Tube-sheet to Shell LIP type joint-Lower allowable stresses

[nileshbwagh]

I am designing U-tube exchanger with tubesheet integral(LIP type) with channel as well as shell.Design temperature is 345 deg.c.
MOC. of shell/ channel is SA-516 Gr.70 and Tubesheet is SA-266 Gr.2.

Allowable stresses of shell/channel are higher (128MPa) than that of tubesheet (122MPa)at design temperature.

Client asked to calculate tubesheet LIP thickness (assuming LIP extension as shell) as per CODE formula for internal pressure i.e. UG-27.
and allowable stresses for LIP thickness calculation (Ug-27 formula)shall be used that of tubesheet.

Due to above, LIP thickness is coming around 8 mm higher than shell. Hence it was decided to increase the shell / channel thickness to match LIP thickness (As LIP can not be tapered less than required thickness)

Question is, should be really consider LIP as part of shell and wherever applicable increase shell/channel thickness equal to or more than required thickness of LIP??

Also is there any merit in carrying out complete UHX calculations using shell allowable stresses same as that of forging (i.e. lower of the joint)??

 

[SnTMan]

nileshbwagh, by LIP type, you mean tubesheet has a hub, for buttweld to cylinder(s)?

If this is so, I think you could find guidance in Appendix 2, 2-1(a) where hub thickness is required to meet minimum thickness per Subsections A, B & C. That is, your hub must meet the thickness requirements for pressure, etc.

Note you can form any required 3:1 taper with weld metal if you chose, rather than increase the cylinder thickness.

Part UHX apparently does not address this specific situatiuon, i.e. hubbed tubesheet, lower allowable than attached cylinder, etc, etc. Probably for a conservative design, stresses in attached cylinder shoud be based on the lower allowable of the materials joined. Another Part UHX complication

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand