TEMMCO have just completed a major overhaul of Turbine Valves,in conjuction with Siemens, on Loy Yang Power Station, Victoria.

WORKSCOPE
To remove, overhaul and re-install 4 Throttle Valves, 4 Stop Valves, 2 Reheat Stop Valves, 2 Interceptor Conrol Valves, 2 LP Bypass Stop Valves and 2 LP Bypass Control Valves and their Actuators as well as 24 Major Control and Non Return Valves critical to the efficienct running of a 500MW Turbine in a 24 day outage.

PROBLEM
These units have a history of severe seat erosion in particular the Throttle and Intercept Valves.

CONDITIONS
The unit runs some 16MPa steam pressure with temperaturs at 548°C. Due to the extreme operating environment the valve seats are manufactured from chrome moly materials with a welded insert of hard facing.

The seats have a shrink fit into the valve chest and to replace them would not only be a time consuming exercise but would cost some hundreds of thousands of dallars each.

The throttle valve seat being nearly a metre down inside the chest has a tapered landing of 45° some 50 mm long into an 80 mm radius blending into a 160 mm bore. This profile must be maintained not only for the valve seating but also to maintain a smooth and efficient steam flow and control.

The intercept seat is some 1.5 metres inside the chest with a facing of 220 mm radius blending into a 450 mm diameter bore.

SOLUTION
TEMMCO develops a process to weld buildup erosion of turbine seats and machine seat profiles including cutting a taper to a radius in one smooth operation.

OUTCOME
TEMMCO not only successfully overhauled all the valves in its work scope but also rewelded and machined 4 off Throttle Valves and 2 off Interceptor Seats within the 24-day time frame.
"At a fraction of the replacement cost".