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Modification on derated vessel. FFS Level 3.

Modification on derated vessel. FFS Level 3.

Modification on derated vessel. FFS Level 3.


We have a vessel on ammonical water service as per ASME SECTION VIII DIV 1.
It was imploded due to vacuum. And was restored due to mechanical jacks and pneumatic pressure.
It was derated after FFS level 3 assessment.the study included details of all the welded patches in analysis.

My question is that now we are planning to install platform structure on that platform. For that we need to install few welded patches on external surface.

Its a cladded vessel with CS oitside and SS inside.

In past we have observed cladding detachment in vessel owing to imploded incident.

What hazards are anticipated in welding or installation of structure on vessel.

External thickness and DYE PENETRANT TESTING of surface is satisfactory.

Does it unvalidate The ffs study fea analysis. Or should we check after welding from inside.

Or am i thinking more.

Best regards

RE: Modification on derated vessel. FFS Level 3.

This would invalidate the FFS work. The Level 3 assessment would need to be re-performed with the modifications.

RE: Modification on derated vessel. FFS Level 3.

Discard this pressure vessel. Fabrícate new pressure vessel with external design pressure.


RE: Modification on derated vessel. FFS Level 3.

r6155: Cost matters. Thanks for the reply.

However, how far a modification can be considered a modification. We are welding the vessels with 10 each external pads for installing the platform. Comparing the size of vessel it is minimum.

RE: Modification on derated vessel. FFS Level 3.

i believe most engineers would agree with r6155 ...... The vessel is not repairable and must be replaced.

What happened to the vacuum relief device that was supposed to be on the vessel ?

Since your operations group is "out of control" do you plan on installing a new vacuum relief device on the reworked tank ?

Do you have pictures to share of the damage ? Can you share them ?

Regarding Codes, rules and FFS guidelines, .... I believe that you are in uncharted territory

Sr. Process Engineer

RE: Modification on derated vessel. FFS Level 3.

If your plant can't see the benefit of replacing an imploded vessel versus hammering it out...

Personally I would never have faith in that vessel.

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