Pipe Trunnion or Dummy Support and Their Stress Calculation

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

What is a Pipe Trunnion?

Piping Trunnion supports are one of the most frequently used pipe supports in the piping industry. This support is widely used in the piping industry due to its ease of construction and erection. The construction and erection of a pipe trunnion or dummy support are very easy because you have to simply weld a pipe (normally one or more sizes less than the parent pipe to which it is to be welded) with the parent pipe.

A pipe trunnion is defined as an additional pipe of similar or lower size welded to an active piping system to provide physical support. However, trunnion supports with the same size pipe are usually avoided due to profile cutting and welding difficulties during construction.

The load-bearing capacity of trunnion supports is usually less and not as comparable to civil structural supports. So, every pipe stress engineer must check the weld point from a failure viewpoint and investigate the ability to carry the piping load (mostly the tangential and longitudinal load and corresponding moment). The chances of weld failure increase with an increase in trunnion length or trunnion height. Usually, trunnions with a height of more than 1500 mm are not suggested.

Sometimes structural steel members in place of pipe are also added to the parent pipe to form trunnion support. The material of the dummy or trunnion to be attached to the parent pipe should be compatible with the parent pipe material.

Factors affecting load-bearing Capability of Trunnions

The load-carrying capability of a trunnion mainly depends on the following factors:

Parent pipe and trunnion/dummy pipe diameter: With an increase in pipe size the load-carrying capacity increases.
Parent pipe thickness: With an increase in pipe thickness the load-carrying capability increases.
Parent pipe material: With an increase in parent pipe material allowable strength (S_h) the load-carrying capability increases.
Design temperature: With a decrease in design temperature the load-carrying capability increases.
Parent pipe corrosion allowance: With a decrease in corrosion allowance the load-carrying capability increases.
Design pressure: With a decrease in design pressure the load-carrying capability increases.
Trunnion/dummy pipe height: With a decrease in trunnion height the load-carrying capability increases.
Reinforcement Pad thickness at the weld interface: Adding a reinforcement pad at the parent pipe and trunnion pipe increases the load-carrying capability of trunnions to a huge extent. However, adding RF Pads at elbows is difficult to construct and hence suggested to avoid.

Applications of Trunnion or Dummy Supports

Wide application of trunnion or dummy supports is found in control valve assemblies. In control valve stations, trunnion or dummy supports are usually welded from parent pipe elbows as shown in Fig. 1 below:

**Fig. 1: Trunnion Supports from Piping Elbow**

Trunnion or dummy supports are quite common to use as adjustable supports on a pump or other rotary equipment for alignment purposes.

Typical Trunnion Support Configurations

A variety of support configurations can be made by welding trunnion supports on pipes. Examples of some widely used typical pipe trunnion support configurations are provided in Fig. 2:

Trunnion Calculation Method

There are various ways in which trunnion checking can be done. However, the Kellogg Method of trunnion checking using an Excel spreadsheet is the most common among EPC organizations. In some organizations, trunnion checking by the WRC method is prevalent. In recent times, Trunnion or dummy support checking using FEA calculations has been increasing among EPC organizations. Various extended modules of stress analysis programs like FE-Pipe/ FE-bend or other FEA programs are used to calculate stresses in the junction point and check if those are acceptable.

In the next paragraphs, I will brief the steps and formulas used while trunnion checking using the Kellogg method.

Inputs Required for Pipe Trunnion Calculation

The inputs that will be required for pipe trunnion calculation are:

Pipe Support loads from stress analysis software.
Parent pipe OD and thickness.
Pipe trunnion OD and thickness.
Parent pipe corrosion allowance.
Parent Pipe material to get stress values.
Pipe design temperature and pressure.
Pipe trunnion height.
RF pad thickness if required/provided.

Steps for Trunnion Calculation by the Kellogg Method

1. First of all run the static analysis in Caesar II/AutoPipe/Rohr II/Start-Prof/Caepipe/Other Pipe Stress Analysis Software to obtain the load values at trunnion nodes from the output processor. It is better to practice taking the maximum value from all load cases (Sustained, operating, design, upset, hydro test, occasional, etc.)

2. After that, calculate the bending stress generated on the pipe shell based on the following Kellogg equation:

**S_b=(1.17 * f * √R )/ (t^1.5) ……(1)**

Here,

S_b=bending stress in pipe shell
R=Outside radius of pipe shell
t=Corroded pipe thickness (actual pipe thickness-corrosion allowance) plus the thickness of reinforcement pad
f=loading per unit length

3. Now from piping stress analysis software, we will get three forces with respect to each trunnion; longitudinal forces, circumferential forces, and axial forces. So accordingly we will have to calculate three f values as mentioned below:

Loading due to longitudinal bending, f_L=M_L/ (Π r²) ……(2)
Loading due to circumferential bending, f_C=M_C/ (Π r²) ……..(3) and
Loading due to axial force, f_A=P/ (2Π r)………..(4)

Where,

M_L=Longitudinal force obtained from Caesar * trunnion effective length
M_C=Circumferential force obtained from Caesar output * trunnion effective length
P=direct axial force obtained from Caesar II output. and r=outside radius of the trunnion.

