Tightening a structural-steel bolt, tiny spurts of orange silicone spread out from a washer beneath the nut. Satisfied, the ironworker moves on to the next bolt.
There is nothing new about direct tension indicators (DTI), one of the methods recognized by the American Institute of Steel Construction for judging structural-steel bolt connections as well as turn-of-nut calibrated wrenches and twist-off bolts.
Depressions on the DTI washer flatten when sufficient tension is reached on a bolt, and can be checked with a small feeler gauge. But eight years ago, Applied Bolting, Bellows Falls, Vt., added that telltale glimpse of orange.
The company’s Squirter DTI features droplets of orange silicone in the washer's depressions. Orange dots are squeezed out at the washer's lip when the bolt is sufficiently tensioned. A feeler gauge can still be used to check, but “you can see right away if the Squirter has discharged,” says Bill Paolucci, project engineer for Shurtleff & Andrews, Salt Lake City, who is using the bolts in the structural steel of the $4.1-billion Prairie State Energy Campus in Washington County, Ill. “I've seen huge savings in not having to retension loose bolts.” The silicone falls away from the bolt in a matter of days.
Squirter DTIs are used most in the power and heavy industry sectors. “We've used the Squirters recently on a few projects: the pipe racks for Total's refinery in Port Arthur, Texas, and for Marathon's Detroit HOUP [Heavy Oil Upgrade Project],” says David Stayshich, corporate construction engineering director for Fluor, Sugar Land, Texas. “The ironworkers really bought into it, and it reduced the time we spent climbing and measuring.”
There are upfront costs with the technology—about 70¢ per bolt. “For 10,000 bolts, that adds up,” says Chris Curven, field bolting assistant with Applied Bolting. Fluor's Stayshich says that, after taking into account time and other factors, his company “came up with savings of about a buck a bolt.”
In an effort to promote its products, Applied Bolting's field technicians have inadvertently moved into ironworker education. “They really dispelled some of the myths about bolting,” says Stayshich. “There is so much talk about torque, but it's really about tension. Chris Curven would come to the site and give demonstrations on the differences.”
Curven and his three fellow field technicians teach many ironworkers, engineers and inspectors the proper use of the Squirter DTIs, and they make house calls. “We work closely with the ironworkers union, we go visit jobsites and give demos on torque versus tension and what can go wrong with bolts,” Curven says.
“The silicone isn't necessary for the DTI—that's just marketing,” notes Charlie Carter, VP and chief structural engineer for the AISC. “Whatever the method, everyone is trying to get to the same level of tension. All the accepted methods can be used properly or improperly.”
Still, Carter says it's possible to over-rely on torque when checking bolted connections in structural steel. “Torque is just a frictional condition on the bolt assembly. It varies on the condition of the washer, bolt and the materials involved,” he says.
Despite advising multiple jobsites every month, Curven and his co-workers can’t give their tension-versus-torque lecture everywhere. In recent months, Applied Bolting has been posting video tutorials for proper DTI usage on its website. “After watching a how-to video for a bicycle shop, we knew could do this,” Curven says.
The company stamps Quick Response codes for the video website on its bolt cans. Users can scan it with a smart phone and learn on the jobsite. “People can get online, see the videos on torque and tension, see the proper use,” says Curven. “It empowers them to do the job.”
