Calculation of storage tank bottom corrosion rate

[dwegner]

API 653 4th edition states that to calculate the corrosion rate of a tank bottom, use the minimum remaining thickness after repairs. Technical inquiry 653-I-04/00, says you must use of the corrosion rate of the corroded area. Do these two statements conflict? I would expect to calculate the corrosion rate based on the minimum remaining thickness before repairs and then apply that corrosion rate to the thickness after repairs to calculate the remaining life.

 

[Bonswa]

I dont like the way that's worded either, but you're doing it right.

Figure out the corrosion rate based on the minimum remaining thickness BEFORE repairs.

The minimum thickness AFTER repairs is to be used for the remaining life. You would take the minimum thickness after repairs and divide it by the corrosion rate to determine whether or not it can last whatever interval you're looking for.