Restriction of ASTM A193 B8 Cl 2 bolting in ASME B31.1 for more than 100 Deg F.

[govindarasu]

Dear Sirs,
There is a restriction in the ASME B31.1, Allowable stress Table A-10 for the use of ASTM A193 B8 Cl 2 bolting material above 100 deg F. The allowable stress values were given up to 100 Deg F only. We understand that the B8 Cl 2 material can not be used more than 100 Deg F.
How ever ASME Sec II D and ASME B31.3 allows the A193 B8 Cl 2 allowed up to 1050 Deg F. In actual 18 Cr 8 Ni material can be used up to 1050 Deg F.
I request any one to advice on the following clarification.

1. The design code we want use is B31.1. The temperature of the heater piping is 300 Deg C to 400 Deg C. Can we use the A193 B8 CL2 bolting.
2. What is the reason B31.1 restricts the A193 B8 CL2 material for above 100 Deg F.

Thank you in advance for the replies.

Regards
Govind

 

[metengr]

1. The design code we want use is B31.1. The temperature of the heater piping is 300 Deg C to 400 Deg C. Can we use the A193 B8 CL2 bolting.

No

2. What is the reason B31.1 restricts the A193 B8 CL2 material for above 100 Deg F.

See below

Because the A 193 Class 2, B8 bolts are susceptible to softening after strain hardening while in service above
100 deg F. Softening means the potential for joint relaxation and leakage. Also, B31.1 Power Piping Code is for external piping applications in elevated temperature service, and they are a committee who can make their own rules for application.

Please read the Notes associated with the stress line for this material in Table A-10

(5) These allowable stress values are established from a consideration of strength only and will be satisfactory for average service. For bolted joints, where freedom from leakage over a long period of time without retightening is required, lower stress values may be necessary as determined from the relative flexibility of the flange, bolt, and corresponding relaxation properties.

 

[govindarasu]

Dear metengr,
Thanks for your explanation. I can understand partially that when the strain hardened material soften if it is subjected to increase in temperature. But I could not realize that ASME Committee restricting even at the atmospheric Temp (100 Deg F). At the same time B31.3 allowed up to 1050 Deg F.
Any way thanks for your reply and If you can give more information such as graph, equations, web reference etc... will be helpful for me.

Thanks
Govind

 

[EdStainless]

The materials allowed up to 1050F are the annealed versions or are at least rated as such.
While the strain hardened grades might be fine to higher temps, the time/temp/strength relationship is not clear cut and 'better safe than sorry' is the mode of operation.

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P.E. Metallurgy, Plymouth Tube