When using welded pipes, depending on the weld type and testing. A certain safety factor is used.

I still have to figure out quality factor for myself

tolerances depend on fabrication process. generally this is 12,5% for asme with SA999

In service part of the pipe can corrode away. to take this into account part of the pipe is reserved for corrosion and not calculated with

Y coefficent is a Asme specific factor used depending on material and design temperature. For x materials under x temperatures 0.4 can be used.