4. Next step is to calculate all bending stresses using equation (1) for longitudinal (S_L), axial (S_A), and circumferential (S_C) forces as calculated from equations (2), (3), and (4).

5. Now Calculate longitudinal Pressure Stress (S_LP=PD/4t) and Hoop Stress (S_CP=PD/2t).

6. In the next step, combine all these forces for proper load cases as shown below and compare the combined value with the allowable stress value provided in terms of the S_h and S_c values as defined in the ASME B31.3 code.

S_L+ S_A + S_LP<= k * S_h
S_C+ S_A + S_CP <= k*S_h And
Trunnion Stress<=S_h

Here trunnion stresses should be calculated as=[{32*Trunnion OD*√(M_L²+M_C²)} / {Π*(Trunnion OD⁴-Trunnion ID⁴)}]

The values of “k” are dependent on loading types. The allowable stress values as suggested in the Kellogg Method are produced below in Fig. 3 for reference.

**Fig. 3: Allowable Stress Values for Trunnion Calculation as per Kellogg Method**

Options to reduce stresses while Trunnion Support Checking

There are various ways by which the calculated stresses on the trunnions can be reduced so that the dummy calculation qualifies with respect to allowable stresses. Some of such tips are

While checking trunnions or dummies, it is found that a major chunk of trunnion supports fails due to circumferential loads. So, orient or place the trunnion in such a way that the circumferential force on the trunnion becomes very less to permit/allow greater trunnion heights.
Reducing the trunnion height or increasing the trunnion size also will reduce the calculated stresses.
RF pads are required to be added to increase the junction thickness and thereby increase load-carrying capabilities which decrease stresses.
Increasing the parent pipe diameter will also qualify the trunnions. However, increasing parent pipe size needs process confirmation.

What is the difference between a Trunnion and a Dummy Leg?

Even though the terms “Trunnion” and “Dummy Leg” are used interchangeably, there is a slight difference between the two pipe supports.

Dummy pipe is welded onto the pipe elbow to extend the line to reach the next support while Pipe trunnions are welded to vertical lines. Usually, two short pipe pieces are welded to vertical pipe for better stability for trunnion application. It’s easier to provide an RF pad on trunnion supports but the same is difficult for dummy legs as the pipe profiling and welding at pipe elbows are usually difficult.

Online Course on Pipe Support Engineering

If you want to learn more details about pipe support engineering then the following online course is a must for you:

Overview of Conductivity and Conductivity Measurement

Written by Anup Kumar Dey in Instrumentation,Piping Interface

What is Conductivity?

Conductivity is the ability of a material to transfer an electric charge from one point to another. To transfer current, charged particles must be present in the solution. It is a standard practice to measure conductivity in aqueous solutions as different salts, acids, and bases dissolved in water act as electrolytes and provides ions. How well a solution conducts electricity is measured by the term conductivity. Ohm’s Law provides the basic idea of Conductivity.

E = I • R
where E = applied voltage between two “plates”
I= electrical current
R=Resistance of the conductor.

From the above equation, conductivity can be defined as the reciprocal of resistance of a solution between two electrodes and it is expressed as:

G = I/R

The units used for conductivity are Mhos or more commonly used Siemens. Mhos and Siemens can be used interchangeably.

However, to compensate for variations in the electrode dimensions, standardized measurements are expressed in specific conductivity units. By multiplying the measured conductivity (G) as mentioned above by the electrode’s cell constant (L/A); Specific conductivity is calculated. Hence, Specific conductivity (C) is given by

C = G x (L/A)
where L=the length of the liquid column between the electrodes
A= area of the electrodes

Conductivity meters use this equation to calculate the conductivity of a solution and display the results.

Resistance is the inverse of conductance. Materials that are in the liquid phase and conduct electrical current are called electrolytes.

Application of Conductivity Measurement

Conductivity measurement is widely used for quality control purposes. For monitoring and controlling of used water, conductivity is one of the important, cost-effective, and stable parameters. That is the reason conductivity measurement has found numerous industrial applications.
The major areas where conductivity is important are listed below:

Treatment of Water Quality
- RO systems; Conductivity measurement of pure water.
- Desalination industry.
- Boiler feedwater protection.
- Water towers.
- Hardness protection in laundries.
- Salinity Testing.
- Condensate and Steam quality protection.
- Wastewater treatment.
- TDS Testing.
Concentration measurements and control
- Finding the concentration of various acids like Hydrochloric acid, Phosphate, Ammonium and ammonia gas, Nitric acid, Sulphuric Acid, etc.
Conductivity measurement can also be helpful in analyzing Carbon dioxide and Sulphuric dioxide in water.

Refer to the following figure (Fig. 1) that lists all the applications of conductivity measurements.

