Bayonet joint

The bottom of the diaphragm is a variation of the bayonet joint. It may be removed from the diaphragm but cannot come off in operation, as sometimes happens with the bayonet type of bottom. 

An improvement on the field-welded joint is the bayonet joint, which... 

Fig. 7.33. Schematic of typical bayonet joint for cryogenic transfer line. Legend 1, outer line, vacuum shell 2, line coupling 3, warm temperature O-ring seal 4, static gas leg 5, vacuum insulation space 6, vacuum barriers 7, additional liquid seal and 8, liquid line.

Tubes are welded to the tubesheet and then rolled and expanded for additional holding power. Rolled joints alone are not sufficient for extended periods of service. For special services, these tubes can be of steel, stainless steel, or other materials. Bayonet tubes are roller expanded into lower tube plate. 

---