Accommodating Expansion

8/20/2019 Accommodating Expansion

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Pipe Expansion 101(the condensed version)


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ACCOMMODATING EXPANSION IN PIPING SYSTEMS

Accommodating thermal expansion and/or movement inpiping systems is handled by using one or more of thefollowing:

The inherent natural f lexibility of the piping system

Engineered pipe loops

Through the use of expansion joints.

Engineered pipe loops simply serve to increase the naturalflexibility of the system.


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“The best and only way to ensure againstexpansion joint failure, is to NOT have anexpansion joint in the first place."


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Natural Flexibility:

Typically the least expensive way to accommodate thermal expansion inpiping systems is by using natural flexibility.

Natural flexibility requires offsets in the system piping.

Offsets can exist due to the routing of the lines, or can be created in theform of Z-bends or U-loops.

Z-Bend U-Bend


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Natural Flexibility cont.:

When designing with natural flexibility you need to know the locations ofstructural members that will act as anchor and support points for the system.

An ASME Code Stress Analysis should be performed to determine thelocation(s) in the system where the least amount of thermal displacementoccurs.

WHY?


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Natural Flexibility cont.:

Locating anchors at the points in the system where the least amount ofthermal displacement occurs naturally, will result in the lowest anchorpoint loads.

Anchor


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But what happens when:

You have long straight runs of pipe with no room to add expansion loops?

or

You have long straight runs of pipe with plenty of room for expansionloops; but adding them would result in excessive pressure drop?

or

Where the existing offsets are too short or too few to provide sufficientnatural flexibility?


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Application of Expansion Joints in Piping Systems:

There are two different types of expansion joints, and it is essential thatthe Designer understand the differences between the two.

The two have completely different applications, act upon the pipedifferently, and must be installed in a different way.

Unrestrained Type – Typically used to accommodate axial movement inpiping systems. Simple bellows joints and packed slip type expansion

joints fall into this category.

Restrained Type – Used to take up offset and angular displacements.Tied bellows, hinge joints, gimbal joints and packed flexible ball jointsare examples.


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Unrestrained Expansion Joints

Bellows Type

Single Bellows Universal Bellows

Externally Pressurized Bellows


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Unrestrained Bellows Expansion Joints

Simple bellows type expansion joints can be used to absorb axial

compression or extension

As well as small amounts ofangular displacement


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Unrestrained Bellows Expansion Joints

Bellows expansion joints should never be subjected to torsionalmovements.

Torsion destabilizes a bellows expansion joint reducing its ability tocontain pressure and absorb movement.

If torsion is present in a piping system, “Restrained” expansion joints arerecommended.

Torsional movement is the rotationabout the axis through the center ofa bellows (twisting).


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Unrestrained Expansion JointsPacked Slip Type

Single Slip Expansion Joint


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Slip type expansion joints are designed to accommodate axialexpansion only.

They will also accommodate pure torsional movements.


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Axial expansion joints are not pressure restrained. When pressurizedthey tend to open up lengthwise.


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Pressure Thrust Load:

The thrust load which tends to force the expansion joint open is referredto as “Pressure Thrust” and is equal to the cross sectional area multiplied

by the system design pressure.

With bellows joints the cross sectional area is the effective area of the

convolutions.

With slip type expansion joints it is the cross sectional area of the pipe.

The Pressure Thrust load acts on the system anchors.


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Unrestrained Expansion JointsUnrestrained expansion joints are not provided with attachments such astie rods or hinges to restrain pressure thrust. Therefore, they can be usedonly in piping systems that incorporate correctly designed anchors andpipe alignment guides.

These components prevent over extension and damage due to distortionunder operating conditions.

ANCHOR ANCHOR

EXPANSION JOINT

INTERMEDIATE

GUIDE

PRIMARY

GUIDE


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When using unrestrained expansion joints it is critical that the line beproperly guided.

Failure to provide adequate guiding can result in premature failure of theexpansion joint.

EJ Type First Guide Second Guide Balance

Bellows 4 Pipe Diameters

14 Pipe

Diameters

Industry

Standard

Slip Joint1 Foot for each inch of

nominal pipe diameter

Industry

Standard

Industry

Standard


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Restrained Expansion Joints

Restrained expansion joints operate on a completely different principlefrom the unrestrained type.

