Heat treatment for P1 to P4 non-pressure part welding 1

[jtseng123]

Our field is going to weld a new trunnion to an existing trunnion to lift a vessel. Please see the sketch.
I think preheat is good enough without PWHT. Am I correct ?

 

[metengr]

No. Based on the attached sketch, PWHT would be applicable to the P-No 4 plate, based on thickness provided.

 

[jtseng123]

Is it not controled by the P-1 material welding which have the total welding size of 38 mm (throat thickness of two fillets + 28 plate thickness) per Table UCS-56, Note (2) ?

 

[metengr]

Total weld deposit thickness may not equate to nominal thickness, which is what the tables follow in Section VIII, Div 1 (if this code is even applicable, which it is not). Nominal thickness is explained in UW-40 (f). Second point, the PWHT exemption for P-No 1 base material with preheat is up to 38mm. The PWHT requirement for P-No 4 base material controls PWHT for this component for nominal thickness 16mm or less.

 

[metengr]

Also, make sure for this lifting trunnion you have NDT performed using wet fluorescent MT on the original welds and your additional welds. This is important for your safety and that of the vessel.

 

[jtseng123]

Consulting to our welding engineer, he states to use E80XX weld rod, preheat and post heat at 300 F, MT root and final passes, 100% UT and hardness test. NDE will be done 48 hours after welding, PWHT is not neccessary.

 

[metengr]

What good will a 300 deg F post heat do for you when, if anything, a post weld bake to remove hydrogen is necessary at 500 deg F???? The diffusivity of hydrogen increases significantly at or above 450 deg F. Also, why not use low hydrogen consumables, like E7018 H4 or E8018 H4?

I would forgo the 300 deg F post heat and perform PWHT because of the P-No 4 base material. Frankly, since this is a nonpressure part application you can do as you please. Just trying to provide good welding recommendations.

 

[jtseng123]

yes, low hydrogen weld rod will be used, and thank you for your opinion.

 

[stanweld]

The joint is readily accessible for PWHT, which I would recommend and the welding electrode be E7016 H4 or E7018 H4. Loading can be somewhat unpredictable during lifts and I would like to be sure that residual welding stress would not contribute to a failure during lifting.

If you do not PWHT, I would recommend buttering the 45mm thick P4 material with the above stated electrodes (2 layes minimum) prior to making the strength joint to prevent laminar tearing of the P4 plate material due to the high residual welding stress applied in the weakest Z-direction of the plate. Preheat at 350 F min. Dehydrogenation PWHT would be recommended, but I assume that you will not do so as this step is not musch less expensive than a stress relieving PWHT.

 

[dhengr]

Jtseng123:
Please explain.
This is really getting to be a scary world. We are preheating , and PWHT the crap out of a detail that appears, to me, to be destined to fail, and nobody says a word about the whole detail. We know nothing about the materials involved, essentially nothing about the existing conditions, welds and their sizes, dimensions, loads, etc. etc. Then, the OP’er is going to weld a new trunnion on the outside of the side/end plate of an existing trunnion. If the proportions of his sketch are anywhere near accurate, he is at least doubling the cantilever lever arm for the trunnion, so I trust he is halving the load to be lifted. Then he is welding the new trunnion onto a side/end pl. which is really only intended to keep the cable from slipping off the trunnion, so except by ASME standards, it may not be CJP welded to the round trunnion. In any case the side/end pl. should be checked for lamellar tearing after the new full pen. weld because of how restrained that joint is, through plate. Ah... Stanweld did mention that, after I started this post. Then move back to the wall of the vessel, double the moment on the trunnion, and check that existing weld. It was not likely designed for double the moment, whatever the margin of safety used. I’d wait to heat treat this until after they try to lift it. The pieces will fit in a much smaller heat treating furnace.

 

[jtseng123]

The load at the trunnion is 250 US tons. Stress is not an issue. All been well checked by FEA and hand calc including weld strength and still have 30% margin. The vessel is brand new, 22' diameter, 110' long, 1 1/4Cr-1/2Mo and PWHT'ed. After shipped to field, found the trunnion is too short to lift and need extention.(fabrication mistake). The existing weld at end plate was checked by MT at shop. Field will do UT at the existing weld before welding the new trunnion. That is the story.

 

[dhengr]

Jtseng123:
I’m glad you had that all handled, my hat’s off to you, and my apologies for doubting. I’ll sleep better tonight, knowing that. It’s still a bit surprising that you can double the moment on that existing trunnion, stay within the code and still have a 30% margin of safety. That must have been a pretty conservative first trunnion design. Still in all, watch that existing end pl. for lamellar tearing when and after you do your new welding to it, that is potentially a very restrained joint, through thickness, and prone to this problem.
Good Luck

 

[jtseng123]

Our final decision is UT the P-4 end plate for lamination prior to welding, build a 3/8" thick butter layer using E7018, and preheat, postheat and PWHT the butter layer. Then bring the new trunnion in and weld to the butter layer by E7018. MT, UT, hardness test will be done. It is not an easy job at field than shop. Our welding engineer will spend a lot a time to come up with the WPS/PQR. For sure there is another WPS without PWHT (temper ...) , but it is too dedicate not suitable for field welding.

 

[Guest102023]

CYA is the overarching advice in this situation.