We are welding to B31.3 CAT D. The piping is Zecor - a type of SS designed to resist sulpuric acid. This filler metal SFA is unassigned. Our procedure allows us to weld Zecor parent material with Zecor-Z filler rod. However, the F-No. is F6. Can we weld Zecor to 316 SS? Not without another PQR IMOP. This is not a weld to the pressure envelope, I might add. A repad on the pipe is Zecor and the Shoe is 316. Any comments? Suggestions?