Sub arc issues.

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My job just got an Esab cab 22 subarc machine. We did some practice pieces ti mimic our weld joint. The welds came out great no problems. Bit when we welded on the actual part the first pass cracked down the middle. Using 316L filler wire, 3/32 dia. have to preheat the part to 500 degrees. Any ideas on why the cracking?
Reply:What you are experiencing is probably solidification cracking. A common problem with austenitic stainless steels.Are you sure you are preheating @ 500F ? This is not good practice for 316L and should be avoided since it can cause sensitization during welding.You would have to provide a lot more information though for us to help you.Do you have a WPS you are following, could you share it?
Reply:It's been quite a while since I've been involved with any sub arc welding but I recall some thing about there being a weld cross section depth to width ratio that shouldn't be exceeded because of it causing excessive internal solidification stresses that can cause the weld to crack.   The solution might be in a different joint design geometry or putting in a some what smaller first pass.   I can think of a lot of other variables that might be involved that you haven't told us about so this is just pretty much an off the cuff SWAG on my part.   Might be some thing worth looking into though.   I'm guessing that some where in the ASME code there's some good guidelines on correct joint design for sub arc welding and controlling the other parameters to avoid cracking.
Reply:AWS Handbook Volume 2 (8th edition) recommends one solution to solidification cracking issues in sub arc welding as being to keep the depth of the weld bead less than or equal to the width of the face of the bead.
Reply:Some general guidelines are low heat input, low interpass temperature, (150  ºC maximum), width to depth ratio of the weld pool should be between approximately 1 and 1,5.Apart from that you should recheck your travel speed, a high travel speed produces teardrop shaped weld pool encouraging centerline segregation of impurities thus increasing the risk of hot cracking.We could go on for hours but unless the OP provides actual data all this is just speculation.