When analyzing a piping system, there are a number of items that must be checked and verified. These items include:
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Operating loads on restraints & terminal points
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Hanger design results
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Equipment evaluations
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Expansion joint evaluation
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Maximum operating displacements
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Code stresses for code cases
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Vessel nozzle evaluation
Restraint loads and displacements are checked in the global coordinate system. This is necessary because restraint loads and displacements are nodal quantities. Element loads and stresses are most often evaluated in their local coordinate system. A good example illustrating the use of a local (element) coordinate system is the free body diagram, of forces and moments. The forces and moments in this free body diagram remain the same, regardless of the position of the element in the global coordinate system. Note however, that each element has its own local coordinate system. Furthermore, the local coordinate system of one element may be different from the local coordinate system of a different element.
While the global coordinate system is typically referred to using the capital letters X, Y, and Z, local coordinate systems use a variety of nomenclature. In almost all cases, local coordinate systems use lower case letters. Typical local coordinate system axes are: xyz, abc, and uvw. CAESAR II uses xyz to denote the local element coordinate system.
The local coordinate system for an element is related to the global coordinate system through a rule. There may be a number of such rules, depending on the type of element. In CAESAR II, the following rules are used to define the local coordinate systems of the piping elements in a model.