS-SP-69

A pipe support span chart is a tabular chart giving a rough idea of supporting distance. These charts are normally mentioned in piping stress analysis project specifications. In the following image (Fig. 3) pipe support span chart from MSS SP-69 is reproduced as a sample.

Sample Piping Support Span Chart (Reference: MSS SP-69)
Fig. 3: Sample Piping Support Span Chart (Reference: MSS SP-69)

2. Pipe Support Spacing Chart for Steel Piping Based on ASME B31.1

The pipe support span as per ASME B31.1 for Steel piping is provided below:

Pipe Support Span Based on ASME B31.1, Power Piping Code
NPS
(Inches)		DN
(mm)		Water/ Liquid
Service (m)		Water/ Liquid
Service (ft)		Steam, Gas,
Air Service (m)		Steam, Gas,
Air Service (ft)
1252.172.79
2503.0104.013
3803.7124.615
41004.3145.217
61505.2176.421
82005.8197.324
123007.0239.130
164008.22710.735
205009.13011.939
246009.83212.842
Table 1: Pipe Support Spacing in ft and m as per ASME B31.1-Power Piping Code

General Notes for Table 1:

  • This support span is valid for horizontal straight runs of standard and heavier steel pipe at a maximum operating temperature of 750°F (400°C).
  • This support spacing chart does not apply in the presence of concentrated loads between supports, such as flanges, valves, and specialties.
  • The pipe support spacing is based on a fixed beam support with a bending stress limiting to 2,300 psi (15.86 MPa) and insulated pipe filled with water or the equivalent weight of steel pipe for steam, gas, or air service, and the pitch of the line is such that a sag of 0.1 in. (2.5 mm) between supports is permissible.

3. Pipe Support Span Chart as per ASME B31.3

Process piping code ASME B31.3 does not provide any span chart for steel piping systems. Users usually develop their pipe support spacing table considering parameters like allowed stress, deflection, etc. A typical pipe support span for process piping for carbon steel and stainless steel pipe material is provided below (Reference: Shell DEP) in Table 2 and Table 3.

3.1 Pipe Support Span for Carbon Steel

Typical Support Span for carbon steel and heavy wall stainless steel
 Vapour serviceLiquid service
Pipe sizeBareInsulatedBareInsulated
DN 15
(NPS ½)		900 mm
(3 ft)		800 mm
(2 ½ ft)		900 mm
(3 ft)		800 mm
(2 ½ ft)
DN 20
(NPS ¾)		1400 mm
(4 ½ ft)		1200 mm
(3.9 ft)		1400 mm
(4 ½ ft)		1200 mm
(3.9 ft)
DN 25
(NPS 1)		3600 mm
(11.8 ft)		2300 mm
(7.5 ft)		3450 mm
(11.3 ft)		2250 mm
(7.3 ft)
DN 40
(NPS 1 ½)		3600 mm
(11.8 ft)		3000 mm
(9.8 ft)		3450 mm
(11.3 ft)		2800 mm
(9.1 ft)
DN 50
(NPS 2)		3600 mm
(11.8 ft)		3450 mm
(11.3 ft)		3450 mm
(11.3 ft)		3300 mm
(10.8 ft)
DN 80
(NPS 3)		6550 mm
(21.4 ft)		4600 mm
(15 ft)		5450 mm
(17.8 ft)		4200 mm
(13.7 ft)
DN 100
(NPS 4)		7500 mm
(24.6 ft)		5550 mm
(18.2 ft)		6100 mm
(20 ft)		4900 mm
(16 ft)
DN 150
(NPS 6)		9150 mm
(30 ft)		6800 mm
(22.3 ft)		7100 mm
(23.2 ft)		5800 mm
(19 ft)
DN 200
(NPS 8)		10500 mm
(34.4 ft)		8050 mm (26.4 ft)7950 mm
(26 ft)		6700 mm
(21.9 ft)
DN 250
(NPS 10)		11800 mm
(38.7 ft)		9050 mm
(29.6 ft)		8700 mm
(28.5 ft)		7400 mm
(24.2 ft)
DN 300
(NPS 12)		12900 mm
(42.3 ft)		9800 mm
(32.1 ft)		9150 mm
(30 ft)		7800 mm
(25.5 ft)
DN 350
(NPS 14)		15150 mm
(49.7 ft)		11850 mm
(38.8 ft)		10850 mm
(35.5 ft)		9300 mm
(30.5 ft)
DN 400
(NPS 16)		16250 mm
(53.3 ft)		12850 mm
(42.1 ft)		11200 mm
(36.7 ft)		9750 mm
(31.9 ft)
DN 450
(NPS 18)		17250 mm
(56.5 ft)		13750 mm
(45.1 ft)		11500 mm
(37.7 ft)		10150 mm
(33.3 ft)
DN 500
(NPS 20)		18200 mm
(59.7 ft)		14450 mm
(47.4 ft)		11750 mm
(38.5 ft)		10400 mm
(34.1 ft)
DN 600
(NPS 24)		18950 mm
(62.1 ft) 		16050 mm
(52.6 ft)		12150 mm
(39.8 ft)		10950 mm
(35.9 ft)
DN 750
(NPS 30)		21000 mm
(68.9 ft) 		17500 mm
(57.4 ft)		13100 mm
(43 ft)		11500 mm
(37.7 ft)
DN 900
(NPS 36)		22700 mm
(74.5 ft)		18500 mm
(60.7 ft)		13700 mm
(45 ft)		12500 mm
(41 ft)
DN 1050
(NPS 42)		23400 mm
(76.8 ft) 		19500 mm
(64 ft)		14300 mm
(47 ft)		13000 mm
(42.6 ft)
DN 1200
(NPS 48)		25000 mm
(82 ft) 		20500 mm
(67.2 ft)		14600 mm
(48 ft)		13400 mm
(44 ft)
Table 2: Pipe Support Span for Carbon Steel and Heavy Wall Stainless Steel

