If the 316 is not low carbon grade, it will have a sensitized HAZ after welding, but it would even if you welded it to another piece of 316. Welding it to a piece of 321 will have no effect on the 316 otherwise, nor vice versa.
I presume that you are doing this because 316L is the only fitting available.
Using 316L filler should work fine.
Is the environment corrosive at all? If so you could be setting yourself up for some galvanic corrosion issues down the road.
My WPS have been qualified for Pno-8 & Gno-1 with ER347. Both 316/316L & SS321 are comes under same P number & G Number. Can i use the same filler rod ER347 for this. one of my friend told me that even if the same filler rod is uder to weld these material. cracking possibility is more. is this true
You could use ER347 to make the weld. I would still recommend ER316L. If your PQR used ER347, you could still use ER316L in your WPS, but you may need to revise your WPS accordingly.
One wonders why you are welding 316L to 321 - 321 being more oomonly used at high temperatures.
The line is actually sour crude oil with design temperature of 3000 psi. We ordered 321 material accordingly. but later we found some shortage in material. But we didn't get SS321 material from any stockist due to very less qty and they don't have the same. Instead they have SS316 ready stock. that's why is checked the possibility of welding 321 with 316.
I am not a metallurgist so will not get carried away but what I do know is if you design something for a specific pressure, temperature or corrosion resistance you do not go and substitute other materials just because someone forgot to order enough material.
I have not seen 321 used for sour crude at ambient to moderate temperatures and high pressures in the past. You have defined a pressure of 3000 psi but not the temperature. I have seen lots of 316L used though in the past in this service.
...and hence no need for 321 in the first place. 316/L should have been fine for the pressure/temperature/corrosion, based on the limited information we've been given- every bit as good as 321, which is only needed if the pipe itself were to be used in the sensitization range of temperatures and then brought back down to lower temperatures and exposed to aqueous or polythionic corrosion.
