Multi-jackbolt Tensioner - Joint Integrity

Joint Integrity

• Thread galling and seizing is significantly reduced because mating bolts/studs are loaded in pure tension without twisting.
• In many applications, elasticity in a bolt significantly helps to keep a joint held together. Tests have shown turbine-type MJTs increase the elasticity of the average bolting system by the equivalent of four stud diameters, and nut-type MJTs increase the elasticity by 4 to 12 diameter equivalents, which would triple or quadruple the elasticity of the bolting system. In other words, MJTs increase elasticity by adding up to 2 to 4 equivalent bolt effective lengths. This is particularly advantageous in high-temperature bolting applications where bolts are subject to creep, because elastic bolting systems will take longer to reach a given relaxation stress than in a rigid system. Elastic bolting systems can also improve the integrity of gasketed joints by compensating for temperature changes, joint movement and changes in internal pressure.
• Stress relief—Most bolts fail at the bottom of the nut in the first two or three threads. Hoop stresses on the nut in MJTs cause an increase in diameter at the bottom and decrease at the top, distributing thread stress more evenly and reducing the likelihood the stud or bolt will fail.