Measurement of Conductivity

The devices that are used to measure conductivity are called Conductivity Analyzers or Conductivity meters. There are two ways in which the conductivity in liquids or slurries is measured:

Contacting (or Electrode) Measurement.
Toroidal (Inductive or Electrodeless) Measurement.

**Fig. 2: Conductivity of familiar solutions**

Contacting or Electrode Type Measurement (Fig. 3):

The two-electrode methodology uses two opposing electrodes.
The anode is supplied with a known current, which is picked up by the cathode when placed in an electrolyte.
The amount of current picked up by the cathode is dependent upon the conductance of the electrolyte.

Probe/Cell Constant of Conductivity Meter:

The cell constant is the distance between the electrodes divided by the area of the electrodes.

K (cm^-1) = Distance between electrodes (cm) / Area of electrodes (cm)

The smaller the cell constant the higher the signal that will be returned to the meter.

Low conductivity solutions use a small cell constant and high conductivity solutions will use a larger cell constant sensor.

Two Electrode Methodology:

Its main drawback is:-

The sensor is susceptible to coating and corrosion, which drastically lowers the reading.
In strongly conductive solutions there can also be polarization effects, which results in non-linearity of the measurement.

The Four Electrode Methodology for Conductivity measurement:

It utilizes the same two-electrode measuring scheme, but it also includes an additional two-electrode system to act as a reference point for the measuring circuit, for use in applications where light coats from the process can occur.
The minimum range for this type of electrode is approximately 5000 micro S/cm.

**Fig. 3: Contracting and Toroidal Measurement**

Toroidal Type Measurement (Fig. 3):

Toroidal conductivity measurement is made by passing an AC current through a Toroidal drive coil, which induces a current in the electrolyte solution.
This induced solution current, in turn, induces a current in a second toroidal coil, called the pick-up toroid.
The amount of current induced in the pick-up toroid is proportional to the solution conductivity.

Advantages of Toroidal Type Conductivity:

The toroidal coils are not in contact with the solution.
The insertion-style Toroidal sensor can be completely coated by a solid OR oily contaminant in the process, with essentially NO lowering of the reading until the coating displaces a significant volume of the surrounding liquid.
The polymeric material housing the Toroids can be chosen to be compatible with corrosive solutions,

Drawbacks of Toroidal Type Conductivity Measurement :

It lacks the sensitivity of contacting measurement.
Toroidal sensors are also typically larger than contact sensors, and the solution current induced by the Toroid occupies a volume around the sensor. Hence, Toroidal sensors need to be mounted in a larger pipe.

Temperature Effects on Conductivity Measurement

Temperature does have a significant effect on the conductivity of solutions.
The same solution concentration at different temperatures has a drastically different conductivity.
In order to measure the conductivity temperature effect must be compensated.

For Temperature, compensation follows the steps shown in Fig. 4

The temperature coefficients of the following electrolytes generally fall in the ranges shown below:

Acids 0 – 1.6%/°C
Bases 8 – 2.2%/°C
Salts 2 – 3.0%/°C
Freshwater 0%/°C

**Fig. 4: Temperature Effects on Conductivity Measurement**

Calibration of Conductivity Analyzers

Moderate to High Range Measurements:

For conductivity measurements in excess of 100 μS/cm, a conductivity standard may be used to calibrate a conductivity loop.
The conductivity measurement may also be calibrated using grab sample standardization.
Care must be taken that the correct temperature coefficient is being used in both the online instrument and the referee instrument to avoid discrepancies based on temperature compensation errors.

High Purity Water Measurements

Conductivity samples below 100 μS/cm are highly susceptible to contamination by trace contaminants in containers and by CO₂ in the air. As a result, calibration with a conventional standard is not advisable.
Many conductivity instruments designed for high-purity water measurements include a calibration routine for entering the constant of the conductivity sensor.
The conductivity sensor used with this kind of instrument must have its sensor constant accurately measured using a conductivity standard in a higher range. Once the sensor constant is entered into the instrument, the conductivity loop is calibrated.
A second method is to calibrate the online instrument to a suitably calibrated, reference instrument in a closed flow loop.

Advantages of Conductivity Measurement

Conductivity offers Fast, Reliable, Nondestructive, Inexpensive &
Durable means of measuring the ionic content of a sample.
Reliability and repeatability are excellent.

Disadvantages of Conductivity Measurement

The principle drawback of conductivity is that it is a nonspecific
Measurement – it cannot distinguish between different types of ions,
giving instead a reading proportional to the combined effect of all
ions present. Therefore it must be applied with some pre-knowledge
of the solution composition OR used in relatively pure (single solute) solutions to be successful.

Factors influencing the conductivity measurement of Conductivity Meters

The correctness of conductivity measurements can be influenced by various factors:

Geometry
Polarisation
Cable resistance and capacitance
Frequency change
Contamination
Temperature

Further Studies for Conductivity measurement:

Refer to the following documents to know more about conductivity and the measurement of conductivity:

Micro Tunneling for Pipeline Installation

Written by Anup Kumar Dey in Pipeline

What is Micro Tunneling?

