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Storage Tank Construction: Procedure and Method Statement

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

Storage tanks play a vital role in various industries, including oil and gas, chemicals, food and beverage, and water treatment. They are used for storing liquids, gases, and even solids. Understanding the construction of storage tanks is essential for professionals in these fields, as well as for those interested in engineering and infrastructure development.

The method statement for storage tank construction provides detailed information on the procedure and rules for conducting all fabrication, erection, and testing of the storage tanks and similar static equipment. All the tasks/activities should be completed with the utmost care, with good workmanship, and in accordance with the specifications to realize satisfactory completion of the entire activities. This document will provide a reference for a proper methodology to realize the activities during a proper sequence for fabrication, erection, and testing of the storage tanks.

What is Storage Tank Construction?

Storage tank construction refers to the process of fabricating and installing tanks used for storing liquids, gases, or solids. This involves various stages, including site preparation, foundation work, tank fabrication (either on-site or off-site), installation of piping and accessories, and adherence to safety and regulatory standards. The construction can involve different materials, such as steel, concrete, or fiberglass, depending on the intended use and environmental conditions. Proper design and construction ensure the tanks’ structural integrity, safety, and efficiency in storage operations.

Reference Codes and Specifications for storage tank construction

The required codes and specifications for the storage tank construction are

  • API 650
  • IS 803
  • ASME Sec IX
  • Approved Drawing / Specification
  • ASME Sec V
Storage Tanks in a Tank Farm
Fig. 1: Storage Tanks in a Tank Farm

Storage Tank Construction Methodology

The storage tank construction methodology can be performed in the sequence listed below:

  1. Identification of Tank Materials
  2. Tank Construction and Fabrication
    • Annular and Bottom Plate Fabrication
    • Shell Plate Fabrication
    • Roof Plate Fabrication
    • Appurtenances
    • Spiral Stairway and handrailing
  3. Storage Tank Erection
    • Annular Plate laying
    • Bottom Plate laying
    • Erection of Cone Roof plates and Structures
    • Shell Course Erection
    • Appurtenances installation

1. Identification of Tank Materials

All items required for tank fabrication, like plates, fittings, and other components of the tankage system, must be clearly identified by marking heat numbers by hard-punching on each part. Each weld joint shall be marked with a joint number and a welder number.

2. Storage Tank Construction and Fabrication

All fabrication works like tank material identification, marking, cutting, rolling and welding must be performed as mentioned in the latest API 650. The workmanship shall be good in every respect. It must be meeting all safety, Quality Control & Non-Destructive Testing requirements, with the coordination of the Engineer-In-Charge.

  • Lay all the plates, Structural & pipes in such a fashion that facilitates proper checking of dimensions & heat no.
  • Mark the components as per the drawings.

2.1 Tank Annular and Bottom Plate Fabrication

  • Mark the plates as per the drawing
  • Perform the cutting operation after proper inspection.
  • All the cutting operations shall be administered by Gas Cutting.
  • Grind the cut edges smoothly to get rid of burrs and slag.
  • Stack the plates at designated places within the fabrication yard in proper Sequence.
  • The backing strip shall be fitted and tacked with an annular plate as per the drawing.
  • After completion of the fabrication, the underside of the annular and bottom plates shall be blast cleaned and painted as per the specification to the satisfaction of the engineer-in-charge.
  • Check the joint position and root gap for welding after welding inspection by weld visual & NDT as per API 650.
Tank Shell and Bottom Plate Fabrication
Fig. 2: Tank Shell and Bottom Plate Fabrication

2.2 Tank Shell Plate Fabrication

  • Lay all the plates within the open area such as how easy it is for marking and cutting.
  • Mark the plates as per the drawing and to the satisfaction of the engineer in charge.
  • The cutting operation including beveling shall be administered by the gas-cutting method on all four sides.
  • Grind the cut edges smoothly to get rid of slag and burr.
  • The stings-prepared plates shall be shifted by crane to the rolling area.
  • The plates shall be fed to the rolling machine. by means of a crane & proper lifting tools and tackles.
  • The plate shall be rolled as per drawing details and therefore the radius shall be checked using a Template.
  • Proper care shall be taken for the graceful curvature. 36’’ Long (5 to 6 mm thick). The template shall be wont to check rolling curvature accurately.
  • The Template shall be checked and cleared by the inspection authority.
  • The rolled plates shall be inspected and shall be within 3 mm of the tolerance limit.
  • The rolled plates shall be shifted to the shot blasting yard to hold out the shot blast as per specification.
  • Final profile and dimensions check shall be administered before sending for erection.

2.3 Tank Roof Plate Fabrication

  • Mark the roof plate as per the drawing.
  • All the cutting operations as per requirement shall be administered after getting clearance from the inspection authority.
  • All the cutting operations shall be administered by the gas-cutting method on all four sides. Grind the cut edges smoothly to get rid of burrs & slag.
  • Structural items of the roof shall be fabricated as per the drawing.
  • These roof plates shall be shifted to the blasting yard to hold out the blasting and painting

2.4 Tank Appurtenances

  • Mark the specified items of the Appurtenances as per the drawing. All the cutting operations as per requirement shall be administered after getting clearance from the inspection authority.
  • All the cutting operations shall be administered by the gas-cutting method.
  • Grind the cut edges smoothly to get rid of burrs & slag.
  • The Flange face is covered with an appropriate cover to guard against damage during handling, fabrication, and transportation.
  • The whole shell nozzle, roof appurtenance, i.e. flanges, flanges to pipe joint, and other requirements, etc. Shall be fabricated as per approved drawings.
  • All the fabrication and welding activities shall be administered after the stage-wise inspection wherever required.
  • The NDT requirements are as per code specification.

2.5 Spiral Stairway, Hand Railing of Storage Tanks

  • All the structural items shall be straightened before marking and cutting.
  • Mark the components as per the drawing.
  • All the cutting operations, as per requirement shall be administered after getting the clearance from the inspection authority.
  • All the cutting operations shall be administered by the gas-cutting method.
  • Grind the cut edges smoothly to get rid of burrs & slag.
  • Fabrication like fitting, welding, drilling, etc. shall be administered as per drawing and after clearance from the inspection authority.
  • After fabrication, these structural items shall be blasted and painted as per requirement.
Hand railing of Storage Tanks
Fig. 3: Handrailing of Storage Tanks

3. Storage Tank Erection

There are two methods for storage tank erection:

  • the Jacking method &
  • the conventional method.

The conventional method is tough & unsafe as compared to the jacking method that’s why the jacking method for Tank erection is used everywhere.

In the jacking method, we calculate the overall weight of tank ages except for the bottom & deck, and accordingly, jacks are used. The number of jacks to be used is directly subjected to the weight of the tank to be lifted.

Jacking method of tank erection
Fig. 4: Jacking method of tank erection

3.1 Laying of Storage Tank Annular Plate

  • Check the extent of the foundation as per specification Latest API 650 clause 8.4.2. After getting clearance for annular plate laying, mark the 0 degrees, 90 degrees, 180 degrees, and 270 degrees coordinates on the inspiration from the point of reference.
  • Lay the annular plate as per the approved drawing. Out radius of the annular plate shall be on the positive side (5 to 10 mm.) so as to realize the ultimately required radius after weld shrinkage.
  • The orientation of the annular plate joint shall be as per the approved drawing.
  • Fit from the annular plate’s joints shall be administered using proper jigs and fixtures as shown in the drawing.
  • Care shall be taken while fit-up, such that there shouldn’t be any gap between the annular plate and backing strip.
  • Annular plate joint welding shall be administered by welding alternative joints in four quadrants.
  • Qualified welders shall be engaged for the welding work consistent with WPS. If any defect is found, the defect weld shall be removed by grinding and re-welding and conducting the LPT check test.
  • Repeat the sequence until the defect is cleared.
  • Complete the welding, and clean the ultimate weld surface by wire brushing and grinding.
  • Remove the jigs and fixtures that were used for the fit-up of the annular joint and grind the tack.
  • Radiography shall be taken as per API-650 Sec-8.

