How to reduce thickness because of Full vacuum

[JAS]

Dear All,
The present condition of the ALREADY FABRICATED COLUMN has FULL VACUUM with 6mm CA.
The information did not pass on to the Vendor and the Column has been fabricated considering PARTIAL VACUUM.
So only the top Shell course & Head fails because of less thickness (Fabricated 18mm with Partial vacuum, and 21.5mm with Full vacuum).
We have tried various options like, Stiffener rings (with different sections, dimensions), addition of Stiffener rings, try to use Coating too by reducing the CA (which Process dont agree).
Will you pls guide me, how to reduce the thickness of Head & Shell, because of Full vacuum.

Thank you in advance.
Best Regards,
Jay

 

[goutam_freelance]

See Sec-VIII-1 'UG-29 STIFFENING RINGS FOR CYLINDRICAL SHELLS UNDER EXTERNAL PRESSURE'

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[SnTMan]

JAS you cannot reduce the diameter or increase the thickness of the affected sections. You presumably cannot reduce the design temperature or design external pressure.

Referring to the cylindrical section only, the length between lines of support is all you have to work with. It can be reduced by the addition of stiffening rings. If for some reason this is not practical for your situation, you are stuck with what you've got.

Note that for a formed head there is no simple Code rule solution such as adding stiffeners. The head is thick enough or it is not. Addition of any reinforcing elements would be a matter of advanced analysis and may or may not be permitted under Code rules and contract.

There is not easy out for you and perhaps no out at all.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Morcuse]

Try an MA 46 -> Protection against buckling analysis. Might be your only way out.

 

[JStephen]

I've not run into a situation where it mattered, but typically, heads include a forming allowance in the design. Is it permissible to survey the head thickness and decrease that allowance in the design based on actual achieved thickness?

 

[jtseng123]

If you have the budget, considering weld overly to build up the thickness.

 

[DriveMeNuts]

As the pressure is less than 15 PSI, it doesn't need to be U-Stamped or even comply with ASME.

There fore use EN 13445-3. It calculates a substantially lower thickness than ASME VIII.

 

[Some Curious Guy]

The 2019 edition of the ASME BPVC Sev VIII DIv 1 code ( which I assume you are using ) allows us to use ASME Div 2 Part 4, design by rules method. Read Appendix 46 and try using that. See if you get some respite.

However speak to your AI first to know his opinion. There is still some confusion whether we can replace Div 1 rules by Div 2 rules even though Div 1 rules are present. I feel you can use it.

 

[r6155]

See Code Case 2286-2
Alternative Rules for Determining Allowable External
Pressure and Compressive Stresses for Cylinders,
Cones, Spheres, and Formed Heads
Section VIII, Divisions 1 and 2

Regards