Hi all,

We just built a vessel. For some stupid reasons, I missed the external load requirement from customer. And when we complete the design, the customer approved the calculation and drawing. Now this vessel have passed the Hydro test, and customer found out the external load and questioning. When I added the external load in the calculation, the shell thickness is slightly under the minim.

Here is my question: I noticed the real yield stress of the Shell plate is 10 ksi bigger than the minimum requirement of the date used in calculation. Can I use the data of the real yield stress in calculation to replace the smaller one? If so, the shell thickness we used is acceptable.

Please let me it is acceptable or not? Please!!! Does code say anything about this? Please help!! Please

Jeff

I believe that these external loads are mostly piping loads. If yes, best would be to ask your client about the actual loads since most of the time standard loads are given which may be very high.

If actual loads are also high, there are various ways to reduce the same, unfortunately you have to use material property as specified in the code.

Regards

I agree with Sanjeev, you have to use the allowable stress values as per UG-23 that does not allow to use actual test values rather refers to Section II-D values.
The allowable stress values of ASME II-D are modified (increased) when you take into account other loadings than internal pressure, did you also practised that?
Is your vessel failed under WRC-107 or 297 analysis?

Sanjeev,

B31 code allows actual test values, somewhere, like to calculate carbon equivelancy especially when PWHT to be waived out because of weld nominal thickness. Does section VIII also permit?

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Thanks & Regards,
Nasir
Welding Engineer
DESCON Engineering Limited.
Lahore, Pakistan.
Mobile # 0092-336-4145402

Jeff,

I agreed with Sanjeev, these are external loads are mostly piping loads. Use B31 Code since Section VIII-1 jurisdictional boundary ends at the first circ. weld.

leem817

Thank you all,

I guess so. Sadly! the sales didn't forward me the PO. I didn't know the external loads requirement. A really stupid mistake. I couldn't forgive myself. I don't know what the customer did when he approved the drawing and calculation. Thank you all anyway.

Wish you all the best

Jeff

Jeff, you didn't make it clear whether your external loads are forces and moments on nozzles or external pressure (like internal vacuum). In the latter case, the shell stability is dependent on Young modulus rather than on yield strength. The easiest way to get away is to change the vacuum loading case to a lower temperature, as it is typical that such condition usually occurs when the vessel is not at the normal service temperature. If it's the nozzle loads, you've got two ways to go: derate these values (often exaggerated by the client) or choose a less conservative method of calculation (you've got a handful of them to choose from).

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Konrad Anikiel

Thank you Akonrad,

Unfortunately, it is external force and moment. The customer doesn't accept the conservative method. We have to add gussets or ring on nozzle. Thank you anyway. Thanks

Jeff

Jeff, just out of curiosity: What calculation actually failed? Some SecVIII-1 formula?

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Konrad Anikiel

A software called FEA. This nozzle is of a very funny oval shape. Thank you for your regarding.

Regards

Jeff