3.2 Pipe Support Span for Stainless Steel

Maximum spans for stainless steel, schedule 10S
 Vapour serviceLiquid service
Pipe sizeBareInsulatedBareInsulated
DN 25
(NPS 1)		2200 mm
(7.2 ft)		1800 mm
(5.9 ft)		2100 mm
(6.8 ft)		1800 mm
(5.9 ft)
DN 40
(NPS 1 ½)		2800 mm
(9.1 ft)		2500 mm
(8.2 ft)		2400 mm
(7.8 ft)		2500 mm
(8.2 ft)
DN 50
(NPS 2)		2800 mm
(9.1 ft)		2600 mm
(8.5 ft)		2700 mm
(8.8 ft)		2600 mm
(8.5 ft)
DN 80
(NPS 3)		6400 mm
(21 ft)		4050 mm
(13.2 ft)		4950 mm
(16.2 ft)		3500 mm
(11.4 ft)
DN 100
(NPS 4)		6400 mm
(21 ft)		4800 mm
(15.7 ft)		5300 mm
(17.3 ft)		4000 mm
(13.1 ft)
DN 150
(NPS 6)		9400 mm
(30.8 ft)		5750 mm
(18.8 ft)		5950 mm
(19.5 ft)		4600 mm
(15 ft)
DN 200
(NPS 8)		10750 mm
(35.2 ft)		6800 mm
(22.3 ft)		6450 mm
(21.1 ft)		5200 mm
(17 ft)
DN 250
(NPS 10)		10750 mm
(35.2 ft)		7600 mm
(24.9 ft)		6950 mm
(22.8 ft)		5650 mm
(18.5 ft)
DN 300
(NPS 12)		10750 mm
(35.2 ft)		8250 mm
(27 ft)		7350 mm
(24.1 ft)		6050 mm
(19.8 ft)
DN 350
(NPS 14)		10750 mm
(35.2 ft)		8700 mm
(28.5 ft)		7600 mm
(24.9 ft)		6300 mm
(20.6 ft)
DN 400
(NPS 16)		11000 mm
(36 ft)		9450 mm
(31 ft)		7750 mm
(25.4 ft)		6550 mm
(21.4 ft)
DN 450
(NPS 18)		11000 mm
(36 ft)		9700 mm
(31.8 ft)		7850 mm
(25.7 ft)		6750 mm
(22.1 ft)
DN 500
(NPS 20)		11500 mm
(37.7 ft)		10500 mm
(34.5 ft)		8400 mm
(27.5 ft)		7300 mm
(23.9 ft)
DN 600
(NPS 24)		12000 mm
(39.3 ft)		11000 mm
(36 ft)		9050 mm
(29.6 ft)		8050 mm
(26.4 ft)
DN 750
(NPS 30)		14000 mm
(45.9 ft)		13000 mm
(42.6 ft)		10500 mm
(34.5 ft)		9500 mm
(31.2 ft)
DN 900
(NPS 36)		16000 mm
(52.5 ft)		15000 mm
(49.2 ft)		11500 mm
(37.7 ft)		10500 mm
(34.5 ft)
DN 1050
(NPS 42)		18000 mm
(59 ft)		16500 mm
(54 ft)		12500 mm
(41 ft)		11500 mm
(37.7 ft)
DN 1200
(NPS 48)		20000 mm
(65.6 ft)		17300 mm
(56.8 ft)		13500 mm
(44.3 ft)		12500 mm
(41 ft)
Table 3: Maximum Pipe Support Spans for Stainless Steel, Schedule 10S Pipe

E. HDPE Pipe Support Span

The maximum allowable span for HDPE pipes will depend on various factors, such as the pipe size, wall thickness, and temperature of the fluid being transported. In general, HDPE pipes require more support than steel pipes due to their flexibility and low modulus of elasticity.

The Plastics Pipe Institute (PPI) provides guidelines for designing supports for HDPE pipes, which includes recommendations for maximum allowable span. According to PPI, the maximum allowable span for HDPE pipes should not exceed the following:

  • 4 feet for 1-inch diameter pipes
  • 5 feet for 1.25-inch diameter pipes
  • 6 feet for 1.5-inch diameter pipes
  • 7 feet for 2-inch diameter pipes
  • 9 feet for 3-inch diameter pipes
  • 11 feet for 4-inch diameter pipes
  • 13 feet for 6-inch diameter pipes
  • 15 feet for 8-inch diameter pipes
  • 18 feet for 10-inch diameter pipes
  • 22 feet for 12-inch diameter pipes

However, it is important to note that these are general guidelines and the actual span may vary depending on the specific application and the design criteria used. It is always recommended to consult with a qualified engineer or piping designer to determine the appropriate support span for a specific HDPE piping system.

F. GRE Pipe Support Span

The maximum allowable span for Glass Reinforced Epoxy (GRE) pipes will depend on various factors, such as the pipe diameter, wall thickness, and the type of fluid being transported.

The Fiberglass Reinforced Plastic Institute (FRPI) provides guidelines for designing supports for GRE pipes, which includes recommendations for maximum allowable span. According to FRPI, the maximum allowable span for GRE pipes should not exceed the following:

  • 2 feet for 1-inch diameter pipes
  • 2.5 feet for 1.25-inch diameter pipes
  • 3 feet for 1.5-inch diameter pipes
  • 4 feet for 2-inch diameter pipes
  • 6 feet for 3-inch diameter pipes
  • 7 feet for 4-inch diameter pipes
  • 8 feet for 6-inch diameter pipes
  • 10 feet for 8-inch diameter pipes
  • 12 feet for 10-inch diameter pipes
  • 14 feet for 12-inch diameter pipes

It is important to note that these are general guidelines and the actual span may vary depending on the specific application and the design criteria used. It is always recommended to consult with a qualified engineer or piping designer to determine the appropriate support span for a specific GRE piping system.

ISO 14692-2002 also provides a typical GRE pipe support span table to be used for FRP/GRE pipes in Table 1 (The same is reproduced below in Fig. 4).

GRE Pipe Support Span as per ISO 14692-2002
Fig. 4: GRE Pipe Support Span as per ISO 14692-2002

G. ABS and PVC Pipe Support Spacing

PVC and ABS pipe support spacing is mainly based on the manufacturer. The following image (Fig. 5) provides some typical values for ABS and PVC Pipe Support Spans.