3.2 Laying of Storage Tank Bottom Plate

  • Lay the middle plate on the inspiration top as per the drawing.
  • With the coordination of the Centre, plates lay rock bottom plates consecutively as per the drawing.
  • Laps shall be maintained while the fit-up of a short seam and long seam as per drawing.
  • Temporary tack welding is to be performed on the long seam to avoid uneven movements, while the fit-up and welding of the short seam are.
  • Short seam welding is going to be administered alternatively to avoid distortion.
  • After the completion of short-seam welding, remove the temporary tacks on the Long- seam by grinding to facilitate the long-seam fit-up. Short seam welding is going to be administered alternatively to avoid distortion.
  • After the completion of short-seam welding, remove the temporary tacks on the Long- seam by grinding to facilitate the long-seam fit-up.
  • Minimum laps shall be maintained while the fit-up of the long seam is as per the approved drawing.
  • Joggling shall be administered by hammering wherever necessary. (Three plates Joining junction.)
  • Before starting the welding, channels shall be tacked along the long seam to avoid distortion. After completion of shot seam welding long seam welding is going to be administered alternatively to avoid distortion. a professional welder shall be engaged and welding shall be performed as per the approved WPS.
  • After completion of welding, thoroughly clean the weld joint by wire brushing and grinding.
  • Sketch to annular plate joint shall be welded only after shell-to-bottom joint welding.
  • All rock bottom plate joint vacuum box tests shall be administered as per the approved process and code specifications.
  • If any defect is found, the defect weld shall be removed by grinding and re-welding and conducting the vacuum box test. Repeat the sequence until the defect is cleared.

3.3 Erection of Cone Roof Plates and Structures

  • After completion of the highest two shell courses erection, fit-up, welding, and curb ring fit & welding shall be done.
  • Erect the fabricated Centre Drum, Roof Truss, and cross girders as per drawing.
  • Complete the welding of the Roof structure by approved welders and as per approved WPS. Erect and Lay the Roof plates on the structure as per the Drawing. While fit from the short seams and long seams Lap to be maintained as per the Drawing.
  • Weld the short seams by welding the alternative joint or sequence mentioned within the drawing to stop the distortion.
  • Provide proper support lengthwise of the long seam and weld the joints as per the drawing sequence.
  • Roof Nozzles and top shell nozzles fit-up and welding shall be carried out as per the approved drawing and subsequently, it’s to be correlated with the priority piping drawing.
Spiral Stairway of Storage Tanks
Fig. 5: Spiral Stairway of Storage Tanks

3.4 Erection of Storage Tank Shell

  • After the completion of the welding of the Annular plates and bottom plates, mark the tank’s inner radius on the annular plates.
  • Fix 25 Nos. of erection tools at equal intervals on the annular Plates & transfer the within tank diameter on the stools.
  • The last 2 shell courses shall be erected by the conventional method.
  • Balance shell courses shall be erected by the Jacking method.
  • The rolled shell plates shall be shifted to the tank foundation area stacked around the periphery by using a crane.
  • Proper care shall be taken while handling the rolled plates.
  • Care shall be taken that the shell plate is erected to the diameter marked on the annular plate. Jigs and fixtures shall be used to align the shell plates.
  • Complete the fit-up except for the ultimate joint which shall be fitted and welded after completion of the welding of the opposite joints. (To avoid shrinkage).
  • Peaking shall be checked at the top, middle, and bottom of the vertical joints employing a Sweep board of 36” long. Plumpness shall be checked for the verticality of the shell course at every 60° and shall be within the tolerance (tolerance 1/200 of the entire shell height).
  • For perfect verticality, channels shall be provided at regular intervals inside the shell course (3 to five meters), providing the channels shall facilitate the alignment of the of the shell course.
  • Tack welds of the fitted vertical joints shall be ground smooth. Offer for inspection and obtain clearance from Engineer-in-charge for the vertical fit-up Complete the primary side welding by using qualified welders.
  • Care shall be taken while welding to avoid peaking and therefore the roundness distortion.
  • After completion of the first side welding, the back-chip shall be administered for sound metal from the other side of the weld by grinding.
  • Back-chipped grooves shall be offered for inspection before starting the welding.
  • Complete the 2nd side welding using qualified welders.
  • Joint Nos. & welder No. shall be marked on both sides of the weld joint. Care shall be taken to avoid peaking and roundness distortion. Clean weld joints from each side by wire brushing and grinding. After completion of welding from each side remove all the temporary jigs and fixtures and flush grind the tacks. (Do the weld refill wherever required) and therefore the portion checked by M.P.T.
  • Check the plumpness, circumference, and therefore the radius, and offer for inspection to the satisfaction of the Engineer-in-Charge. While erecting subsequent coarse 3 mm-thick spacers shall be kept between the shell courses.
  • Erection channels shall be fixed between the jacked shell and erected shell course plates at regular intervals to align and hold the last shell in a vertical position.
  • Check to peak at vertical joints of shell employing a sweep board of 36″wide, acceptable tolerance shall the as per API-650.
  • Complete welding of last course vertical seam inside after getting clearance from the Engineer-in-charge. Back chip & welding shall be administered following as same as for other shell courses to the satisfaction of Engineer – in – Charge.
  • After completion of welding, weld visuals, verticality, & circumference shall be verified and recorded to the satisfaction of the Engineer-in-Charge. Fit up the horizontal seam between the 2nd and 1st shell courses.
  • Check the verticality of the last shell course, Verticality (plumpness) tolerance shall be as per API – 650 (maximum out of plumpness at the highest of the shell relative to the rock bottom of the shell to not exceed 1/200 of total shell height from top of the last shell to bottom).
  • While welding, care shall be taken for banding and therefore the roundness. Back-chip shall be administered by grinding for the sound metal and to the satisfaction of the Engineer-in-Charge. Complete the 2nd side welding and clean the joint thoroughly from each side by grinding and wire brushing. Check banding, and plumpness, and record within the approved format to the satisfaction of Engineer-in-Charge.
  • Offer welds visually to the satisfaction of the Engineer-in-Charge. Mark the RT spots as per the instruction of the Engineer-in-Charge, and complete the RT as per API-650 requirements. Offer the RT film for review to the Engineer-in-Charge, and if any repair occurs, the repair spot shall be repaired by grinding for the sound metal, Re-weld the repair spot as per code API -650 sec-8 requirements.
  • Take the repair spot RT and re-offer for the inspection to the satisfaction of the Engineer-in-Charge. Spiral staircase erection shall be administered as per drawing, including brackets & avoiding fouling with welds.
  • Remove all the temporary cleats and tacks by grinding. If any defect is found the defect shall be repaired by grinding the defect area for the sound metal plus 150mm from both ends of the defect.
  • Conduct the DP test on the repair spot. perform the entire
  • Process until the repair is cleared to the satisfaction of the Engineer-in-Charge.
  • After completion of the shell to the bottom outside welding visual inspection is going to be administered to the satisfaction of the Engineer-In Charge.
  • On completion of the shell-to-bottom welding/NDT and having completed all erection and welding work on the tank inside associated with the roof and roof structure, all unwanted materials, and scrap shall be far away from inside the tank.
  • RT of the vertical and horizontal joints shall be completed.
  • Sketch to annular plate joint fit-up shall be administered after completing the shell-to-bottom welds.
  • A vacuum box test shall be administered for the rock bottom plate short seam, long seam, and sketch to the annular plate joint. If any repair occurs, an equivalent shall be repaired and re-tested as per the approved procedure and API-650.
Storage Tank Construction at Site
Fig. 6: Storage Tank Construction at Site

3.5 Installation of Tank Appurtenances

  • Flanges to pipe joint shall be prefabricated and required NDT shall be completed before erection.
  • Mark the nozzle location as per the drawings. Cut the openings by gas cutting after proper Inspection-by-inspection authority.
  • Erect the nozzles as per the orientation & the elevation shown within the drawing. Install RF. pads wherever required before nozzle erection.
  • Suitable jigs & fixtures shall be provided to stop the distortion during the welding.
  • Orientation, elevation, & projection shall be maintained as per the drawing and offer for the inspection clearance. Proper care shall be taken for welding by providing jigs & fixtures to stop distortion.
  • Welding shall be as per WPS and to be welded by the qualified welder.
  • The man-hole neck shall be fabricated, and therefore the longitudinal joint shall be radiographed. All the RF Pad welds shall be pneumatically tested at a pressure of 1.05 Kg/Cm². The pneumatic test shall be administered to the satisfaction of the engineer in charge.
  • All the shell nozzles finally weld from each side and RF Pads welds shall be inspected visually and by LPT, to the satisfaction of the engineer-in-charge.

