Features of Expansion Joint

Presented by Jeba Anand Nadar

Topic

• Introduction• Design Variable• Bellows movement• Pressure Thrust• Spring force• Types of expansion joint

Introduction

Expansion joint is an assembly designed to absorb vibration, dimensional changes such as those caused by thermal expansion or contraction of a pipeline ,duct or vessel etc.

Expansion joint may be added to system in order to increase flexibility when there is a insufficient room for loop.

Expansion joint may vary in terms of number and type of convolution, material, number of plies, stiffness and allowable movement.

A bellow is a flexible seal. The convoluted portion of an expansion joint is designed to flex when thermal movements occur in the piping system. The number of convolutions depends upon the amount of movement the bellows must accommodate or the force that must be used to accomplish this deflection.

CONTD ……

The convoluted element must be strong enough circumferentially to withstand the internal pressure of the system, yet responsive enough to flex.

The longitudinal load (pressure thrust) must then be absorbed by some other type of device. These devices include pipe anchors, tie rods, hinges, or gimbal structures.

Expansion joint are made of metals (such as stainless steel), fabric(Glass fibre), plastic(PTFE) and Elastomer(rubber).

The standard used for metallic expansion joint are EJMA (Expansion Joint Manufactures Association) and ASME 31.3 APPENDIX ‘X’

Expansion joint present maintenance problem due to fatigue failure mode.

What metallic expansion joints do:

Compensate motionCompensate expansionReduce tensionDamp vibration and noise transmissionsCompensate ground and foundation settlingCompensate inaccurate assemblyServe as dismantling joints on fittings

Design Variable

• SIZE/DIAMETER -

• Refers to the diameter of the connecting pipe. It affects its pressure-retaining capabilities and ability to absorb certain types of movements.

• MOVEMENT –

• Metal bellows are designed to absorb thermal and / or mechanical piping or ducting system movements while retaining system operating pressure at the system temperature.

• Bellows can absorb the Axial, Lateral and Angular Rotation.

• PRESSURE –• Minimum and maximum pressure requirements. • Pressure is possibly the most important factor determining the design of an expansion joint. • Care should be exercised to insure that these specified pressures are not increased by unreasonable safety

factors.

Design Variable

• TEMPERATURE –

• Minimum and maximum operating temperature

• Temperature will affect the expansion joints pressure capacity, allowable stresses, cycle life and material requirements

• FLOWING MEDIUM –

• The substances that the expansion joint will come in contact with.

• In some cases, due to excessive erosion or corrosion potential, or in some cases of high viscosity, special materials should be specified.

• OVERALL LENGTH –

• Maximum/minimum length of expansion joint

• POSITION OF BELLOWS–

• Position of bellow- horizontal ,vertical etc

Bellows Movement

• The various dimensional changes which an expansion joint required to absorb such as those resulting from thermal changes are as follows :-

• AXIAL COMRESSION / EXTENSION:-• The dimensional shortening /lengthening of an expansion joint along its longitudinal axis

• It has been referred to as axial movement, compression / elongation

LATERAL DEFLECTION:

• The Relative displacements of two ends of an expansion joint perpendicular to its longitudinal axis.

• This has been referred to as lateral offset, lateral movement, parallel misalignment, direct shear or transverse movements.

Bellows Movement

• ANGULAR ROTATION :• The displacement of the longitudinal axis of the expansion joint from its straight line portion into a circular

arc. Angular rotation is occasionally referred to as rotational movement.

• TORSIONAL ROTATION :

• The twisting of one end of expansion joint with respect to other end about its longitudinal axis.• The twisting generally produces very high shear stresses in bellows. For this reason it is very important to

use special hardware to limit the amount of shear stresses in bellows.

PRESSURE THRUST

• Pressure thrust force is created by the system pressure acting on the area of the “mean” diameter of the bellows.The magnitude of pressure thrust force (Fs) in lbs. Is determined by the following equation:

• Fs= P a• P= Pressure (psig)• A= Effective area of the expansion joint

• When an unrestrained expansion joint is introduced into the system ,this is equivalent to cutting the pipe because the inherent flexibility of the expansion joint bellows makes it unable to transmit the force in the pipe. In addition the cross sectional area is increased due to depth of bellow convolutions

PRESSURE THRUST

Metal bellows cannot restrain longitudinal pressure loads without integral retraining hardware such as tie rods, hinges, gimbals or external pipe anchors. Longitudinal pressure load on a bellows results in “pressure thrust”.

With a thin wall convoluted bellows welded to two flanges, the bellows reaction to pressure thrust results in the bellows growing in length until the bellows “squirms” and / or the convolutions stretch out to become the tube from which they were formed.

Squirm can lead to immediate failure of the bellows. It is the responsibility of the expansion joint manufacturer to design the bellows to avoid squirm during operating conditions or pressure testing.

MA MAPRESSURE THRUST CONTAINED

BY PIPE.PRESSURE THRUST NO LONGER

CONTAINED BY PIPE.SYSTEM NOW REQUIRES

MAIN ANCHORS.

