What is a Metallic EXPANSION JOINT ( Bellows )

What is a Metallic EXPANSION JOINT ( Bellows ) 

Metallic Expansion Joints are installed in pipe work and duct systems to prevent damage caused by thermal growth, vibration, pressure thrust and other mechanical forces. The main element of the Expansion Joints is the bellow.

 

The bellows are made up of a series of convolutions, with the shape of the convolution designed to withstand the internal pressure of the system, but flexible enough to accept axial, lateral and angular deflections.





Why should we use a Metallic Expansion JOINT 

 

Any pipe connecting two points is subjected to numerous types of action which result in stresses on the pipe.

Expansion bellows absorb these stress as cushions to accommodate the dimensional changes caused by thermal expansion or contraction of pipeline, duct or vessel which containing the system pressure.

 

 

What are the components of a Metallic Expansion Joint 

 

An Expansion bellow consists of Bellow element with usually 2 plys formed as convolution, Tie rods, Angle indicator, Pipe / Flanges, shipping Bar, Protective covers and internal liners, attachments such as Red pop type leak indicator, nipple connections for instrumentation line and pressure gauges . On the connecting Piping, there is color plates that supports the bellow cover that slides over the cover during movements.

 

 

Typical Failure Modes and Damage Locations in Metallic Expansion Joint :




How to inspect Metallic Expansion Bellow:

Conduct Periodic Visual Surveillance, in addition to the regular scheduled TA inspection to ensure there is no leak between 2-ply or from nipple joints.

 

Cover :

·         Cover plate resting position is acceptable condition

·         Cover plate ring support or L shaped intermittent supports without bent and no              cracks

·         Cover Plate inner side Wear-out limit 

·         Wear level of the cover support ring 

 

Collar:

·         Cracks on the Collar welds and support to the cover plate support

 

Convolution:

·         Fretting damages on Convolution Surface 

·         Abnormal bending / flat spots / excessive compression at convolution

·         Straight or L shaped Nipple Joints are not damaged or bent

·         Inside: Ensure during header internal inspection, there is no debris or foreign objects in the convolution gap such as Catalyst balls 

 

 Weld Joints with adjacent pipes

·         Angle indicator within the allowed movement tolerance limits

·         Tie Rods ( if applicable ) is in-tact and no deformation

·         Insulation cladding shall not overlap with the bellow cover

·         Weld integrity and deformation shall be evaluated along with Spring Hanger 

 


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