Norbar Case Study
Tanks project in Northern WA
Overview
Bolted tanks provide many benefits ranging from easier transportation of the individual sections, fast assembly, normally pre-finished with corrosion protection and typically easier maintenance. However, these bolted tanks are prone to leaks and failures if the bolt tension is not correctly controlled during installation. It is for this reason our team were engaged to be part of the tank construction project near Port Hedland WA.
The customer had a requirement to tighten these critical fasteners to specific kN bolt loads depending on each joint’s geometry. In total our team ultrasonically tightened 18 tanks with a total of 19,061 bolts ranging from M16 to M42. The required bolt load varied as did the bolt material including property classes Gr 8.8, Gr 10.9 and Gr 12.9.
Our experienced personnel, along with our ultrasonic technology, was used as it is the most accurate method to measure bolt tension in the field and we have been mastering this skill for over 32 years.
As the bolt is tightened the velocity of sound reduces and fastener will elongate. The change in properties of the bolt before and after preload paired with the bolt geometry, is used to accurately determine the amount of tension within the installed bolt.
Norbar Technical Services in conjunction with Boltstress Ultrasonics are an industry leader in provision of services for critical bolt tensioning for a variety of mining and processing equipment including bolted tanks.
The Technology
The Boltstress bolt tension monitor uses time-of flight (TOF) to precisely determine bolt tension. An ultrasonic signal is sent down one end of the fastener and the time it takes to return to the transducer is measured. This measurement is recorded as a reference measurement (unloaded fastener length).
Our Method
- A calibration procedure was carried out on a sample of each new batch of bolts and different bolt size to ensure that all relevant materials, tooling and equipment complied with the customers ITP & QA documentation.
- Our team recorded an ultrasonic baseline (loose) reading for each fastener as it was installed.
- The fasteners were lubricated as per the tightening procedure with Molykote.
- Tightening was carried out in stages, firstly to 50% where an ultrasonic measurement was recorded and then 100% of our target where the final ultrasonic measurement was recorded.
- All data was saved and reports generated.
Proven Results
Hydrostatic testing was carried out post tensioning and all 18 tanks passed with no
leaks or bolt failures. Controlled bolting using ultrasonic measurement far exceeds relying on torque tightening as seen from the below sample results from this project.
Time Saving
Our experienced personnel efficiently carried out this work whilst maintaining safe work practices with zero incidents or injuries.
Precision Measurement
The use of ultrasonic bolt tension measurements began during the Apollo Space Missions. Scientists discovered that as well as bolt material stretching when tightened the velocity of sound also reduced by a factor 3x greater. Consequently, the definition and accuracy are intrinsically 3 x more accurate than any mechanical method.
Data Capture
All data is recorded and saved, reports are generated and provided. This data can also be used for future re-monitoring to ensure long term reliability
Learn more about our torque tools and other products:
Hand Torque Tools
Powered Torque Equipment
Torque Measurement
