Ultrasonic bolt stress tester

AN ON-SITE ultrasonic bolt stress testing service provided by tool maker Norbar could eliminate bolt failure and leaks before they cause costly downtime.

 Bolt testing

Bolt testing

The Norbar ultrasonic testing service is applied to Australian-engineered and manufactured Technofast EziTite hydraulic nuts, used for slewing ring bolting on stackers, reclaimers, shiploaders and cranes.

The testing is used to measure bolt tension, stress or elongation, to see if it is the correct amount, or if it needs to be replaced.

Measuring the bolt first on installation then during a service allows the exact force to be compared.

Ultrasonic waves are then bounced through the length of the bolt before and after the tensioning process, to determine the resultant elongation by measuring the bounce-back time.

When tested on a 14,000 tonne per hour iron ore loader in Western Australia, the technology accurately projected operating uptime, after testing 100% of the bolts instead of just one in 10.

Norbar national sales and regional manager Robert Bruce said avoidance of downtime was critical as well as keeping sites safe and profits flowing.

"We appreciate the elegance of Technofast's hydraulic nuts and bolts, which ensure the exact tension each time, and across multiple bolts," he said.

"Our system is focused on prevention and our end goal is to eliminate critical bolted joint failure, leaks, costly downtime, potential safety hazards and guesswork."

Bruce said the huge increase in safety and boost in production continuity on the ore loader was an outstanding outcome.

"Testing undertaken by our on-site services teams provides hard evidence of projected lifespans and safety, encompassing 100% of bolt tension levels, not estimates derived from bolt torque or tension figures," he said.

"Even with the best bolt tightening methods, bolted joints still fail so having hard evidence of how a joint performs during tightening and in service gives engineers proof and information that allows preventative actions to be implemented."

Bruce said slew ring bearings used to be serviced by two workers, with one to operate a pump and the other to tighten the bolts.

The bolts themselves were tightened using either a standard torque wrench or a generic hydraulic bolt tensioner.

He said while both methods were effective to tighten the bolts to a functional level, there was no way to accurately measure the bolt tension applied.

"This former method was both inaccurate and laborious, leading to only 10% of the bolts being checked to see if any had relaxed in service [and] consequently, the bearings experienced premature wear rates, leading to very high replacement costs and significant production losses," Bruce said.

"In addition to the efficiency losses, this method carried an increased risk of pinch points, had cramped working conditions and line-of-fire hazard potential."

Bruce said Norbar improved servicing speeds to 15 seconds per bolt.

"Some of the time saved during initial installation was a result of the experience of the technicians involved, but the biggest time saving was in the re-monitoring phase, where 10 times more work could be achieved in a quarter of the time," he said.

"Ultrasonic measurement means the technician can zero-in on problematic bolts and then make intelligent corrective actions in a targeted way for maximum efficiency."

Technofast founder and chief executive officer John Bucknell said EziTite fasteners were an advance on older and less efficient manual and hydraulic bolting technologies.

"They can be custom engineered to such outstanding standards of speed, precision, and reliability that they are used, for example, on nuclear reactors and coolant pumps, or such very high-load applications where reliability and avoidance of unnecessary downtime is critical," he said.

"They ideally complement the speed, safety, and uptime gains of the Norbar on-site services to eliminate bolt failure and leaks before they lead to extremely costly downtime."

A growing series of reports, each focused on a key discussion point for the mining sector, brought to you by the Mining Monthly Intelligence team.

A growing series of reports, each focused on a key discussion point for the mining sector, brought to you by the Mining Monthly Intelligence team.


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