DNV-RP-F112 and ASME B31.8 Chapter VIII Allowable Stresses

I got a stress analysis job for a subsea manifold piping ssystem. The material of the piping system is 2205 duplex stainless steel. The client requires to design the piping system according to DNV-RP-F112 and ASME B31.8 Chapter VIII. Therefore, the temperature derating factor will be 0.73 instead of 1.0 at the operating temperature of 100 deg C and the combined stress design factor is 0.8 in stead of 0.9. My question is how Caesar II handles these different design factors. Should I check the stresses manually after I get the results using B31.8 Ch. VIII code?

Caesar II calculates all three code stresses for B31.8 Ch VIII (Hoop, Longitudinal, and Equivalent) and compares each to its allowable stress. Then the one that is the highest percentage of its allowable is the one that is reported in the code stress column. You don't have to check anything by hand.

Thank you, Loren. The problem is B31.8 Ch VIII use the following design factors:

Hoop Stress: 0.72 (pipeline)
Longitudinal Stress: 0.8
Equivalent Stress: 0.9
and Temperature Derating Factor: 1.0 @ 100 deg C

DNV-RP-F112 has more stringent requirements in account of hydrogen induced stress cracking(HISC)corrosion in subsea duplex stainless steel with cathodic protection. The temperature reducing factor has been lowered to 0.73 @ operating temperature of 100 deg C and the equivalent stress design factor 0.8 in DNV-RP-F112. I can put 0.72 X 0.73 = 0.53 in Fac for hoop stress in CAESAR II input file. But, how about longitudinal stress and equivalent stress? And, as CAESAR II only prints out the highest percentage of its respective allowable stress of the three stresses, how can I get all three stresses if I have to check them manually?

please comment.

The factors for "F2" and "F3" are fixed, since B31.8 VIII specifies these as constants. You can only input "F1".

At the present time, you can't obtain all three stresses in the output report (simply because there isn't enough room). We are working on an improvement here, but that won't help you in the short term.