expansion joint basics

WARM GREETINGS

LONESTAR

LONESTAR INDUSTRIES

METAL EXPANSION JOINTS / BELLOWS

PresentationBy

R.V. RAMACHANDRAN

LONESTAR

LONESTAR INDUSTRIES

TOPICS

BASICS - BELLOWS EXPANSION JOINTS

TYPES, SELECTION & APPLICATION

SPECIFYING BELLOWS EXPANSION JOINTS

TYPICAL CAUSES OF FAILURE

STORAGE & PRESERVATION

GOOD PRACTICES IN INSTALLATION

BASICS

BELLOWS TYPE EXPANSION JOINT

Any device containing one or more Bellows (a flexible, corrugated member) with End Connections

BASICS

Why an Expansion Joint?

Any pipe connecting two points is subjected to numerous types ofactions, which result in stresses on its wall.

These stresses are due to,

Internal or External pressure at working temperature,Frequent changes in temperature or pressure,Movement imposed on pipe section by external restraints such as equipment rigidly connected to it, Vibration of Equipment or Structure to which the pipe is connected,Thermal expansion,

BASICS

Why an Expansion Joint?

Let us consider the stress due to the movement and thermal expansion.

The stress on the wall of the piping is related to the force or movement exerted on it by external restraints.

When either the values of the stresses or the values of the external forces or moments exceed the maximum allowable values, the flexibility of the pipe must be increased artificially.

This can be done either by altering the layout of the pipe or by inserting high flexibility section into it.

This is precisely the function of Expansion Joints.

BASICS

Bellows

A flexible element, having one or more corrugations / convolutions and end tangents with Lb/Db ≤ 3.

The straight un-convoluted portions at the end of the Bellows is termed as tangent.

BASICS

Axial Movement

The dimensional shortening of an Expansion Joint due to thermal expansion of pipe and / or dimensional increment due to pipe contraction along its axis.

Movement

BASICS

Lateral Deflection

The relative displacement two end of the Expansion Joint, perpendicular to its axis due to thermal expansion / contraction of the pipe

Movement

BASICS

Angular Rotation

The Rotational displacement of the longitudinal axis from its initial straight line position into a circular arc.

Movement

BASICS

Torsional Rotation

The twisting of one end of the Expansion Joint with respect to the other end about its axis.

Movement

BASICS

Since a pipe under internal pressure or vacuum will have its wall subjected to circumferential and longitudinal loading, introducing a discontinuous member such as a Bellows will transfer the longitudinal-pressure forces to the main anchors.

Pressure thrust is the product of internal pressure times the Bellows effective area.

Pressure Thrust

BASICS

Pressure Thrust – contd…

The effective area / pressure thrust area of a Bellows is based on the mean diameter of the Bellows convolutions.

If adequate main anchors cannot be provided to absorb the pressure thrust or if connected equipment cannot accept the pressure thrust loading then the joint must be equipped with tie bars. However a tie rod equipped Bellows cannot absorb the axial movement.

If no main anchors are present, the bellows cannot absorb the pressure loading without ripping open; in the case of vacuum loading, the joint would collapse.

BASICS

The force required to deflect a Bellows axially,

The spring rate is a function of the dimensions of the Bellows and the material from which it is made,

Spring Rate

BASICS

Excess internal pressure may cause a multi-convoluted Bellows to become unstable and squirm.

Squirm is detrimental to Bellows performance, it can greatly reduce both life and pressure capacity.

The two types are

- Column squirm and - In-plane squirm.

Stability

BASICS

Column squirm is a gross lateral shift of the centre section of the Bellows. It results in curvature of the Bellows centre line.

Column in-stability

BASICS

In-plane squirm is a shift or rotation of the plane of one or more convolutions such that the plane of these convolutions is no longer perpendicular to the axis of the Bellows.

Inplane in-stability

BASICS

Un-reinforced Bellows

A bare Bellows without a Reinforcing member in between its convolutions is termed as Un-reinforced Bellows.

Bellows - Categories

BASICS

Reinforced

A Bellows fitted with a member in between its convolutions to reinforce the root of the convolution against internal pressure is termed as Reinforced Bellows.

