Piping standards typically recommend that the code stress should be less than the allowable stress. This is a safety criterion, but not a guarantee that the material will not fail. For temperatures below the ambient temperature, B31.3 includes a supplementary safety check that involves the property Minimum Design Metal Temperature (MDMT).
Most B31.3 materials in the software provide MDMT, as defined by Minimum Temperature Curve (A-D) and shown in the following Material Database Editor examples.
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Material Number 110, with Material Name A181 70, uses Minimum Temperature Curve A. The MDMT value depends on the pipe thickness as defined on B31.3 Figure 323.2.2A, or Table 323.2.2A.
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Material Number 240, with Material Name A369 FP2, uses Minimum Temperature Curve O. This is not actually a curve, but a fixed value of -20° F as defined in B31.3 Appendix A.
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When a material uses Minimum Temperature Curve Z or the material specifies no curve, then the material has no MDMT.
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