×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Floor Plate Projection distance problem

Floor Plate Projection distance problem

Floor Plate Projection distance problem

(OP)
Can anyone tell me why API650 asks for a minimum 50mm (2 inches) floor plate projection from the outside of the shell?
I have a contractor who has ended up with 45mm (just less than 1-13/16") and hence the tank does not strictly comply with API650.

For tanks already in service, API653 would reign, and the minimum could then drop to 9.5mm (3/8 inch).

So what is the main purpose for the 50mm. Is it something to do with the HAZ? to allow for proper sealing? or just good amount?

Ideas anyone?

RE: Floor Plate Projection distance problem

Kiwi..

I believe that I read that the minimum floor plate distance involves the resistance to rotation that is desired at the bottom of the shell. This slight roation occurs when the tank is full and varies with the tank design as well as the liquid SG.

If the distance is too short, then the tank is (slightly)more prone to rotation at the shell to floor joint.

Try posting on this forum   www.ast-forum.com

Regards and please tell us what you find out

-MJC

  

RE: Floor Plate Projection distance problem

The chime provides distribution of the shell weight onto the earthen subgrade so may have to be greater than 2" sometimes.  If it's on a concrete ringwall it is less critical.  Either way the Standard now requires a minimum of 2".

Joe Tank

RE: Floor Plate Projection distance problem

If this is a shop fabricated tank, designed per App. J, J.3.2.3 still requires just the 1" + weld thickness outside the shell.  
As a matter of consistency, I design all tanks (including App. J tanks) with the 2" chime.

RE: Floor Plate Projection distance problem

(OP)
This is a 19.5m dia tank constructed on an existing foundation. The spec and drawings all show "50mm min" but it's not what we've ended up with.

I think that originally the annulars were cut to the correct diameter (with no allowance) then the tank has been fabricated using the top down method (jacking the tank roof and shell strake by strake from the ground). The bottom strake of the shell may now be approx 10mm larger diameter than originally proposed, (hence the 5mm each side too small)

RE: Floor Plate Projection distance problem

Kiwi,
Are you the tank fabricator or the poor inspector that is stuck with this problem?

Joe Tank

RE: Floor Plate Projection distance problem

(OP)
JoeTank,

I'm the client's designer / engineer (and also API guy), and noticed this when I went for a site visit after the tank has been constructed and was being painted.
The Client has their own staff monitoring the job, but obviously weren't checking these details. They are more involved in safety.
So I guess I'm kinda stuck with it. Not sure what (if anything) can be done about it. All comments welcome

RE: Floor Plate Projection distance problem

What type of foundation is there under the shell?

RE: Floor Plate Projection distance problem

(OP)
The foundation is an Earth mound with asphalt over-lay

RE: Floor Plate Projection distance problem

How extensive is the problem?

RE: Floor Plate Projection distance problem

(OP)
The floor plate projection (chime) is the same the whole way around the tank - 5mm short

RE: Floor Plate Projection distance problem

Kiwi,
The 2" projection is just a nominal dimension.  It's not based upon a stress analysis, it's just a practical figure.  The recent API actions to make it 2" for all tanks with either sketch plates or annular plates was based on practical considerations and provide one set of rules, not two.  I'd figure out a way to have all parties accept it.  Trying to rework it would do more harm than good.

Joe Tank

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!


Resources