Reinforcing rings are used if the circumferential stresses become excessive as a result of high operating pressures.

The reinforcing rings absorb circumferential Stresses so that the wall of the Bellows can remain relatively thin and flexible overall.

Bellows - Categories

EXPANSION JOINT - CATEGORIES

Untied Expansion Joints

Tied Expansion Joints


Untied Expansion Joints

The Expansion Joints free to travel along its axis

Pressure Thrust Load will act on anchors

Anchors to be designed for both pressure thrust load and spring forces


Tied Expansion Joints

The Expansion Joints are restrained to travel along its axis (exception – pressure balanced types)

Pressure Thrust Load is contained within the Expansion Joint

Pressure thrust load need not to be considered for anchor design

UNTIED EXPANSION JOINTS - TYPES

Single Expansion Joint

Simplest form of an Expansion Joint

Compensate Axial, Lateral and Angular movements –individually or combined of small magnitude

UNTIED EXPANSION JOINTS

Untied Single Expansion Joints - Illustration

UNTIED EXPANSION JOINTS - TYPES

Universal Expansion Joint

A pair of Bellows connected with a Centre Spool

Compensate large amount of Axial, Lateral and Angular movements – individually or combined

UNTIED EXPANSION JOINTS

Untied Universal Expansion Joint - Illustration

TIED EXPANSION JOINTS - TYPES

TIED SINGLE

TIED UNIVERSAL

HINGED

GIMBAL

PRESSURE BALANCED – ELBOW

INLINE PRESSURE BALANCED


Tied Single Expansion Joint

A Single Expansion Joint installed with Tie Rods

Compensate only Lateral Movement of smaller magnitude

Tied Single - Contd…

TIED EXPANSION JOINTS – TYPES


Tied Universal Expansion Joints

Universal Expansion Joint (a pair of Bellows with Centre Spool) with overall tie rods

Shall be used in a 90 Degree piping offset – both single plane and two plane

Due to the presence of Overall tie rods, no external axial movement


Tied Universal – contd…


Hinged Expansion JointHinged Expansion Joints are intended to compensate the angular rotation in one plane. The arrangement consists of pair of hinges connected by a hinge pin.

Hinged Expansion Joints – contd…

The hinges are designed to restrain the pressure thrust loads and other external loads such as dead weight and wind.

Hinged Expansion Joints are used, to absorb angular movement when the movement occurs in only one plane.


Hinged Expansion Joints - Illustration

2 Hinged Expansion Joints can be used in “Z” Offset pipe section to compensate huge lateral movement

The expansion of offset pipe is absorbed by the natural flexibility of the horizontal pipe section

It is a good practice to keep the distance L1 as maximum and L2 as minimum


Hinged Expansion Joints - Illustration

3 Hinge System shall be considered to compensate both sections of pipe expansion

The distance L1 & L2 shall be kept to a maximum and L3 to minimum



Gimbal Expansion Joint

Gimbal Expansion Joints are used to absorb angular movement when it occurs in all planes.


Gimbal Expansion Joints –contd…

The construction of a Gimbal Joint incorporates a pair of hinges connected to a common floating Gimbal Ring.


Gimbal Expansion Joints –contd…

The Hinges & Gimbal Ring are designed to restrain the pressure thrust loads and other external loads such as dead weight and wind.

A Single Gimbal Expansion Joint is intended to compensate angular rotation in all directions.


Gimbal Expansion Joints –Illustration

In a multi-planer piping system, at multi-plane “Z”bend, 2 Gimbal Expansion Joints shall be used

The thermal expansion in the offset leg is absorbed by flexibility in the horizontal pipe runs


In a multi-planer piping system, at multi-plane “Z” bend, 2 Gimbal Expansion Joints shall be used

An additional Hinged Expansion Joint shall be employed in the horizontal pipe segment, when it is insufficiently flexible to absorb the expansion of the offset leg.

Gimbal Expansion Joints - Illustration


Pressure Balanced Expansion Joint – Elbow

Is capable of compensating axial and / or lateral movement and at the same time to contain the pressure thrust load within the Expansion Joint Assembly


Pressure Balanced Expansion Joint – Elbow


Pressure Balanced Expansion Joint – Elbow – contd…

This is achieved by tie rod restraints which connects the Line Bellows and an Opposite Balancing Bellows subjected to the line pressure

This type of Expansion Joint can be used only at a change in direction of pipeline.


