PAGE 3• ENTIRE ARTICLE IN PDF FORMAT (985 kb) SPACE RESTRICTIONS With the wide range of materials available and the flexible nature of their design, MJTs have been used in many space-restricted areas. Special MJT’s have been designed for applications where severe costs would have occurred if the traditional methods were employed. For example, several cases have occurred where an end user received a pressure vessel or heat exchanger where it was made incorrectly and the flange bolt circle was too tight to use a socket on the existing nuts. In a recent case, a refinery had rigging crews on site to install a new heat exchanger. The maintenance crew had to make a decision whether to call in an on-site machining crew or come up with an alternative. Due to the small O.D. requirements on the nuts, ‘turbine’ style MJTs with a 1.5x thread diameter O.D. were fabricated and on-site in two days. This saved the company tens of thousands of dollars in losses, as the rigging crews were able to keep working, not counting the savings in on-site machine costs.
In some cases, fasteners are located inside or around a piece of equipment that is very difficult to access, especially with the large wrenches that are most commonly used. For instance, some of the frame bolting on reciprocating compressors is located inside the inspection door of the doghouse. The ease of using a hand torque wrench makes reaching these areas easy (Fig 11).
Since only hand
tools are required and since MJT’s tighten studs in pure
tension, there are cost savings vs. other methods. For example,
the piston end nut on reciprocating compressors generally requires
clamping of the piston rod to torque and untorque the nut if work
on the piston is required (Fig. 12a). This can severely damage
the rod surface, which must slide through packing material that
could also be damaged. In many cases, the nut has to be machined
away to get the piston off. In one extreme case, a liquid gas company Another time saver is the ability to adjust the bolt prestress in a short time. For instance, extensiometers are commonly used to check bolt tension. In the instance where stud heating is the method, one must apply heat, let the unit cool, check the stretch and if the value is off, the whole process must be repeated. With Multi-Jackbolt Tensioners one can dial in a new torque setting and bring up the value in a matter of minutes. As an example, it took one turbine manufacturer three days to bolt up a unit for hydro testing with stud heaters and checking with extensiometers. This was reduced to one day with MJT’s and extensiometers.
Many bolting
applications in the petrochemical industry wind up having the fasteners
upside down on part of the equipment. It is very difficult work
to lift heavy tools overhead and sometimes the work even has to
be done while laying on ones back.
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Some
OEM’s are looking to decrease the overall size of their machinery
housings because the stud to stud spacing can be tighter with MJT’s
(FIG. 10).
EASE
OF USE 
had
a remote plant site and every time they did piston work they loaded
the whole piston and rod onto a truck and shipped it to a facility
to untorque and retorque the nuts. By utilizing the Multi-Jackbolt
concept, they were able to do the job on a workbench, saving shipping
cost and valuable downtime (Fig. 12b). 
Large
preloads are easily achievable with hand tools only and this is
often a solution to big problems. For example, a large petrochemical
producer was able to apply high loads to the anchorbolts on reciprocating
compressors and in this case was able to stop movement of the compressor
avoiding the need to regrout them. According to the end user, the
estimated cost savings were in the hundreds of thousands of dollars.
Figure
13 shows a preheater being tightened with MJT’s with two
men. Small, light air tools were used except for the final pass
which requires a light hand torque wrench. The job was performed
in a tenth of the time and the workers were very happy to avoid
the discomfort of using the old, heavy tools that were previously
required.