Oil Tank nozzle minimum thickness. 1

[Joss10]

Dear folks,
I´m looking for some information about the subject in order to inspect a tank as per API 653, some people is talking about 0,1" but nothing like this is stated in API 653, as per API 650 new connections have minimum 1/2".
Thanks in advance for any information on the subject.

 

[JStephen]

For API-650 in carbon steel, it is "Extra Strong" pipe wall thickness, which will be 0.500" in the larger sizes. Stainless tanks have a reduced thickness. API-12F and API-12D tanks use Standard Weight thicknesses, I believe.
This is the as-built thickness. Somewhere in there, API-653 should specify a minimum remaining thickness or a way to calculate minimum thickness to remain in service- it's not expected that nozzle thickness has to remain exactly as-built to remain in service.

 

[Joss10]

Thanks JStephen,
There is nothing in API 653 for nozzles, it only establishes a minimum of 2.5 mm for shell.
For nozzles it asks to calculate it by internal pressure and you know the tank design pressure is very low.

 

[JStephen]

Yes, looking at that, I think some clarification in the standard would be helpful. In 4.3.9.1, it says that details shall be reviewed for "compliance with the as-built standard", then in 4.3.9.2, "Nozzle wall thickness shall be evaluated for pressure and all other loads". I would take the latter condition to apply to minimum corroded nozzle thickness, rather than compliance with the as-built standard in the corroded condition.

In 4.3.3.1, for evaluation of corroded shells, they calculate a minimum remaining thickness and then add "but not less than 0.10 inch". That would be a reasonable way to approach nozzle thickness as well.

Also, see 5.3.2.3 in API-650, which allows CA to be added to the minimum required nozzle thickness based on pressure and applied loads- which implies that corroded thickness can be less than the as-built thickness.