Pipe Stress Analysis
Effective pipe stress analysis is critical in order to ensure the following:
- Compliance with legislation.
- Piping is well supported and does not sag or deflect under its own weight.
- Deflections in the pipework are well controlled when thermal and other loads are applied.
- Stresses in the pipe wall in both the cold and hot conditions are below the allowable threshold.
CPA can provide a full and comprehensive Pipe Stress Analysis service on an ad-hoc basis if required. Our high quality analysis can be conducted to various applicable international standards (e.g. ASME B31.1, B31.3). Such analyses include:
- Thermal Analysis – Analysis for free and restrained thermal growth conditions.
- Deadweight Analysis – Analysis at ambient temperature with a system of hangers at specific locations to support the weight of the system, for allowable stress and reactions at equipment connections.
- Seismic Analysis – Either equivalent static or dynamic analysis.
- Wind Load Analysis – Equivalent static stress analysis.
- Transient Analysis – For various transient loading conditions such as: turbine trip, pipe whip, safety relief valve trip etc.
This is done using analysis software such as CAESAR II whereby the model is constructed from piping general arrangement, piping isometric drawings and piping and valve specifications.
Once the system is accurately modeled, taking care to set the boundary conditions, comprehensive stress analysis calculations are done and modifications to the model are made to ensure compliance with the relevant requirements. Such modifications may include one of more of the following tools:
- Restraints – A device which prevents, resists or limits the free thermal movement of the pipes restraints can be either directional, rotational or a combination of both.
- Anchors – A restraint which provides substantial rigid strength, ideally allowing neither movement nor bending moments.
- Expansion Loops – A purpose designed pipe loop which absorbs thermal growth; usually used in combination with restraints and cold pulls.
- Cold Pull or Cold Spring – This is used to pre-load the piping system in the cold condition in the opposite direction of the expansion, so that the effects of expansion are reduced. Cold Pull is usually 50% of the expansion of the pipe run under consideration. Cold Pull has no effect on the code stress but can be used to reduce the nozzle loads on machinery or vessels.
- Spring Hangers – These are used to support a piping system that is subjected to vertical thermal movements. Variable Effort Spring Hangers to are usually incorporated for vertical thermal movements up to approximately 75mm, the variation between the preset and operating loads should be no more than 25% of the operating load. Constant Effort Spring Hangers are usually incorporated for vertical thermal movements in excess of 75mm.
- Solid Vertical Support – These are used in places where vertical thermal movement does not create undesirable effects or where vertical movement is intentionally prevented or directed. Solid supports in the form of rods or pipe shoes are often used for these configurations. It is important that free horizontal movement of the pipe is not impeded unless the horizontal restraint is desired.