Carbide Participation from PWHT
Carbide Participation from PWHT
(OP)
We are considering the fabrication of a pressure vessel being lined through the explosion bonding process.
This vessel needs to be PWHT.
Our concern is carbide precipitation into the liner from the PWHT.
Specs:
Vessel shell and heads ,,, SA516
Vessel thickness,,,,,,,,,, 45-57 mm
Liner,,,,,,,,,,,,,, Alloy 59 (N06059)
Liner thickness,,,,,,,,,,,,,3 mm
Liner to nozzles,,,,,,,,,, Alloy 59 TIG welding overlay.
PWHT procedure temp,,,,,,, 570 C
Process,,,,,,,,,,,,,,,,,,,Versatic Acid
Operating conditions: 95 bar, 200 C.
Is Carbide Precipitation into the liner and it's surface a concern?
Thanks in advance.
This vessel needs to be PWHT.
Our concern is carbide precipitation into the liner from the PWHT.
Specs:
Vessel shell and heads ,,, SA516
Vessel thickness,,,,,,,,,, 45-57 mm
Liner,,,,,,,,,,,,,, Alloy 59 (N06059)
Liner thickness,,,,,,,,,,,,,3 mm
Liner to nozzles,,,,,,,,,, Alloy 59 TIG welding overlay.
PWHT procedure temp,,,,,,, 570 C
Process,,,,,,,,,,,,,,,,,,,Versatic Acid
Operating conditions: 95 bar, 200 C.
Is Carbide Precipitation into the liner and it's surface a concern?
Thanks in advance.





RE: Carbide Participation from PWHT
RE: Carbide Participation from PWHT
RE: Carbide Participation from PWHT
RE: Carbide Participation from PWHT
I wouldn't be worried about diffusion of carbon from the base metal into the liner because it will only diffuse a very short way into the liner so at the surface won't be any carburization.
Also you plan to have weld overlays in your nozzles performed via TIG. This will certainly bring more carbon into your weld overlay than the PWHT would ever be able to do on it own (mix up of base metal and welding material).
Be sure the chemistry of the top layser of your weld overlay has the correct chemistry (Fe will strongly reduce corrosion resistance). Perform checks on a sample.
RE: Carbide Participation from PWHT
Given the time/temp of PWHT C diffusion isn't an issue, but any that is there will for carbides and reduce corrosion resistance.
Usually you would do PWHT after nozzle fabrications and before the overlay is applied.
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Plymouth Tube
RE: Carbide Participation from PWHT
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Carbide Participation from PWHT
Considering the expense you are going to it makes sense to retain one of the folks at the Nickel Development Institute who are very well versed in corrosion issues in chemical process industries. Follow best practices!
For the 'back' cladding between clad sections, I have a general comment applicable to all alloys: 3mm is nowhere near enough depth to permit the attainment of full overlay chemistry at the weld surface (assuming conventional weld processes). Aim for three layers to achieve maximum corrosion resistance.
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"