API-650: Corrosion Allowance in Hydrostatic Shell Thickness (5.6.3.2)

[TheEverest]

Why corrosion allowance(CA) is not added in the calculation of hydrostatic test shell thickness(t_t) in the given formula in 5.6.3.2?

 

[Geoff13]

Hydrotest is done when the tank is new, and thus no corrosion needs to be allowed for.

 

[IFRs]

The hydrotest is a short term non-repeating event that as noted usually only occurs when the tank is new. For these reasons a corrosion allowance is not added to the design shell thickness and the allowable stresses are higher than for long term product loading. Using a product design density of 1.0 (water) for oil tanks results in excess cost but purchasers may not realize that the hydrotest condition is a separately considered load case.