PAGE 4• ENTIRE ARTICLE IN PDF FORMAT (985 kb) TIME SAVINGS A very common comment on Multi-Jackbolt Tensioners is that it must take a long time to torque up all of the jackbolts, but, in fact, MJT’s have reduced installation times compared to other bolting methods. As mentioned in a previous example, adjustments to the preload can be made quickly by dialing in a new torque value and torquing the jackbolts to the new value. The use of air tools also greatly speeds up the tightening process. Although special air tools can be purchased to apply a very accurate torque, it has been found that with proper guidelines, standard air impact tools can do the job without the higher expense. The standard procedure calls for the use of air tools to speed up the rounds of tightening and a final pass with a calibrated hand held torque wrench.
On some flanges with concealed gaskets the speed of the system can be increased by selecting four or eight tensioners 180º apart to bring metal to metal contact of the flanges. The remaining tensioners therefore do not require additional passes just to create gasket crush. However, it should be noted that manufacturer procedures should not be superceded without consultation.
Other time factors that can be encountered are not that obvious at first glance. For instance, stud seizure into a blind hole such as in a turbine housing is a fairly common occurrence. It can sometimes take several shifts or even days to remove frozen studs that often have to be drilled or machined out on-site. Since MJT’s tighten a stud in pure tension, there is no galling or ripping of thread surfaces which can occur when applying a high torque to achieve stud tension. Therefore, once the jackbolts are unloaded in a MJT, the nut body can be removed leaving the stud as if it had been hand tight. The stud is then easily removed with nominal torque applied. In some instances time is saved because the preparation, such as with the piston rod example used earlier, is so time consuming (i.e. clamping the rod in a special jig and rigging up special tools to apply a large turning force). Additionally, valuable crane time is not wasted on time consuming bolting.
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Figure 14 shows a bank of heat exchangers in a refinery. The job required (96) 3-1/4” studs
to be tensioned to 45,000 psi bolt stress. This job previously
took 3 days to perform using the previous method of hydraulic wrenches.
Using the Multi-Jackbolt system, the only special tooling required
were low-cost in-line regulators combined with standard air impact
tools. All four exchangers were bolted up in a total of 8 hours
using two workers. 
Another
major time savings can be accomplished by using multiple workers
to tighten several MJT’s simultaneously. Since only hand
tools are used, the tooling required is easily obtainable and economical,
especially in emergency situations. Figure 15 shows a job where
(18) 6-3/16” tensioners were tensioned using four workers
90º apart from each other in a very restricted space. Extensiometers
were used to check stud stretch and, including doing calculations
and taking breaks, the entire procedure was performed in 2-1/2
hours. The previous method using a combination of fabricated components
and hydraulic rams was estimated to have taken 150-200 man hours.
In a drastic example, for instance on a turbine casing, as many
workers as can fit next to each other can be working on the unit.