MDMT for stiffening rings per ASME VIII-1

[Jano6924]

Gentlemen:

In ASME-VIII-1 paragraph UCS-66(a) states that:

Components, such as shells, heads, nozzles, manways, reinforcing pads, flanges, tubesheets, flat cover plates, backing strips which remain in place, and attachments which are essential to the structural integrity of the vessel when welded to pressure retaining
components, shall be treated as separate components. Each component shall be evaluated for impact test requirements based on its individual material classification, governing thickness as defined in (1) and (2) below, and the minimum design metal temperature

Since a stiffening ring is an attachment essential for the structural integrity of a vessel, the determination of the MDMT for a stiffener is a must. However since ASME-VIII-1 does not provide rules to calculate the “required thickness” and the “coincident ratio” for a stiffening ring, my conclusion is that, for carbon and low alloy, I have only two options to determine de MDMT for a stiffening ring.

a) Use the rules of UG-20(f), if applicable, and based on governing thickness as shown on Figure USC-66.3(f), or…
b) Use Table UCS-66 based on governing thickness as shown on Figure USC-66.3(f) and the curve applicable for material of stiffener.

For the case of stainless steel stiffeners I shall follow the rules in UHA-51, except that UHA-51(g) cannot be used since there is no way to calculate the coincident ratio for a stiffening ring.

Please let me know if I’m correct on this subject, if not, please comment.

Best Regards.

 

[SnTMan]

Jano6924, essentially correct I'd say. It might be possible to arrive at a required thickness for the stiffening ring, perhaps backing it out of the required moment of inertia, but a headache for sure.

I personally am leery of trying to apply UG-20(f) to discrete components, but I can't say it's wrong.

I'd go with UCS-66(a).

Regards,

Mike

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

 

[Jano6924]

Mike:

Thanks for your comments. As a fact I shall tell you that I also considered using the required moment of inertia to calculate the required thickness for a stiffener ring, but I’m not quite sure this would be an acceptable approach.

With regards of UG-20(f) I read this paragraph a number of times and could not find anything against using it for this purpose.

Again, thanks for your comments.

Best Regards.

 

[SnTMan]

Jano6924, I think backing out a required thickness for a given section would perfectly acceptable, but I wouldn't bother

Regarding UG-20(f), again I expressed only my personal preference.

Regards,

Mike

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