Storage tank construction is a complex and multifaceted process that requires careful planning, design, and execution. Whether for oil and gas, chemicals, or other industries, the principles of storage tank construction remain critical for protecting resources and the environment while ensuring the safety of personnel and the surrounding community.

Differences Between Jacking and Conventional Methods of Tank Erection

The major differences between the storage tank erection methods by conventional and jacking methods are provided here: Storage Tank Erection: Conventional vs Jacking Method

Click here to know more details about storage tanks

Pressure Relief Valve (PRV): Definition, Types, Working, Location, Sizing, Codes and Standards

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

A pressure relief valve is used to release excess pressure from a system during overpressure situations thus avoiding catastrophic failure. So, a Pressure relief valve is an important process safety device and is widely used in the chemical, petrochemical, power, and oil and gas industries. The pressure relief valve (PRV) is designed to open at a predefined set pressure. So whenever the system pressure exceeds the set pressure, the PRV pops and releases the overpressure and when the excess pressure is removed the PRV closes again. The main advantages of installing a pressure relief valve in a system are:

  • They vent the fluid to safeguard the system from overpressure.
  • They reclose and prevent loss of fluid when system pressure returns back to acceptable.
  • Installation of the PRV system minimizes damage to system components.
  • They are reliable and versatile

What are Relief Events?

Relief events are obligatory events that prevent efficiency or performance and increase cost but must be met considering the safety of the operating plant. Examples of potential relief events are

  • External fire
  • Flow from a high-pressure source
  • Heat input from associated equipment/ external source
  • Pumps and compressors or other equipment failures.
  • Failure of Cooling Medium
  • Ambient heat transfer
  • Failure of the Control system
  • Liquid expansion in pipes and surge
  • Blocked discharge, Gas blowby
  • Failure of the Condenser system
  • Chemical reactions
  • Operating error
  • Closed Outlets
  • The entrance of Volatile Fluid

Potential Lines of Defense against Relief Events

To act against the above-mentioned potential relief events the following defense methods are followed.

  • Inherently Safe Design
  • Low-pressure processes
  • Passive Control
  • Overdesign of process equipment
  • Active Control
  • Install Relief Systems

What is a Relief System?

A relief system is an emergency system used to safeguard plants during relief events by reducing pressure or discharging gas during abnormal situations. The relief system consists of

  • A relief device, and
  • Associated lines and process equipment to safely handle the material ejected

Why Use a Relief System?

Installing relief systems in operating plants is a must from the process and technical safety points as

  • Inherently Safe Design simply can’t eliminate every pressure hazard
  • Passive designs can be exceedingly expensive and cumbersome
  • Relief systems work!

Code Requirements for relief system design

General Code requirements include:

  • ASME Boiler & Pressure Vessel Codes
  • ASME B31.3 / Petroleum Refinery Piping
  • ASME B16.5 / Flanges & Flanged Fittings

Relieving pressure shall not exceed MAWP (accumulation) by more than:

  • 3% for fired and unfired steam boilers
  • 10% for vessels equipped with a single pressure relief device
  • 16% for vessels equipped with multiple pressure relief devices
  • 21% for fire contingency

Locating Pressure Relief Valves

The location of Pressure Relief valves is decided by Process Engineers. They mention the PRV requirements in the P&ID. Below are the General guidelines on where relief devices are required, although there are likely to be other special cases in any process.

  • All vessels
  • Blocked in sections of cool liquid lines that are exposed to heat
  • Discharge sides of positive displacement pumps, compressors, and turbines
  • Vessel steam jackets
  • Low-pressure storage tanks require both vacuum and pressure relief devices since tanks are typically not designed for full vacuum.
  • Wherever formal hazard identification procedures such as Hazard and Operability (HAZOP), Process Hazard Analysis (PHA) indicates
  • Piping systems where overpressure can arise due to process control failure.

Types of Pressure Relief Valves

Conventionally Pressure relief valves are categorized into the following three groups:

  • Relief Valve
    • Adjustable
    • Electronic
  • Safety Valve
    • Low Lift
    • High Lift
    • Full Lift
  • Safety Relief Valve
    • Conventional spring-loaded safety relief valve pilot-operated
    • relief valve
    • Balanced-bellows type relief valve
    • Power actuated
    • Temperature and Pressure actuated relief valve

The above-mentioned pressure relief valve types are produced in graphical form in Fig. 1 below

Types of Pressure Relief Valves
Fig. 1: Types of Pressure Relief Valves

Relief valves are spring-loaded and characterized by gradual opening and closing. They are actuated by the upstream pressure and are suitable for incompressible fluids. Adjustable relief valves allow the pressure setting adjustment through the outlet port. Electronic relief valves offer zero leakage with electric controls to monitor and regulate the system pressure.

On the other hand, safety valves are used for compressible fluids (gas and vapors) and are characterized by the rapid action of opening and closing. Safety valves are widely used in steam plants for boiler overpressure protection. They are classified into three groups based on the amount of travel or lift during the pop-up. Low-lift safety valves have a small capacity and the valve lifts 1/24th of the bore diameter. High-lift safety valves travel 1/12th of the bore diameter. Whereas Full-lift safety valves travel at least 1/4th of the bore diameter and are best suited for steam services.

The safety relief valve can be used for gas or liquid service depending on the application. They have the characteristic of both rapid and gradual opening.

Conventional Pressure Relief Valve

Spring-loaded conventional pressure relief valves are best suited for applications where excessive back pressure is absent. The back-pressure directly affects the operational characteristics of these PRVs. Refer to Fig. 2 which represents a conventional safety relief valve with its basic elements.

Conventional type Pressure Relief Valve
Fig. 2: Conventional type Pressure Relief Valve

There are three basic components of a conventional pressure relief valve

  • An inlet nozzle to be connected to the system requiring protection.
  • A movable disk for fluid flow control, and
  • A spring for controlling the disk position.

While designing a conventional pressure relief valve, consideration of seat leakage to be checked as leakage means continuous loss of system fluid and the valve seating surface can be damaged. Depending on the seating material, conventional pressure relief valves are classified into the following two types:

  • Metal-seated valves, and
  • Soft-seated valve

Pros & Cons of Conventional Pressure Relief Valves

Advantages

  • Most reliable type if properly sized and operated
  • Versatile — can be used in many services

Disadvantages

  • Relieving pressure affected by back pressure
  • Susceptible to chatter if built-up back pressure is too high

Balanced Bellows Type Pressure Relief valve

To reduce the effects of backpressure, spring-loaded balanced bellows pressure relief valves (Fig. 3) are developed. The PRV design incorporates a bellow that offsets the effect of back pressure. The bellow isolates the spring, bonnet, and guiding surfaces from direct contact with the process fluid.

