Hydraulic nuts speed gas turbine assembly

Hydra-Tight Ltd. has developed a new generation of high-temperature hydraulic nuts, which are now being used by ABB for its GT11N2 design, which is a gas turbine rated at 110 MW. The outside components and casing operate at 340 C. These engines use 300 nuts each and are fitted to the compressor, turbine and combustion sections, as well as bearing housings, foundation bolting, internal vane carriers, intake and exhaust sections. The first installation, with three GT11N2 units, is fully operational in Kentucky, USA.

ABB reports it took only two and one-half hours to fit 78 hydraulic nuts, establishing the correct load and uniformity, then pressurizing 20 at a time and checking each bolt for adjustments. For other gas turbines, ABB allows seven days for this procedure.

Hydra-Tight spent three years developing a range of high-temperature hydraulic nuts, capable of sustained use up to 450 C. This has now been pushed up to 600 C. Hydra-Tight reports that the fundamental problem has been the serviceability of the hydraulic seal over long periods at such high temperatures.

The answer was found in a specially developed metallic seal insert. The nuts are integral load locking, with a threaded collar on the nut body.