Pressure Balanced Expansion Joint – Elbow – Illustration


Inline Pressure Balanced Expansion Joint


In this assembly the Line Bellows is tied with the Balancing Bellows having twice the Effective area.

Due to tie arrangement, when the line Bellows is getting compressed to compensate the Pipe Expansion, the balancing Bellows will extend the equal amount, thus the volume across the Expansion Joint is maintained, hence no pressure thrust load

Inline Pressure Balanced Expansion Joint – contd…

Inline Pressure Balanced Expansion Joint – Contd…

Inline Pressure Balanced Expansion Joints are used in straight pipe between two anchors to compensate the axial pipe growth, at the same time not to transfer the pressure thrust load to anchors.

They can accommodate small amount of lateral movement also.


EXPANSION JOINTS – SPECIAL TYPES

EXTERNALLY PRESSURIZED EXPANSION JOINTS

There are certain applications the Expansion Joint is intended to compensate huge amount of axial movement.


Externally Pressurized Expansion Joint – contd…

An internally pressurized Expansion Joints with more number of convolutions to compensate the required axial movement is totally unstable even under small pressure.

Externally Pressurized Expansion Joints in which the flow medium pressure is guided external to the Bellows, is a ideal solution to compensate huge axial movement.

Since the Bellows inside is subjected to only atmospheric pressure, there is no instability or squirm.


REDUNDANT PLY DESIGN

2 – Ply Construction

Each ply designed to withstand the Design / Operating conditions

Redundant Ply Design – Contd…

If one ply fails, the other ply will take its place until a scheduled replacement


EXPANSION JOINT – ACCESSORIES

Control Rods

For individual Bellows in an Universal Expansion Joint

To limit the movement per Bellows

Not designed to withstand the Bellows Pressure Thrust Load in the event of Anchor failure


Limit Rods

Installed in Untied Expansion Joints to restrict the Bellows movement range during normal operation.

In the event of a main anchor failure, they are designed to prevent the Bellows over-stretching or over-compression while restraining the full pressure thrust load.


Pantograph Linkages

A scissors-like device

Primary function is to positively distribute the movement equally between the two Bellows of the Universal Expansion Joint throughout its full range of movement.

Pantograph linkages are not designed to restrain pressure thrust.


Internal Sleeve

A cylindrical body welded inside the Expansion Joint, one end free to allow the Bellows to move

EXPANSION JOINT - ACCESSORIES

Internal Sleeve – contd…

They prevent the direct contact of flow medium with Bellows

They are used

to hold friction losses to a minimum

to ensure smooth flow

to prevent flow induced vibration resulting from turbulence of flow

to prevent the erosion of Bellows by flow medium containing solid particles, catalyst etc

to facilitate packing to prevent the entry of undesired elements in the flow medium

to facilitate insulation to bring down high the flow medium temperature to the required level


Purge Connection

Whenever required they are installed at the sealed end of each inner sleeve of an Expansion Joint

A liquid or gas can be injected thru purge connection between the Bellows and internal sleeve to keep the area clear of erosive and corrosive media and / or solids that could pack the convolutions.

Purging may be continuous or intermittent or at start up or shut down as required


External Shroud

A cylindrical member to cover the Bellows outside, removable type, made of two or three halves

One end fixed and other end free to allow Bellows to move

Facilitate for external insulation of Bellows

Prevent the damage of Bellows

– from falling objects, – during handling and transport– from weld arc strike / spatter during welding

at adjoining areas


Shipping Brackets

Brackets or Rods fixed at both sides of a Bellows

Generally painted in yellow colour

Helps to maintain the Overall Length of the Expansion Joint during transportation, handling and installation

They should be removed after completion of installation of Expansion Joint, Pipe Supports, & Guides and prior to Pressure testing of the line

