Couplings bolting

Radial fit bolts are a special feature used in all types of turbomachinery. They are of increasing importance to users that are both reliability-minded and concerned about life-cycle costs. The radial fit coupling bolt was originally developed for coupling steam turbine shafts by Pilgrim International in Oldham, UK. It is equally useful to coupling other equipment, including, of course, hot gas expander shafts. 

In the chambers, crevice corrosion, galvanic corrosion, and general corrosion of the aluminum ladder were observed (Fig. 5.3). Crevice corrosion was also observed on couplings, bolts, and valves. The aluminum steps in some valve chambers were attacked by chlorides/phosphates. 

Yokes. The need to couple the end cover to the body of the vessel may be avoided if yokes, external to the vessel, are used to resist the load arising from the internal pressure acting on the closures. However the necessity to move the vessel out of the yoke and remove one of the closures to gain access to the inside of the vessel limits its use for chemical process equipment. Yokes may be pinned, welded, bolted, or wire wound. Both the vessel and yoke maybe wire wound (136). 

For very low pressures, beaded-end pipe equipped with single-bolt band-type couplings is available. 

Bolted joints are friendlier than quick-release couplings. The former are usually dismantled by a fitter after issue of a permit to work. One person prepares the equipment and another person opens it up the issue of the permit provides an opportunity to check that the correct precautions have been taken. In addition, if the joints are unbolted correctly, any trapped pressure is immediately apparent and the joint can be remade or the pressure allowed to blow off. In contrast, many accidents have occurred because operators opened up equipment which was under pressure, without independent consideration of the hazards, using quick-release couphngs. There are, however, designs of quick-release couphngs which give the operator a second chance. 

The load is now transmitted through ordinary couplings, one half mounted on the motor shaft and the other half on the driven shaft. They are bolted together with a rubber pad between the two. The motor and the driven machine are mounted on a common bed (Figure 8.2). They are now able to provide margin for misalignment of the two shaft ends and thus extend more flexibility. 

A number of turbomaehinery users have speeified Pilgrim s CHAT (Coupling Hole Alignment Tool, Figure 6-33), in addition to radial fit bolts. CHAT is a further development of the radial fit bolt, designed to aehieve eoupling hole alignment in the least amount of time and to a toleranee that permits radial bolt assembly. The CHAT tool is based on the same prineiple as the bolt and also uses hydraulie power. 

Figure 6-33. The coupling hole alignment tool (CHAT) has a longitudinally split sleeve for greater expansion. Like the radial fit bolt, it is hydraulically tensioned, but there is no hydraulic separation of core and sleeve.

A hot alignment check is performed exactly like an ambient alignment check with the added safety precautions required for hot machinery. The accuracy of a hot alignment check depends on how soon after shutdown dial indicator readings can be taken. Readings may be taken within a few minutes with the use of shaft-mounted brackets that span a flexible coupling. To speed up the process, assemble the brackets to the fullest extent possible prior to shutdown so that they need only be bolted to the shafts once the machine stops rotating. 

With the shear-type coupling, the elastomeric element may be clamped or bonded in place, or fitted securely to the hubs. The compression-type couplings may be fitted with projecting pins, bolts, or lugs to connect the components. Polyurethane, rubber, neoprene, or cloth and fiber materials are used in the manufacture of these elements. 

The specific installation procedure is dependent on the type and mounting configuration of the coupling. However, common elements of all coupling installations include spacing, bolting, lubrication, and the use of matching parts. The sections to follow discuss these installation elements. 

Rigid couplings The mechanical components of rigid couplings (e.g., hubs, bolts, compression sleeves and halves, keyways, and keys) should be visually inspected for cracks, breaks, physical damage, wear, and/or fatigue. Any component having any of these conditions should be replaced. 

Fig. 19.32 Bolt and wire type atmospheric galvanic couple test specimen...

Looks like you ll be busy for a while, I say, as the couple pay for a ram s head pendant for him and a lightning-bolt brooch for her, and their place is taken by a round-eyed girl still clutching the consent form for ear-piercing and fingering her own bright pink lobes with awe. She starts to inspect the stars. 

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