Loose type flange (lap joint) or slip-on with Titanium and C.S. 1

[Peregrino7]

This is a vessel made with Titanium plates (no cladding) of 13mm with two forged covers at both sides. Nozzles necks are with Titanium as well.
Vessel ID = 1800mm (70”) design pressure = 13 bar (188psi) and Design Temp = 65ºC (150ºF),
Vendor is proposing that all main flanges and nozzles flanges to be C.S. and in order to avoid that C.S. to stay in contact with the fluid or any welding between C.S. and Ti, the vendor is proposing a loose type flange (lap joint) also named slip-on, as per ASME VIII app. 2 - Fig. 2-4 (1a).

I have the following questions:

1) What are the disadvantages of this type of flanges? These types are not usually specified for Vessels in refinery services (anyhow this equipment is for an LNG plant)
2) Is there any other option or a better suggestion to solve the problem of C.S. flange and Titanium cylinders and nozzle necks?
3) Bolts for these flanges are to be SA-320 (S.S.). Is this ok for this combination of materials?
4) Any suggestion with the material and type of gasket for tubeside is much appreciated.

Kind regards, and thanks for your help..!



PGh.

 

[SnTMan]

See Sec. VIII, Div. 1, Appendix 2, Fig (1a). The Code refers to it as the "lap", and the figure shows that the lap thickness is greater than or equal to the neck thickness.

I think this should be all that is needed, at least for this class of work.

Regards,

Mike