NOTE: APPLYING ONLY ON ASME IX GTAW PIPING WELDING
Some contractors use the essential variable tables (QW-352 thru 357) to minimize their costs. For instance, they might test the welder for stainless steel material by using carbon steel material. Consider the actual project material is stainless steel and you do not want to waste stainless steel material for testing. You ask the welder to weld in carbon steel material but with stainless steel filler metal. Based on the essential variable table P number 1 (Carbon Steel) qualifies P 8 (Stainless Steel), and the F number is the same. So you qualify your welder for stainless steel material by using carbon steel material but stainless steel filler metal.
Because of the viscosity during melting is different between SS filler & CS filler which is affect to welder manual manipulation ability. As the Inspector, the SS filler should to be used in order to qualify the welder on SS products.
For detailing references, find some more information in my paper as below:
WELDER QUALIFYING BY OTHER MATERIAL