SPECIFYING A METAL EXPANSION JOINT / BELLOWS

Consider the following prior to

preparing a Technical Specification

for a Bellows type Metal Expansion Joint


Piping System Layout

Material compatibility

Flow Medium

Pressure

Temperature

Insulation

Movement

Vibration

Special features

Lifting Lugs

Others which may affect the performance of an Expansion Joint


Review of Piping System Layout,

to determine the location of Expansion Joints

to check the availability of supporting structures for anchoring / guiding of the piping

for the magnitude and direction of thermal movements to be compensated while selecting the location and type of Expansion Joint

to incorporate special hardware to prevent the torsional rotation of Bellows


Material compatibility

Specify the Bellows material compatible for flow medium

Considerations to be given for,

– the possibility of Chloride ion stress corrosion in Austenitic Stainless steel,

– the possibility of Caustic induced stress corrosion in Nickel alloys

– the possibility of leaching of corrodents from insulating materials

Failed Bellows underChloride Atmosphere


Flow mediumIndicate details of flow medium such as,

Velocity,a thicker sleeve is required if the flow velocity is higher toprevent the turbulence andresonance vibration

Density,certain flow material will settle and pack in between the convolutions resulting in pre-mature failure


Flow medium – contd…

Composition,

to check the compatibility of material used in the EJ assembly

Direction,

Single or bidirectional, bidirectional flow requires a telescopic type of sleeve and / or higher thickness sleeve to prevent buckling due to back flow and to prevent the damage of the Bellows.


PressureThe system design and test pressures should be specified withoutadding arbitrary safety factors. Excess Bellows thickness required to withstand the unrealistic higher pressures will produce adverse effect on Bellows fatigue life and result in Bellows design of higher stiffness.

TemperatureMaximum, minimum and installation temperatures should be specified accurately. Pre-positioning / pre-stressing of the Expansion Joint during installation shall be required in case of significant variation in the ambient temperature.


Movement

The system designer shall specify the movements of connecting equipments / anchors and mis-alignment (if any) in addition to the thermal movement of the piping.

Similar to pressure, the movements being specified should be realistic. Adding excessive safety factor requires the Bellows of higher number of convolutions compromising the Bellows stability.

Insulation

If required to be performed at site, the details shall be provided to consider the weight of the same in the design.


Vibration

Specify the amplitude and frequency of vibration to be imposed on Bellows such as those caused by machineries such as pumps, blowers etc.

A resonant condition in the Bellows will result in cracking and failure.


Additional Requirements / Special features

Thick Cover

In cases of hazardous flow medium / very high pressures, it is desired to specify higher thickness external cover to prevent the radial escape of flow medium and to prevent the harm to working personnel.

Limit Rods

Limit rods, specifying limit rods will prevent the Bellows from stretching out and getting damaged in the event of failure of main anchors.



2 – Ply testable Bellows

– A 2 – ply testable Bellows, with each ply designed to withstand the specified conditions. The annular space between the plys can be monitored for leakage and can be planned to replace the joint in the next scheduled maintenance.



Lifting Lugs

Specify the Lifting lug (s) when the weight of Expansion joint exceeds 250 kgs. If more than one lug is furnished then each lug shall be designed to carry the assembly weight.

Other details

Other details which may affect the performance of the Expansionjoint such as environmental details (saline, atmosphere contaminated with SO2 etc.) shall also be included.

STORAGE & PRESERVATION Metal Expansion Joint / Bellows

STORAGE:

Area

Free of moisture, dampen-chemicals, dirt and work traffic

Not exposed to weld spatter or molten metal or falling heavy objects

Cleared of any sharp objects or protrusion


Preservation

Cover with water proof / resistant sheets

Do not remove desiccant / protective coating in the packing; keep them through out the period of storage

Do not stack Expansion Joints one above another


Preservation

Do not remove the shipping brackets, they should remain in place.

Keep the Expansion joints on horizontal flat surface resting on weld end pipe or flange

Do not place the Bellows element directly touching the ground

Do not keep the Expansion Joints on bare earth.

INSTALLATIONMetal Expansion Joint / Bellows

Considerations

Consider the Bellows Expansion Joint as a highly engineered product and not a general commodity item.

Utmost care shall be given at all stages of Installation of an Expansion Joint


Inward Inspection:

Check for possible damages during transit when an Expansion Joint is received at site.

