1.1 These engines, with a nominal capacity of 8.3 MW, had been derated to 4.0 MW (and run for minimal periods averaging 700 hours/annum) for many years, due to a combination of visible vibration and bedplate distortion, and ever-changing web deflections. When the deflections exceeded 600 μm (compared with a normal recommendation of 1/10,000 x stroke of 1600mm, or 160 μm) the engines were shut down. The changing web deflections were caused by oil penetration into the grout and concrete around the middle part of the bedplate, combined with corrosion of the soleplates at the coupling and non-drive ends, which had forced the bedplate upwards.
1.2 In 1986 a consultant had been engaged by the engine manufacturer, to investigate the condition of the foundation, and the fastening system, i.e. grout, baseplates, and anchor bolts. The consultants identified correctly one of the major causes of the problem – oil penetration – but missed the question of corrosion of the bases, and the design of those bases. They also missed the opportunity to recommend the use of an oil and corrosion resistant epoxy grout. The proposed repair would have been very difficult, since it involved raising the engine by 800 mm on large hydraulic jacks, and the removal of approximately 24 m3 of concrete. A system of mechanical restraints to counter the lateral forces was also proposed. This repair was, not surprisingly, never attempted.
1.3 Alphatec Engineering offered a complete and comprehensive repair of the foundation by the pressure injection of epoxy adhesives and high tensile strength steel reinforcement, removal of the existing grout and engine support systems, support of the engine in its existing position, realignment of the engine with hydraulically adjustable soleplates, and placement of epoxy grout to properly support the engine bedplate in both vertical and lateral planes.
1.4 The alignment of the engines is now close to original specifications, and the epoxy grout can be expected to maintain the position of the bedplate, and thus the alignment, for 15 to 20 years.
1.5 The concrete foundation, although possibly undersized, appears to be functioning reasonably well, but will now be subject to more stress than in the past. Yearly inspections should be undertaken to ensure continued vibration damping performance, and maintenance of integrity.
1.6 The engines have now been uprated to 7.5 MW, and are being operated for longer periods, possibly reaching 2,000 hours average in 2003