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The welding after PWHT and hydro test

The welding after PWHT and hydro test

The welding after PWHT and hydro test

HI fRIENDS,I need your technical advice.
I have an ASME SECTION VIII DIV-2 VESSEL in which the internal ladder rungs are to be welded below the manhole to reach to the base of the vessel.
It is 60 mm thick vessel with internal ladder rungs .
THE VESEL PWHT AND HYDRO TEST COMPLETED .Manufacturer forgot to weld this ladder rungs inside the vessel below the Manhole before doing the PWHT and Hydro test.
Can I weld the ladder rungs to the shell internal using a fillet weld after completing this PWHT/Hydro test?
Does it requires PWHT after welding this ladder rungs to shell?
Do I need to rehydrotest the vessel along with these ladder rungs after PWHT ?
What the technical things to be follwed if I want to weld these ladder rungs to the already PWHT/Hydrotested vessel?
This vessel is in mild sour service with 7 PPM H2S service.
Advice is highly apprciated ASAP as we are holding the box up of this vessel in construction site
Saji Panakakttil

RE: The welding after PWHT and hydro test

Welding is not permitted after PWHT and hydrostatic testing are completed during vessel construction. If welding and PWHT are required for repair or to add a component during fabrication, hydrostatic testing must be repeated before stamping.

RE: The welding after PWHT and hydro test

I had one internal welding to a non-pressure part inside a vessel after PWHT several years ago. But it was for the Section VIII-1 vessel.

RE: The welding after PWHT and hydro test

Better get with your AI (and Owner, if other than yourself) and work it all out...



The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: The welding after PWHT and hydro test

Since the vessel is stamped, repair is done per the NBIC in which case the repair plan must be signed by a P.E. experienced in PV design. I believe in your case that metengr is correct - not having Div. 2 to review anymore.

RE: The welding after PWHT and hydro test

Hi Saji,
This issue is quite interesting with few overviews. Clearly welding is done on the wetted surface, after final PWHT.

In DIV-2 Code,
Clause allows weld repairs on P-No.1 Gr. Nos. 1-3 materials and to P-No. 3 Gr. Nos. 1-3 materials, after final PWHT but
prior to the final hydrostatic test without additional PWHT, UNDER CERTAIN CONDITIONS. These requirements do not apply when the welded repairs are minor restorations of the material surface such as those required after the removal of construction fixtures and provided that the surface is not exposed to the vessel contents.

If it applies to your Project: NACE Publication 8X194 Materials and Fabrication Practices for New Pressure Vessels Used in Wet H2S Refinery Service: Clearly states
Welding After PWHT: Almost all users have specified that no welding, hammering, or cutting be performed after PWHT.

[highlight #FCE94F]Hence PWHT can't be avoided UNDER ANY CIRCUMSTANCES[/high.

Subjecting the entire vessel to Repeated Hydrotest may not be the best engineering solution always,DIV-2,Clause 8.4 ALTERNATIVE PRESSURE TESTING, provides a few options , which may be worth considering.
You need to prepare a clear rationale and talk to the AI.
Your statement does not tell clearly , if the vessel is stamped. All those suggested options including Alternative pressure test are worth considering before final stamping.

If the vessel is stamped then you've to work out a rationale with the approval of the AI as guided by the NBIC,Part-3. As stated by SnTMan,depending on your location you may hire a Chartered/Professional Engineer to write/approve the whole proposal.

If would be interesting hear what was finally done on this case.


Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist

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