Bolt tensioning system increases turbine profitability

AN Australian hydraulic bolt tensioning system is being used by some of the world’s leading electricity organisations to achieve major time and money savings when manufacturing and maintaining turbines.

Bolt tensioning system increases turbine profitability

Technofast Industries’ HydraNut is being employed in manufacturing in Japan and in maintenance in Korea, where they are cutting both downtime and labour costs on gas turbine casings.

HydraNut – which recently won an internationally coveted Platts Global Energy Award – is also being used on nuclear powered steam turbines in the US, where they reduce the time taken for regular maintenance tasks from about 20 hours to less than two hours.

The HydraNut uses precise and rapidly employed hydraulic tensioning technology to fasten and loosen bolts. The technology supersedes cumbersome and time-consuming manual methods such as heavy flogging tools or costly heat elongation.

Instead of relying on traditional wrenches or torque tools to fasten nuts with twisting forces of various degrees of accuracy, HydraNut applies hydraulic force vertically and evenly without torsion to stretch the bolt with exactly the degree of force needed for fastening in different applications. Loosening the nuts is simply a matter of releasing their lock rings and their hydraulic tension.

Use of HydraNut can cut the time taken for major jobs from days to hours – and cut routine jobs from hours to minutes.

High efficiencies have also been achieved by the use of HydraNut in Asia-Pacific applications, including their use as direct replacements for standard nuts on gas turbine half and vertical joints.

In this application, a HiTemp HydraNut system is interconnected and pressurized simultaneously, which gives an evenly applied load over the full flange and ensures that bolts are correctly loaded. Using HydraNut, the half joint bolts (20 2.25 inch and 10 2 inch) were tensioned in one hour and 12 minutes. Vertical bolt joints (42 1.75 inch and 8 2 inch) were tensioned in one hour and 50 minutes.

“The previous method of torque tightening the bolts was time-consuming and labour intensive, causing bolt, nut and flange damage, thus making subsequent removal difficult,” said Technofast Industries’ CEO John Bucknell.

Different designs of the HydraNut have been used by a leading Japanese manufacturer to speed up production of their massive stator cores for large steam turbine generator sets.

Using HydraNut, the through bolts that clamp the stator core rims together are tightened simultaneously, applying an even and accurate load across the whole assembly. This increases production capabilities for the manufacturers while enhancing the accuracy of the job and reducing hazards to workers using clumsier and slower methods.

Westinghouse Electric have taken advantage of the time savings and hazard reduction offered by Hi-Temp HydraNut, which are so called because of their patented seal design’s capability to be energized after thousands of hours at the elevated temperatures encountered on turbine casings. Ease of removal is assured by the fact that the bolts are held in tension while the lockring is unscrewed under zero load.

Judges at the 2004 Platts Global Energy Awards in New York said the HiTemp HydraNut was outstanding technology – “Technofast’s revolutionary application of high-temperature hydraulic tensioning is revolutionizing maintenance in nuclear facilities, permitting the completion of complex bolting operations in hours rather than days, saving its customers millions of dollars in downtime, and drastically cutting workers’ exposure to dangerous ionizing radiation.”

Bucknell said Technofast’s High-Temperature Hydraulic Nuts and Stud Tensioning Systems were replacing the current practices of using heat-induced elongation or torque methods to tension studbolts.

“These practices are costly not only because of the number of studbolts that have to be replaced, but also because they are very time consuming. The global nuclear industry probably has the world’s highest safety standards and it imposes a major cost to any unnecessary exposure to radiation. HydraNut also offer non-nuclear electricity companies major benefits in reducing downtime and increasing production,” he said.

HiTemp HydraNut – which can withstand temperatures up to 650 deg Celsius (1200 deg Fahrenheit) – also have widespread applications throughout other efficiency and safety-conscious industries, says Bucknell.


A growing series of reports, each focused on a key discussion point for the energy sector, brought to you by the Energy News Bulletin Intelligence team.

A growing series of reports, each focused on a key discussion point for the energy sector, brought to you by the Energy News Bulletin Intelligence team.


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