Location of Saddle supports for Horizontal Shell & Tube Heat Exchangers.

[DK44]

1. While modelling two saddles for horizontal Shell & Tube Heat Exchangers in PV Elite, it is observed that the location of saddles is made with reference to Shell node and the total Tangent length is considered as total Shell length. Where as for vessel with two saddles, the Tangent length is the end to end tangent length and saddles are located with reference to that TL. Accordingly overhanging end channels are neglected for Heat Exchangers leading to unbalanced location of saddles with respect to Exchanger CG which accounts all parts end to end. Can this be elaborated.

1.1 Does 1/4 th. distance rule for location of saddles apply with respect to Shell nodes only and not for end to end TL of Total exchanher?

2. Calculations of saddle loads due to weight distribution of Exchanger not included. Can it be elaborated?

3. For many and almost all cases M2 of left saddle and right saddle has wide variation.

4. The principle of possible close matching of maximum negative and positive BM is mostly not achieved.

5. However, not withstanding the above, the stresses are within limits irrespective of saddles imbalanced location with respect to Exchanger CG. Is it suffice for design.

6. The BM diagram for the above circumstances does not appear to be appropriate. Can a BM diagram be included.

 

[DK44]

May I request expert friend's views and remarks for guidance on the subject.

 

[Trestala]

I am assuming that the shell node you are referring to is at the junction between shell and girth flange? So the considered length is at that junction up to the tangent line on shell side. That is the effective length that should be considered for calculation of stresses since the girth flange should act as a rigid/stiffening component.

Due to the location of the girth flange and a possible nozzle located near the tubesheet, saddles can't really be placed where COG is right at the center of the two saddles.

 

[DK44]

Thanks Raymond N.

7. What I am concerned is while the saddles are placed on the Shell with reference to the Shell nodes as you said, let us say for example the Floating Head type Heat Exchanger, what about the overhanging effects of weights of Channels / Shell Covers on both sides of saddles beyond them.

8. As always M2 of left saddle differs with M2 of right saddle is the corresponding location of saddles is balanced.
Could you advise on the shape of the BM diagram.