Using inconel 625 filler rods to avoiding PWHT 1

[banaeian]

Is that possible to use Ni base alloy filler rod for joining Carbon Steel (SA106 B) spools in PWHT condition and avoid PWHT of joints,In Sour services? Nace MR 0175 to be considerd.

 

[metengr]

This is something that I have heard before in the welding industry. Here is my view;

the use of austenitic filler metals to join base metals that require PWHT does absolutely nothing to the base metal heat affected zone. If your PWHT objective is to reduce residual stress AND to temper (lower the hardness) the base metal heat affected zone, using Ni or any other austenitic filler material will not achieve these results. PWHT requirements in the B&PV Code were placed their for deliberate reasons.

Austenitic filler metals can be used for dissimilar metal weld joints, corrosion resistance overlays and to help to reduce residual stresses in a weld joint. But beyond these limited benefits, no benefit can be derived regarding the base metal heat affected zone.

 

[EdStainless]

Listen to Metengr. He has seen enough of these jobs screwed up over the years. Do it the right way and PWHT.

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[andyenergy]

Agree entirely.

There is much misconception about using Inconel as a filler wire in ferritic steels to avoid PWHT. It's seen as some sort of wonder filler that can sort all kinds of problems and, avoid time consuming and expensive PWHT.

It is useful in providing a sink for potential hydrogen when carrying out non-PWHT repairs but also generally needs to be used in conjuction with a temper bead approach to produce HAZ refinement. Not applying PWHT will not deal with (reduce) residual stresses in the HAZ, which may be less using Inconel but still present.

 

[weldtek]

Metengr, what are your thoughts as to buttering edges with the Ni based filler, prior to PWHT, followed by welding the joint with Ni based filler w/o PWHT?

 

[metengr]

weldtek;
This is absolutely fine, and I endorse it. As long as the base metal has received a PWHT after buttering, the remainder of the weld joint can be completed using austenitic filler w/o a final PWHT. By the way, have you gotten approval to begin attending NB or ASME Code meetings?

 

[weldtek]

metengr,
Not as yet, though I'm still very interested in doing so. By the way, I probably need to initiate a seperate post for this, but, I'm wondering if you have looked at the Summer NB Bulletin. I have some q's pertaining to the article on PV efficiency.

 

[stanweld]

Two of our petrochemical plant Customers have mandated use of NiCrFe filler metals for repair of 5Cr pipe without PWHT for the past 5 years. The hydrogen sink described by andyenergy effectively precludes hydrogen cracking in the HAZ. Half bead and temper bead techniques were employed in welding procedure qualification and in production to somewhat lessen residual stress. My company has taken the position that the Owner is fully liable for repairs so made as we are not in agreement due to the same concerns expressed by metengr.

There have been no failures in the deposited weld metal or 5 Cr HAZ but cracking has often occured in the 5Cr base material within 1" to 2" of the completed repair after a few of years. And we repair, yet again, as directed by the Owner.

 

[metengr]

weldtek
Yes, I also receive a copy of the NB Bulletin, and have looked at the same article.

 

[banaeian]

Thanks all for the valuable replies to question.
I have to add, base on NACE MR 0175, under certain conditions carbon steel materials and even welding as long as hardness is less than 22 HRC need no any PWHT. Regarding the subject spools are just to be used in sour services and all condition are meet. If hardness for base metal, HAZ and weld metal kept the lees than 22 HRC, is that still need PWHT, in case of using Inconel 625?,What about E7018 or E6010?

 

[metengr]

banaeian;
The need for PWHT is based on base metal thickness and chemical composition in most recognized Codes and Standards. Specific service requirements that require a maximum hardness of 22 HRc for the weld region go above and beyond minimum requirements established in Codes and Standards for PWHT. In other words, PWHT may be selected to achieve the necessary hardness reduction.

Yes, what you state is correct IF the measured base metal and weld metal hardness is below 22 HRC AND you do not violate the maximum wall thickness for the PWHT exemption.

If hardness for base metal, HAZ and weld metal kept the lees than 22 HRC, is that still need PWHT, in case of using Inconel 625?

Again, PWHT is specified by wall thickness for carbon steel. If you can tell us your wall thickness, and specific Code application, we might be able to help you. I doubt that would you be able to keep the base metal HAZ below your stated 22 HRc using Inconel 625 or any other filler metal, including E7018 and E6010.

 

[banaeian]

Thanks metengr;
The material is carbon steel A106 B, A105, generally P No. 1 with thickness less than 19.05 mm, reference code and standard is ASME B31.3 and NACE MR 0175.
As I understood, there is no requirement for PWHT base on B31.3 and even MR 0175 for above conditions, as long as there is a PQR for Inconel 625 as filler metal with above base metals and hardness less than 22HRC in HAZ, Weld metal and base metal, it is possible to use inconel 625 without any subsequent PWHT base on MR 0175 for sour services.

 

[stanweld]

If your thicknesses don't require PWHT and you can easily meet the NACE requirements with E7018 electrodes. Why do you want to use ENiCrMo-3 (625)? It doesn't make sense from a metallurgical or economic standpoint. Also there are other repair methods listed in the NBIC that could be employed as alternatives to PWHT.

 

[banaeian]

Stanweld,
I will follow your advice.
But the main reason for using Inconel 625 is to minimise the risk of SSC and SCC in sour gas services.

 

[stanweld]

banaeian,
How? Welding with 625 does not lower the hardness of the carbon steel HAZ. The HAZ hardness is a function of the base material carbon equivalent and preheat/interpass temperature and weld heat input. The use of 625 provides weld metal resistant to SCC and mitigates hydrogen embrittlement (cold cracking; however increased welding residual stress should be expected because of the coefficient mismatch. Corrosion may be accelerated in the HAZ as well due to galvanic mismatch.

 

[banaeian]

Stanweld,
This idea raised from an article I read but cannot remember where, it described that; it is possible to ignore PWHT of P5 materials in case of using Inconel 625 for welding. You know that the P5 materials shall be PWHT base on code requirements. Do you have any idea about that?
By the way, is that extendable to P1 material in sour services as described above?