Horizontal Support Spacing for PVC and ABS Pipes
Fig. 5: Horizontal Support Spacing for PVC and ABS Pipes

H. Online Video Courses on Piping Support

To learn more about piping support design and engineering you can opt for the following video course.

LPG Storage Tanks: Meaning, Types, Selection, Specification, and Design Calculations

Written by Anup Kumar Dey in Mechanical,Piping Design Basics,Piping Interface,Process

LPG (Liquefied Petroleum Gas) storage tanks or LPG Tanks are containers designed to store large quantities of propane or butane, which are commonly used as a source of fuel for heating and cooking in both residential and industrial applications. They are safe and efficient. LPG tanks are typically made of steel or another durable material that can withstand the high pressure and low temperatures required to store LPG in its liquid form. LPG is liquefied to maximize its storage efficiency inside the LPG Tanks.

LPG storage tanks come in various sizes, from small cylinders used for portable stoves and heaters to large tanks used for industrial purposes, such as powering forklifts and other heavy equipment. The capacity of LPG storage tanks can range from a few hundred liters to several thousand liters, depending on the specific application and the amount of LPG needed.

LPG tanks can be used in the form of LPG cylinders, LPG bulk tanks, Underground LPG storage tanks, etc. Flat-bottom cryogenic storage tanks are one variation of the most efficient LPG storage facility, having a capacity in the range of 1,000 to 30,000 m³.

LPG storage tanks must be designed and installed in compliance with strict safety regulations to prevent accidents and leaks. This includes regular inspection and maintenance to ensure that the tank is in good working condition and that any potential issues are addressed promptly.

Types of LPG Storage Tanks

There are several types of LPG storage tanks, each designed for specific applications and with varying capacities. Some of the most common types of LPG storage tanks include:

  • Aboveground LPG storage tanks: These are large tanks that are installed above the ground and are typically used for storing LPG in bulk for commercial and industrial applications.
  • Underground LPG storage tanks: These tanks are installed underground and are commonly used for storing LPG in residential areas where space is limited.
  • Horizontal LPG storage tanks: These tanks are designed to be installed horizontally and are commonly used for storing LPG in industrial settings.
  • Vertical LPG storage tanks: These tanks are designed to be installed vertically and are commonly used for storing LPG in residential areas and small commercial settings.
  • Mounded LPG storage tanks: These tanks are installed on a concrete platform or mound and are commonly used for storing LPG in industrial settings.
  • Propane cylinders: These are small portable tanks used for storing LPG for outdoor cooking and camping.
  • Cylindrical Storage Tanks
  • Spherical Storage Tanks

Each type of LPG storage tank has its own advantages and disadvantages, and the choice of the tank will depend on the specific application and the amount of LPG needed. Proper installation and maintenance are critical for ensuring the safe operation of LPG storage tanks.

Spherical or horizontal cylindrical type (bullet type) storage tanks are generally used to store LPG. The horizontal cylindrical types are usually used for small-capacity or underground installations and Spherical ones are used for higher capacities. The design of high-pressure LPG storage tanks is critical. Many parameters need to be considered during design. This article will provide basic information about the same.

Selection of LPG Storage Tank Types

A tank type will usually be selected considering the cost or the size of transportation. The spherical type is usually employed for sizes greater than 500 m3. The horizontal cylindrical type is usually used for sizes smaller than 100 m3. Both types will be applicable for volumes ranging from 100 to 500 m3. The type of this capacity range will be decided by the total weight. Where the tank is installed underground, the horizontal type shall be selected, even if the vessel capacity exceeds 100 m3.

LPG Storage Capacity

Definition of Capacity

  • Nominal capacity- All this capacity can be used, defined as below in Fig. 1. This capacity is usually used as a tank name.
  • Geometrical capacity- Volume inside a vessel which is called “a water volume” in NFPA.
  • Storage capacity- The volume from the tank bottom to the maximum design level. This volume varies depending on the operating temperature.
  • Net Working capacity- Volume between HLL and LLL or HHLL and LLLL
Figure explaining the storage tank capacity
Fig. 1: Figure explaining the storage tank capacity

LPG Liquid Level

(1) Maximum liquid level (maximum Storage Capacity)

Many countries specify a maximum LPG liquid level (max. storage capacity) in their regulations. In countries that have no such regulations, NFPA shall be applied. NFPA-58 and 59 specify details of the maximum liquid level including liquid volume correction factors and equations concerning capacity and temperature (Refer to NFPA 58 Para. 4-4 and Appendix-F)

Few regulations specify that a vapor space of 10% shall be secured under the severest conditions, thus resulting in the following equation.

V = W/0.9d

Where V = tank geometrical volume (m3);   W = Storage capacity (kg) and  d = Density at the maximum design temperature (kg/m3)

NFPA specifies the coefficient of the above equation, i.e. 0.9 as follows.

  • 9 to 0.95 at 100° F
  • 98 to 0.99 at the maximum storage temperature.

This maximum liquid level fluctuates according to operating temperatures as below Example ;

The following figures are the results of example calculations according to the physical properties of Pure Propane per NFPA.

NFPA Calculation
NFPA Calculation

From the above, it is not possible to set a fixed level for the highest limit point. Therefore the highest limit of level should be compensated with the storage temperature or a differential pressure type level indicator shall be used.

(2) Minimum LPG levels

Refer to Fig. 2

Figure showing tank levels
Fig. 2: Figure showing tank levels

H2; 150 mm or 10 minutes from the maximum filling volume

H3; A height of the Deadstock area. The height shall be calculated by the reasonable dead stock volume.

The recommended height for the spherical tank is shown below.

Where ;

  • D: Diameter of the sphere
  • H: Height of level
  • V: Sphere volume
  • Vb: Sectional Volume of the height H
  • H4: 300 mm/ minimum 100 mm

Note 1; High and low-level (HLL and LLL) alarms shall be set at the maximum and the minimum operation respectively. If high-high and low-low levels (HHL and LLL) for an emergency shutdown or an automatic diversion system are provided, set points shall be selected at lower than the maximum and higher than the minimum design, but not inside of the maximum and the minimum operation.

Sphere Maximum Capacity

The maximum sphere capacity is limited due to the wall thickness. The wall thickness is limited by the manufacturing and the stress relief requirement.

