CREEP ANALYSIS/ CLAD VESSEL/ CREEP RANGE 2

[ala11553]

Dear all

I'm new to this forum and looking for some advice regarding the CREEP of materials.

I have a column with the following parameters

Design Pressure= 50 barg; Design temperature= 425C; operating temperature= 380C; MOC= SA516 Gr.70+316L Clad; Design Code: ASME Sec.VIII, Div.1; Cyclic Service: N/A

Now, the datasheet says that, if the column is working in the Creep range, it shall be designed using Sec. VIII Div.2 and a creep analysis shall be performed. However, neither the datasheet nor specification specifies the temperature limit for creep range.

I have already checked the temperature Limit for creep range for carbon steel as per API579 and found out to be 371C. However, the Sec.II part D, the time dependent (creep) allowable stress value for SA516 Gr.70 starts only at 400C.

My queries are
1) Do I need to consider this vessel under Creep range or not, as temperature limits as per API and ASME are different?
2) Can I perform the Creep analysis using ASME Sec.VIII, Div.2?
3) Does the clad material (316L) have any effect on creep?
4) There is only a weight saving of 5MT while design using Div.2. In this case, can we stick to Div.1?

It would be really appreciable if anyone of you can provide some advice…

Thanks in advance

 

[TGS4]

There are (currently) no rules in VIII-2 on how to handle creep. The only place with rules is API 579-1/ASME FFS-1 in Part 10.

You did correctly by referencing API 579-1/ASME FFS-1 for the start of the creep regime. Even though the allowable stresses are not governed by creep at 371°C (that starts at 400°C), creep is still there - although it could be argued that it is negligible.

This may boil down to not a technical matter, but a contractual matter. If your contract says that you evaluate the creep behaviour, then you may be stuck. Do I think that it is going to change your design - unlikely.