Piping hinged type

Figure 7-111. Simplified sketch showing a hinge-type corrugated expansion joint suitable for refinery piping systems.

Fig. 13. Semirigid piping systems (a) two-hinge arrangement (b) universal-type arrangement.

Dual-beUows assembhes, ie, universal-type expansion joints, are particularly vulnerable to squirm, and can experience elastic squirm at one-fourth the pressure of an individual bellows. When large amounts of offset are encountered, as is often the design basis, a pinwheel effect occurs because of unbalanced pressure forces. This effect tends to rotate the center-spool pipe which may lead to bellows mpture. Eor this reason the center spool should always be stabilized by hinges or tie-rod lugs to prevent such rotation. 

Multiplane piping systems requiring hinged expansion joints may be dealt with similarly. Obviously the problem will be more involved and in many applications the use of gimbal-type joints is necessary. 

The characteristics of the broken pipe should be taken directly from the design of the system and the location and type of the postulated rupture. In the case of pipe whip it is usually conservative to assume a full circumferential rupture and to assume that the pipe will form a hinge at the nearest rigid... 

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