Operating and Design Conditions

Operating Conditions

(1) Operating temperature: Operating temperatures are not so important for the design of tanks; they are merely used to design pumps connected to tanks. The maximum operating temperature and minimum operating temperature as pump design bases shall be determined separately. The operating temperature of a tank shall be determined based on the following conditions.

  • The temperature of rundown from process units
  • Ambient air temperature (annual mean or annual highest mean temperature)
  • The temperature of products when they are received from a tanker.

 (2) Operating Pressure: An operating pressure shall be an equilibrium pressure at operating temperature. Where the mole fraction of contents of the liquid in the tank fluctuates, the most severe case in normal operation shall be considered.

Design Conditions

(1) Design Temperature: A design temperature shall be determined based on the assumed highest temperature, with consideration given to input heat generated by solar radiation. Generally, design temperatures are specified per country based on the ambient air conditions of the district where the plant facilities are to be constructed. Major oil companies may have their own design standard for temperature selection. Where the country’s regulations or the client’s design standards do not specify design temperatures, NFPA shall be applied. Design temperature determination standards are closely connected with design pressures.

Major oil companies, in some cases, have specified the lowest design temperature as a design standard; they employ the equilibrium temperature of a tank internal at atmospheric pressure as the lowest design temperature. Low-temperature service materials, therefore, shall be used for tanks storing propane or lighter fluids.

(2) Design Pressure: The equilibrium pressure of a tank internal at the design temperature shall be used as the tank design pressure. Where the country’s regulations or the client’s design standards do not specify a design temperature, NFPA shall be applied as per the table below. Some major oil companies specify a higher temperature e.g. 65° C to be a mechanical design temperature, in their standards. In this case, however, they do not employ the equilibrium pressure of the internal at the specified temperature as design pressure, but the design pressure will be specified separately or the minimum design pressure specified in NFPA is otherwise used.

Note 1: Refer to NFPA 58, Para. 8-2.2

The NFPA specifies the equilibrium pressure at a design temperature of 41, 46, and 54° C, respectively, to be a design pressure, for each type of vessel as given below.

  • Vessels up to 4.5 m3 incl. in-capacity (54°C)
  • Vessels over 4.5 m3 in capacity (46°C)
  • Underground vessels (41°C)

LPG Storage Tank Nozzles

(1) Tank nozzle information to be provided by basic engineering. The following items of nozzle information shall be provided by the basic design group.

  • Size, number, and location of inlet and outlet nozzles. Note: The pump suction nozzle shall be inserted 300 mm from the tank bottom.
  • Size, number, and location of the sampling nozzle(s) and water draw-off nozzle, if required
  • Size and number of the spare nozzle(s), if required
  • Size and number of the vent and drain nozzle. A minimum of one vent and drain nozzle shall be provided.
  • Size and number of nozzles for safety relief valves. A minimum of one spare PSV shall be provided.

(2) Nozzle for instrumentation

Nozzle information for instrumentation will be provided by others.

(3) Nozzles to be decided by the detailed engineering group

The Instrumentation on LPG Storage Tanks

Level

Generally, two-level instruments will be installed to permit mutual calibration to be carried out, because LPG tanks cannot open without the tank shut down. One level instrument may be permitted if it is possible to remove and calibrate it by installing an isolation valve such as a radar type. To use the LPG tank capacity as effectively as possible, it is necessary to compensate the level with a temperature instrument or use a differential pressure type level instrument

Temperature

Generally, a temperature indicator shall be installed at the bottom crown

Pressure

Generally, two pressure gauges should be provided at the sphere’s top and bottom. One pressure instrument should be provided and indicated in the control room. Two pressure relief valves, each having a 100% capacity shall be provided. This configuration allows PRV maintenance without a sphere shutdown.

Water Drain

A Water draws offline shall be installed on each LPG tank. Two isolation valves shall be provided on the water draw offline: a distance of more than one meter shall be provided between the valves to prevent freezing the valves as figures below. As an alternative system, a water draw-off pot is provided, and the vent line from the water pot is returned to the flare line or the LPG tank.

Others

Insulation and Painting: For aboveground tanks, in some cases, cold insulation or fire protection may be provided, according to the client’s request. In such a case, it is possible to reduce the safety valve relieving capacity.

Tank Heaters or Coolers: A tank heater or cooler shall not be installed in the tank. However, an external heater may be required in the coldest areas, i.e. North East of China or Siberia, to avoid a vacuum in the tank.

Work Flow of LPG Storage Tank Basic Design

Codes and Standards for LPG Storage Tanks

There are several codes and standards that apply to the design, construction, installation, and operation of LPG storage tanks. These codes and standards are designed to ensure that the tanks are safe and reliable and that they comply with regulatory requirements.

Here are some of the key codes and standards that apply to LPG storage tanks:

  • NFPA 58: This is the National Fire Protection Association’s standard for the storage and handling of Liquefied Petroleum Gases (LPG). It provides requirements for the design, construction, installation, and maintenance of LPG storage tanks, as well as guidelines for emergency procedures and training.
  • ASME Boiler and Pressure Vessel Code: This code provides rules for the design, fabrication, and inspection of pressure vessels, including LPG storage tanks. It covers a wide range of factors, such as materials, pressure ratings, welds, and nondestructive examination.
  • API 2510: This is the American Petroleum Institute’s recommended practice for the design and construction of LPG storage facilities. It provides guidance on the selection of tank materials, tank size, and tank location, as well as requirements for tank foundations, piping systems, and safety equipment.
  • DOT Regulations: The US Department of Transportation (DOT) has regulations that govern the transportation of hazardous materials, including LPG. These regulations cover the design, construction, and testing of LPG cylinders, as well as requirements for labeling, marking, and documentation.
  • State and Local Regulations: In addition to federal regulations, there may be state and local regulations that apply to the installation and operation of LPG storage tanks. These regulations can vary widely depending on the location, so it is important to consult with local authorities and experts in the field.

By following these codes and standards, LPG storage tanks can be designed, installed, and operated safely and efficiently, with minimal risk to people and the environment.

