Wear Plate & Saddles

[JStephen]

A question about wear plates versus saddles. In looking back through the Zick paper on saddle design and also in Bednar's handbook, it appears a steel saddle will have a top flange plate, with an optional wear plate between that plate and the vessel. However, in Megyesy's handbook, that top flange plate appears to be the same thing as the wear plate, although Megyesy says it is based on the same Zick analysis. Anyone have any insight into this difference? It does affect the design in various ways.

 

[TomBarsh]

The Zick paper is based on concrete saddles, obviously not welded to the shell. The wear plate helps reduce stress in the shell at the saddle under the conditions given in the Zick paper.

A steel saddle may or may not have a "top flange"; the purpose is not the same as that for the wear plate. The flange is to "emulate" the width of the concrete saddle. The broader width of the top flange versus the vessel bearing on only the thickness of the saddle web plate will make a big difference in some stresses in the shell. But typically the ring compression stress based on omitting the top flange is still within the allowable so a top flange isn't necessary.

Typically a top flange is throwing money away. It's just to emulate the width and rigidity of the concrete saddle. And to do so you should make certain to stiffen it with gussets, etc.

My opinion only.

 

[EngAddict]

The wrapper plate also has an effect on the effective thickness you may use in calculations. Provided it is wide enough and extends enough, you can use a combined thickness of the shell and wrapper. This can greatly reduce stress if you have large moments. Of course this is based on wrapper plates that are welded to the shell. In such cases (I would say recommended for steel cradles) you use a sliding plate under the base plate of the saddle.