Remaining Life of Vessel

The remaining life should be based on the actual thickness found minus the minimum required wall thickness for the design temperature and pressure (MAWP); in an oversimplified approach, if you require a minimum wall of 0.5", but you have an extra CA of 0.25" and you find you lose 0.125" a year - you then, technically have 2 years service left. Corrosion allowance is just that - an allowance that is sacrificed and is not required for strength at the design temperature and pressure.

You must check with your local jurisdiction/governing body/agents - because, one of two codes may be enforced:

1. National Board Inspection Code (NBIC) NB-23
2. API 510 for pressure vessels

You should not apply API 653 to pressure vessels - it is for 'tanks' only

One should use extreme care if there is any question concerning the usable life of a pressure vessel. Even if the minimum thickness is met, there is always the possibility of hydrogen embrittlement. Pressure vessels blowing apart under high pressure well below rated values can cause incredible damage including death. If unsure of the integrity of the vessel, Use of a Rockwell tester is advised. If you do not own one, have the vessel tested by a trusted lab.

Tnx for replying... I'll follow ur advise and recomendation...

You may add Fatigue and Creep for your failure mode. Need to conduct metallurgical replication check for detecting dislocations.

We have to differentiate between Pressure Vessels and Storage Tanks. The pressure vessels are subjected to a pressure of not less than 15 psi and designed and constructed under the rules of ASME, where the storage tanks are atmospheric or have a pressure of less than 15 psi are designed and constructed under the rules of API.

So the standard API 653 "Tank Inspection, Repair, Alteration, and Reconstruction" covers carbon and low alloy steel tanks (not pressure vessels) built to API Standard 650 and its predecessor API 12C.

I would suggest first you have a reputable ASME/NBIC engineer/inspector do a full fitness for service evaluation on the vessel. They usually perform a internal visual inspection, gather UTT as well as other types data needed to calculate the remaining life of your vessel. They should also produce a report detailing how they came up with the conclusions and also have a PE review and stamp the report. Using an outside 3rd party inspector engineer do the inspection will cost more but I think it is well worth it. If you do an API 650 inspection on the tank and calculate the remaining life according to this standard then the tank will only be good to be used as an atmospheric tank. If you are thinking about converting the tank to an atmospheric tank you will have to install the appropriate vent to ensure the tank will not ever be pressurized. As a general rule I follow the original code/standard of construction of a tank or vessel for any inspections or repair.

All the previous comments and suggestions are broadcast in the blind, not taking into consideration ANY of the important specifics. They should be viewed as general philosophy comments and NOT recommendations for the specific vessel and condition.

For ANY 'Code Stamped' vessel, a complete documented life history is an essential part of the evaluation of the vessel. One cannot assume code proscribed maintenance and repair procedures were follow during the vessel prior life unless those were properly documented.

Thank you very for all your replies, i have learned plenty of things from your replies

One might start with the vessel's periodic inspection reports, which are necessary for burst/collapse indemnity insurance purposes and held in the facility's General Register. The deterioration of the vessel with time is there to examine and consider.

A telephone discussion with the insurance company's Engineer/Surveyor will also be worthwhile; that individual's name and contact information will be on the periodic inspection reports.