Check for broken hardware, loose shipping bars, dents and scratches.

Check the container for Gaskets, Fasteners, Removable Liners and any other components which form a part of Expansion Joint assembly


LIFTING & HANDLING

Lift only with designated lifting lugs.

Do not use chains or any other handling devices directly on Bellows element or Bellows Cover.

Do not use Shipping bars (painted in yellow) to lift the Expansion Joint. They are not designed to lift the Expansion Joint.


LIFTING & HANDLING

Never lift an unrestrained Bellows / Expansion Joint. Doing so will result in damage and the unit will fail in service.

For Expansion Joints not provided with lifting lugs (less than 500 kgs.) the best lifting method should be evaluated at the time of installation.

Do not remove the shipping bars (painted in yellow) till the completion of installation including all pipe restraints.


CARE DURING INSTALLATION

Ensure adequate care to prevent Dents & Score Marks on thin Bellows.

Safe guard the Bellows from arc strike and weld spatter.

Keep the Bellows free from corrosion. Certain chemicals, dirt and metal filings will damage the Bellows material.



Do not use cleaning chemicals such as soap, detergents and solvents containing chlorides, caustics or sulphides. They can lead to stress corrosion and will be known only after sometime after put into the operation.

Use only chloride free insulation material if insulation of Expansion Joints is required.

Do not use wire brush, steel wool and any other abrasive tools on Bellows. Scratches and abrasion will reduce cycle life and causepremature failure.



Verify the opening / space into which the Expansion Joint will be installed / slided that it does not exceed the installation tolerance designated in the specification.

Check the area; they should be free of any sharp objects or protrusions. If not removable, they should be notified so that they can be avoided.

Check for the edges of the connecting pipes. They should be clean, smooth and parallel to each other.



Check the ends of the Expansion Joints for any protective covering and remove them.

Check inside the Expansion Joint for desiccant bags or any othermaterial and remove the same.

Do not remove the shipping bars until the installation is complete.

Lift the Expansion Joint using the lifting lugs and position into piping.



Orient the Expansion Joint with flow arrow pointing in directionof flow when there is a presence of Sleeve / Flow Liner.



Do not use the Bellows to correct for misalignment of piping unless it has been considered in the design.

Cover the Bellows with chloride free fire retardant cloth in case of Expansion Joints with Weld Ends. This will help to prevent the arc strike, weld spatter etc., which will damage the Bellows.

Use proper electrode to weld the Expansion Joint to the adjacentpiping.



Orient the Flanges of Expansion Joint so that the bolt holes arealigned with pipeline flanges in the case of Expansion Joints with flange ends.

Do not force / rotate the Expansion Joint to match the bolt holes of the mating flange. This will cause torsion on the Bellows and will severely reduce the Bellows capability and may cause premature failure.

It is good practice to leave one pipeline flange loose until theExpansion Joint is installed.



Install gaskets and bolt to the required torque recommended by the flange manufacturer.

Do not entertain the movement of the Expansion Joint (Compression, Extension, Offset and Rotation) due to piping misalignment which has not been anticipated and considered in the design.

The most common installation error is forcing the Bellows to fitan excessive, beyond- construction-tolerance gap in the piping. Any misalignments of greater magnitude will result in premature failure of Bellows.



Ensure that construction personnel make the piping fit the Expansion Joint and not vice versa.

Installation of Anchors, guides and pipe supports shall be in strict accordance with the piping system drawings.

Any field variances from planned installation may affect proper functioning of the Expansion Joint and must be brought to the attention of competent design authority for resolution.


Checking prior to pressure testing

A careful inspection of the entire piping systems shall be made withparticular emphasis on the following: -

Are anchors, guides and supports installed in accordance with the system drawings?

Is the proper Expansion Joint in the proper location?

Is the Expansion Joint’s flow direction and pre-positioning correct?

Have all of the Expansion Joint shipping devices been removed?


Checking prior to pressure testing

Are all guides, pipe supports and the Expansion Joints free to permit pipe movement?

Has any Expansion Joint been damaged during handling and installation?

