Hello, there:

The same models with the same Caesar II setting (by Caesar II default) are as attached, the only different is the Code. Caesar II calculated sustain stresses are 10 times different:

Based on B31.11, SUS case (w+p1) of Node 9420:
Calculated code stress: 3 KSI
Allowable stress 18.8 KSI
Ratio: 16%

Based on B31.3, SUS case (w+p1) of Node 9420:
Calculated code stress: 31.6 KSI
Allowable stress 20 KSI
Ratio: 158%

Would you please explain how Caesar calculated the SUS stress for different code? Should the system passes checking or not? Please help.

It is about corrosion. You inserted 6.35mm corrosion even your pipe is lined.

Never used B31.11 but sound like is not considered for B31.11. By the way, shouldn't be? 1102.3.2 (d) "The thickness of pipe used in calculating
longitudinal stresses shall not include allowances covered
in paras. 1102.4.1 and 1102.4.2."