T23: purging required? 1

[WeldUK]

I am preparing some welding procedures for T23 tubes (7 to 15mm thick). This grade is a first time for us, although we have welded low-alloy grades before (91 and 92).

Is back-purging required for root runs in T23? I have found publications that recommend purging root runs for any low-alloy grade with Cr>2%, other for Cr>3%. The material we are weldign has approx 2.3% Cr.

 

[metengr]

Backing gas (GTAW) or back-purging is not required for this low alloy, CSEF steel.

 

[metengr]

I am going to retract my statement (first reaction) for purging on Grade T23 and T24 base materials. I should have probably checked my copy of a recent EPRI publication regarding Creep Strength Enhanced Ferritic Steel Welding Guideline, 2011 Report. Senior moment! I know that previous welding that I have seen on steam-touched T23 tube to T23 tube butt welds were not purged and the welding went extremely well. This work was done before the EPRI publication.

Back to the EPRI document, there is specific reference to recommending the use of a purge for the lower chromium CSEF steel grades to reduce oxidation and to promote increased fusion. The purge can be Argon-grade gas and it is recommended to hold the purge until the root and hot passes have been completed.
I just wanted to be sure I gave you current and reliable advice.

 

[WeldUK]

Thanks Metengr, one of the publications I quoted was actually the EPRI Guideline (my CSEF bible). I have the 2007 version though (the one that was downloadable for free!).

The welds are being made for R&D purposes, so I will purge as I would not like root defects to influence the test results.