Converting API 650 to API 620 tank

[drials2]

Guys,

Has anyone ever looked into/done this before? The 650 tanks are on the smaller side (50,000 bpd working capacity) so I am thinking it is at least possible and not out of the realm of possibility.

David Rials.

 

[JStephen]

That's really just not something addressed by the standards.

The problem is that API-620 has requirements about how a tank is built- not just the completed geometry, but the inspections that are to be done in the construction process, etc. If that isn't done, there's no way to do it after the fact.

It's a similar issue, to if a tank is not built to any standard, can you go back after the fact and make it meet API-650 or ASME or whatever? You can correct obvious deficiencies, you can evaluate the design, but can't go back and change the past and cause it to have been made a particular way.

 

[fegenbush]

I agree with JStephen. It is not address how to achieve the additional inspection requirements of API 620. Notably, the combination hydrostatic and pneumatic tests and the radiography are difficult to achieve in the same quality of new construction.

What is the intended outcome? Is the owner looking for additional working pressure?

 

[drials2]

We are a midstream company and have 2 new 650's that we think may have needed to be 620's. I would think the testing (except for the floor) could all be done after the fact.

 

[JStephen]

One thing you might look at is the pressure rating for the roof based on top angle area in Appendix F versus API-620. I suspect your design pressure will go down, not up, when you start looking at that change. API-650 App. F allows higher compressive stress in the compression ring area.

The radiography is an issue, and the more and better records you have of how that was done, the better. The general issue is you have requirements for "one shot in the first 10' welded" and have no idea what sequence it was all welded in, or who welded what, etc. Any requirements for inspection of the root pass, gauging material, etc., become a problem after it's all finished.

The allowable stresses and the impact testing exemptions are considerably different between the two codes, with API-620 being more conservative in both cases.

 

[LittleInch]

Normally the stress levels in a 650 tank are just about maximum for the steel if it's been designed right. I've never heard of anyone doing this, but that's not to say it can't. Have you asked a tank supplier to look into it yet??

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