API 650 tank re-rate by applying spot xray?

[tr6]

For a tank that has been in service, designed, and constructed to API 650 with no x-ray performed: Does the Code (any Code) allow the owner to perform a spot x-ray on the shell to effectively reduce the required minimum thickness? I have looked in API 579 but did not find anything that addresses that?

 

[bimr]

The American Petroleum Institute, the entity that maintains the API 650 Standard, does not certify tanks as meeting API 650 nor does it certify tank builders.

It is up to the tank owner to ensure compliance if he wants his tank to be constructed to API 650.

A one time inspection by a certified inspector for tank compliance may be used to set the baseline for tank management, but it is not required.

 

[JStephen]

tr6, it makes a certain amount of sense, but the codes just aren't set up to handle that situation.
In a more general case, if a tank is not built to compliance to API-650 in the first place, there is no provision or procedure to go back later and examine or test it and certify it.
In your case, the only actual limitation would be that you are supposed to take shots more or less equally for all welders, with qualifying shots for each welder, and if you don't have records of who welded what, you can't do that.
Another limitation is that the builder is responsible for complying with the code, and if you uprated it later, you'd presumably have a split responsibility.
A similar situation would occur if you wanted to take an Appendix A tank and "convert" it to a standard-design tank.
A related issue is that if you calculate thickness based on a joint efficiency less than one, then logically, the required thickness away from joints would be correspondingly smaller, and repads could be designed differently away from joints, etc. I don't remember to what extent this approach is allowed in 650 or 653, though, but if allowed, it might accomplish some of what you're wanting to accomplish with the additional radiography.

 

[amos4]

Does the Code (any Code) allow the owner to perform a spot x-ray on the shell to effectively reduce the required minimum thickness?
Why do you need X-ray for in-service tank? If thickness of shell plate is your concern then you should employ spot UT not RT. RT is only useful during construction stage to control the weld qualities.

 

[Duwe6]

It is not 'allowed' in 653, but it is not disallowed. If it were my tank, and I had no evidence that any RT's were made during the construction, I would perform my own testing, either RT or UT, of at least the extent* required by API-650. Now you can decide if a 100% Joint Efficiency is warranted. This will make a major difference in the 'useful life' of your tank if this tank experiences any shell corrosion and thickness loss.

*based on watching a number of tanks being erected, use a quantity of 3 or more welders for your calc's of the number of spots required on the circumferential 'round' seams [they probably had 2 or 3 guys welding those seams]. And do almost all the round-seam testing on the lower half of your tank.