1960 API 650 Tank Material Specification

[NZ Tank Eng]

Hi All,

I am doing a change-of-service assessment of an old 1960s API 650 tank manufactured by the Chicago Bridge & Iron Company. The material specified on the drawing for a few of the lower thicker shell courses is BS 2762-ND-1B. Can someone please indicate which of the API 650 material groups would be the closest match and/or what would be a modern equivalent specification?

Thanking you in anticipation.

 

[IFRs]

Hard to know what CBI was doing - the first edition of API 650 was 1961 and it did not include British Standard materials. Prior to API 650 was API 12C. If it was built to API 650 1st edition, the shell steel would most likely have been an ASTM A131 or A283, these would be no better than current Group I steels. CBI might have found an equivalent British Standard steel for this tank but they should not have put an API nameplate on it. At the very least you should pull coupons for chemical and mechanical testing to identify the material and perform strength and toughness testing. Steel of that era was not particularly tough and was more sensitive to brittle fracture than current steels. Are you changing to a more severe service? Have you been able to establish the corrosion rate?

Good luck and report back what you find!

 

[NZ Tank Eng]

Thanks, IFRs.

I manage to download a copy of BS 2762 which states the yield and ultimate stresses for that particular grade plate to be 235MPa and 432MPa respectively with a max carbon content of 0.2%.
The shell strakes have fared relatively well, and the change will be to a less severe service. The upper (relatively thinner) shell courses are shown in the drawings to be ASTM A 283-C.

 

[IFRs]

OK, so the material is slightly stronger than A283, have you determined why CBI chose to use it instead of A283? Does the BS 2762 material specification include toughness or impat testing? What is the size of your tank, how thick are the courses (strakes) and what is your minimum design metal temperature? I would still suggest getting a coupon for testing, to determine if the material meets current toughness requirements, particularly if the stored liquid is hazardous. You will be held responsible for the tank's integrity by your company and the public...