3 laps joint for above ground tank as per API 650

[Amirrul]

Hi all, need your professional view on my case:

Our tank is fabricated following API 650 and now the concern is on 3 plate lap joint. We have 3 bottom plate that sit together and was welded with lap joint. Is this consider as 3 plate joint?.

This is the clause on API 650 section 5.1.5.4.2

"5.1.5.4.2 Three-plate laps in tank bottoms shall be at least 300 mm (12 in.) from each other, from the tank shell, and from joints between annular plates and the bottom. A three-plate lap is created where three plates come together and all plates are joined to one another by lap welds. A location where a pair of bottom plates are lap-welded to each other and are lapped onto an annular plate constitutes a three-plate lap, but lapping a single bottom plate onto a buttwelded annular plate splice does not constitute a three-plate lap weld since the two annular plates are not joined together by a lap weld. These lap joint connections to the butt-weld annular plate are illustrated in Figure 5.3d."

thanks

 

[HTURKAK]

The joint of BP9-BP10-AP1 is three plate lap joint, the joint of BP8-BP9-AP1 is also three point lap .The distance between them shall be at least 300mm. Pls see the definition Figure 5.3d—Spacing of Three-Plate Welds at Annular Plates.

 

[Amirrul]

Thanks HTURKAK. Sorry i attached a wrong drawing. Attached drawing is the correct 3 laps joint. Current issue is the 3 bottom plate laps to each other. Is this consider as 3 plate laps joint also?. No lapping on the annular plate actually. Thanks.

 

[HTURKAK]

Dear Amirrul (Petroleum)

Three plates can be sketch plates or two sketch plates plus one annular plate. In your case , for instance, the joint of BP1+BP8+BP9 is three sketch plate lap. Your quote ' No lapping on the annular plate actually' is not possible. There will be 3 plates lap joints including the annular plates.

 

[IFRs]

Amirrul - you did not attach anything to your second message. Inside your red circle are two three-plate laps, exactly as pictured in figure 5.3d, and as Hturkak said.

 

[Amirrul]

Hi all, this is the actual site photo. Appreciate your advice on this.

And any consequence if we dont follow the minimum 300mm distance? Any integrity issue?

 

[IFRs]

The 3-plate lap between B1-B2-B3 is too close to the annular plate-to-bottom seam. It needs to be 12" per the first sentence in 5.1.5.4.2 that you included in your OP. It violates the standard. Will it lead to premature or catastrophic failure? Hard to say but I'd just fix it and move on. It's in the standard for some reason(s).