Importance of Bolt Torque
Gaskets will over their design life relax leading to a reduction in energy required to form a seal, which is considered in the design Viking Johnson mechanical couplings and proven with long term testing that predicts the seal performance at the end of the 50-year design life. In addition, Viking Johnson has established a correlation between bolt diameter / torque and the gasket pressure, meaning if the correct bolt torque is applied at initial bolt up the “gasket pressure” is well above the design pressure thereby allowing for degradation over the 50-year design life expectancy.
If bolt torque at installation is less than recommended, then relaxation will follow similar a degradation pattern over the coupling life and while it may not leak initially with a lower initial gasket pressure than required at some point in the future it may drop below that required to accommodate the design pressure in the pipeline leading to a leak.
All Viking Johnson products are supplied with a product label and installation instructions that clearly define the maximum and minimum bolt torque that must be applied to ALL BOLTS in the fitting. Correct fitment of a product must always be checked using a calibrated torque wrench, which should register at the very least the required minimum value stated on all bolts without any movement of the nut. If this occurs, continue round the product again until the torque required is achieved.
NOTE: so long as the correct bolt torque is applied and validated with a calibrated toque wrench there is no need to come back later to tighten the bolts again. Simply tighten, check and forget.
Viking Johnson always provides a maximum and minimum bolt torque for each product, and we recommend that at initial bolt up the higher value is used to verify correct installation. In the event the installation is checked within say 24 hours, while some bolt relaxation will occur it will still be within the tolerance and hence pass the inspection.