Typically when back pressure is variable and exceeds 10% of the set pressure, a balanced-bellows type pressure relief valve is used.

Balanced Bellow type Pressure relief valve
Fig. 3: Bonnet Bellow type PRV

Pros & Cons of Balanced Bellows type Pressure Relief Valve

Advantages

  • Relieving pressure not affected by back pressure
  • Can handle higher built-up backpressure
  • Protects spring from corrosion
  • Possess good temperature and chemical properties

Disadvantages

  • Bellows are susceptible to fatigue/rupture
  • May release flammables/toxics into the atmosphere
  • Requires a separate venting system

There are two types of balanced bellows safety relief valves:

  • Balanced bellows
  • Balanced bellows with auxiliary balancing piston

Pilot-operated Pressure Relief Valves

A pilot-operated safety relief valve is a pressure relief valve where a self-actuated auxiliary pressure relief controls the pressure-relieving. The opening or closing of the relief valve is governed by the pressure of the flowing medium. A pilot is used to sense the process pressure and to pressurize or vent the dome pressure chamber, which controls the valve opening or closing. Three main components consist of a pilot-operated pressure relief valve (Fig. 4)

  • the main valve,
  • a floating, unbalanced piston assembly, and
  • an external pilot.
Pilot-Operated Pressure Relief Valve
Fig. 4: Pilot-Operated Pressure Relief Valve

The pressure on the top side of the main valve’s unbalanced moving chamber is controlled by the pilot. Generally, a resilient seat is attached to the lower end.

Advantages of Pilot-Operated Pressure Relief Valve

The main advantages of pilot-operated safety relief valves are:

  • The set pressure is unaffected by the valve backpressure.
  • As the system operating pressure decides the opening of the relief valve, the system can be operated at maximum working pressure.
  • Economical as compared to other types.
  • Less susceptibility to chatter.

Pilot-operated Pressure relief valves can be classified based on various parameters as mentioned shown below:

  • Depending on the type of moving members
    • A piston-type.
    • A diaphragm-type.
  • Based on the type of pilots
    • A pop-action pilot
    • A modulating-action pilot
  • Based on the flow of pilots
    • A flowing-type pilot.
    • A non-flowing-type pilot

Power Actuated Pressure Relief Valve

Power-actuated pressure relief valves (Fig. 5) are controlled by a device requiring an external power source. Energy sources like water, electricity, or steam control the opening and closing of the pressure relief valve. They are mostly used for forced-flow steam generators with no fixed steam or waterline and in nuclear power plants.

Temperature Pressure actuated Pressure Relief Valves

A temperature and pressure-actuated pressure relief valve (also known as T&P safety relief valve-Fig. 5) is actuated by the temperature or pressure of the inlet side of the relief valve. The valve consists of two primary controlling elements, a spring, and a thermal probe. They serve dual purposes.

  • Prevention of temperature rise above specified and
  • Prevention of over-pressure from rising above a specified value.

They are mostly used for vessels, tanks, and heaters carrying hot fluids.

Power and Temperature Actuated Safety Relief Valve
Fig. 5: Power and Temperature Actuated Safety Relief Valve

Vacuum Relief Valve

A Vacuum Relief Valve is designed to prevent an excessive internal vacuum by admitting fluid. Once the normal condition is restored, they reclose and prevent further fluid flow.

When to Use a Spring-Operated Pressure Relief Valve

  • Losing entire contents is unacceptable
    • Fluids above the normal boiling point
    • Toxic fluids
  • Need to avoid failing low
  • Return to normal operations quickly
  • Withstand process pressure changes, including vacuum

Pressure Relief Valve Accessories

A number of pressure relief valve accessories help the valve in its operations to achieve the intended use. They are:

  • Test gags hold the safety valve closed during the hydrostatic test.
  • Lifting mechanisms to lift the valve disk. Available in three types
    • plain lever,
    • packaged lever, and
    • air-operated lifting devices.
  • Bolted caps are available for standard pressure relief valves in addition to the screwed caps.
  • Valve position indicators for remote indication of the PRV opening

Working of a Pressure Relief Valve

For a spring-loaded pressure relief valve, the spring force holds the disk in position keeping the valve in a closed position. When the pressure of the line exceeds the set pressure, the disk starts to lift allowing the fluid to flow through the outlet and release pressure. With a further increase in inlet pressure, the disk lifts further. When the disk has traveled to its designed value, the valve is fully open and the system pressure is released.
Once the overpressure inside the system falls below the spring force the spring pushes back the disk in positive to close the valve preventing further release of fluid.

For pilot-operated pressure relief valves, the inlet pressure is directed to a small safety valve that acts on top of the piston. As the top area of the piston is designed greater than the bottom area under fluid contact, the pressure on top is higher which pushes the piston to close the relief valve. When the inlet pressure rises above the set pressure, a net upward force acts on the piston forcing the piston to pop up and release the pressure.

Codes and Standards for Pressure Relief Valve

Pressure relief valves are governed by codes and standards. The most widely used pressure relief valve codes and standards are:

  • ASME BPVC (Sec I, Sec III, Sec IV and Sec VIII)
  • ISO 4126
  • API 520
  • API 521
  • API 526
  • API 527
  • PED 97/23/EC
  • EN4126
  • JIS B 8210 (Japan)
  • KS B 6216 (Korea)
  • SAA AS 1271 (Australia)

Relief Valves – Pressure Terminologies

Let us understand some additional basic terms which are widely used in relation to relief valves.

The set pressure is the pressure at which the relief valve starts to open. It is normally the same as design pressure and is measured at the valve inlet. For spring-operated relief valves small amount of leakage (simmer) starts at 92-95% of the set pressure.

Overpressure is the pressure increase over the set pressure of a pressure relief device, during discharge and is usually expressed as a percentage of the set pressure (normally overpressure is set to pressure +10%) Relief valve achieves its full discharge capacity at overpressure

Accumulation is the pressure increase over the DP/ MAWP of equipment during discharge through the protecting pressure relief valve and is usually expressed as a percentage of the DP/MAWP.

Generally there is confusion between the terms Accumulation and Overpressure. When we say ‘accumulation’, it means we are talking about the vessel, and when we say ‘overpressure’, we are talking about the pressure relief valve

Blowdown is the pressure difference between the set pressure and the pressure at which the valve reseats. It is usually expressed as % of the set pressure and refers to how much the pressure needs to drop before the valve reseats.

Reseat Pressure is the pressure at which the valve is fully closed.

The cold differential test pressure is the pressure at which the valve is adjusted to open on the test stand, and incorporates the effects of superimposed back pressure and operating temperatures

Pressure Relief Valve Sizing

Correct sizing of Relief Valves is crucial. If the relief valve is undersized it may not relieve sufficient quantity of fluid to prevent pressure build-up. This consequently may result in high pressure. If the relief device is oversized, the relief valve may become unstable during operation.

The sizing of a pressure relief valve is done by the Process team based on the governing codes and standards. The most widely used reference for pressure relief valve sizing is API 520. The parameters that affect the PRV sizing and selection are

  • Set the Pressure of the relief valve
  • Process Design temperature and pressure
  • Size of inlet and outlet piping
  • Backpressure on the pressure relief valve outlet
  • Fluid Service
  • The required capacity of the relief valve
  • Flow condition (liquid flow, gas flow (critical and sub-critical), steam flow, and two-phase flow)

The sizing of the pressure relief valve is a complex method requiring a multi-step process as listed below:

  • Defining the Protected System
  • Locating the relief valve
  • Defining the over-pressure condition
  • Selecting the relief device
  • Obtaining Data for Relief valve Sizing
  • Determining the flow condition types

The above steps can be easily shown in the form of a flowchart as shown in Fig. 6.

