I am getting a little confuse during the stress analysis of a gas line (my first experience of stress analysis) with ASTM A-106 gr. B pipe. We know that allowable stress for A-106 Gr. B pipe is 20000 psi as per Table A-1 of B31.3. But in report it is showing that allowable stress is 35000 psi for hydro-static load case WW+HP (circled red in below image). Why is it so? Is there any clause in ASME B31.3 regarding this? Can anyone clarify this? Any reference will be appreciated. Thanks in advance.