Is any Expansion Joint misaligned? Measuring the Joint overall length, inspection of the convolution geometry and checking clearances at critical points on the Expansion Joint and at other points in the system can determine this.

Are the Bellows and other movable portion of the Expansion Jointfree of foreign material?


LINE TESTING

Inspect the entire system to ensure proper installation of anchors, guides and pipe supports in strict accordance with piping system drawings.

Remove shipping bars (painted in yellow) prior to pressure testing once the pipe line anchors, guides and pipe supports are in place.

Pressurise and test the line with Expansion Joint.


LINE TESTING

Some water may remain in the Bellows convolutions after the test. If this is detrimental to the Bellows or system operation, work out the ways to remove such water.

Do not subject the Expansion Joint to test pressure higher than the specified.

Use water for pressure test free of chloride.

If the system has been designed for a gas, and to be tested with water, Check whether any provision has been made to support the dead weight. Provide additional support due to the weight of water, if not there.


Checking during pressure testing

Extreme care must be exercised while inspecting any pressurized system or component.

A visual inspection of the system shall include checking for the following: -

Check the evidence of leakage or loss of pressure.

Check for Distortion or Yielding of anchors, Expansion Joint hardware, the Bellows and other piping components.


Checking during pressure testing

Check for any unanticipated movement of the piping due to pressure.

Check for Evidence of instability (Squirm) in the Bellows.

Check for the evidence of binding of the Guides, Expansion Joints and other movable parts of the system.

Check for any evidence of abnormality or damage, the same shall be reviewed and evaluated by competent design authority.


Checking after system commissioning

Perform a visual inspection and ensure that the thermal expansion is being absorbed by the Expansion Joints in the manner for which they are designed.

Check the Bellows Expansion Joints for evidence of any unanticipated vibration.

TYPICAL CAUSES OF EXPANSION JOINT FAILURE

Vibration

Fatigue

Excess Pressure

Excess Movement

Improper shipping & handling

Improper storage

Wrong sleeve direction

Pre-mature removal of shipping brackets

In-sufficient protection of Bellows during installation

Anchor failure in service

Torsional rotation of Bellows

Erosion

Packing of flow medium

Corrosion


Vibration

Metal Bellows Expansion Joint is not a Vibration Isolator.

In applications where the possibility of vibrations – originating from rotary machines such as Pumps, blowers etc., Metal Expansion Joint shall be used with proper evaluation.

Metal Bellows can be used in applications where the Vibration is of low amplitude and high frequency.


Vibration

The higher flow velocity results in turbulence and flow induced vibration; a properly designed internal sleeve to be used.

Metal Bellows will fail imposed with vibration of higher amplitude and low frequency such as originating from Reciprocating Machines.

It is important to furnish the Vibration Data such as amplitude and frequency of the system to the Bellows designer.


Vibration

It should be ensured that frequency of system vibration do not coincide with Bellows Natural frequency.

The Bellows will be designed to have its Natural Frequency 2/3 times less than the system frequency or greater than 2 times thesystem frequency.


Fatigue Failure

Evaluate the total system thoroughly to specify the life of the Expansion Joint in terms of cycles, while preparing the specifications.

This is based on different modes of plant operation.

If the Plant operates at different modes with varying operating conditions, the cyclic requirements based on each operating conditions should be specified.

If the specified data is based only on Normal Operating Conditions then any Bellows designer will consider only these data for design. In actual system operation the Bellows Expansion Joints imposed with different modes of varying operating conditions will prematurely fail.


Excess Pressure

Do not operate the system at a pressure higher than the specified design pressure.

The excessive pressure will cause higher membrane stress resulting in reduced Bellows life.

The pressure higher than the specified pressure will lead to Bellows Instability.

The Bellows will lose its profile /shape. The results are reduced pressure capability, reduced movement compensating capability and sudden failure.


Excess Movement

Ensure that the Bellows Expansion Joints are not imposed with higher thermal movements than the specified value.

The higher magnitude of movement than the specified design movement during operation will cause higher bending stresses in the Bellows resulting in pre-mature failure.

Evaluate thoroughly for realistic thermal movement of piping andmovement of connected equipments etc.

