Stress value in Wall Thickness equation in B31.3

An EPC took the stress value of SMYS in wall thickness calculation of plant piping according to ASME B31.3 because for 48in pipe dia or more, the thickness calculated by using allowable stress are far larger than the standard available thicknesses in the market. Is this right? because according to my understanding B31.3 use allowable stress values from table A-1 not SMYS values. On the other hand how should the vendor perform calculations to get the standard thickness values when using allowable stress values from table A-1.