API 653 water tank inspection

[mariolucas75]

Dear Forum pls help me with the following,
There is water storage tank inspection in accordance to API 653.
I want to calculate shell minimum thickness in accordance to API 653.
So I use formula from 4.3.3.1 a paragraph which is tmin = 2.6(H-1)DG/SE
Value S (stress) is taken from API 653 table 4.1.... but here we have two options:

1) allowable product stress
2) allowable hydrostatic test stress

So please advise me which of the values is appropriate to use .... in this current case storage product is water (that looks like hydrotest) but product stress and hydrostatic test stress values differ in 4.1 table .... so how to calculate tmin ? (tank is not corroded at all if this helps).

Thank you

 

[mk3223]

I would say that the "S" for calculating tmin per 4.3.3.1 is to use the "Allowable Product Stress" as defined in API 653.

And, the "Allowable Hydrostatic Test Stress", St, is for calculating the hydrostatic test height, Ht per 4.3.3.2.

 

[IFRs]

If "G" is involved use product stress.

 

[Geoff13]

A hydrostatic test is a one-off overload test at the completion of repair or reconstruction. The hydrotest is done under controlled conditions and with careful monitoring. The hydrotest allowable cannot be used for the operation of the tank as it would be in an over-stress condition when full.

You must use the allowable product stress to check the tmin for future safe operation.