Horizontal Pressure Vessel Saddle Base Contact

[NeilWig]

I have a pressure vessel mounted in structural steel (refinery). The vessel has one fixed saddle, and one sliding saddle. Aproximate weight is 60 tons. The vessel dynamically loaded due to heating and cooling cycles (thus the sliding saddle).

The sliding saddle sits on three I-Beam sections with a base plate welded to them. The slider is a teflon pad aproximately 1/4" x 15" x 180"

The fixed saddle is bolted to three I-Beam sections with a base plate welded to them. The saddle is bolted in place with four 1 1/2" bolts located in the corners of the saddle base.

Given the vessel is mounted within structural steel, what are the contact requirements of the fixed saddle?

Thank You

 

[doct9960]

What do you mean by contact requirements? Are you asking if the bolts should be fully tensioned or snug tightened?

 

[NeilWig]

I am looking for the contact requirement from the plate welded to the structural steel support, and the base of the pressure vessel saddle.

 

[doct9960]

NeilWig,

This is more of a structural issue than a vessel issue. You will probably get a better response from forum507

I have an old copy (9th edition) of AISC Manual of Steel Construction ASD. Regarding Column Base PLate Finishing, it refers to Section M2.8 of the AISC Specification. It says...

"Rolled steel bearing plates 2 in. or less in thickness may be used without milling,* provided a satifactory bearing is obtained; rolled steel bearing plates over 2 in. but not over 4 in. in thickness may be straightened by pressing or, if presses are not available, by milling for all bearing surfaces (except as noted in Subparagraphs c and d of this section), to obtain a satisfactory contact bearing; rolled steel bearing plates over 4 in. thick shall be milled for all bearing surfaces except as noted in Subparagraphs c and d of this section)."

What I have seen done in the field is that if there's insufficient contact and the gap is less than 1/4", they just pack the gap with steel shims.

 

[JStephen]

I think that's the spec for column base plates, which I would not apply to this situation, due to the much higher loading anticipated in that usage. The intent in that case is to avoid overloading the concrete below.

I'm not entirely clear on why this would be a concern. You can check local web buckling and yielding directly under the load per AISC provisions. You can check bending in the saddle itself by treating it as a beam. You can check web bucking and yielding in the saddle similar to a beam.

If the result of excessive contact pressure is to simply increase the contact area, then I would say it was a non-issue- for example, if plate A is supported by plate B, and they only touch at a couple of points.