Pressure Relief valve Sizing Flowchart
Fig. 6: Pressure Relief valve Sizing Flowchart

Most major pressure relief valve manufacturers provide sizing software having the unlimited capability to accept wide variability of fluid properties and decide the right pressure relief valve. Some typical software for pressure relief valve sizing is developed by:

  • Anderson Greenwood Crosby
  • PRV2SIZE software Emerson Automation Solutions
  • PRV2SIZE software Pentair Software
  • VALVESTAR® by LESER Safety Valves
  • SIZEMASTER – Relief System Sizing Software by Farris
  • VALVIO by HEROSE
  • Fluid-Flow

In absence of pressure relief valve sizing software or manufacturer’s standard tables, the effective orifice area can be manually calculated using the following equations:

Pressure Relief Valve Sizing Equations
Fig. 7: Pressure Relief Valve Sizing Equations

After getting the effective area, the Standard pressure relief valve orifice designation (size) is selected from the following table:

Standard Orifice Designation for Pressure Relief Valve
Fig. 8: Standard Orifice Designation for Pressure Relief Valve

Pressure Relief Valve Symbols

Pressure relief valves are designated by special symbols as shown below:

Pressure Relief Valve Symbols
Fig. 9: Pressure Relief Valve Symbols

Fig. 9 also provides the P&ID representation of a typical Pressure Safety Valve. Set pressure and Orifice Designation is clearly mentioned in the P&ID, along with the identifier and symbol of the pressure relief valve.

Relief Valve Chattering

Chattering is the rapid opening and closing of a pressure relief valve at low flow rates. Under normal process conditions the vessel pressure is below the set pressure of the relief valve. As the pressure increases and exceeds the relief valve set pressure the valve opens. As soon as the valve opens there is flow resulting in a pressure drop between the vessel and the valve. If this pressure drop is large enough, the pressure at the relief valve can be low enough so that the relief valve closes. The flow stops, the pressure at the relief valve increases back to the vessel pressure because there is no flow to cause a pressure drop and the relief valve opens again.

  • Spring relief devices require 25-30% of maximum flow capacity to maintain the valve seat in the open position
  • Lower flows result in chattering, caused by rapid opening and closing of the valve disc
  • This can lead to the destruction of the device and a dangerous situation

Chatter – Principal Causes

Valve Issues

  • Oversized valve
  • Valve handling widely differing rates
  • Relief System Issues
    • Excessive inlet pressure drop
    • Excessive built-up backpressure

Oversized valves will partially lift at set pressure & then re-seat resulting in “chattering” of the disc which could damage the seat/disc surfaces and cause the relief valve to fail. It is good practice to install multiple relief valves for varying loads to minimize chattering on small discharges.

The general rule to prevent relief valve chattering: line pressure drop between equipment and inlet of RV during relief case must be <3% of RV set value.

Difference between a PSV and PRV

  • A Pressure Relief Valve (PRV) opens gradually in relation to the pressure, on the other hand when the pressure reaches a certain value a Pressure Safety Valve or PSV opens suddenly to release the overpressure.
  • PRV is normally used for liquid systems while PSV is for gaseous systems.
  • The set point of PRV is usually 10% above the working pressure while the set pressure in PSV is generally 3% above the working limit.

Online Courses on Pressure Relief Valve

If you still have doubts, undertake the specially designed below-mentioned courses to improve your understanding of the subject:

Few more useful Resources for you…

Pre-Commissioning and Commissioning Checklist for Flare Package
Flare systems: Major thrust points for stress analysis
Stress Analysis of PSV connected Piping Systems Using Caesar II
Articles related to Process Design
Piping Layout and Design Basics
Piping Stress Analysis Basics

Meaning and Requirements of ASME U Stamp on Pressure Vessels

Written by Anup Kumar Dey in Mechanical,Piping Design Basics

The ASME U Stamp is an indication of quality for Pressure Vessels. It ensures that the design, fabrication, inspection, and testing of pressure vessels conform to ASME’s guidelines. ASME U stamp is provided on the body or the nameplates of the pressure vessels as a certification to meet ASME requirements. Globally, more than 100 countries use the ASME BPVC code for the pressure vessel design and U-stamped vessels follow the requirements of ASME Sec VIII Div 1. For the maximum protection of life and property, ASME provides rigorous rules for Pressure vessels. In many countries, the government made it compulsory to purchase ASME U-stamped vessels.

Advantages of ASME U Stamp

The main advantages of the ASME U Stamp are listed below:

  • In many countries, for pressure vessel installations in human occupancy, the ASME U stamp is a must.
  • ASME U stamp is a mandatory requirement of most Insurance companies.
  • ASME U stamp is accepted under all jurisdictions.
  • Sometimes for approvals by local regulating agencies, the ASME U stamp is a requirement.

ASME U Stamp requirements

The pressure vessels under ASME U stamp requirements are specifically inspected by a third-party authorized inspector. The inspector must review and approve the calculations as well as witness the ASME hydro test. Such inspectors are commissioned by the National Board of Boiler and Pressure Vessel Inspectors. A complete data report is furnished in form U-1 containing the signature of the authorized inspector. The manufacturers of such pressure vessels need to be registered with the National Board for the production of ASME U-stamped pressure vessels. Also, they need to maintain a permanent data record of all pressure vessels.

The manufacturers wishing to qualify as ASME certified need to go through the following stringent safety procedures:

  • Preparation Stage: The manufacturer must fulfill all requirements, and fill all checklists.
  • Application stage: Submit the complete application along with a signed Accreditation and Certification Agreement Form and the required fee.
  • Assessment Stage: ASME review team will examine the design, manufacturing, inspection, and quality system of the applicant. Once the assessment is complete, the team will submit an evaluation report to the higher authority.
  • Certification Stage: Once the applicant successfully demonstrates the implementation of quality programs in every stage of vessel manufacturing, he is entitled to the ASME certification. Upon receipt of the accreditation, the manufacturer can stamp the ASME mark on the vessel’s surface or Nameplates. Fig. 1 below shows a sample ASME certification stamp template.
Sample ASME Certification Template
Fig. 1: Sample ASME Certification Template

For more details about the marking methods, nameplate details and data reports kindly refer to UG-118 to UG-120 from the latest edition of ASME BPVC Sec VIII Div. 1.

There is a timeline involved for each stage mentioned above. The following flow chart (Fig. 2) by the ASME provides a guideline for the same.

ASME Certification Timeline
Fig. 2: ASME Certification Timeline

Is ASME U stamping a mandatory requirement?

No, the U stamp is not a mandatory requirement. The requirement is decided by the client company. As pressure vessels operate in a wide variety of processes and environments, It is crucial to design and fabricate vessels of the highest possible standard and quality. ASME U stamp satisfies that requirement. Failure to obtain an ASME vessel can sometimes put the business at risk.

When do Pressure Vessels need Certification or U-Stamping?

Any vessel carrying pressure in excess of 15 PSI falls under the ASME Code and should be stamped or certified by the ASME. However, there are other factors as well.

How to find ASME Certified Companies in a country?

To find the list of ASME-certified companies kindly visit the following site: https://caconnect.asme.org/directory/?_ga=2.17247673.1842524440.1614010223-219895220.1614010223. Provide the country and certificate type and then click on the search button. It will list all the companies that have active ASME certification during that time.

Online Course on Pressure Vessels

If you wish to learn more about Pressure Vessels, their design, fabrication, installation, etc in depth, then the following online courses will surely help you:

Drip Legs: Definition, Purpose, Configuration, Selection, Installation, and Sizing

Written by Anup Kumar Dey in Engineering Materials,Mechanical,Piping Design Basics

What is a Drip Leg in Steam Piping?

Drip Legs are vertical piping pockets installed in steam piping to collect condensate. Installing drip legs in the proper location serves the purpose of a successful, water-hammer-free, system start-up.

