vacuum ring

[altoid3000]

We are having some trouble placing vacuum ring on a tower. We are using ASME Section VIII Div 1. We looked in appendix 1-8C, 1-8E and found that the max distance of the centroid of the vacuum ring from the center of the seam weld is 0.84". Since it is RT-1 radiography, we got to radiograph the seam welds. But if we put the ring at 0.84", that does not give us enough clearance to push the X ray film (Source is inside the vessel, film outside)

We are thinking of redesigning the ring (may be I section) to keep centroid at 0.84" but the edge for welding far way from the seam weld. Has any one done this before ? Have anyone run into similar problem before?

 

[jte]

altoid3000-

You are not talking about regular vacuum stiffening rings on a shell, but about the required stiffener at a cone to cylinder junction, right? It might help us with perspective if you give us more details like the diameters and thicknesses involved. To get numbers around your value, I'm guessing you're somewhere around a 60" ID with 3/8" plate.

I guess I'd have three options for you: First, do the x-raying prior to welding on the stiffening ring (or is it a PWHT vessel?). Second, as you were thinking, use a shape such as an Ell as your ring. You'll weld it on a bit farther away and still retain the centroid within your 0.84" limit. Third, and best from my perspective, is to increase the plate thickness of your cone/shell so that you don't need a stiffener (or use a cone with a knuckle).

jt

jt

 

[metengr]

If this is a repair to an existing vessel do you have the option of performing an ultrasonic examination of the seam weld? Ultrasonic examination is a viable method for volumetric examination. What repair code are you using API or the National Board Inspection Code? If you are using the NBIC, by all means I would substitute the UT for RT-1.