API 650 Anchor Chair Design - Shell Stress

[EmilianoS87]

Hi, on API 650 paragraph 5.12.7 refers to AISI reference as an acceptable procedure for anchor chair design. When I check the reference in order to calculate shell stress an anchors there is a difference in the Z reduction factor with other references like Denis Moss Pressure Vessel Handbook (3rd and 4th edition). In one reference it uses .177 factor and in the other 1.77 factor on the same formula. Anyone have any insights in these particular topic?

Thanks in advance.

"5.12.7 Attachment of the anchor bolts to the shell shall be through stiffened chair-type assemblies or anchor rings of sufficient size and height. An acceptable procedure for anchor chair design is given in AISI Steel Plate Engineering Data, Volume 2, Part 5, “Anchor Bolt Chairs.” See Figure 5.28 for typical chair detail. When acceptable to the Purchaser, hold down straps may be used. See 5.12.15 for strap design requirements and Figure 5.29 and Figure 5.30 for typical hold down strap configurations."

 

[HTURKAK]

I will suggest you ;

- use 0.177 as stated in AISI Steel Plate Engineering Data ( but i would like to remind you that this is based on P.P. Bjilaard study "Stresses from Local Loadings in Cylindrical Pressure Vessels", ASME 1955.. but i did not hear this formula is unreliable )..

- If you are in doubt, develop FEM with a well known software , perform analysis and see ..







I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[IFRs]

Just curious, how does the .177 vs 1.77 affect the rusults if that is the only change? The API industry has used the AISI formulae for a long time but that does not guanratee that an error has not be present. Can you post links to or PDFs of the other resources? Perhaps there is something else that is different - an assumption, unts, etc?

 

[JStephen]

I would be inclined to use the AISI version, as it has been around longer.
Moss doesn't give any justification for his value, and doesn't mention he's updating an old erroneous value, so presumably, he was actually using the AISI version as well.
I do have a copy of the Bijlaard paper ordered just to see. Of course, that value may not actually be shown in there.
The AISI book shows his name as Bjilaard, but online, I find the i before the j.

For the range of thicknesses and sizes used on tanks, the Moss equation will give values of 20% to 95% of the AISI version. IE, the AISI is the more conservative of the two.

 

[r6155]

Also check with Bednar, as say AISI Design References

Regards

 

[EmilianoS87]

Thank you all, I will check all the references and do a FEA to pinpoint test accuracy and let you know

 

[JStephen]

I did get a copy of the Bijlaard paper referenced through ASME. It is of no help on this particular item. In it, he comes up with shell bending equations and extracts certain solutions via double-series and numerical computer (which was cutting edge in 1955!). But there is not anything specifically regarding anchor chairs or stress concentration factors for them, or anything resembling the anchor-chair stress formula as published. I think the numerical results were based on an infinitely long shell, even.

My guess is that there will be a lot of difficulty in matching results from this method to FEA. The original physical problem was idealized in some unknown way, the idealized problem was solved via some approximate method, and that solution was then curve-fitted or simplified further to come up with the published equation.

 

[JStephen]

Does anyone have Troitsky's Design of Tubular Structures? If so, does it address this specific item?
And, the AISI book lists Buthod's Pressure Vessel Handbook. In googling that, all I find is Megyesy's Pressure Vessel Handbook with a foreword by Buthod. Is/was there a separate Pressure Vessel Handbook by Buthod, or is that the same one?

 

[r6155]

EmilianoS87
Can you send us data: tank diameter / height.
Anchor bolts are required?, Why?

Regards

 

[HTURKAK]

I have TUBULAR STEEL STRUCTURES Theory and Design (by Troitsky ) .I think the same book..

It addresses thickness of the shell for external bolting chair .. copy and paste of the proposed formula

I have Megyesy's Pressure Vessel Handbook with Buthod's FOREWORD and i do not know seperate book from P. Buthod

Another book fro BERDNAR ( Pressure Vessel Design Handbook )









I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[JStephen]

I've got Megyesy and Bednar, will check them tomorrow.
I would have assumed that the AISI book pulled that equation directly from some other source, not that the unknown author/editor had to do a bunch of research, manipulation, computation, etc. I was really expecting it to be in the Bijlaard paper.
I did run across another ASME technical paper where they were comparing FEM results against a couple of other methods, am tempted to run that one down, too.

 

[Geoff13]

I would use the 0.177 published in AISI Steel Plate Engineering Data Volume 2. This is the original publication, and numerous structures have been built using this formula. Some of these structures have experienced significant events (seismic, high winds, over-pressure, etc.) without revealing problems in this method. Anchor chairs are too small (size and cost) to refine with FEA.

As for the source, the Volume 2 acknowledgements list a number of companies and organizations that contributed to the volume. I believe one of them contributed this article based on their in-house engineering work on the topic, and thus you won't find the original source document.