Problem:

How to consider Fatigue load case in AutoPIPE (method #1)?

Solution:

AutoPIPE V8i 09.01.xx.xx and higher can perform an extensive fatigue evaluation using Nuclear Pipping codes only. A new enhancement to add user defined fatigue curves was introduced in AutoPIPE V8i 09.03.xx.xx, and furthermore an enhancement to apply modulus ratio to S(alt) when calculating allowable fatigue cycles was added in v09.05.xx.xx   Again, these fatigue features are only available for models using Nuclear piping codes (i.e. ASME NB, NC or Nd).

There is a vast amount of fatigue information in AutoPIPE's Help menu, please see the following AutoPIPE help section:

Help > Contents> Search Tab> enter "Fatigue" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information.

Including a complete example, "ASME NB - Fatigue Evaluation Example", details about assigning a "User" Fatigue curve, etc... 

An enhancement has been logged (TFS-E110599, CAE-CR-3268) to add fatigue analysis for non-nuclear ASME piping codes. Please see the following for suggestions on performing a Fatigue analysis when using one of these non-nuclear piping codes. 

Non-nuclear piping codes does not have any elaborate fatigue calculations. However simple fatigue calculations for thermal cycles and harmonic loads can be done.

For thermal cycles, you can enter the "range reduction factor f" on the Pipe Properties dialog, shown below:

Note: place cursor in this field and press F1 keyboard button to see detailed information on this settings.

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.

See Also

"Fatigue" - AutoPIPE load case

Bentley AutoPIPE

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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