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Valve Techbook 2017

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Page 30 of 35 | September 2017 | 29 VALVE TECHBOOK: CASE STUDIES Since 1999, Vanessa TOVs have been used on molecular sieve offshore operations in Malaysia. Some of the Vanessa valves replaced rising stem ball valves for a CO2 membrane system that featured a two- to four-hour open/close cycle; those valves are still in operation. Hundreds of rising stem ball valves have also been replaced in gas plants in solid bed molecular sieve applications, and there are many more cases of TOV evaluation and adoption in response to the recommendations by major molecular sieve process licensors. Conclusion In offshore applications, 100% metal-constructed TOVs such as Vanessa represent a robust fire-safe valve for services (e.g., crude oil) containing debris and other solid particles. Furthermore, TOVs are valves that are not affected in terms of performance by piping loads that may distort the valve body compared to sealing plane/trim. This differs from comparable ball valves, where two seating planes will become misaligned with each other, thus increasing the friction with the ball in between and, therefore, increasing operating torque. Such benefit is even more significant in emergen- cy-type of operations. Non-rubbing in a triple offset valve also means lower wear of sealing components. This is how a TOV fundamentally differs from high-performance but- terfly valves (typically featuring rubbing for approx- imately 20 percent of rotation) and it is an extremely crucial feature whenever the valve is used in process applications entailing a high number of cycles, includ- ing those found offshore. Compared to gate and ball valves, the savings in terms of weight and footprint reduction are massive. Furthermore, TOVs are easier to operate than gate valves even with a manual gear because of a low running torque and no need for extra safety factors during actuator sizing. TOVs also have the ability to open against full pressure without any need for upstream depressurization, which is another collateral cost-reducing benefit compared with ball valves that may require a bypass line instead. n Marco Ferrara and Sergio Casaroli are Vanessa Triple Offset Valve subject matter experts For Emerson Automation Solutions.

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