Challenge: The old method of bolting was difficult, time consuming, and preload accuracy was questionable. A combination of specially fabricated components and hydraulic rams were used to provide the power to turn the large diameter nuts. Manipulation of a very heavy 50 ton ram, „dead man“, and wrench were required.
The „dead man“ weighed about 150 lbs., the wrench about 250 lbs. Three workers were required for the procedure. There is potential for back strain injuries, pinch point injuries, and dropping of heavy components. Blocks were welded to the lower nuts to keep them from turning.
Installation required 150 to 200 man hours and standard removal required 150 to 250 man hours. The last removal required 260 man hours due to breakage of tools, galling of the base metal on the flange, and a broken and bent hydraulic cylinder system.
Solution: (18) 6-3/16″ nut style multi-jackbolt tensioners (MJTs), (18) 6-3/16″ flexnuts. Superbolt JL-M (moly) lubricant was utilized to keep jackbolt torque to a low 156 ft-lbs.
Installation was completed in about 2-1/2 hours (about 8 man-hours) utilizing 1/2″ air impacts and hand torque wrenches. Bolt stretch was confirmed with a dial indicator. Jackbolt heads were drilled for safety wire for additional precaution.
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