Micro Tunneling (M/T) is a process that uses a remotely controlled Micro Tunnel Boring Machine (MTBM) combined with the pipe jacking technique to directly install product pipelines underground in a single pass. This process avoids the need to have long stretches of an open trench for pipe laying, which causes extreme disruption to the community.

Important Features of Micro Tunneling

Micro tunneling is currently the most accurate pipeline installation method. Line and grade tolerances of one inch are the micro tunneling industry standard. This can be extremely important when trying to install a new pipeline in an area where a maze of underground utility lines already exists.

Micro tunneling can be used to install pipes from eight inches (200 mm) to twelve feet (3600 mm) in diameter. Therefore, the definition of micro tunneling does not necessarily include size. The importance of trenchless pipe jacking for the laying of supply and disposal conduits and for replacing pipes is growing continuously.

Importance of Micro Tunneling in the Oil Industry

Increasingly, the existing technologies are failing to install new pipelines in demanding oil fields and rough terrains. This happens due to:

High groundwater
Difficult ground condition. (E.g. Mountains – situated nearby many oil fields, rocky ground, perennial rivers, etc.)
Ground with Mixed Gravel

While drilling in gravel with the present HDD technique, the chances of ground collapse are high. So, in this case, no drilling is possible through HDD.

Solution for all the above-mentioned problems – MICRO-TUNNELING

Advantages of Micro Tunneling

Reduced disruption of the community
Reduced liability for personal injury and property damage
Increased service life and asset value for the utility owner
Increased worker safety
Reduced restoration costs
Precise installation
Wet Conditions/Marine Crossings: often the only option
The faster rate of progress than the convention
A reduction of earth movement to a minimum
Consideration of residents and the environment
Lowering of groundwater is unnecessary
Minimal influence on traffic

Wherever horizontal directed drilling technology (HDD) cannot be used:

for difficult and rough gravel soils,
soils with erratic blocks,
in city centers,
where there is no space to extend and retract,

Micro tunneling methods are a true alternative.

Shaft/Well Construction

Construction of a Shaft / Well is one of the primary jobs for carryout Micro Tunneling.

Purpose: To get a safe working platform under the desired depth.

Bottom Plugging

Plug the bottom of the shaft with Reinforced Cement Concrete using a concrete box with the help of divers and a crane. Additives are used to prevent the cement from dissolving in water and increase the plasticity of the concrete for achieving a better flow of concrete into the cutting edge.

After successful bottom plugging the shaft is ready for Micro Tunneling work.

Micro Tunneling Machine(Fig. 1)

Examples of Micro-Tunneling Equipments — **Fig. 1: Examples of Micro-Tunneling Equipment**

Micro Tunneling Method (Fig. 2)

Micro tunneling is a high-performance and environmentally friendly alternative to pipeline construction with trenches; it can also be used in the most demanding of circumstances: groundwater and difficult geologies are no problem for micro tunneling, and it has proven to be a very good method of avoiding obstructions in city centers.

**Fig. 2: Schematic Representation of Micro-Tunneling Method**

The cutter head (1) removes with its tools – cutters, knives, chisels, or discs – the surrounding soil. This is taken to the crusher chamber (2). This is where any stones are crushed (3). Water is initially pumped into the crusher chamber in a closed circuit, mixed with the soil there, and then pumped back out of the drill hole.

The separating system then separates the water from the soil. The soil is disposed of and the water is pumped back into the crusher chamber. The pipe is pushed into the soil using the hydraulic cylinders in the jacking frame. A laser beam dictates the location of the pipe axis. The target board (4) reports the position of the laser point to the machine operator in the control container. Hydraulic cylinders (12) mean that the cutter head can be angled, thus correcting the position. The operator controls the entire system from the control container.

Pipe Jacking Method

Pipe Jacking is a method of Tunnel Construction where hydraulic Jacks are used to push especially made pipes through the ground behind a tunnel boring machine or shield. The method provides a flexible, structural, watertight finished pipeline as the tunnel is excavated.

Pipe jacking utilizes a jacking device to push pipe horizontally into the ground, forming a continuous string of pipe. Material is excavated as the pipe is pushed in. A thrust wall is constructed to provide a reaction against the jack. High-pressure jacks provide the substantial forces required for jacking concrete pipes.

Pipe jacking is an economical alternative to and much less disruptive than using open-cut construction to install new underground pipes. Because it is performed with a closed system, pipe jacking decreases the risk of environmental contamination during construction.

Jacking Frame (Fig. 3)

The jacking frame is the main device that plays a vital role in Pipe jacking. The pipe is pushed into the soil using the hydraulic cylinders in the jacking frame.

Inter jack (Fig. 3)

An inter-jack station is a ring of hydraulic jacks within a steel framework that is inserted into the pipe string at strategic points. Each inter jack divides the pipe string into more manageable jacking lengths. Each length, whether between jacking frame and inter jack, inter jack and inter jack, or inter jack and face, can be advanced individually and independently from the rest of the pipe string. It is the equivalent of having several smaller pipe jacks in operation at the same time in one bore, with each inter jack using the pipe length behind it as its thrust wall.

