Dahn55 I suggest that you look at the welding joint design carefully for the L.P and L.F problem between the W,N Flanve and the pipe material. If W.N flange is thicker and the pipe is less thick then joint design is important . Usually in restricted space problem "J" bevel is chosen - to meet B 31.3. Many welders have failed in RT examination. Joint design might contribute to this. I would suggest that you do a Weld Procedure qualification for this thickness and material snd for a particular joint design . Do all tests needed to meet WPR including root bend, face bend, RT, impact tests if needed to meet WPR. Then do a individual PQR (Welder performance qualification record) to meet ASME / B 31.3 code needs. TIG welding will vastly improved with internal purging continued with inert gas ( argon). Blue tint problem is due to excessive oxidation and also higher welding current at the HAZ for 316 L materials. Argon flow rate should be close to 10-15cfm. Did you try Reverse polarity with D.C for welding. Your problems would be solved if you take these care and attention C.V.Srinivasan Nishi Engineers pvt Ltd Chennai India March 24 E-mail:nishi@vsnl.com >It's bit difficult to guess the reasons. However, exploring >every possible reasons may help > >1. Whether Argon urging was done ? >2. What is the thickness difference between pipe & neck of >WNRF flanges. > >In case of insufficient purging, problem in root passes may >occur. Also, though unlikely in this case, a huge difference >in thickness results in differential cooling rates & weld >drops may solidifiy before proper fusion. This is more >common in CS/AS where thermal conductivity is high. > >'Hope this helps. > >Regards > >PLC