ABSTRACT

When we come back from lunch we find our boss's boss on the job site, reviewing our data. He wants to see how we managed to measure the tension or preload in these bolts, so

Flanges adjacent to rotating equipment

Wall All Sch 40 or Over 40 through thickness below Sch 80

Line flanges

All sizes

All thicknesses

0.005 in./in. of contact diameter

we plug in our ultrasonic instrument and remeasure the preload in bolt number 1, the first bolt we tightened to a preload of 9600 lb. To our embarrassment we find only 900 lb of tension in that bolt. And we find a wide range of residual preloads in the other 15 bolts. We think that our instrument is misbehaving, but the boss disagrees. He gives us a lecture on bolt relaxation, which some people call "torque loss." Here's what he says.