The use of inter jack reduces the potential for pipe failures since the maximum force on any individual ‘sub-string’ depends on the number of pipe sections plus the friction factor over that length of pipe. Each inter jack is controlled independently from the operator’s station and can, where necessary, be individually lubricated with the correct control and lubrication pump set-up.

ELS (Electronic Laser System) Control system for pipe jacking

In order to recognize the position of the Tunnel Boring Machine (TBM) (horizontal and vertical deviations, the pitch and roll tendency of the machine, and the yaw angle) suitable sensor technology is necessary to guide a TBM. ELS is an intelligent sensor unit with a sturdy metal case. The device is roughly the size of a shoebox and is watertight up to 5 meters submersion. It is dry-filled with an inert gas under slight pressure. The ELS is installed on the back of the tunneling machine so that the guidance laser makes contact with the target. The device is connected via a cable that supplies the power and transmits the measurement results.

Bentonite / Micro tunnel Lubrication Units

Designed primarily for the mixing and pumping of Bentonite and Polymers used as lubricants for Microtunnel and Pipejack construction, the Concrete Eurodrill range of Microtunne Lubrication Units (MLUs) offer complete systems including mixers, storage tanks, and injection pumps to meet a variety of requirements. They all incorporate the well-proven Colcrete Colloidal Mixer, which produces a very stable product, which resists water separation and retains its lubrication properties for longer when injected. A variety of pumps can be fitted, usually based on well-proven grout pumps such as the Mocol and Minicol ranges.

JACKING PIPES

Micro tunneling techniques require the jacking of a pipe into the ground using often high jacking forces, the correct choice of pipe with the ability to withstand the required jacking forces during installation and the right properties in terms of final product performance is as important as choosing the right machine to install it in the first place.

A wide range of pipe materials is available for installation using pipejacking and micro tunneling techniques, the choice depending on the requirements of the client, the ground conditions, transportation costs, and the length of the pipeline. Materials including reinforced and un-reinforced concrete, polymer concrete (concrete aggregate within a matrix of resin), glass fiber/resin-based pipes, vitrified clayware (both glazed and unglazed), steel, ductile iron, and also plastics are available as jacking pipe. In the majority of cases, the pipe material is either concrete or clayware, manufactured for pipe jacking to strict standards.

Separation Plant

The separating system separates the water from the soil. The soil is disposed of and the water is pumped back into the crusher chamber.

Different soil conditions – Different M/T Machine

Rocks: Modern technology offers new, uncomplicated options even when drilling through rocks with high degrees of hardness. In places that previously required detonation or mortise work, micro tunneling is now seen as a reliable alternative.

Stones and erratic blocks: Innovative technology creates new options: The use of mixed drill heads, which are fitted with knives and cutters for cohesive soils, as well as chisels and discs that can crush erratic blocks or rock layers, means that even the most difficult of soils can be drilled.

Flowing soils: Soil-aligned apertures in the cutter head mean that the soil excavation can be adjusted to suit the mass required by the pipe displacement.

Special Areas of Use: You can reap the rewards of micro tunneling, especially in demanding areas: no river is too broad, and no water is too deep.

River Crossings: River tunnels with excavations are largely a thing of the past. Even the broadest currents can be crossed safely using micro tunneling.

Overview of Construction Site (Fig. 4)

Online Video Courses related to Pipeline Engineering

If you wish to explore more about pipeline engineering, you can opt for the following video courses

Few more Pipeline related useful Resources for You..

Underground Piping Stress Analysis Procedure using Caesar II
Comparison between Piping and Pipeline Engineering
A Presentation on Pipelines – Material Selection in Oil & Gas Industry
Corrosion Protection for Offshore Pipelines
Start up and Commissioning of the Pipeline: An Article
DESIGN OF CATHODIC PROTECTION FOR DUPLEX STAINLESS STEEL (DSS) PIPELINE
AN ARTICLE ON MICRO TUNNELING FOR PIPELINE INSTALLATION
A short presentation on: OFFSHORE PIPELINE SYSTEMS: Part 1
Factors Affecting Line Sizing of Piping or Pipeline Systems

Piping Stress Analysis Specification | Flexibility Specification

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

Every Organization prepares its own piping stress analysis specification or flexibility specification to cater as a guideline for stress analysis of critical lines and for uniformity of jobs performed by pipe stress engineers. From project to project, this specification may vary slightly but overall the contents are almost similar. In this article, I will explain the points which must be addressed/ included while making a flexibility specification.

Scope/Purpose of Flexibility Specification:

All engineering documents must inform their end-user what the content is all about and must start with Scope or Purpose. This part document will supply information about how the user will be benefited from the document. What is the purpose of preparing the document? What points are covered in the document and which points are excluded?