Materials for LPG Storage Tanks

LPG storage tanks can be made from a variety of materials, depending on the specific requirements of the application. Some common materials used for LPG storage tanks include:

  • Steel: Steel is a common material for LPG storage tanks, due to its strength, durability, and resistance to corrosion. Steel tanks can be either aboveground or underground, and can be coated or painted to provide additional protection against corrosion.
  • Stainless steel: Stainless steel is a common material used for cryogenic LPG storage tanks. It has good strength, durability, and resistance to corrosion at low temperatures.
  • Nickel alloys: Nickel alloys, such as Inconel or Monel, can be used for cryogenic LPG storage tanks. They have good resistance to corrosion and embrittlement at low temperatures.
  • Aluminum: Aluminum is another material that can be used for LPG storage tanks. Aluminum tanks are lightweight and corrosion-resistant, making them a good option for portable applications or locations with high humidity or salt air.
  • Composite materials: Composite materials, such as fiberglass-reinforced plastic (FRP) or carbon fiber, can be used for LPG storage tanks. These materials are lightweight, corrosion-resistant, and have good impact resistance.
  • Concrete: Concrete tanks can be used for underground storage of LPG. Concrete tanks are durable and can withstand high pressure, making them suitable for large-scale industrial applications.

LPG Storage Tank Sizes

LPG storage tank sizes can vary widely, depending on the specific application and the amount of LPG that needs to be stored. Some common LPG storage tank sizes include:

  • Small LPG cylinders: These are typically used for portable applications, such as camping or outdoor cooking. They typically have a capacity of 1-20 pounds (0.5-9 kilograms) of LPG.
  • Residential LPG tanks: These are often used to supply propane for heating and cooking in homes. They typically range in size from 100 to 1,000 gallons (380 to 3,785 liters) of LPG.
  • Commercial LPG tanks: These tanks are used to supply propane for commercial applications, such as fueling forklifts or powering industrial equipment. They typically range in size from 1,000 to 30,000 gallons (3,785 to 113,562 liters) of LPG.
  • Industrial LPG tanks: These tanks are used to supply LPG for large-scale industrial applications, such as power generation or chemical manufacturing. They can range in size from 30,000 to 250,000 gallons (113,562 to 946,353 liters) of LPG or more.

The specific LPG storage tank size that is required will depend on several factors, including the amount of LPG needed, the location and environment in which the tank will be installed, and the specific regulations and safety standards that apply to the installation. It is important to work with an expert in LPG storage tank installation to determine the appropriate tank size for the specific application.

LPG Storage Tank Specification

To specify an LPG storage tank, several factors need to be considered, including the required storage capacity, the type of LPG being stored, the location and environment in which the tank will be installed, and the specific regulations and safety standards that apply to the installation.

Here are some key steps to consider when specifying an LPG storage tank:

  • Determine the required storage capacity: The storage capacity of the tank will depend on the amount of LPG required for the intended application. This may be based on factors such as the size of the property, the number of appliances being powered by the LPG, and the expected usage patterns.
  • Identify the type of LPG: There are different types of LPG, including propane and butane, and the tank must be designed to store the specific type of LPG being used.
  • Choose the appropriate tank type: Based on the required storage capacity and the intended application, select the appropriate type of LPG storage tank, such as aboveground, underground, horizontal, or vertical.
  • Consider location and environment: Determine the location and environment in which the tank will be installed, taking into account factors such as accessibility, ventilation, and weather conditions.
  • Check regulations and safety standards: Ensure that the installation complies with all relevant regulations and safety standards, including local building codes and fire safety regulations.
  • Consult with an expert: Consult with an expert in LPG storage tank installation to ensure that the tank is properly specified and installed and that all safety and regulatory requirements are met.

By following these steps, it is possible to specify an LPG storage tank that meets the specific needs of the application while ensuring safety and compliance with regulations.

Uses of LPG Tanks

Liquefied petroleum gas is used in a number of applications. So in all such applications, the LPG tanks are required to store the LPG. Some of the typical uses of LPG Tanks are:

  • Heating homes.
  • Cooking appliances.
  • Alternative fuel for cars and other vehicles.
  • Refrigerant.
  • Industrial uses like
    • as an energy carrier.
    • as feedstock for the chemical synthesis.
    • for facilitating the different industries’ access to this substance.

What Is Modal Analysis and Why Is It Necessary? Caesar II Piping Modal Analysis Steps

Written by Anup Kumar Dey in Caesar II,Civil,Piping Stress Analysis

Modal analysis is a powerful technique used in vibration engineering fields to understand the dynamic behavior of structures, mechanical systems, piping and pipeline systems, and other physical entities. It plays a crucial role in optimizing designs, improving product performance, and ensuring the safety and reliability of various engineering applications. In this comprehensive guide, we will delve deep into the world of modal analysis, to learn the following:

  • Meaning of Modal Analysis
  • Why is Modal Analysis Important?
  • Criteria for Modal Analysis of Piping System
  • Applications of Modal Analysis
  • Modal Analysis Methods
  • Piping Modal Analysis Software Programs
  • Caesar II Piping Modal Analysis Procedure
  • And Many more…

What is Modal Analysis?

Modal analysis is a technique used to study the dynamic characteristics of structures and systems. It provides valuable insights into how these entities respond to external forces or vibrations. Modal Analysis is the study (analysis) of the dynamic behavior (dynamic analysis) of the structural, piping, or pipeline system and is used to find the natural frequencies of vibration for the concerned structural system. Different modes of vibration (vibration characteristics) of the analyzed piping system are determined using Modal Analysis. The modal analysis helps to show the movement of different parts of the structure under dynamic loading conditions.

The primary goal of modal analysis is to determine the natural frequencies, mode shapes, and damping ratios of a system, which collectively describe its dynamic behavior.

Natural Frequencies:

These are the frequencies at which a structure or system tends to vibrate when subjected to an external force or disturbance. Natural frequencies are characteristic of the system’s mass, stiffness, and geometry.

Mode Shapes:

Mode shapes represent the spatial distribution of motion within a structure or system at a specific natural frequency. They describe how different parts of the system move in relation to each other during vibration.

Damping Ratios:

Damping ratios quantify the energy dissipation in a system, indicating how quickly vibrations decay after an external disturbance is removed.

