Repairs after PWHT P5-A J-Groove 2

[rmillercwi]

A severed tube was found in a j-groove tube panel after several years in service. The severed tube was given to us for analyisis. After measuring the failed weld surface area, it was determined that improper weld technique/insuficient joint opening was employed. The suggested repair method is to increase the fillet weld size significantly. Naturaly the customer would like to avoid PWHT if possible. 2" od tube, 150mw, slip joint design, p5a to p5a. Suggested weld process GTAW. No impact requirements.

Asuming the repair process to fall under NBIC requirements,
I have read the repair section PART RD welding method 4 in the NBIC code. I understand the pre-requisite to actual work is a working WPS without PWHT created to the rules of the original code of construction. The process of repair is straightfoward with exception of the post heating. The postheating is used to remove any remaining Hydrogen. Why would there be any hydrogen if the welding process was performed with GTAW?

Does it make sense to even consider adding weld to each and every tube to header weld in a P5A configuration without PWHT?

Please advise

 

[metengr]

Not necessarily. Was the tube failure along the toe of the weld joining the stub tube to the header on the header side or was the failure along the toe of the weld -stub tube side?

The temper bead method for RD-1060 is recommended for this type of repair. The post weld bake can be omitted provided a low hydrogen filler metal was specified. Hydrogen can be generated by improper handling of filler wire and from contaminates on the surface of the weld joint. I believe in the 2004 Edition of the NBIC the post weld bake can be omitted if the precautions I mentioned above are followed.

 

[rmillercwi]

Thanks Met,

The tube failure was (as you percieved), located at the weld toe closest to the header. I.E.,macroetch confirmed adequate fusion of the weld toe to the tube and significant LF inside the groove. Knowing the CNC machine capabilities in this application ,the most relevant LF was found along the bottom of the hillside as built (3 row panel). The j-groove face should have been opened up in this area prior to welding.

The proposed fix is to LPT all the welds for obvious signs of failure (we are assuming very few if any) and beef up the rest of the welds to say a 3/8" fillet. Catastrophic failures to be addressed as a separate issue.

Low hydrogen filler metals (author assuming this means 7018 type stick welding) will not work in this application. The weld area is too tight for SMAW. We would surely end up with numerous arc strikes, poor weld starts and stops and inconsistent weld profile unless we only addressed the problem area. Its GTAW or nothing in my opinion. Or, I am uniformed regarding issues related to Hydrogen. (related to filler metals coated with flux)

In advance, I thank you for your response.

 

[metengr]

GTAW is fine, and I would suggest using Welding Method RD-1060 (2004 Edition of the NBIC). When you order the filler metal for gas shielded arc welding just make sure you have low hydrogen wire as designated by the suffix H4 in AWS 5.28 (see 13.1 Diffusible hydrogen test). This will allow you to omit the post weld bake after temper bead repairs.