Restrained expansion joints typically require offsets in the system pipingand absorb movement by lateral bending and/or rotation.

Restrained expansion joints have the advantage of eliminating pressurethrust forces and providing flexibility with minimal forces.

Guiding requirements with restrained expansion joints are far lessstringent.


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Tied Bellows

UniversalTied Bellows

Hinged Joint

DoubleHinged Joint

Gimbal Joint

DoubleGimbal Joint


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Single Ball Joint Double Ball Joint

Rotation Only Ball Joint


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Pressure thrust loads are contained

within the joint, resulting in loweranchor point loads.

Because restrained joints aredesigned to accommodate lateral

and bending movements, theguiding requirements are far lessstringent.

Typical 3 Ball Joint Linkage

Restrained expansion joints provide piping systems with increased flexibility byallowing relatively free lateral and bending movements.


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Expansion Joint Allowable Displacements

EJType

Movement Type PressureThrust Axial Lateral Bending Rotational

SingleBellows

Yes small small No Yes

Packed Slip Joint

Yes No No Yes Yes

UniversalTied Bellows

No Yes Yes No No

Hinged No No

Yes

(1 Plane) No No

Gimbal No No Yes

(2 Planes)No No

Packed Ball Joint

No No Yes

(Any Plane) Yes No


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Bellows Joint Advantages:

Bellows Joints do not require access; i.e. they can be direct buried.

(A telltale device is recommended if buried)

No maintenance is required.

Bellows Joint Disadvantages:

No in place maintenance or repair can be performed – it must be

replaced if damaged.

When failure occurs the system must be shut down. Chance of personal and/or property damage when failure occurs.

Installer can easily misuse joints when correcting for pipe

misalignment.


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Packed Expansion Joint Advantages:

Fabricated from materials similar to the pipe line.

Rugged construction – The wall thickness of every part of the joint is at

least as heavy as the pipe line in which it is installed.

Allows for safe packing injection under full line pressure.

In the event that a leak occurs there is no need to shut the system down

for repair.

Packed Expansion Joint Disadvantages:

Must be located to allow access.

May require occasional addition of injectable packing.


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Expansion Joint Failure Modes

Bellows Joints Packed Joints

In-Plane Squirm

NONE(If properly installed & maintained)

Column Squirm

Fatigue

Creep Fatigue

Burst, Collapse, Over Stretching

Corrosion

To avoid imposing any of these failure modes on a system, it isimperative that the system be reviewed completely prior tofinalizing the design.


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Expansion Joint Selection:

When selecting what type of expansion joint to use, the designer mustfirst review the system design parameters:

Piping layout, including the locations of any equipment connections.

Service (Steam, Condensate, etc.); including pressure & temperature.

The availability of supporting structures for anchors, supports and

guides.

The magnitude and direction of thermal displacements that will occur

during system operation.

Seismic provisions (if require).


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Governing Bodies:

Just as there are different types of expansion joints; there are differentStandards and Codes which govern their design.

Bellows Joints: Expansion Joint Manufacturer’s Association (EJMA)

Slip Type Expansion Joints: ASTM F 1007 (2007)

Ball Type Expansion Joints: ASTM F 1298 (2006)

In addition; expansion joints should be designed to the requirements ofthe appropriate ASME Piping Code (B31.1, B31.3, etc.)


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Anchors:

One of the most important parts of a piping system; and often the mostoverlooked; are the anchors.

Properly designed, located and installed anchors are critical to the safeuninterrupted operation of a piping system.

Typical Bolt Down Anchor Typical Anchor with Pipe Spool


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Typical Anchor Loads:

Deflection Loads : Bellows Spring Rate x Maximum Deflection or Slip Joint Packing Friction

(1,000 lbs./inch of Nominal Pipe Diameter).

Pressure thrust load.

Additional thrust load due to test pressure.

Support/Guide friction loads.

Branch connection loads.

Dead weight loads on vertical and sloping pipe.

Shock loads, due to quick opening valves or bursting safety discs.

Centrifugal thrust loads.

Wind loads.

Seismic loads.


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Anchor Designs:

Main Anchors: Designed to accommodate any and all load types,including full pressure thrust loads.

Intermediate Anchors: Only need to be designed for light constructionsince pressure thrust loads are absorbed by main anchors.

