We are joining 2.25Cr1Mo tubes to 2.25Cr1Mo tubesheet by Internal Bore Welding (Autogenous pulsed arc GTAW from inside the tube) The tube size is 32 mm OD and 3.7 mm thick( Actual tube thickness measure 4.0 mm). We experience inconsistancy in the weld penetration while using the same welding parameters which have worked very well in the past 10 years.
On analysing the problem we observe that in the past, the tube and tubesheet had around 0.007 % sulphur and the current tube and tubesheet are having 0.002 % sulphur and the problem is related to low sulphur level.
I am looking for practical tips which could be tried to overcome the inconsistacy in the penetration pattern.