When you are Australia’s largest gas turbine combined cycle power station, with a nominal capacity of 630 MWs, station design errors don’t come cheap.
In fact, research has shown that mean direct costs for design errors in construction projects amount to 6.85 percent of the contract value, with mean indirect costs sitting at 7.36 percent.
Darling Downs Power Station (DDPS) learned this the hard way when a design error crept into the construction phase, negatively impacting gas turbine operation for several years and necessitating multiple valve replacements.
The station, commissioned in November 2010, first noticed an issue in September 2011 when GT1 fuel gas valves failed leak test during start up, after combustion linear change.
In March and April 2012 the problem repeated, this time with both GT2/3 fuel gas valves.
The problem was temporarily remediated by stroking the valves and recalibrating them. However, in 2015, the station moved from baseload to cycling operations, meaning that GTs had to be stopped and started frequently.
Stroking and recalibration was found to be no longer effective and valve replacement was the only viable solution. The system configuration of the valves is such that it was difficult to identify which valve was leaking, meaning that an entire set of four valves required replacement.
With turnaround times for valve overhaul averaging at three months, the firm was also forced to procure additional sets of valves to meet operational requirements.
Over time, turbine start reliability and availability significantly decreased, while maintenance costs rocketed.
This issue persisted with turbines continuing to fail leak test for almost four years before the error was correctly traced back to an issue with the design phase of the plant.
Presenting at the Gas Turbines Conference, Origin’s Ashwin Shinde will share further details of this case study, including the simple problem and solution that, if detected earlier, could have saved the firm considerable dollar amounts worth of unnecessary maintenance costs and allowed for significantly smoother operations.