Why is Modal Analysis Important?

Modal Analysis provides an overview of the limits of the response of a system. All elements of the piping systems like flanges, valves, pipes, etc. have an internal frequency at which they vibrate naturally. At this frequency, the components will allow an energy transfer from one form to another with minimal loss. When this frequency reaches the “resonant frequency,” the system amplitude increases to infinity, and high vibration is observed. Hence, modal analysis is used to find out all such frequencies so that the occurrence of resonance can be prevented. Modal analysis is also known as modal and frequency analysis.

Natural frequencies give us an idea of how fast the piping system is going to vibrate. The term natural means, that the system is in free motion without any external forces. So by performing modal analysis the following two points are discovered

  • The natural frequency of the piping system and
  • The corresponding modes of vibration

Criteria for Modal Analysis of Piping System

While performing stress analysis for piping/pipeline systems you might have come across the term two-phase flow. Most of the flowlines are believed to have two-phase flow. Several processes and oil & gas piping systems, too, carry the two-phase flow. Conventionally all two-phase flow (Slug Flow) lines are believed to be vibration-prone.

The stress analysis basis or flexibility specification of most of the relevant organizations informs the stress engineers to perform modal analysis for such systems and properly support these lines using hold-downs, guides, and axial stops to reduce the extent of vibration. It is a standard engineering practice to keep the natural frequency of vibration-prone lines in excess of 4 Hz. Now the question is how to calculate the natural frequency or modal frequencies of a complex piping system.

The modal analysis module of Caesar II dynamic analysis is also used to calculate the natural frequency of pipe systems connected to compressors and reciprocating pumps. Harmful vibrations will result when the pipe’s natural frequency is close to that of connected rotary equipment. In order to avoid resonance and subsequently fatigue failure, many organizations follow the below-mentioned two criteria while modal analysis

  • f/fn>1.25 and
  • f/fn<0.75

Here, f=excitation frequency of the rotating equipment and fn=piping natural frequency.

Applications of Modal Analysis

The modal analysis finds applications in various fields, including:

  • Structural Engineering: In civil engineering, modal analysis helps assess the dynamic response of buildings and bridges to earthquakes, wind loads, and other environmental factors. It aids in designing structures that can withstand these forces and prevent catastrophic failures.
  • Aerospace Engineering: Modal analysis is used to study the vibrations and dynamic characteristics of aircraft, spacecraft, and rocket components. This information is crucial for designing lightweight yet robust structures to enhance fuel efficiency and safety.
  • Mechanical and Piping Engineering: In mechanical and piping systems, modal analysis assists in optimizing the design of components like engine parts, automotive suspensions, industrial machinery, and piping systems. It ensures that these components operate efficiently and do not fail under dynamic loading conditions.
  • Automotive Industry: Modal analysis is used to evaluate vehicle chassis and suspension systems to improve ride comfort and handling. It also plays a role in reducing noise, vibration, and harshness (NVH) in automobiles.
  • Electronics and MEMS: Modal analysis is applied to micro-electro-mechanical systems (MEMS) and electronic components to understand their dynamic behavior and improve reliability.

Methods of Modal Analysis

Modal analysis can be performed using various methods, including:

  1. Experimental Modal Analysis (EMA): This involves measuring the dynamic response of a physical system using sensors (e.g., accelerometers) and then extracting modal parameters through mathematical techniques like the Fast Fourier Transform (FFT) or system identification.
  2. Operational Modal Analysis (OMA): OMA is conducted on an in-service structure or system without artificially inducing vibrations. It relies on ambient vibrations or external excitations (e.g., traffic loads) to extract modal parameters.
  3. Numerical Modal Analysis: Numerical simulations, such as finite element analysis (FEA) or computational fluid dynamics (CFD), are used to predict the natural frequencies and mode shapes of a system based on its geometric and material properties. This method is often employed in the design phase.

Significance of Modal Analysis

The modal analysis offers several significant benefits:

  • Design Optimization: By understanding a system’s dynamic behavior, engineers can make informed design choices to improve performance, reduce vibrations, and enhance durability.
  • Failure Prediction: Modal analysis can identify potential failure modes and structural weaknesses, allowing for preemptive maintenance or design modifications.
  • Quality Assurance: Manufacturers can use modal analysis to ensure that products meet performance specifications and standards, leading to higher-quality and more reliable products.
  • Safety: In civil and aerospace engineering, modal analysis contributes to the safety and integrity of structures and vehicles by ensuring they can withstand dynamic loads and environmental conditions.
  • Cost Savings: By avoiding overdesign and optimizing structures or systems, modal analysis can lead to cost savings in terms of materials and manufacturing.

Software for Piping Modal Analysis

Various software is available in the market to determine modal responses of structures by modal analysis. For piping and pipeline systems modal analysis is performed using the following software

  • ANSYS
  • Caesar II
  • AutoPipe
  • Start-Prof
  • Rohr 2
  • Caepipe

Out of the above, Caesar II by Hexagon is the most widely used software for modal analysis of Piping Systems.

Dynamic Modal Analysis Module of Caesar II

So, here comes the importance of a Caesar II dynamic module called the Modal analysis module. The complex job of calculating the natural frequency of the piping system becomes very easy with the use of this module. The vibration response or dynamic response of any system can be easily determined using modal analysis. In the actual case, Modal analysis breaks up a complex system into a number of modes of vibration, each of which has a unique vibration response. This article will elaborate on the steps followed for performing the modal analysis using Caesar II.

Modal Analysis Steps in Caesar II

To start the modal analysis you must have a stress system. So from the isometric model, the system follows conventional methods and perform the static analysis and make the system safe in all respect with respect to static analysis. Now follow the below-mentioned steps for dynamic Modal analysis:

Caesar II Modal Analysis Procedure

Click on Analysis-Dynamic Analysis as shown in Fig. 1 to open the dynamic module in Caesar II. It will open the window which is shown in Fig. 2.

Dynamic Module in Caesar II
Fig.1: Starting Dynamic Module in Caesar II
Selection of Modal Analysis in Dynamic Module in Caesar II
Fig.2: Selection of Modal Analysis in Dynamic Module in Caesar II

Now click on Analysis type and select Modal from the drop-down menu. You will get the following window as shown in Fig. 3.

