Fatigue life cycle analysis using ASME Sec VIII Div - 2 for temperatures above 450 degC

[Khandalkar]

Hello,
I am working on pressure vessel equipment designed as per ASME Sec VIII Div- 2 (Design by Analysis). This vessel is subjected to thermal stresses. The material is Crome-moly steel Grade 91 & 92 material. Referring to Finite Element Analysis for Fatigue life cycles calculations as per ASME Sec VIII Div - 2.
Pressure that the vessel will be subjected up to 150 barG 600 degC temperature.
If I follow ASME Sec VIII Div-2, Annex 3-F shows temperature only upto 371 degC.

If I refer EN 12952-3, it allows temperature upto 600 degC but need to follow Linear-Elastic analysis.
High stresses are observed for linear elastic FEA analysis & getting very low numbers of fatigue life cycles as per EN-12952-3.
If I follow Elastic- plastic non-linear analysis as per EN-12952-3, need to run multiple analysis for shake down which increases computational efforts tremendously.

What is the procedure if ASME code to be followed for life cycles calculations for high temperatures > 450 degC ?


SAM

 

[davefitz]

This reply does not directly answer the question, but please note:
- martensitic P91/P92 does not "shake down" fabrication stresses the same way that lower alloy ferritic structures had
- 600C design temperature implies that a weld creep strength reduction factor must be applied to all welds that are not true circumferential butt welds that only need to cope with axial pressure stress plus secondary stresses.
-EN 12952-3 tables B-1,2,3 fatigue analysis may also include fracture mechanics implications of the weld geometry and weld QC inspection limitations.
- P91/P92 welds have a pronounced "metallurgical notch effect" that occurs parallel to the plane of the weld interface, a so called soft zone, that complicates the finite element modeling for elastic-plastic models.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick