I am working with the client regarding storage tank (API 650 code)- build 1960 - 304 SS Material - ID =14' , H = 20'

Per fabrication drawing, the shell thickness was = 3/16" = 0.1875" so per specification I build the tank model in TANK software. No problem.

last month, they did the inspection at couple of places and the Ave. wall thickness is = 0.201"

My question - How come the value get higher. I thought because of the Corrosion (If any for 304 SS),it will be lower?

Please let me know your expertise.

Can I enter this valve = 0.201" as nominal thickness in TANK software.

I appreciate your help.

Regards,
Mayur

Hello Mayur

It is the practice of some mills to supply oversize plates. This is because plates are sold by weight, not by guage thickness. It means that more money is involved. In my experience, this is common practice in the case of carbon steel, but rare in the case of stainless steel.

There is another possibility. The thickness tester may not have been calibrated accurately for stainless steel. Carbon and stainless steels have different characteristics. I would give this careful consideration.

I would be a bit suspicious in this case.