Abbreviations and Definitions:

Mention the detailed names of abbreviated terms. Definitions are also required to provide in this section.

Reference Documents:

In this section, the specification will inform the references used for making the specification. The Specification will list all the codes and standards, in-house work instructions, or specifications that will be used in the project.

Criteria for Stress Analysis:

This part mentions the minimum criteria which have to be adhered to while performing pipe stress analysis. Code equations that need to be followed etc.

Stress Critical line list:

This section mentions the criteria for deciding stress critical lines. The factors like line size, temperature, equipment connection, etc force the stress engineer to consider the system for stress analysis using Caesar II software.

Analysis Software:

This section mentions which pipe stress analysis software (Caesar II, Start-Prof, AutoPIPE, CaePIPE, Rohr2, etc) to use for that specific project. The version of the software must be included. It is always better to perform the analysis with the latest version of the software.

Analysis Parameters: In this point explain the required parameters for analysis like:

Installation temperature: Mention the installation or ambient temperature of the location where the project site is.

SIF for 45-degree branch connections: Inform the engineers to use any specific criteria for calculating SIF for 45-degree branch connections.

PSV Reaction Force: Inform the engineer how to calculate the PSV reaction forces. Any dynamic load factor if needed to be used.

Slug Loads/Two-Phase flow: Inform if any specific requirement is there for two-phase flow lines like the frequency of the system needs to be maintained above 4-5 Hz, for Slug flow if dynamic analysis to be performed, etc.

Wind Loads: Mention the criteria for wind loads (what’s the size), what shape factor to consider, which code to follow and parameters to be used etc.

Seismic Loads: The criteria, code for seismic analysis, what’s the seismic co-efficient, etc.

Tank Settlement: if any tank settlement value has to be considered for analysis of tank piping. Settlement data is normally obtained from the Civil Department from the soil investigation report.

Friction Effects: What will be the friction coefficient for various contact surfaces?

Displacements of Tie–in Points: Criteria for consideration of tie-in points and battery limit conditions.

Thermal Displacements of Equipment: If the equipment is to be modelled or displacement values to be used.

Support Lift Off: Any criteria for hot sustained checking or using ALT Sustained cases as per B 31.3?

Insulation Density: Any guideline for the value of piping insulation density throughout the project.

Pipe Sagging: The accepted value of pipe sagging in sustained case. For example for process lines 10 mm and for flare and steam lines 3 mm.

Flange Leakage Checking: Criteria and method for flange leakage checking if any.

Allowable Nozzle Loads: If any multiplication factor is to be used along with standard allowable nozzle loads. For example twice API 610 values for Centrifugal Pumps, 3 times API 617 for Centrifugal compressors, and Twice API 661 for Air Fin Coolers etc.

WNC Checking: Criteria for alignment/anchor-free analysis and accepted displacement values if any for rotary equipment. If springs are to be kept in an unlocked condition.

Modelling Criteria: If guide and line stop to be modelled without friction and gap if any density is to be considered for flare headers during modelling etc.

Stress Analysis Documentation: In this section briefly describe which reports (For example input echo, restraint summary, stress summary, etc.) are to be submitted to clients as the final stress analysis document of each stress system.

Any guidelines for supporting the piping system?

The above points are the minimum required points. Additionally, you can add many more points depending on the project requirements. So, hopefully, by now you will be able to produce the flexibility specifications of your own.

START-PROF Piping Stress Video Training Series [In-Depth]

Written by Alex Matveev in Piping Stress Analysis,Start-Prof

Before starting this video series let tell you some basic idea of Pass/Start-Prof.

What is PASS/START-PROF?

Piping And Equipment Analysis & Sizing Suite or PASS/START-PROF is a comprehensive pipe stress analysis program similar to other Stress Analysis software like Caesar II, AutoPipe, Caepipe, Rohr II, etc. PASS/START-PROF software checks the piping flexibility, stability, and fatigue strength at ease. It performs all related sizing calculations following international and national codes & standards.

It is the world’s first Pipe Stress Analysis Software and first developed in 1965 in Russia. It possesses a highly powerful analysis features and efficient solver with user-friendly 3D graphics. At the same time, their detailed help system from generations of piping design experts is really praiseworthy.

The aim of PASS/START-PROF software creation is that it is planned for regular designers without special knowledge in pipe stress analysis and/or detailed knowledge of standards.

Uses of START-PROF:

PASS/START-PROF can be used to analyze piping and pipeline systems from the following industries:

process piping industry
power piping industry
gas and oil transportation industry
district heating piping
hot water supply etc,

The software can be used for stress analysis of underground, above ground, vacuum, high pressure and/ or high temperature, also cryogenic piping considering various types of restraints, spring hangers, pipe fittings, and expansion joints. PASS/STARTPROF offers an automatic selection of variable and constant spring hanger supports.

The material database of PASS/START-PROF is wide considering the various range of materials that are used in pipelines which include all types of steels, nonferrous materials, plastic pipes and fittings, orthotropic materials such as fiberglass, reinforced plastic, glass-reinforced plastics, and glass-reinforced epoxy.

