An expansion joint by itself provides accommodates any axial, longitudinal and angular movements in a pipelines, ducts and vessels. The addition of accessories to an expansion joint increases the complexity but also it’s capabilities. Some of the accessories for the expansion joints include,
Liners or baffles are the fixed or flexible sleeve of stainless steel placed inside the bellows to extend the life of metallic expansion joints. Liners protect the convolutions from erosion due to the chemical and electro-chemical attack of flowing media. Where the turbulent flow of media is occurs rather than laminar flow due to curved shaped convolution inner side of bellows, this may leads to cause increase in pressure nearer to expansion joint . High velocity flowing media also causes resonant vibration in bellows, where liners are recommended to use to provide smooth and laminar flow and to reduce vibrations.
The possibilities of erosion may occurs, where the pipe systems carries catalyst, abrasive, and other high temperature media requires high guage sleeves, and also for the reverse flow of media high guage sleeves are required.
Internal sleeves are not to be used where high viscosity fluids like heavy oil, tars, etc. are being transmitted, since these kind of fluids cause packing up, coking, which causes premature expansion joint failure. Usually the internal liner is welded in to the flanges of expansion joints.
A bellows is made up of a series of convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept axial, lateral, and angular deflections. Bellows is the only flexible element of expansion joints. The series of convolution has one or more thickness ply depends upon the design requirements. The primary function of bellows is to accept deflection repetitively and the deflection result in the stresses. These stresses must be low as possible to provide a long life cycle.
In order to withstand the high pressure, thickness of bellows should be greater enough but the thinnest bellows provides more flexibility and deflections. Conflict may occurs in designing of bellows on considering both pressure and flexibility.
A Bellows must withstand up to 3000 cycle with designed pressure and deflection, after completing 10,000 cycles , the bellows tends to failure. A bellow compressed or expanded for a period of time and returns back to its original position is considered as a one cycle. For example if a bellow is compressed for one year and return back to its original position is said to be one complete cycle.
A ring made of metal tube or metal strip to be placed in the end of bellows, which is used to weld flanges. Collars make the bellows inflexible at its end, this may avoid the cracking of root in bellows.
The ends of the expansion joints is equipped with the flanges for the purpose of bolting with the mating flanges of piping systems. Flanges are available in many shapes like squared flanges, rounded flanges, etc.
The primary function of the limit rod is to restrict the bellows axial, lateral, angular movement during an operation. If the main anchor tends to failure, the limit rod restrain the full pressure and dynamic forces of flowing media. Limit rods are designed to prevent the over-compression and over-extension.
Control rod is usually a bar or rod attached to the expansion joints. The primary function of the control rod is to provide the equal distribution movement between the two bellows of universal expansion joints. Control rods are not used for the purpose of restraining pressure thrust.
Tie rod is usually a rod or bar have threaded on its whole length and nut on it, attached to the expansion joint assembly. Where its primary function is to limit the range of axial movement with the help of adjustable nuts on tie rods. It also restrain full pressure thrust during continuous operation and permitting lateral deflection of expansion joints. If two tie rod is used in the expansion joints, it allows the joints to permitting angular deflection.
HOLLOW REINFORCING RING:
“T” shaped (in cross section) component fitted on the roots of convolution of bellows in expansion joints. The primary function is reinforcing against the internal pressure of bellows, where it restrict the lateral deflection. These rings are made up of carbon steel, stainless steel, or other suitable alloys and its fabricated from tubing or solid round bars.
The ends of the expansion joints equipped with the suitable beveled pipes for welding to mating equipment or pipes.
It is the special form of control rod attached to the expansion joint assembly and look like scissor –like equipment. The primary function of pantographic linkages is to equally distribute the deflection movement between the two bellows of universal expansion joint, but it not restrain pressure thrust like control rod.
Protective covers are thin carbon steel or stainless steel metallic sheet which covers the bellows external convolutions and primary function of these covers to prevent damage during maintenance process, contact with other pipes, hangers, and other equipment. It is applicable in systems like, where the fluids or steam can penetrate on bellows exterior in such cases thick walled covers are recommended to use for protection.
In a piping system where the sediment is accumulated between the exterior of internal liners and the inside of bellows. The threaded purge connectors are used continuously or periodically for injecting the fluid to blow out the collected sediments.