Purpose of Drip Legs

Drip Legs are installed in steam mains to serve the following purposes:

  • Drip Legs are used for removing entrained moisture from the steam transmission and distribution lines to ensure high-quality steam for use in various plant applications, while also preventing damaging and dangerous water hammer.
  • As steam travels at high velocity through piping, moisture forms as the result of piping heat losses and/or improper boiler control resulting in condensate carryover.
  • Drip legs are therefore located at points where condensate may accumulate to allow for drainage by gravity down to a steam trap for proper discharge from the system. Since condensate drains by gravity, drip legs must be located on the bottom of the piping and designed with diameters large enough to promote the collection.

Drip Leg Installation guidelines

Due to heat loss and system start-up energy consumption, condensate is formed inside the steam pipes. For proper working of the steam system, this condensate must be drained by installing drip legs in main lines at appropriate locations.

  • Drip legs should be located at Vertical Lifts, Drops, or at the end of the steam line.
  • In the straight run of piping every 30 to 50 meters.
  • Installed directly ahead of the regulating or control valve, Manual Valves Closed for a Long Time.
  • Ahead of expansion joints or elbows.
  • Provide proper support (no sagging)
  • Provide slope towards Drip legs.

Drip Leg Categories

  • DRIP Applications: drip traps
  • PROCESS Applications: process traps
  • TRACING Applications: tracer traps. Steam tracing refers to using steam to indirectly elevate the temperature of a product using jacketed pipes or tubing filled with steam

Drip Leg Configuration

Because condensate drainage from steam systems is dependent upon gravity, the drip leg (Fig. 1) diameter is critical for optimum removal – larger is better.

Figure of a properly configured drip leg.
Fig. 1: Figure of a properly configured drip leg.

Fig. 2 below shows a typical loop used in a drip leg.

Typical Drip Leg Loops from Steam Mains
Fig. 2: Typical Drip Leg Loops from Steam Mains

Selection of Drip Leg Sizes

The selection of drip leg sizes for draining the main steam line depends on the types of warm-up methods as mentioned below:

  • Supervised Warm-up Method: Warming up of the power plant principal piping normally follows this method. Such lines are warmed up only once in a lifetime and hence long drip leg is not required.
  • Automatic Warm-Up Method: Such a warm-up method is used for frequent steam use leading to the requirement of bigger drip legs. A static head (dimension H in Fig. 2) is used in such cases.

Fig. 3 below provides the recommended Drip leg Sizes (Drip Leg Diameter and Leg Length) with respect to the main steam piping size.

Recommended Drip Leg Sizing
Fig. 3: Recommended Drip Leg Sizing

A carefully designed drip leg enables steam traps to effectively drain the condensate from steam mains. For that, the drip legs should be large enough to allow the condensate to drop out of the steam at the pipe bottom. Recommended drip leg sizing table (Fig. 3) provides a good reference for such a scenario. In case the drip leg is not sized properly, the condensate will blow along with the steam without separating out as shown in Fig. 4.

Effect of Drip Leg Sizing
Fig. 4: Effect of Drip Leg Sizing

Click here to know about Steam Traps: Steam Traps: Definition, Types, Selection, Features, Codes & Standards

H-beam vs I-beam: Major Differences | H-beam and I-beam Size Chart

Written by Anup Kumar Dey in Civil,Construction,Maintenance,Mechanical,Piping Interface

When it comes to structural engineering and construction, the choice of beam design plays a crucial role in ensuring the integrity and safety of a structure. Among the most common types of beams used are H-beams and I-beams. While they may seem similar at first glance, each type has its own set of characteristics, advantages, and applications.

H-beam or I-beam

Both H-beam and I-beams are structural steel materials used widely in the construction industry by civil engineering professionals. By a novice, both these members may seem to be similar. The horizontal elements of the I and H beam are known as flanges, while the vertical element is called as the “web”. The web resists shear forces, and the flanges are designed to resist most of the bending moment that the beam experiences.

In general, The design of both I-beam and H-beam is governed by any of the following criteria:

  • deflection: The target criteria should be to minimize deformation
  • vibration: the stiffness and mass should be decided based on vibration tendency.
  • bending failure by yielding
  • bending failure by lateral torsional buckling
  • bending failure by local buckling
  • local yield due to the high magnitude of concentrated loads.
  • shear failure
  • buckling or yielding of components

However, both are quite different from one another. In this article, We will explore the main differences between I-beam and H-beam.

What is an H-beam?

H-beam is an incredibly strong structural steel member. As the cross-section of this beam resembles the capital letter “H”, it is known as H-beam. Fig. 1 shows a typical example of an H-beam. The main characteristics of H-beams are:

  • Shape: The cross-section is symmetrical, providing uniform strength in all directions.
  • Dimensions: Available in various sizes, typically larger than I-beams.
  • Weight: Generally heavier than I-beams, which can affect transportation and handling.
H-beam Example
Fig. 1: H-beam Example

H-beams have an equal thickness in the two parallel flanges without any taper on the inside surface. Depending on the height and flange width; H-beams are classified into three categories. They are

  • Wide Flange Series H-beam
  • Medium Flange Series H-beam and
  • Narrow Flange Series H-beam.

H-beam Size Chart

Typical H-beam size and weight chart is provided in the table below: Refer to Fig. 2

H beam size and weight chart: Wide Flange Series (HW)

Grade

Size of the Section (in mm)

Cross-Sectional Area

Weight

Member Designation

 

H

B

t1

t2

r

cm2

kg/m

  

100 X 100

100

100

6

8

10

21.9

17.19

100x100x6x8

125 X 125

125

125

6.5

9

10

30.31

23.79

125x125x6.5×9

150 X 150

150

150

7

10

13

40.55

31.83

150x150x7x10

175 X 175

175

175

7.5

11

13

51.43

40.37

175x175x7.5×11

200 X 200

200

200

8

12

16

64.28

50.46

200x200x8x12

200

204

12

12

16

72.28

56.74

200x204x12x12

250 X 250

250

250

9

14

16

92.18

72.36

250x250x9x14
 

250

255

14

14

16

104.68

82.17

250x255x14x14

H beam size and weight chart: Medium Flange Series (HM)

150 X 100

148

100

6

9

13

27.25

21.39

148x100x6x9

200 X 150

194

150

6

9

16

39.76

31.21

194x150x6x9

250 X 175

244

175

7

11

16

56.24

44.15

244x175x7x11

300 X 200

294

200

8

12

20

73.03

57.33

294x200x8x12

H beam size and weight chart: Narrow Flange Series (HN)

175 X 90

175

90

5

8

10

23.21

18.22

175x90x5x8

200 X 100

198

99

4.5

7

13

23.59

18.52

198x99x4.5×7

200

100

5.5

8

13

27.57

21.64

200x100x5.5×8

250 X 125

248

124

5

8

13

32.89

25.82

248x124x5x8

250

125

6

9

13

37.87

29.73

250x125x6x9
H-beam Cross Section
Fig. 2: H-beam Cross Section (Reference for table dimensions)

What is an I-beam?

I-beams are also structural steel members but their cross sections resemble the capital letter “I”. Consisting of two flanges and one web, an I-beam has a slope on the inner surface of the flanges. Depending on the use, I-beam sections are available in a range of weights, flange widths, sections, depths, and web thicknesses. The major characteristics of I-beams are:

  • Shape: The cross-section is also symmetrical but generally has narrower flanges compared to H-beams.
  • Dimensions: Available in a range of sizes, often lighter than H-beams.
  • Weight: Typically less weight than H-beams, making them easier to handle in certain applications.

Fig. 3 below shows a typical example of I-beams.

