If you're talking about the [Fac] entry on the "Allowable Stress Dialog", valid entries here range from 0.0 to 1.0. Check the "Help Text" here for details.

You can't just change the piping code, you have to analyze according to your Project Specifications. Each Code has its own rules as to how allowable stresses, and actual stresses are computed. In B31.4 you have the issue of "restrained" and "un-restrained" pipe and there are different stress equations for each.

You're not comparing apples and apples.