Adding arbitrary safety factors will also result in highly flexible joint compromising the stability or result in un-economical design.


Improper Shipping & Handling

Dents, gouging, scratches, score marks produced on thin Bellows as a result of improper shipping and handling of Metal Expansion Joints will reduce the life of the Bellows. Though the failure will not happen immediately, the life span of Bellows will get reduced to great extent and failure will be sudden.


Improper Storage

There were several cases of shorter Bellows life where they were not stored / preserved properly.

The condensation and settlement of dissolved gases in the atmosphere (saline, SO2 etc.,) will produce adverse effect on Bellows material resulting in corrosion and erosion.

Storing of Expansion Joints in high traffic areas result in hitting of thin Bellows with hard objects / sharp edges damaging the Bellows.


Wrong Sleeve direction

During installation, placing the Expansion Joint with its sleeve against the flow direction will result damage of Bellows.

The back flow will lead to buckling of sleeve and cause Bellows failure.

Premature removal of shipping brackets

Do not remove until the completion of installation of anchors, supports and pipe guides.

The premature removal of shipping brackets lead to imposing of unwanted huge loads on Bellows resulting in deformation and failure.


Insufficient protection of Bellows during installation

Arc strikes and weld spatter on Bellows from adjoining weld will damage the Bellows.

During installation and till completion of installation cover the Bellows with chloride free fire retardant cloth.



Improper / inadequate design of anchors will result in distortion, bending and failure.

Improper installation of anchors, deviating from the Piping System Drawings will also result in failure of anchors.

It is preferred to specify the Limit rods which are designed to withstand the Bellows pressure thrust load. In the event if the main anchor fails, the Expansion Joint remains in its position without stretching out.



Any Expansion Joint will function only between two anchors. The anchors are meant for withstanding the Bellows Pressure Thrust Load and Spring forces where Unrestrained / Untied Expansion Joints are employed. In cases where Restrained / Tied Expansion Joints are employed the anchors should bear the Bellows spring forces.

The failure of anchors will result in stretching out of Bellows and results in failure.


Torsion

Torsional movement / rotation of Bellows is one of the importantcauses of Bellows failure.

Bellows should not be subjected to torsion as the same produce severe stress on Bellows resulting twisting and failure.

The piping system should be adequately designed to avoid the imposition of torsion on Bellows.

The Expansion Joints will also be designed with special hardware to restrain the Expansion Joint from absorbing the torsion.


Erosion

The flow medium containing the abrasive particles such as Catalyst, Ores, Slurry etc., should clearly be defined in the specification.

The abrasive nature of flow medium will erode the Flow Liner andBellows which results in failure.

A higher thickness sleeve in hardened material will be a solution in applications where the flow medium has abrasive particles.

In some cases, a special abrasion resistant lining of inside Expansion Joint will be considered to come out this problem.


Packing of flow medium

A flow medium containing dust particles combined with moisture will lead to packing in between the convolutions and the annularspace between the Bellows and Liner.

The packing will result in improper functioning of Expansion Joint and lead to failure.

Insulating the annular space effectively and / or Purging with air / nitrogen in the annular space periodically will prevent the packing / settlement of medium.


Corrosion

Corrosion is the main cause of Bellows failure in several applications having adverse environment and / or adverse flow medium.

External corrosion

In the form of pitting and general metal loss.


External corrosion

The saline nature of plant atmosphere and / or gases / pollutants in the atmosphere in combination with moisture lead to accumulation on Bellows material resulting corrosion.

Presence of chloride will result in stress corrosion cracking on austenitic stainless steel.


Internal corrosion

The flow medium of higher pH will lead to inter granular corrosion and cracking and lower pH will result in Trans-granular corrosion and cracking.

Hydrogen stress cracking is another cause in aged material. In hydrogen services, the hydrogen is getting diffused at areas where the hardness is greater than 360 BHN and results in cracking.


Internal Corrosion

Corrosion of thin walled Bellows due to condensation of SO2 Gas to H2SO4 and accumulating in the annular space between the Bellows and Liner,

Condensation will occur because of temperature drop due to

Sudden plant breakdownPower failureExposure of Bellows outside to cold conditions

expansion joint basics

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