Maximum Plate Thickness Allowed per API 650

[TankDude]

Section 2 of API-650 states the maximum plate thickness allowable for each different material and grade. For most materials it is allowed to use thicker plate for inserts, however for A573-70 (2.2.2(g)) it states that 1.5 inches is the maximum period. I was wondering if anyone knows why and also if anyone knows any way of getting around this in order to use a thickened insert. Thanks.

 

[JoeTank]

It's been like that for a long time which suggests to me that there is little need for that material in the 1.5+" thickness range. I don''t recall seeing any inquiries or requests to API to increase the thickness limits of A573 materials. Good question though.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[LeonEarle]

You don't say what group of material you are using or the MDMT so I'll make a guess. If you are using group 4 materials, you can drop back to 516-70 (commonly dual graded with 573-70) and although your allowables go down a bit, 516-70 can be used "for inserts and flanges" up to 4".

 

[TankDude]

My MDMT is (+) 28 F and I my shell plate is 1 1/8" A573-70 from Group IVA. For thickened inserts I typically simply double the shell thickness (easy rule of thumb), so I will be well past 1 1/2" for the insert. As I mentioned, section 2.2.2(g) states that A573-70 can be used "for plates to a maximum thickness of 1.5 in.". A colleague of mine contends that there is no limitation for the thickness of an insert made of this material since it does not specify for insert plates as the other material limations do (though there are others that read this way, like A283C (2.2.2c). I contend that since it simply says "plates" then it is for all uses, shell and/or inserts. Regardless of the reasons, can anyone weigh-in with their opinion. He also contends that you can dual certify the material, but I always thought that this was only good for qualifying yield strength and toughness and would not preclude the maximum thickness limitations set forth by the standard. Anyone? Help!

 

[JoeTank]

TankDude,
I think your coworker is wrong about the thickness limits. The general limits apply to all plates whether a shell plate, insert plate, thickened insert plate, etc. On a few grades of material, the Standard allows thicker plates for inserts and flanges.

Regarding dual certs, once a material grade is selected, ALL of the rules are applied based on the grade selected as basis of design, fab and erect. It was not inteneded to mix-and-match requirements based on both material grades.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[TankDude]

Thanks Steve! I am glad that we are in agreement.

 

[IFRs]

You can probably use less than twice the shell plate thickness for the insert. Run the calculations for reinforcement and see if you can stay under 1.5 inches. You can also add reinforcement inside the tank, but I have never seen this on a thickened insert plate....