Modal Analysis in Caesar II
Fig. 3: Modal Analysis in Caesar II

You will get four input spreadsheets as lumped masses, snubbers, control parameters, and advanced.

Click on Control parameters and it will open the window shown in Fig. 4.

Change the frequency cut-off to your desired frequency based on your project specification. If you need to arrest all frequencies below 5 Hz and set that value as 5. The stiffness factor for friction can be used up to a value of 100. However, few organizations prefer not to use friction forces in dynamic analysis so use the stiffness factor as zero.

Now select the static load case for which you want to extract the natural frequencies. Normally it is advisable to select the operating temperature case.

Input data for Dynamic Modal Analysis
Fig.4: Input data for Dynamic Modal Analysis

Run the Modal Analysis

Now you are set for analysis, So click on the run button similar to what you do for static analysis. The analysis will extract all the natural frequencies in which the piping system will experience below your cut-off frequency values. Fig. 5 shows such a typical modal run screen.

A Typical Caesar run result of modal analysis
Fig.5: A Typical Caesar run result of modal analysis

How to interpret Modal Analysis Results

After the analysis run is complete the output screen will open. Select Natural frequencies to check the extracted natural frequencies of the system. Most of the time we check the animation view to get a feel of the actual vibration process. Select Natural frequencies and then click on the animation button as shown in Fig. 6.

Selection of animation button during Modal Analysis
Fig.6: Selection of animation button during Modal Analysis

In the animation, view and check how the system is experiencing vibration. Accordingly, provide support. Normally guide and line stop support with zero gaps will be required to arrest the vibration frequencies. Accordingly, provide support. Sometimes hold-down supports will be required. So, each time in the animation view find out the location where the system is vibrating and provide support near it. In most cases, the vibration occurs

  • Near rigid bodies (valves, flanges, etc.)
  • Long unsupported pipe spans
  • Long pipe runs where guide support is not provided
  • Straight lengths of pipe without line stops

So each time provide support at vibrating places in the piping system and re-run the modal analysis as mentioned above.

As soon as you provide a guide and line stop supports the system will become more rigid and expansion stresses will increase. So each time you change some support type you have to perform static analysis and make the system safe from all considerations and then proceed to the dynamic module.

Video tutorial on Modal Analysis Basics and related theories

The following video tutorial gives a nice explanation of the modal analysis basics and modal analysis theories.

Video Tutorial on Modal Analysis Basics and Modal Analysis Theories

Modal analysis is a vital tool in the field of engineering, enabling us to unlock the secrets of dynamic behavior in structures and systems. Whether it’s arresting the vibration of piping and pipeline systems, designing safer buildings, improving the performance of vehicles, or enhancing the reliability of electronic components, modal analysis plays a crucial role in shaping the modern world. With ongoing advancements in technology and analytical techniques, modal analysis continues to evolve, opening up new possibilities for innovation and engineering excellence.

Few more useful resources for you.

Slug Flow Analysis Using Dynamic Spectrum Method in Caesar II

Basics of Pipe Stress Analysis

Piping Layout and Design Basics

Pump Commissioning and Start-Up: Pump Commissioning Checklist

Written by Anup Kumar Dey in Mechanical,Piping Design Basics,Piping Interface

Pre-requisites for commissioning and start-up of a Process Pump:

Before commissioning and starting up of any equipment some preparation must be done. There will be some mandatory requirements, that should be fulfilled. So Process Pump is not an exception. At the same time process pumps, being vibration prone and sensitive, the utmost care has to be exercised. So before starting up the pump set, make sure that the following requirements are met:

  • The pump set has been properly connected to the electric power supply and is equipped with all protective devices.
  • The pump has been primed with the fluid to be handled. 
  • The direction of rotation has been checked. (The correct direction of rotation of motor and pump is in the clockwise direction (seen from the motor end))
  • All auxiliary connections required are connected and operational.
  • The lubricants have been checked.

Filling in the lubricant in bearing bracket of Process Pump:

Fill the bearing bracket of the Process Pump with lubricating oil. The constant-level oiler is screwed into the upper tapping hole of the bearing bracket. If no constant-level oiler is provided on the bearing bracket, the oil level can be read in the middle of the oil level sight glass arranged at the side of the bearing bracket. Note that Insufficient lubricating oil in the reservoir of the constant-level oiler damages the bearings. So

  • Regularly check the oil level.
  • Always fill the oil reservoir completely.
  • Keep the oil reservoir properly filled at all times.
Process Pumps
Bearing Bracket with constant level oiler of typical Process Pump
  1. Remove the protective cage.
  2. Unscrew the vent plug (2).
  3. Hinge down the reservoir of the constant-level oiler (1) from the bearing bracket (5) and hold it in this position.
  4. Pour in the oil through the vent plug tapping hole until oil appears in the connection elbow of the constant-level oiler (3).
  5. Fill the reservoir of the constant-level oiler (1) with oil up to the maximum level.
  6. Snap the reservoir of the constant-level oiler (1) back into the operating position.
  7. Screw the vent plug (2) back in.
  8. Fit the protective cage.
  9. After approximately 5 minutes, check the oil level in the reservoir of the constant-level oiler (1). It is important to keep the reservoir properly filled at all times, to ensure an optimum oil supply. Repeat steps 1 – 8, if necessary.
  10. To verify the correct function of the constant-level oiler (1), slowly drain the oil through the drain plug (4) until air bubbles can be seen in the oiler.

Note that, An excessively high oil level can lead to a temperature rise and to leakage of the fluid handled or oil.

Shaft seal

  • Shaft seals are fitted prior to delivery.
  • Observe the instructions on dismantling or reassembly on the operator’s manual.
  • If applicable, fill the reservoir of non-pressurized external fluid in accordance with the general arrangement drawing.
  • Prior to starting up the pump, apply barrier pressure as specified in the general arrangement drawing.
  • Apply the quantities and pressures specified in the datasheet and the general arrangement drawing.

Filling and venting the Process Pump:  

Before starting up the pump set, vent the pump and suction line and fill both with the fluid to be handled.

