This is my first dissimilar base metal procedure. It is A516-70 to SA240have been given the filler metal of E309LT-1 AWS spec. A5.22 whats the next step to make sure this works with the 2 base metals. Thanks for any help want to do this right no guessing.
The next step is to get the proper tests from the code for your application, then spend lots of time experimenting to get your process dialed in correctly, then test your procedure.
The ASTM A240 is a stainless plate specification(Group A or B), so you will have to qualify the procedure for Carbon/Stainless dissimilar materials to D1.6.
Good luck, let us know how all of this turns out for you. Do you have a lab that you will be using? Just out of curiosity, is this a groove weld or a fillet weld procedure?
Since you are welding high strength low alloy steel to an austinetic stainless steel (assuming you are welding a 300 series stainless), you can qualify the WPS in accordance with AWS D1.1 if that is what is required by the project specification.
AWS D1.1 is as applicable as AWS D1.6 since one is for carbon and low alloy steels and the other is for stainless steels.
Either type 309 or 310 filler metals should work without a problem. Both are used by industry on a regular basis, so either can be used to qualify the WPS for a dissimilar combination of CS or LAS to ASS.
It is a 300 series SS and they are asking for D1.1 but the information for the A240 will be in D1.6 such as the min preheat and interpass temps correct? Also what decides if a weld gets PWHT?
There is usually no need to preheat austenitic stainless steel unless it is just to evaporate surface moisture. Interpass temperature is usually controlled to minimize some undesirable microstructures and sensitization. Since you are welding to a carbon/low alloy steel, I doubt sensitization is a concern.
Unfortunately the answer is that you do have to qualify the WPS. You are welding dissimilar base metals, so the WPS is not prequalified. Nice try though!