MM

SPRING FORCE

In addition to longitudinal pressure thrust loads, movement within a bellows requires a “force” to cause the bellows to compress, extend or angulate. Bellows “Spring rate” is a design consideration. To calculate the load (force) imposed on equipment adjacent OR pipe anchor to the expansion joint.

F = K· X Where : F - The load (force) imposed on equipment on either side of the bellows. K - The bellows spring rate (expressed as pounds / inch of movement for axial and lateral movements, and inch / pound per degree for angular movement) X - The anticipated or specified movement

The result is referred to as “spring force” For a bellows expansion joint without integral longitudinal pressure restraining hardware, one must add the bellows spring force to the pressure thrust force to determine the total force imposed on adjacent equipment or pipe anchors.

TYPES OF EXPANSION JOINTS

1.SINGLE TIED / UNTIED EXPANSION JOINT

2.UNIVERSAL TIED / UNTIED EXPANSION JOINT

3.HINGED EXPANSION JOINT

4.GIMBLE EXPANSION JOINT

5.PRESSURE BALANCE EXPANSION JOINT

SINGLE UNTIED EXPANSION JOINT

Single Expansion Joints have one bellows. Axial compression and extension, lateral and angular movement can be accommodated.• These expansion joints do not restrain the internal pressure thrust.

The piping designer must provide the system with separate anchoring and guiding to resist the pressure thrust.

Where small thermal movements are involved and proper anchoring and guiding is feasible, a single expansion joint is the most economical installation.

SINGLE TIED EXPANSION JOINT

It also have one bellows, except the overall length is restrained by tie rods designed to contain pressure thrust.

A tied single is usually designed for lateral offset so that the tie rods can remain fully engaged and loaded with the pressure thrust force. Tie rods are termed as limit rods when there is gap provided between nut and flange of tie –rod assembly

A two tie rod design can accept angular deflection in a single plane.

As tie rod contains pressure thrust forces, main anchors not required.

UNTIED UNIVERSAL EXPANSION JOINT

It consist of two bellows separated by a pipe spool.

This configuration accommodates large lateral movements, in addition to axial compression and extension and angular deflection.

These expansion joints have no restraints to resist pressure thrust and like the singles, the piping designer must provide separate anchoring to handle pressure thrust

TIED UNIVERSAL EXPANSION JOINT

contain two bellows separated by a pipe spool and tie rods designed to contain the pressure thrust force. These expansion joints are generally designed to accommodate lateral movement only.

A universal expansion joint can be designed to have a very low lateral spring force to minimize forces on adjacent equipment.

A two tie rod design can also accept angular deflection in a single plane.

The tie rods are usually at or near ambient temperatures and, therefore, do not expand and contract as a function of the temperature of the media within the pipe. As a result, the thermal expansion of the length of pipe between the tie rod end plates is forced into the bellows as an axial movement. The bellows design must accommodate this axial thermal expansion as well as the specified lateral movement.

HINGED EXPANSION JOINT Hinged Expansion Joints have a single bellows with overall length restrained by hinge

hardware designed to accommodate pressure thrust(main anchors not required)

A hinged expansion joint generally used in set of 2 or 3 to absorb Lateral deflection in one or more directions in single plane piping system.

Each individual expansion joint in such system is restricted to pure angular Rotation by its hinges

Bellows are protected from torsional loads Can be designed to support dead weight of piping and equipment, wind loads and similar externally applied forces.

Universal Hinged Expansion Joints have two bellows separated by a pipe spool with overall length restrained by hinge hardware designed to contain pressure thrust.

A hinged universal expansion joint accepts large lateral movements in a single plane with very low spring forces.

HINGED EXPANSION JOINT

GIMBLE EXPANSION JOINT Gimbal Expansion Joints have a single bellows and gimbal hardware designed to resist

pressure thrust.• The gimbal expansion joint hardware operates like the universal joint on a drive shaft to

accommodate angular movements in any plane.

Bellows are protected from torsional loads

Can be designed to support dead weight of pipe

Universal Gimbal Expansion Joints are similar to the hinged universals except that the two expansion joints are gimbal type.

The advantage of this arrangement is the ability of the expansion joint to accept large lateral movements and independent angular movements in any plane.

PRESSURE BALANCED EXPANSION JOINT Pressure Balanced Elbows are expansion joints which can consist of a single or double

bellows in the flow section, and a balancing bellows of equal area on the back side of the elbow.

Tie rods attach the outboard end of the balancing bellows to the outboard end of the flow bellows. Under pressure the tie rods are loaded with the pressure thrust force.

If the flow bellows compresses in service, the balancing bellows extends the same amount without exposing the adjacent anchors to pressure thrust forces.

However, the spring forces associated with bellows movements are imposed on the adjacent equipment.

A pressure balanced elbow type expansion joint can• accept axial compression, axial extension, lateral • Movements and very limited angular motion.

PRESSURE BALANCED EXPANSION JOINT

SUMMARY OF EXPANSION JOINT