16” Main Anchor with 6” Service Connection 300 PSIG Design

Directional Anchors:Prevent movement in one or moredirections while allowing movementin another. They may act as eithermain or intermediate anchors; orfunction as a guide.


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Nypro Chemical Plant, Flixborough, England

On March 27, 1974 a vertical crack in Reactor No. 5 was discovered leaking cyclohexane and the plant wasshutdown for investigation.

A serious problem was found with the reactor and a decision was made to remove it and install atemporary 20” bypass assembly to replace it.

The design of the bypass included a bellows joint that was intended to absorb the thermal expansion ofthe line as well as accommodate an existing offset.

On June 1st

the bellows ruptured; resulting in the escape of a large quantity of cyclohexane. Withinminutes 40 tons of cyclohexane leaked from the pipe forming a vapor cloud estimated to be as large as650 foot in diameter.

The cyclohexane vapor cloud found a source of ignition, resulting in an explosion that completelydestroyed the plant.

The explosion was estimated as being equivalent to 15 tons of TNT.

28 fatalities were reported including 18 employees in a near by control room, 9 site workers and 1 deliverydriver that died of a heart attack. The failure occurred on a weekend and only a small number ofemployees were at the plant.

1,800 buildings within a 1 mile radius were essentially destroyed and buildings as far as 8 miles awayexperienced structural damage.

The blast was heard and felt as far as 25 miles away.


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Nypro Chemical Plant, Flixborough, England - June 1, 1974


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What went wrong?


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The design of the bypass pass line failed to account for the pressure thrust loadassociated with the bellows expansion joint.

This combined with the imposed offset, resulted in uneven loading on the bellowscausing the corrugations to “Squirm” which ultimately lead to the failure.

Squirm is caused by excessive unconstrainedpressure and is made worse as angularmovement of the bellows is introduced.


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Some place in the United States:

In May of 2009 ATS received a request to supply 2 each 8” & 6” single slip expansion joints with anchor bases.

The joints were required for an emergency outage, to replace expansion joints thathad failed.

The 8” joints were for steam service and the 6” for condesate.

The order was received on May 7th and the four joints shipped on May 11th.

Now Flash Forward to January 2011


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Same place in the United States:

In January of 2011 we received a call informing us that the expansion joints that wehad supplied in 2009 had failed.

The Customer again needed replacements on an emergency basis.

STOP Right There

2 Sets of expansion jointsin less than 2 years?????


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When 2 essentially identical expansion joint failures occurin the same section of pipe?

It’s most likely not the fault of the expansion joints.

Piping drawings and details were requested as well as any information thatcould be provided relative to each of the failures.

An ASME Code stress analysis was performed on the system based on theinformation receive.


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System Piping Arrangement


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Vault Piping Arrangement


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Vault Piping Arrangement


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The results of the stressanalysis found that thepiping inside the vault had

sufficient natural flexibilityand most likely was not thecause of the failure.

The maximum calculatedstress ratio SE/S A = 0.16


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So what went wrong?

• As of today the cause of the failure is still unknown.

• The Customer has contracted an independent engineering firm to performa forensic analysis of the failure.

• Based on the little information that we have, it was recommended that thepiping system outside of the vault be included in the review.

• An alternate arrangement was proposed for the piping within the vault that would accommodate the thermal expansion of the system and at the sametime eliminate the potential for additional expansion joint failures.


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Using a 3 ball joint linkage as shown provides the following advantages:

Eliminates the need for anchorsin this vault.

Eliminates the pressure thrustforces acting on the system.

Accounts for any settling oralignment issues with pipingexternal to the vault.

8” HPS Line w/3 Ball Joints


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Conclusions:

When choosing an expansion joint you must know the magnitudes,directions and types of movements that it needs to accommodate.

Selecting the proper type of expansion joint is key to having a trouble

free (Leak Free) system.

If you have an expansion joint that is chronically developing leaks,

don’t automatically assume that it is the fault of the joint. Many times,

the failure is due to deficiencies in the piping system itself.

If you need help with an expansion problem.

Ask an Expert


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Questions?Edward W. Patnode, P.E.

President/CEO

ADVANCED THERMAL SYSTEMS, INC.

15 ENTERPRISE DRIVE, LANCASTER, NY 14086Toll Free: 800-443-9194

Phone: 716-681-1800

Fax: 716-681-0228

Email: [email protected]

www.advancedthermal.net

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