API 653 Reinforce of a last shell rim and top angle

[jfacevedob]

Dear Sir

In a supported cone roof storage tank which sever corrosion troubles in the area of the horizontal welded join between the shell plate and the top angle (see detail “e” Fig. F.2 API 650), to reinforce the affected area where the rafters are fixed to the shell we are proposed to install a lap welded reinforce plate of approx. 23.25” height around the top side of the shell. The top angle is an L4”x4”x3/8 and after install the reinforce plate 3/8” below the top angle we would get a welding space between the horizontal joints of 3” instead of 6” recommended by API 653 Fig. 9.1.

If the the area to be reinforced is not in contact with the product. Is our proposal conform to API 653? If not please tell me why is not conform to API 653?.

 

[JStephen]

Section 9.3.1.7 limits the size of a lap-welded patch plate 48"x72". Unless there's some other section that addresses this, it's not an API-653 detail to begin with, and the 3" vs 6" wouldn't matter.

 

[jfacevedob]

Dear Stephen

Due to the limits of lap-welded patch plate to rieinforce the area wher the rafters are fixed for a 200 ft dia. Tank with 108 outer rafters we have to use 108 patches of 23.25"x61" with aprox. 8.7" between patches instead of use a continuous reinforce rim make of 32 plates of 23.25"x 235"

 

[IFRs]

If the area is above the liquid level, I think you can take some liberties with the design of the repairs and perhaps not be in strict compliance with API 653, use good engineering judgment and make sure this area satisfies other needs ( wind buckling, frangibility, etc ). The liquid level would have to be limited by shell overflows, not just operational or management controls. The tank would essentially have a lap welded extension welded to the shell for reasons other than liquid storage.

Better though would be if you can remove and replace butt welding entire vertical section say 20 feet at a time with a rolled section of plate with the top edge bent. Can this be done?

 

[jfacevedob]

Dear IFRs

Thanks for your reply, replacement of sections of butt welding plates was another of our recommendations