This video series is created by PASS distributor in Australia – Moonish Engineering

VIDEO 1: How to Create New Project in Start Prof

To access all other tutorial videos simply click on the next mentioned below!

What is a Restriction Orifice (RO)? Its Applications, Types, Working, and Sizing

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

A restriction orifice is a device designed to control the flow of fluids by introducing a deliberate constriction in the flow path. It functions by reducing the diameter of the pipeline at a specific point, which results in a pressure drop and flow restriction. Typically, a restriction orifice is a simple, plate-like device with a precisely machined hole, but its impact on the flow characteristics of a system is substantial. In this article, we will describe the significance of restriction orifices, their functionality, working, types, applications, standards, and steps for their design.

What is a Restriction Orifice (RO)?

Restriction orifice or RO, in short, is a flow control instrument device whose primary function is to provide a restriction to the flow so that a controlled or restricted flow is achieved. Due to this restriction by the orifice plate, a pressure head drop from the upstream of the orifice to the downstream is observed. For a specific temperature and pressure condition, the orifice area at the outlet determines the volumetric flow rate of the fluid inside the pipe. Due to the high-pressure drop at the restriction orifices, it can create acoustic-induced vibration. Hence, studies must be performed by specialists.

The orifice plate is basically a thin plate with an orifice in the middle. The plate is inserted between two flanges of a pipe for providing restriction or flow measurement.

Purpose of Restriction Orifice

Restriction Orifice is used primarily for two main reasons:

If there is a requirement for Reduced flow or
If there is a requirement for high-pressure drops.

The device is sized depending on the required pressure drop. They are designed to slip between the piping flanges. Restriction orifice comes with single restriction orifices or multiple restriction orifices in Series.

How Restriction Orifices Work?

The fundamental principle behind a restriction orifice is based on fluid dynamics. When a fluid flows through a constricted area, its velocity increases, and its pressure decreases. This is described by Bernoulli’s equation. By selecting an orifice of appropriate size and shape, engineers can precisely control the flow rate and pressure drop across the orifice. It is calibrated based on the installation’s technical requirements to achieve the correct pressure or flow rate. Depending on the needed values, either simple restriction orifices (with one or multiple holes) or multi-stage restriction orifices can be used.

Applications of Restriction Orifice

Engineers and designers are familiar with a restriction orifice in the following applications for impeding flow or reducing pressure.

They are installed downstream of blowdown valves to ensure a controlled flow rate in the blowdown piping or blowdown header.
They are installed in the minimum flow bypass lines around centrifugal pumps.
They are installed in Wellhead applications
A restriction Orifice is sometimes used to restrict excess flow in case ruptures.
Minimum bypassing
Injection, cooling, and flushing of fluid.
Sampling.
The steam let down.
Use as a simple static mixer
N₂ purge or constant gas seal
Controllability improvement

Restriction Orifice Standard

There is no direct standard addressing the design of restriction orifice, but some associated references are available as listed below:

ISO 5167 Part 1 and Part 2
ISA RP 3.2
API -RP 550/551
API 2531
IEC 60534-8-3
API Manual of Petroleum Measurement – Chapter 4
AGA Report No.3
API MPMS 14.3.2
ISO 5024
ISO 5168

Working Principle of Restriction Orifice/Orifice Plate

Both Restriction Orifice and Orifice plate work following Bernoulli’s principle that states that pressure drops across the restriction orifice are directly proportional to the volumetric flow rate passing through the orifice plate.

While fluid flows through the plate, fluid velocity changes that in turn, as per Bernoulli’s equation change the pressure. This change in pressures upstream and downstream is measured to calculate the volumetric flow rate.

Restriction Orifice Types

Restriction Orifice Plates are of three types

Single-Stage Restriction Orifice:

A plate with an orifice bore of the required size for intended pressure loss is known as a single-stage restriction orifice.

Multi-hole Single Stage Restriction Orifice:

To reduce the noise generated, single-stage multi-hole restriction orifice plates are used. As the high-velocity flow at the RO inlet is distributed through several holes, the noise is reduced. To avoid the cavitation problem, multi-hole restriction orifices are used. The flow distribution through multiple holes improves the cavitation factor which in turn reduces the overall noise.

Multistage Restriction Orifice Assembly:

Multistage restriction orifices are widely used for very high-pressure reduction when a single-stage RO is not capable. It consists of a number of single-stage RO devices. The design can be single-hole or multi-hole. The restriction orifices in a multistage RO are usually arranged in an eccentric manner. The minimum distance between each stage is usually the internal diameter of the pipe.

