Question|| Creep Limit & Creep Consideration ASME BPVC VIII-1 1

[abuanaselmasry]

I'm designing now a heating coil of SA-333 6 material that works at 375°C. By checking ASME BPVC II-D(M); Table A1 Note T-1, Allowable stresses for temperatures of 370°C and above are values obtained from time–dependent properties. The coil will work under this conditions for 24 hours every start up. This means if we have 2 shutdowns per year, then for 30 years of service this coil will work under creep conditions for 1,440 hours.
The question is; Is there any consideration that I need to take care about it during designing this coil? or, ASME II-D has already taken the required consideration during establishing the allowable stress? (as per my understanding till 10,000 hours, no further creep consideration is required).

In addition, based on your experience, what are other consideration that I need to care about in material procurement, fabrication notes and other aspects for the time-dependent equipment.

Thanks in advance.

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer

 

[metengr]

The allowable stresses in the time dependent regime have considerable margin, and are governed by creep or stress rupture. Secondary stresses should be considered, like thermal fatigue. However, this is outside the scope of design by rules of Section VIII, Div 1.

Material procurement is addressed by the proper material specification designation. Minimum fabrication rules are addressed in the code.

 

[abuanaselmasry]

Thanks a lot. I have recieved similar replies on LinkedIn. All replies states that for the membrane stresses, code allowabls are ok. Intension to the secondary stresses shall be given.

Regards,
M.Salaheldin
Static Equipment Mechanical Design Engineer