I-beam example
Fig. 3: I-beam example

I-beam Size Chart

I-beam size charts for some common structural sections are provided below:

Designation

Dimensions

  
 

Depth
– H –
(mm)

 

Width
– B –
(mm)

 

Web Thickness
– d –
(mm)

 

Cross-Sectional Area
(cm2)

Weight
(kg/m)

  

UB 127 x 76 x 13

127

76

4

16.5

13

  

UB 152 x 89 x 16

152.4

88.7

4.5

20.3

16

  

UB 178 x 102 x 19

177.8

101.2

4.8

24.3

19

  

UB 203 x 102 x 23

203.2

101.8

5.4

29.4

23.1

  

UB 203 x 133 x 25

203.2

133.2

5.7

32

25.1

  

UB 203 x 133 x 30

206.8

133.9

6.4

38.2

30

  

UB 254 x 102 x 22

254

101.6

5.7

28

22

  

UB 254 x 102 x 25

257.2

101.9

6

32

25.2

  

UB 254 x 102 x 28

260.4

102.2

6.3

36.1

28.3

  

UB 254 x 146 x 31

251.4

146.1

6

39.7

31.1

  

UB 254 x 146 x 37

256

146.4

6.3

47.2

37

  

UB 254 x 146 x 43

259.6

147.3

7.2

54.8

43

  

UB 305 x 102 x 25

305.1

101.6

5.8

31.6

24.8

  

UB 305 x 102 x 28

308.7

101.8

6

35.9

28.2

  

UB 305 x 102 x 33

312.7

102.4

6.6

41.8

32.8

  

UB 305 x 127 x 37

304.4

123.4

7.1

47.2

37

  

UB 305 x 127 x 42

307.2

124.3

8

53.4

41.9

  

UB 305 x 127 x 48

311

125.3

9

61.2

48.1

  

UB 305 x 165 x 40

303.4

165

6

51.3

40.3

  

UB 305 x 165 x 46

306.6

165.7

6.7

58.8

46.1

  

UB 305 x 165 x 54

310.4

166.9

7.9

68.8

54

  

UB 356 x 127 x 33

349

125.4

6

42.1

33.1

  

UB 356 x 127 x 39

353.4

126

6.6

49.8

39.1

  

UB 356 x 171 x 45

351.4

171.1

7

57.3

45

  

UB 356 x 171 x 51

355

171.5

7.4

64.9

51

  

UB 356 x 171 x 57

358

172.2

8.1

72.6

57

  

UB 356 x 171 x 67

363.4

173.2

9.1

85.5

67.1

  

UB 406 x 140 x 39

398

141.8

6.4

49.7

39

  

UB 406 x 140 x 46

403.2

142.2

6.8

58.6

46

  

UB 406 x 178 x 54

402.6

177.7

7.7

69

54.1

  

UB 406 x 178 x 60

406.4

177.9

7.9

76.5

60.1

  

UB 406 x 178 x 67

409.4

178.8

8.8

85.5

67.1

  

UB 406 x 178 x 74

412.8

179.5

9.5

94.5

74.2

  

UB 457 x 152 x 52

449.8

152.4

7.6

66.6

52.3

  

UB 457 x 152 x 60

454.6

152.9

8.1

76.2

59.8

  

UB 457 x 152 x 67

458

153.8

9

85.6

67.2

  

UB 457 x 152 x 74

462

154.4

9.6

94.5

74.2

  

UB 457 x 152 x 82

465.8

155.3

10.5

104.5

82.1

  

UB 457 x 191 x 67

453.4

189.9

8.5

85.5

67.1

  

UB 457 x 191 x 74

457

190.4

9

94.6

74.3

  

UB 457 x 191 x 82

460

191.3

9.9

104.5

82

  

UB 457 x 191 x 89

463.4

191.9

10.5

113.8

89.3

  

UB 457 x 191 x 98

467.2

192.8

11.4

125.3

98.3

  

Common Beam Standards

Common standards that govern the shape and tolerances of structural beam sections are:

  • AISC Manual
  • IS 808
  • ASTM A6,
  • DIN 1025
  • BS 4-1
  • AS/NZS 3679.1
  • EN 10024
  • EN 10034
  • EN 10162

H-beam vs I-beam: Difference between H-beam and I-beam

H-beam vs I-beam: Dimensions and Weight

  • An H-beam has a significantly thicker web than an I-beam.
  • An I-beam normally has a slope of 1:6 to 1: 10 in the flange whereas the H-beam has a uniform flange.
  • An H-beam is heavier as compared to an I-beam.
  • The distance of the flanges can be widened as per requirement for an H-beam section but the same is fixed for the I-beam.
  • The moment of inertia is different for both beams.
  • In an I-beam, the size of the web is greater than the size of the flange whereas in an H-beam it may not be true.

H-beam vs I-beam: Mechanical Properties

  • The cross-section of the I-beam is poor against twisting as compared to H-beam.
  • In general, H-beams are more rigid and can carry more load as compared to I-beams.
  • H-beams are used as columns while I-beams are used as beams.

H-beam vs I-beam: Manufacturing

  • An I-beam is manufactured as a single piece throughout, but an H-beam is normally manufactured by welding 3 pieces of metal.
  • An H-beam can be produced to any desired size and height whereas the production of I-beams is limited by the milling machine capacity.

For easy comparison, the differences between H-beam and I-beam are provided in the following table.

FeatureH-BeamI-Beam
Cross-Section ShapeResembles the letter “H”Resembles the letter “I”
Flange WidthWider flanges than I-beams.Narrower flanges than H-beams.
Web DepthH-beams have deeper web.I-beams have shallower web.
WeightGenerally heavier than I-beams.Typically lighter than H-beams.
Load-Bearing CapacityH-beams possess higher load capacity.I-beams have lower load capacity.
StabilityH-beams have better lateral stability than I-beams.I-beams are more susceptible to buckling.
ApplicationsMajor application of H-beams are found in bridges, high-rise buildings, heavy machinery, etc.I-beams are widely used in residential, commercial, light industrial, etc.
CostH-beams are generally more expensive.I-beams are typically less expensive.
HandlingH-beams require more robust lifting equipment. So, they are difficult to handle.I-beams are comparatively easier to handle and transport.
VersatilityThey are suitable for heavy-duty applications.I-beams are the best for lighter loads.
DeflectionH-beams experience less deflection under load.Comparatively more deflection under heavy loads.
Connection TypesOften welded for continuous supportCan be bolted or welded
Table 1: H-beam vs I-beam

This table summarizes the key differences, making it easy to compare H-beams and I-beams at a glance.

In conclusion, both H-beams and I-beams have unique properties that make them suitable for different applications in construction and engineering. H-beams offer higher load-bearing capacity and stability, making them ideal for heavy-duty applications, while I-beams provide a lightweight, cost-effective solution for lighter loads. The choice between the two should be based on a thorough understanding of the specific requirements of a project, including load conditions, cost considerations, and structural integrity.

Frequently Asked Questions: H-beam and I-beam

1. What is the primary difference between H-beams and I-beams?

The primary difference lies in their cross-sectional shapes. H-beams have wider flanges and a deeper web, while I-beams have narrower flanges and a shallower web, affecting their load-bearing capacities and applications.

2. Which beam is stronger: H-beam or I-beam?

H-beams generally have a higher load-bearing capacity due to their wider flanges and deeper web, making them suitable for heavy-duty applications. I-beams are lighter and more suited for lighter loads.

3. In what applications are H-beams typically used?

H-beams are commonly used in bridges, high-rise buildings, and heavy machinery support where high strength and stability are required.

4. Where are I-beams commonly found?

I-beams are typically used in residential construction, commercial buildings, and lighter industrial applications, where the loads are lower.

5. How do the costs compare between H-beams and I-beams?

H-beams are generally more expensive due to the larger amount of material used, while I-beams are typically less expensive, making them a cost-effective option for lighter applications.

6. Are H-beams easier to install than I-beams?

I-beams are usually easier to handle and install due to their lighter weight. H-beams require more robust lifting equipment during installation.

7. Can both beam types be welded or bolted?

Yes, both H-beams and I-beams can be either welded or bolted, but the choice depends on the specific structural requirements and design considerations.

