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| Applies To | ||

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| Product(s): | AutoPIPE, | |

| Version(s): | 2004, XM, & V8i | |

| Environment: | N/A | |

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| Original Author: | Bentley Technical Support Group | |

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Dec 2014, AutoPIPE V8i 09.06.01.10

Can ASME B31.3 in AutoPIPE V8i 09.06.00.15 perform a fatigue analysis on a piping system due to both thermal and pressure?

Using AutoPIPE V8i 09.06.xx.xx and lower:

For thermal cycles, you can enter the "range reduction factor f" in the tools/Model options/Result. By default this factor is 1.0 and it does correspond to 7000 thermal cycles or 20 years of daily cycles. You can press F1 while in this field and will be able to see a table or equation for this factor as a function of number of cycles. This factor f appears in Equation (1a) and (1b) of ASME B31.3 and is also used in many other codes. If you have several operating temperatures, each with different number of cycles, then an equivalent number of cycles N can be calculated using Equation (1d) of ASME B31.3.

As for high cycle fatigue as is the case of vibrations caused by reciprocating equipment and is usually entered as harmonic H cases, the user is able to manually create a code case H1 and set allowable using Tools/Code combinations/user allowable stress. The allowable in this case is based on stress limit at the end of fatigue curve. For Carbon steel materials, the allowable is usually 12500 psi (0 to peak). For Austenitic stainless, the limit is 13600 psi at 1.0E+11 cycles. The user may want to divide this allowable stress by stress concentration factor for a butt weld.

However, AutoPIPE V8i 9.1 and higher can perform a full thermal fatigue analysis using ASME class I piping code (NB). For this code AutoPIPE performs extensive fatigue evaluations.

With regards to pressure fatigue analysis, ASME BPVC Section VIII Division 2 contains design fatigue curve data in Annex 3-F. Fatigue analysis is found in Annex 5-F. From ASME B31.1 see section 101.2.5, and from ASME B31.3 see section K304.8. Section K304.8.4 and K304.8.5 are special considerations for destructive testing and fatigue life of components beyond that recommended by ASME BPVC Section VIII Division 2. This has been logged as an enhancement (CAE-CR-3268) to be added to a future version of the program.

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