The allowable stress for API 650/653?

[SJEC]

I am working on a tank originally designed per API 650 appendix M. Our client want to find what is the MAWP and MAWV. The design temperature is 400F. I am trying to solve the problem by using API 653 and have following questions:

1. Can I use allowable stress listed in API 653 table 4-1 or I should use API 650 allowable stress to re-rate the tank. Is here anybody know the background about why these two standards have different values on allowable stress.

2. Regarding reduction factor listed on API 650 table M-1, if I use allowable stress listed on API 653, Can I use the same reduction factor on these allowable stress?

Thanks

 

[TankDude]

My advice would be to use API-653 allowables and apply the Appendix M reduction factors to these. As for why there are different values between 650 and 653, I don't know for a fact but my guess is that the reduction in allowable stress by 653 is meant to account for potential unknowns when evaluating an existing tank.

 

[JoeTank]

API653 covers Appx M tanks too. Get the latest addendum.

Joe Tank

 

[JoeTank]

API653 uses higher allowable stresses than API-650 (for the basis for the retirement of tanks) as that has been the standard practice for oil companies for decades. That long standing practice was incorporated into API-653 wghen it was written in early ninety.

Joe Tank