Seat ring with flat cover 1

[mrsteam]

I have a design that uses standard pipe as a shell. At the top of the shell we are adding a very short run of a larger diameter pipe of heavier schedule (call this the seat ring), attached to the main shell by a lap joint double fillet weld (main shell fits on ID of seat ring), in order to provide a seating surface for the flat cover, with an o-ring groove machined in. Bolting is by means of swing bolts, with lugs attached to the main shell (not to the seat ring).

Question is how do I treat this seat ring, and what calculations do I need? I initially considered it a flange per Appendix 2, but now I think that might not be accurate, considering bolts are not attached to the seat ring. So now I'm thinking this is just another section of shell, and should be treated as such. In such case, all I would need is the thickness requirements for the shell, and geometry constraints for the lap joint? Any comments?

Another problem is related for use with lethal substances... UW-2 indicates that Category B joints should be of either type 1 or 2 only, and this lap joint would be type 4. Any recommendations on this?

I thank you all for any insight.

 

[SnTMan]

mrsteam, I think you can treat your seat ring as you propose since you are transmtting no bolt moments to it. Your cover will need to consider the bolting moments however.

If you are in lethal service I do not believe you can ignore the UW-2 requirement. Lap joints are not permitted. It should be fairly easy to design this joint as a butt joint although at some extra expense.

Regards,

Mike

 

[arto]

There's an old Transactions article that might be useful:

by Paul Seide "On the Bending of Cylindrical Circular Shells by Equall & Equally Spaced Radial Shear Forces and End Moments" JAM March 1961 pp 117-126.

Check the weld shear to hold the ring on [Blodgett's Design of Weldments" might come in handy

 

[mrsteam]

Thank you very much for your replies. I have checked with the local Boiler & Pressure Vessel authority, and they have also agreed that I could assume this seat ring to be a slip-on flange, and show calculations for the geometry constraints on the lap joint, and shear stress on the fillet weld.