pwht of cladded vessel

[payaam2000]

Dear All

we are subjected to a vessel with data below:
SA350 lf2 + 7mm inconel625 overlay
asme sec Viii div 1
Base metal thickness is 45mm
sour service.
nozzle: sa350lf2 + 7 mm inconel625 overlay (8")

now shell has been fabricated (a350 + inconel 625 overlay)
vendor is going to weld nozzles on the shell with deep groove figure

my question is that when nozzle welded to shell , should vessel to be subjected to PWHT?
if yes, doesn't it any harmful effect on inconel weldedoverlay.
again if yes, doesn't it create separation of inconel and carbon steel layers along with interface zone (because of different thermal expansion coefficient of inconel and a350)?

best regards

 

[metengr]

Yes, PWHT is required for the nozzle and shall base materials. There will be some effect (sensitization) to the 625 overlay in the form of loss of toughness and corrosion resistance upon exposure between 1000 to 1500 deg F. I would suggest you evaluate the effects of PWHT on corrosion resistance.

 

[payaam2000]

Dear Metengr

thanx for your note. I would like to ask:

1-Is there any problem if pwht of shell (including assembled nozzles) to be performed in furnace and not locally weld line?

2- would you please inform me regarding the any separation issue in interface of inconel and carbon steel (due to different thermal expansion)

3- i could not understand your statement "I would suggest you evaluate the effects of PWHT on corrosion resistance". Do you mean some tests such as hardness test on the inconel surface after PWHT?

best regards

 

[metengr]

1-Is there any problem if pwht of shell (including assembled nozzles) to be performed in furnace and not locally weld line?

No.

2- would you please inform me regarding the any separation issue in interface of inconel and carbon steel (due to different thermal expansion)

There would be minimal risk because the coefficient of expansion between the Ni-base weld metal and carbon steel is not that significant.


3-

i could not understand your statement "I would suggest you evaluate the effects of PWHT on corrosion resistance". Do you mean some tests such as hardness test on the inconel surface after PWHT?

Exposure of 625 to PWHT can result in secondary hardening and affect on corrosion resistance. My point was to perform a simulated PWHT on a coupon of the base material with the 625 cladding and evaluate corrosion resistance for your application.

 

[EdStainless]

The 625 overlay should have been selected on the basis of its corrosion resistance after weld dilution and sensitization.
If someone was expecting the overlay to perform like wrought 625 then they are going to be disappointed.

The 625 overlay will have increased carbon and Fe levels from the welding. During PWHT there will be some aging effects.
It will likely get harder, less ductile, and may form phases which lower the corrosion resistance.
This needs to be tested.

There will also be overlay repair at the nozzle connections. You need to know how this will be done.
The details like how far back they will remove the 625, and how they will re-overlay the inside of the joint matter.

There should be no separation unless the welding was of very poor quality (with many voids and lack of fusion).
Only very sudden quenching could lead to cracking at the interface.


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Plymouth Tube

 

[payaam2000]

Dear Metengr / Dear Edstainless

thanx for your explanation.

in the joint between nozzle and shell, Inconel 625 buttering will be performed.

Also would you please advise me regarding below questions:

1- suppose that Shell has no nozzle. In this case is it necessary to perform PWHT due to overlay activity. (Assume that elongation is less than 5%)

2- if vessel is cladded with 3mm inconel 625 with metallurgical bonded plate instead of overlaying (I mean hot rolling or explosion cladding),and due to welding of nozzle to shell pwht is mandatory. In this case does PWHT have any harmful effect on cladded vessel?

Best regards

 

[Ripz]

For that thickness of shell, applying the overlay makes PWHT mandatory.

 

[metengr]

payaam2000
First, please review the rules for PWHT in ASME Section VIII, Div 1. Second, corrosion testing should be performed on a coupon that simulates the PWHT in production to determine if PWHT has affected the corrosion resistance of the 625 weld or clad material.