Bellows joint

Bellows The pipework either side of a bellows joint shall be supported so that the bellows itself is not supporting any of the weight of the attached pipework. 

Thermal expansion and the resultant pipe stresses must be considered in any piping system design. For example, if the temperature changes from 50 to 600°F, the increase in length would be 4.9 in. per 100 ft for steel pipe and 7.3 in. per 100 ft for brass pipe. This amount of thermal expansion could easily cause a pipe or wall to buckle if the pipe were fastened firmly at each end with no allowances for expansion. The necessary flexibility for the piping system can be provided by the use of expansion loops, changes in direction, bellows joints, slip joints, and other devices. 

Figure 42.11a shows the deformed shape of the bellows joint with an axial extension of 5 mm at an internal pressure of 0.96 MPa and a transverse displacement of 75 mm. Figure 42.1 Ifc shows the transverse loads required to effect the displacement as a function of internal pressure (0.1 and 0.96 MPa). Four main stages can be observed. The first stage, stage I, is the linear elastic range here the load-defiection curve is linear and the stress in the bellows is below the yield strength. The second stage, II, is a primary yielding range localized...

In general, weld repair of any cracked metallic bellow is not recommended, as it is not possible to restore the original bellow functionality after repair. That will further jeopardize its operational integrity. Therefore it is always considered safe to replace the entire expansion joint bellow assembly from the reliability point of view. Procuring a new bellow joint for replacement normally takes a minimum of 10 to 14 weeks subject to the supplier / manufacturer constraints. Shutting down SRU totally and flaring Acid gas for extended periods imtil the replacement of bellow is not permitted as it is anti-environmental. 

It has been postulated that a rupture in the large expansion joint would result in a 4000 gpm leakage and that a rupture from a small joint would yield a 3000-3500 gpm leakage. This is significantly less than a postulated 60,000 gpm leak which would result from a medium-size-diameter line break therefore, the consequences of a bellows joint failure are much less severe and result in a lower rate of water level drop in the reactor tank. This slower rate provides enough time for the reactors to be scrammed. A bellows joint failure... 

The bellows joints are dye-penetrant tested every 3 years. 

The movement-absorbing devices used in semirigid and nonrigid piping systems are usually called expansion joints. Based on the method by which the pressure seal is effected, joints are either of the packed type or the packless or bellows type. Selection depends not only on the required movement but also on the severity of service in terms of pressure and temperature, tolerabiUty of leakage, and the number of service cycles. 

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. 

Bending or torsional flexibihty may be provided by bends, loops, or offsets by corrugated pipe or expansion joints of the bellows type or by other devices permitting rotational movement. These devices must be anchored or otherwise suitably connected to resist end forces from fluid pressure, frictional resistance to pipe movement, and other causes. 

Expansion joints for free-movement systems can be designed for axial or offset movement alone, or for combined axial and offset movements (see Fig. 10-171). For offset movement alone, the end load due to pressure and weight can be transferred across the joint by tie rods or structural members (see Fig. 10-172). For axial or combined movements, anchors must be provided to absorb the imbalanced pressure load and force bellows to deflect. 

FIG. 10-172 Constrained-bellows expansion joints. (From Kellogg, Design of Piping Systems, Wiley, New Yotk, 1965.)... 

Because of the inherently greater susceptibility of expansion bellows to failure from unexpected corrosion, failure of guides to control joint movements, etc., it is advisable to examine critically their design choice in comparison with a stiff system. 

Pressure thrust, which is the product of the effective thrust area times the maximum pressure to which the joint will be subjected during normal operation. (For shp joints the effective thrust area shall be computed by using the outside diameter of the pipe. For corrugated, omega, or disk-type joints, the effective thrust area shall be that area recommended by the joint manufacturer. If this information is unobtainable, the effective area shall be computed by using the maximum inside diameter of the expansion-joint bellows.)... 

Chemical-plant exchangers requiring expansion joints most commonly have used the flanged-and-flued-head type. There is a trend toward more common use of the light-wall-bellows type. 

Figure 31.4(b) Rubber or metallic expansion bellows for enclosure jointing and end terminations (Courtesy Best Crompton)... 

Expansion joint bellows Exhaust supports Bearing support Bearing ease eover Shaft Disk... 

If possible, eliminate inherently weak equipment like sight glasses, hoses, rotameters, bellows, expansion joints, and most plastic equipment. The spare parts consumption from the shop and warehouse will indicate what is wearing out. 

At the Flixborough plant there were six reactors in series. Each reactor was slightly lower than the one before so that the liquid in them flowed by gravity from No. 1 down to No. 6 through short 28-in.-diameter connecting pipes (Figure 2-5). To allow for expansion, each 28-in. pipe contained a bellows (expansion joint). 

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