B7 Studs Minimum Temperature Limits 3

[mgbc]

ASME B31.3 lists the minimum allowable temperature for B7 studs as -40C.

We have recently found B7 studs in a stainless steel piping circuit with a design rating of -101C. We are trying to assess the risk of operating our plant with the B7 studs in place.

My question: Does anyone have charpy information or experience of what the Ductile Brittle transformation temperature is for B7 material ?

 

[metengr]

mgbc;
At -100 deg C, I think you will be below 10 ft-lbs Charpy V-notch (CVN) impact value, and in the lower shelf ("brittle&quot region of the Charpy impact curve for this material. The reason for the -40 deg C minimum design metal temperature is to assure safe operation of this material from an adequacy of toughness standpoint. I would be very concerned about using this material in the event you have an overpressure condition or dynamic event in your process that could cause sudden failure of the B7 studs.

 

[bvi]

You should change them out to an appropriate material, such as A320, L7A. This is borderline for -101C, but would have even greater strength than your B7 bolts, whereas change out to B8 bolts would be going to a decreased bolt strength.

 

[LSThill]

mgbc (Petroleum) and Team Members

I agree with CB4 and the Piping Classification Specification for Cryogenic Process &
Low Temperature Process


Cryogenic Process: -325F to 400F ASTM A320, B8 CL 2 stud, w/ 2 heavy hex nuts ASTM A194, GR8

Low Temperature Process: -150F to 400FASTM A320, B8 CL 2 stud, w/ 2 heavy hex nuts ASTM A194, GR 8

-50F to 650F Stud Bolts ASTM A320, L7 stud w/ 2 heavy hex nuts ASTM A194, GR 4

Note: Process Piping "The Completed Guide to ASME B31.3 by Charles Becht IV.


Leonard Thill