8. What factors should be considered when choosing between H-beams and I-beams?

Factors to consider include the type and magnitude of loads, span length, budget constraints, and the specific application requirements.

9. Do H-beams and I-beams have different deflection limits?

Yes, H-beams typically exhibit less deflection under load compared to I-beams, making them more suitable for applications where deflection limits are critical.

10. What are the maintenance requirements for H-beams and I-beams?

Both types of beams require regular inspections for signs of corrosion or damage. The maintenance needs will depend on the environment and exposure conditions, such as humidity and industrial pollutants.

What is a Needle Valve? Types, Symbols, Working

Written by Anup Kumar Dey in Engineering Materials,Mechanical,Piping Design Basics

In a piping system, There are a lot of ways to isolate the flow. Many types of valves and blinding systems are available for this. But the use and purpose of the Needle valves are very different. Needle valves are sometimes referred to as Plunger valves. This helps piping professionals to perfectly control and regulate fluid flow and pressure. The Needle valve got its name because of its narrow needle-like plug and port arrangement. The needle valves are small in size but fluid flow controlling is of exceptional accuracy.

Needle valves are linear motion valves, Which are used in instrument systems for throttling small volumes. A needle valve is a manual valve that is used where continuous throttling is required for flow regulation. Needle valves are somehow similar to globe valves in design with the biggest difference of sharp needle-like disks of this. The needle valve has an isolation system with very precise which is attended by the fine movement of the shaft, which enables the gearbox to move the piston tube in a sliding motion for opening and closing position. In this article, we will help you to understand the following:

  • What is a Needle valve?
  • Symbols and uses of Needle valves
  • Parts of Needle valves
  • Working Principle of Needle valve
  • Advantages and Disadvantages of Needle valves

What is a Needle Valve?

Needle valve
Fig. 1: Needle Valve

A needle valve is a type of valve that can be used to regulate or complete the isolation of the fluid. The unique feature of the valve is the structure of a small plunger with the shape of a Needle. The plunger features a small handle to operate the easy and precise operation of the valve. When fully attached, the extended end of the valve fits exactly into the seat, a part of the appliance that is being regulated. In case of the valve is opened by mistake, then also space between and needle and the seat is so less, that a minimal amount of substance will be allowed to pass through it.  

Needle Valve Symbol

Like Every pipe fitting and Special Item, the Needle valve has its own symbology system. Common Needle Valve Symbol is shown in Fig. 2.

NEEDLE VALVE SYMBOL
Fig. 2: Needle Valve Symbol

Parts of a Needle Valve

Needle valves consist of three major parts, the valve body and seat, the stem and stem tip, and the packing and bonnet. The stem incorporates fine threads to allow micrometer-like needle adjustment relative to the seat.

Needle valve parts
Fig. 3: Parts of a Needle Valve

Referring to the above image and corresponding marked serial numbers name of parts of the needle valve is as below:

  1. Valve handle
  2. Nut
  3. Bonnet
  4. Valve body
  5. Seat
  6. O-ring
  7. Packing
  8. Stem
  9. Handle screw

The needle valve body is normally made up of Brass, Bronze, Stainless Steel, or any other alloy materials. Valve seats are usually manufactured from PVC, CPVC, Plastic, PTFE, or Thermoplastic Materials.

Depending on the position of the needle, needle valves are available in three basic configurations.

  • as a simple screw-down valve (T-type needle valve)
  • oblique needle valve (angle pattern) that offers a more direct flow path, and
  • controlled outlet flow at a right angle to the main flow.

Needle valves normally provide Z- or L-shaped flow path through the body.

Application of Needle Valves

Wherever precise flow measurement is the required role of the needle valve comes into play. In comparison with a diaphragm valve, a Needle valve can handle more differential pressure.

Needle valves find their application in almost every industry wherever control or metering of steam, gas, oil, air, water, or other non-viscous liquids is needed. Needle valves are widely used in Power generation, Zoological sciences, Cooling, Instrumentation control, and Gas and liquid dispensation industries.

In slurries and viscous media, the needle valve is avoided as a small orifice can easily be blocked by thick material or solids.

Role of Needle Valves

The major roles that a needle valve performs are

  1. Flow control
  2. In pump start
  3. Pressure regulation
  4. Turbine by-pass
  5. Flow discharge
  6. Air regulation
  7. Reservoir inlet

Use of a Needle Valve

A needle valve finds its wide uses in the following applications:

  • All analog field instruments are installed with a needle valve to control the flow movement.
  • Needle valves help in situations where the flow needs to stop gradually.
  • The needle valve can be used as an on/off and throttle valve.
  • This can be used where metering applications are required such as steam, air, gas, oil, or water.
  • A needle valve is helpful with sample points in piping where a very little flow rate is required.
  • This valve can be used on gas bleeder lines.
  • Needle valves are used in automated combustion control systems in which accurate flow regulation is required.
  • It is used with constant pressure pump governors in order to reduce the fluctuation in the pump discharge

Types of Needle Valve

Depending on the operation style, three types of needle valves are available in the market. They are:

  • Manually operated threaded needle valve
  • Motorized Needle Valve: Use an electric or pneumatic actuator for operation.
  • Angle Needle Valve: Turn the output by 90 degrees instead of in-line.

Working Principle of Needle Valves

Needle valves can be operated either manually or automatically. Manually operated needle valves use a handwheel to open or close their disc. When Handle is turned in a clockwise direction its plunger lifts to open the valve and allow fluid to pass through. When the Handle is turned in an Anti-clockwise direction the plunger moves closer to the seat to decrease the flow rate and finally intercepts the flow of fluid.

Automated needle valves are connected to the hydraulic motor or an air actuator that helps to automatically open and close the valve. The motor or actuator will help to adjust the position of the plunger according to the timer or external data fed into the system, that is gathered during monitoring.

Both manually and automatically operated needle valves provide precise control of fluid flow rate. The handwheel is accurately threaded which means it takes multiple turns to adjust the position of the plunger from the seat. As a result, the needle valve can help better in regulation the flow rate in the system.

Needle Valve Design Standards

Frequently used needle valve design standards governing the valve design and selection are:

  • ASME B16.34
  • BS 7174 P4
  • MIL-V-24586
  • PIP PNDMV09N

Needle Valve Selection

The parameters that affect the selection of the right needle valve are

Advantages of Needle valve

The main advantages that a needle valve serves are

  1. With the help of this valve flow control at a very low rate with higher accuracy is possible.
  2. Needle valves are smaller in size. So, there is no issue of space during its installation.
  3. Throttling even with less volume of fluid is possible with this valve.
  4. Flow rates can be adjusted precisely.
  5. Its operation is easier.

Disadvantages of Needle valve

A few drawbacks of needle valves are

  1. There is a high-pressure loss in the needle valve because of the high restriction of fluid flow.
  2. They can be used only for low-flow rate piping systems.
  3. There can be damage to the seat and needle if the fluid has solid particles.
  4. It is not possible to say if it is in an open or closed position just by examining the handle position.
  5. Immediate opening or closing is not possible in these types of valves. Immediate operations can damage the seat of the need valve.

Ball Valve vs Needle Valve

The main differences between a ball valve and a needle valve are tabulated below:

Ball ValveNeedle valve
Ball valves use a Spherical ball for valve operationUses a needle to open and close the valve
Ball valves are Quarter turn ValveNeedle valves are Linear motion valve
Ball valves have Poor flow controlNeedle valves have precision flow control
Table: Ball Valve vs Needle Valve

About the Author

A major part of this article is written by Mr. Vaibhav Raj, a Piping Engineer by profession, currently working with a leading MNC as an Asst. Manager (Piping). To date, He successfully executed four Oil and Gas Projects in India with various clients Like EIL, RIL, SHELL, and RSPL. He is the lead author of the blog “ALL About PIPING“.