Stiffening (vacuum) rings

[wfn217]

ASME VIII says to use Fig.UG-29.2 to determine the maximum allowable unsupported length (gap) for a ring, but it does not say how many gaps are allowed. Is this figure supposed to be the total allowable gap for all gaps? We want to install the ring as two halves and there would be two gaps.

 

[doct9960]

Interpretation: VIII-1-95-110

Subject: Section VII , Division 1 (1995 Edition); UG-29(c)
Date Issued: August 2, 1996
File: BC95-401

Question: Is it permissible under the requirements of UG-29(c) in Section VIII, Division 1 to use an internal stiffening ring having two or more unsupported shell arcs?

Reply: No.

 

[vesselfab]

the text in ug-29 pretty well goes over everything

but, i think the intent was gaps at weld and not gaps in the ring itself.

the halves of rings should be welded together with full penetration welds after fitting to vessel.

after doing this, you should not have any gaps in ring unless you want minor gap per ug-29 for vent or drain.

we don't even consider this for passing over a longitudinal seam, even though we could. We grind the seam flush, fully radiograph the area, then install the ring as if the shell was seamless.

The stiffener ring should be pretty much continuous, but there are exceptions in UG-29

 

[wfn217]

vesselfab,
Permissible gaps at weld (in-line intermittent weld) are shown in Fig. UG-30. This is discussed in UG-30(c). Fig. UG-29.2 is for gap in the stiffening ring.

doct9960,
This is an external ring.

 

[vesselfab]

ok let me re-phrase (i did not do well the first time)

but, i think the intent was ""small"" gaps at "point of attachment to shell"" and not ""full width"" gaps ""radially projecting from shell all the way to outside of ring"" in the ring itself.

every thing else stands

if you put the ring on in two (2) halves, it should be continuous and the two (2) halves welded with full penetration welds.