B31.3 allows you to use a material below its MDMT specified in Table A-1 when the conditions for reduction are met as defined by Paragraph 323.2.2 (b), (c), (g), and (h). The software requires a full analysis only if the MDMT report from the error check gives a status of Impact.
You will use the existing (or default) set of load cases and manually create a new load case with a Stress Type of MDMT in the Load Case Editor, such as shown in the following graphic.
The MDMT load case of W+T2+P2 uses T2 to perform impact testing because it is the lowest specified temperature for this example.
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MDMT load cases must be basic load cases, not combination load cases.
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You can perform analysis without Pressures specified in Piping Input. For SUS/OCC Case Sh, specify an allowable stress (SH1, SH2, ... SH9) to use, or use the default Sh_min.
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The software uses Corrosion in the calculations when it is defined in Piping Input.
After completing the error check, run Static Analysis .
Example Report
In the Static Output Processor, select the MDMT load case and the MDMT Report. The report only contains data for B31.3 and MDMT load cases.
1 - Data generated by the error checker
The software produces the same Error Check data described in Analyze MDMT with Data Generated by the Error Checker, except that NA values for MDMT now display as blank
The same data is also available in the Miscellaneous Data report.
2 - Data generated by a full analysis
See MDMT Full Analysis Results for information on Stress Ratio, Reduction, and Final MDMT.
The software only generates this data for elements with a Status of Impact from the Error Check .
3 - Warnings
Negative warning numbers apply to data from Error Check (Data in block 1) when Status is Unknown.
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Pipe thickness is larger than 3.0 inches and is out of range. This warning only applies to material with a Minimum Temperature Curve of A, B, C, or D.
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The material has no MDMT defined in the material database.
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The thermal expansion coefficient is defined in the temperature field. The material has no valid temperatures.
Positive warning numbers apply to data from the full CAESAR II analysis (Data in block 2) when Status is Impact.
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When the reduction is subtracted from the base MDMT, the final MDMT is below the cutoff values -55°F (for stress ratio > 0.3) or -155°F (for stress ratio £ 0.3).
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The software can't perform a reduction because the base MDMT is below or equals the cutoff values -55°F (for stress ratio > 0.3) or -155°F (for stress ratio £ 0.3).
5
The stress ratio ³ 1.0 and the reduction is zero.
OR
The allowable stress is zero and a stress ratio cannot be calculated.
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Unknown and Impact elements display in red.
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The load case title row displays in red when the code stress in the Stresses Report is larger than the allowable stress.
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The software excludes rigids, flanges, and expansion joints from the MDMT analysis. The components do not display in the report, such as elements 40 – 50 and 60 – 70 in the example report.
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The report displays no data for other stress types, such as SUS, OPE, OCC, and EXP.