Limit Load Analysis (LLA) is a powerful tool for design at temperatures below the creep range, and there is desire to extend the method to the elevated temperature (creep) regime. However, there is no direct relationship between LLA and elevated temperature allowable stresses and failure modes, such that the basic LLA methods or results must be manipulated in some way to be generally meaningful for elevated temperature design. The most direct way to judge simplified methods is against a rigorous solution; this requires an inelastic material model consistent with allowable stresses. Such a creep model was described in Part 1 of this work (the Omega model), and subsequently applied in a rational way to the problem of primary load carrying capacity and design using a simple sample problem. In this paper, extension is made to the case of a typical steam header, and existing simplified (LLA) methods are compared against further detailed transient inelastic finite element analysis. Recommendations are then made for the application of LLA to evolving ASME high temperature design rules.

Paper published with permission.

This content is only available via PDF.