Types of Orifice Plates:

The plates used in restriction orifice design can be of the following types:

Square edge bore or standard bore orifice plate.
Quadrant edge bore
Eccentric bore orifice plate
Segmental bore orifice plate
RTJ-type orifice plate with an integral gasket
Paddle-type orifice plates

Inputs for Restriction Orifice Design

The following inputs are required for the design of the restriction orifice:

PFD and P&ID
Hydraulic Calculation Sheet
PMS
Line operating conditions like upstream-downstream pressure, temperature, flow rate, line size, Density, Viscosity, molecular weight, Cp/Cv, vapor pressure, etc.

Restriction Orifice Design Steps

Based on the service and requirements, RO needs to be sized for critical or pre-critical conditions. During sizing, the pressure control RO plates consider the maximum pressure drop lesser than the critical pressure, and flow control RO plates consider the critical pressure drop. ISO 5167 is generally followed for sizing restriction orifices.

The design of the Restriction orifice or RO is carried out as per the steps similar to as mentioned below:

Determination of Application
Data Preparation for the orifice
Restriction orifice sizing (by design engineer or vendor)
Checking of critical design elements like cavitation index (Kc=0.93), pressure drop, minimum orifice diameter, allowable space in piping routing, etc.
Filling out the necessary information in P&ID and RO datasheets

Installation of Restriction Orifice

The restriction orifice is physically a thin plate with one or more holes in it. In piping application, They are normally inserted in between two flanges. It is possible to inadvertently leave out the plate when the piping is assembled, or, more likely, to forget to replace it when the piping is reassembled, following maintenance or cleaning. So leaving out the orifice is difficult.

Restriction Orifices — **Restriction Orifice Types**

Safe solution

To prevent this, one should make it impossible to assemble or reassemble the piping without including the orifice. A simple, practical, and foolproof method are: the restriction orifice has its own spool piece. So in such a situation, there will not be scope for forgetting the RO element during installation or Construction.

Orifice upstream and downstream requirements

It is a standard engineering practice to keep 10 pipe diameters (10D) upstream (before the orifice) and 5 pipe diameters (5D) downstream of the restriction orifice.

Restriction Orifice Symbol

The following symbols are used in P&ID to describe restriction orifice and orifice plates.

Restriction Orifice vs Orifice Plate

The major differences between the Restriction orifice and orifice are tabulated below:

	Restriction Orifice	Orifice
Purpose	A restriction Orifice is used for killing the high pressure or reducing pressure; a pressure-reducing device.	An orifice is used for flow measurement.
Hole Profile	The hole of the restriction orifice has a straight profile	The hole profile of the orifice is straight at first but then beveled (notched) with a 45° slope
Pressure Drop	Restriction Orifice causes High-Pressure drop	The pressure drop in a normal office is low.
Fluid Velocity	Restriction orifices work on sonic Velocity to ensure choked flow.	The flow through the orifice is a subsonic flow.
Acoustic Induced Vibration	Restriction Orifice is highly Susceptible to AIV and high noise can generate	Flow through usual orifice plates is not Susceptible to AIV.

Table: Difference between Orifice and Restriction orifice

Factors for Sizing RO device

There are various factors that must be considered while sizing restriction orifice.

Pressure Drop:

For sizing and selecting the restriction orifice, the pressure drop is a critical parameter. The required minimum thickness of a RO device is dependent on the pressure drop across the device.

Flow Rate:

As the pressure drop is dependent on the flow rate changes, the restriction orifice needs to be sized for a normal flow rate. For critical RO, the downstream flow rate should be considered.

Sonic Flow:

Choked or sonic flow conditions may arise due to a decrease in density and an increase in velocity when a gas accelerates through a restriction. A Sonic flow in the pipeline generates high noise and vibration in the pipeline that may cause mechanical failure. To avoid this, the maximum pressure drop across a single-stage restriction orifice plate must be limited to a critical pressure drop.

Cavitation:

In liquid flow restrictions with very large pressure drops, cavitation may occur. While passing through the restriction orifice, the velocity of liquid drops, and pressure increases. Due to these, vapor bubbles can collapse and flashing can occur. this phenomenon is known as cavitation. To avoid cavitation, the restriction orifice should be sized to maintain the cavitation index less than the incipient cavitation index of the RO plate. Inlet pressure, outlet pressure, and vapor pressure are the parameters for the cavitation index, and the incipient cavitation factor will be dependent on the beta ratio of the plate.

Noise Level:

Noise levels in RO can be predicted by calculating sound power generated due to pressure reduction. Next, the transmission losses can be subtracted to find the sound level at any pre-decided location. To reduce the noise in the restricted orifice, the following options can be selected when sizing.

Reduction of the pressure drop.
Increase the number of stages of reduction.
Using multi-hole RO plates.
Optimizing the pressure drop across each stage.
Increasing the margin between the cavitation index and incipient cavitation index.

Click here to know the sizing procedure of restriction orifices for single-phase fluids

Reference: CHEMICAL ENGINEERING/ APRIL 13, 1987

About the Author: Part of this article is written by Mr. Amir Razmi, an International, dynamic, and multi-functional chemical engineer with 16+ years of experience in engineering and EPC of oil and energy projects from pre-contract activities to execution, and closeout.

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