  • Vent the pump and suction line and fill both with the fluid to be handled.
  • Fully open the shut-off element in the suction line.
  • Fully open all auxiliary connections (barrier fluid, flushing liquid, etc).

Final check before Starting the Process Pump:

  • Remove the coupling guard and step guard, if any.
  • Check the coupling alignment; re-align the coupling, if required.
  • Check that the coupling and shaft can easily be rotated by hand.
  • Re-install the coupling guard and step guard, if any.
  • Check the distance between coupling and coupling guard. The coupling guard must not touch the coupling.

Water cooling:

Observe the cooling water quality. Also, observe the following quality data of the cooling water:

  • Not deposit forming
  • Not aggressive
  • Free from suspended solids
  • Hardness on average 5 °dH (~1mmol/l)
  • pH > 8
  • Conditioned and neutral with regard to mechanical corrosion
  • Inlet temperature tE= 10 to 30 °C   Outlet temperature tA= maximum 45 °C

Cooling of the pump:

The casing cover, the bearing bracket and the casing support on the baseplate can be cooled. Observe the following quality data of the cooling water:

  • Maximum permissible cooling liquid pressure: 10 bar
  • Maximum permissible cooling liquid test pressure: 15 bar
  • Observe the specified cooling liquid quantity.

Cooling of the shaft seal:

  • Cool the shaft seal.
  • Provide sufficient quantities of cooling liquid (see table).
Cooling Liquid Quantities for Process Pump Operation

Heating up/keeping warm the pump (set):  

Prior to pump start-up, heat up the pump as described in the operating manual. Observe the following when heating up the pump (set) and keeping it warm:

  • Make sure the temperature is increased continuously.
  • Max. heating speed: 10 °C/min (10 K/min)

If the pump is used for handling fluids with fluid temperatures exceeding 150 °C, make sure that the pump has been heated throughout before starting it up. The temperature difference between the pump’s surface and the fluid handled must not exceed 100 °C (100 K) when the pump is started up.

Start-up:

  1. Fully open the shut-off valve in the suction head/suction lift line.
  2. Close or slightly open the shut-off valve in the discharge line.
  3. Switch on the motor.
  4. Immediately after the pump has reached full rotational speed, slowly open the shut-off valve in the discharge line and adjust it to comply with the duty point.
  5. When the operating temperature has been reached and/or in the event of leakage, switch off the pump set and let it cool down. Then retighten the bolts between lantern and casing.
  6. Check the coupling alignment and re-align the coupling if required.

Check that

  • The piping system connected to the pump set has been cleaned.
  • Pump, suction line and inlet tank, if any, have been vented and filled with the fluid to be pumped.
  • The filling and venting lines have been closed.
  • Never operate the pump with the shut-off elements in the suction line and/or discharge line closed.
  • Only start up the pump set with the discharge side gate valve slightly or fully open.
  • Never operate the pump set without liquid fill.
  • Prime the pump as specified. (⇨ Section 6.1.4 Page 31)
  • Always operate the pump within the permissible operating range.

In case of Abnormal noises, vibrations, temperatures or leakage

  • Switch off the pump (set) immediately.
  • Eliminate the causes before returning the pump set to service.

Checking the shaft seal

The mechanical seal only leaks slightly or invisibly (as vapor) during operation. Mechanical seals are maintenance-free.

Operating limits

  • Comply with the operating data indicated in the datasheet.
  • Avoid prolonged operation against a closed shut-off valve.
  • Never operate the pump at temperatures exceeding those specified in the datasheet or on the nameplate unless the written consent of the manufacturer has been obtained.

Ambient temperature

Observe the specified limits for permissible ambient temperatures.

  • Permissible ambient temperature: Maximum 43 °C: Minimum See datasheet

Frequency of starts

The frequency of starts is usually determined by the maximum temperature increase of the motor. This largely depends on the power reserves of the motor in steady-state operation and on the starting conditions (d.o.l., star-delta, moments of inertia, etc). If the start-ups are evenly spaced over the period indicated, the following limits can be used for orientation for a start-up with the discharge-side gate valve slightly open:

Frequency of Starts of a Process Pump

Do not re-start the pump set before the pump rotor has come to a standstill.

The density of the fluid handled

The power input of the pump increases in proportion to the density of the fluid handled. Hence always observe the information on fluid density indicated in the datasheet and make sure the power reserve of the motor is sufficient.

Abrasive fluids

Do not exceed the maximum permissible solids content specified in the datasheet. When the pump handles fluids containing abrasive substances, increased wear of the hydraulic system and the shaft seal are to be expected. In this case, reduce the intervals commonly recommended for servicing and maintenance.

Pump Commissioning Checklist

The commissioning of Process Pumping systems is a complex process that requires a structured approach. A pump commissioning checklist validates the operation of pumps through correct installation, proper lubrication, and simulation of instrumentation and protection devices. The following checklist highlights some of the areas that need to be verified when commissioning pumping systems:

  • Pumps in place and properly grouted, anchoring installed as per specification
    • Pump tag and nameplate permanently affixed
    • Pump environment clean with adequate access for maintenance
    • Distribution piping complete, including pipe fittings and accessories, bleed and makeup water lines and safety reliefs; piping type and  flow direction labeled on piping, valves properly tagged
    • System flushing complete and strainers cleaned
    • Required valves and balancing valves installed and balancing completed; TAB report reviewed for pump flows, pressure or head, electrical data
    • Temperature, pressure, and flow gauges and sensors installed per specification; test ports installed near all control sensors
    • Flow switch and flow meters installed as required and per specification
    • Expansion tanks verified to not be air-bound and system completely full of water
    • Air vents and bleeds at high points of systems functional
    • Vibration isolation devices installed and functional
    • Factory alignment/field alignment correct
    • No visible leaks
    • Pump lubricated
    • Automatic valves stroke fully and close tightly
    • Pump electrical supply disconnects in place and labeled; all electrical connections tight
    • Motor safeties in place and operable
    • All control devices, tubing, and wiring complete; control system interlocks hooked up and functional
    • Water treatment system or plan installed
    • VFD commissioned in accordance with the manufacturer’s instructions.
  • Specific commissioning actions will depend on the type and extent of the system to be commissioned.

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