The plant, a fossil-power combined cycle unit located in Ontario, Canada, had two main steam isolation parallel slide gate valves (PSG’s) installed in HP steam – main steam stop applications.
The design pressure and temperature for the application are 2350 psig @ 1050°F (162 bar @ 566°C). However, the plant was experiencing severe leakage when the valves were required to isolate.
From initial plant start-up, the frequency of valve maintenance of up to twice per year per valve. The cost of $40,000 per repair was a particular concern for the plant.
These repairs were strictly limited to disassembly, cleaning and visual inspection, grinding the seats and discs and reassembly.
Well before their expectations they were faced with having to replace valve seat rings and discs. They therefore decided to look at their alternatives for an upcoming outage.
Zero-leakage
The plant found a solution by installing two 12″ 2500# C12A ValvTechnologies IsoTech® parallel slide gate valves during their spring 2014 outage. The IsoTech® valve was the perfect remedy, as it utilizes a RiTech™ 31 chrome carbide hardcoating on the disc and seats, providing a more robust, stable sealing surface at elevated temperatures.
The IsoTech® valve is a through-conduit, position-seated design, which protects the valve seats from the flow stream, resulting in a valve that provides zero-leakage and requires zero maintenance, according to the manufacturer.
ValvTechnologies was so confident in this valve's ability to withstand demands of steam isolation that they backed the valve with a four year performance warranty.
Zero maintenance
To date, the valves have been installed and in-service for over two years and have experienced over 270 cycles with zero maintenance required. The valve's ability to provide zero-leakage has resulted in drastically reduced downtime, which combined with the maintenance cost savings, has presented a two-year return on investment (ROI) on the original purchase/installation cost.
