Expansion Bellows are also known as Expansion Joints. These are a mechanical device that consumes thermal transfer. These bellows are consisting of one or more metallic as well as for non-metallic bellows. The expansion bellows are used in the piping system when the space restrictions do not allow to provide sufficient flexibility by traditional methods to maintain the stress of the system in the decided limit. It also requires when conventional solutions produce unacceptable conditions like unnecessary pressure drop.
Design Considerations for Piping Systems with Expansion Bellow
There are few designs considering while choosing or implementing Expansion Bellow in the piping system.
While designing the piping system, choose expansion bellow, which fulfills all the recommendations of the Expansion Joint Manufacturer Association (EJMA).
The type of the Expansion Bellow shall be selected by considering the amount of the thermal evolution of the appropriate piping and the shape of the piping profile, which is related to the position of the Bellow.
While selecting expansion bellow, it is required to check piping system operation under cyclic loading condition.
It is required to check whether the expansion Bellow is perfect for the Piping system or not. It depends on how much pressure bellow can suffer during operation or during the hydro test.
This Expansion Bellow shall not be constrained Torsional Rotation.
The materials of the Bellow have to be compatible with the type of flowing medium. Stainless Steel series is compatible with Chloride Stress Corrosion. Nickel Alloys are compatible with acidic and the presence of Sulphur.
Bellow Design Pressure:
The Design Pressure of the Bellow is calculated by the exact highest working pressure of the pipeline, which is under operation. While specifying the Design pressure of the Bellow, no ad-hoc cushion is allowed.
Test Pressure of Expansion Bellow:
The Test Pressure can be 1.5 times than the design pressure in hydro test and can be 1.1 times in pneumatic with proper adjustment for temperature emendation factor. At room temperature, the test pressure must not create membrane stresses above yield strength.
Expansion Bellow Design Temperature:
If ambient temperatures change significantly during pipeline construction, the highest, least, and base temperature shall be stipulated accurately. Also required to make suitable pre-compression of the Bellow which can be analyzed and managed subsequently.
Displacements absorbed by Expansion bellow:
The displacements to be incorporated by the Bellow can be calculated depending on the required piping growth, including the terminal changes. The original metal temperature of the piping system cannot significantly achieve the design temperature, which is used for the estimation of the conventional thermic growth of the piping system. The connected situation of the piping supports such as guides and anchors in the range may not fundamentally be correct as compare to the design. The Bellows can be used to avoid the same while handling process solutions that can compress or estimate to prepare the convolutions.
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