Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

3 laps joint for above ground tank as per API 650

3 laps joint for above ground tank as per API 650

3 laps joint for above ground tank as per API 650

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

" 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."


RE: 3 laps joint for above ground tank as per API 650

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.

RE: 3 laps joint for above ground tank as per API 650

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.

RE: 3 laps joint for above ground tank as per API 650

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.

RE: 3 laps joint for above ground tank as per API 650


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?

RE: 3 laps joint for above ground tank as per API 650

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 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).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close