Pipe Stress Analysis

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Carpenter and Paterson can provide a full and comprehensive Pipe Stress Analysis service.

We can conduct piping stress analysis to ANSI B31.1, B31.3, B31.5, and other various European standards. Typical of the services we provide are:

• 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

Pipe Stress Analysis

Why?

The reasons a pipe stress analysis is carried out on a piping system are as follows:

• To comply with legislation
• To ensure the piping is well supported and does not sag or deflect under its own weight
• To ensure that the deflections are well controlled when thermal and other loads are applied
• To ensure that the loads and moments imposed on machinery and vessels by the thermal growth of the attached piping are not excessive
• To ensure that the stresses in the pipework in both the cold and hot conditions are below the allowables

How?

Using analysis software such as CAESAR II, the model is constructed from piping general arrangement, piping isometric drawings and piping and valve specifications. Once the system is accurately modelled, 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 above requirements.

The modifications may include one or more of the following tools

Restraints

A device which prevents, resists or limits the free thermal movement of the pipe restraints can be either directional, rotational or a combination of both.

Anchors

A restraint which provides substantial Rigid strength, ideally allowing neither movements nor bending moments.

Expansion Loops

A purpose designed device 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 are usually incorporated for vertical thermal movements up to approximately 50 mm, 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 50 mm

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.