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Valve Techbook 2017

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28 | September 2017 | VALVE TECHBOOK: CASE STUDIES for implementing a safety integrity system (SIS). The design purpose of an SIS is to protect personnel, equipment and the environment by mitigating the likelihood and severity of the potential risk. In a mod- ern industrial facility, the SIS is designed to prevent or reduce hazardous events by taking the process to a safe state when predetermined conditions are violated. SIS is commonly an emergency shutdown sys- tem (ESD), high integrity pressure protection system (HIPPS), safety interlock or safety shutdown system. SIS typically includes the design and implementation of a variety of shutdown and/or blowdown valves. Based on the probability of failure, there are four safety integrated level (SIL) classes going from SIL 0 (none, lowest risk) to SIL 4 (highest risk). Higher reliability/plant availability is achieved by using proper safety components (design), installing such components according to manufacturer's guide- lines and testing them both at initial startup, as well as at specified intervals or after any modification. This is why an inherently safer SIL 3 Vanessa TOV, coupled with appropriate automation and controls, can contribute to delivering an overall safer system. Vanessa TOVs feature a non-symmetric design which implies that, depending on installation direc- tion, the valve can fulfill a safety function facilitated by the flow (open to close) or pressure (close to open). This is possible in view of extremely low running torque values due to the non-rubbing rotation and the asymmetric trim design. Case Studies Early Vanessa TOV adoption in the Norwegian North Sea For most offshore platforms in operation in the Norwegian North Sea, ball and gate valves had been considered by a major oil and gas company the stan- dard for most of their flow isolation applications for decades. However, in 1994, this oil and gas customer chose to test Vanessa TOVs during a yearly routine production shutdown as a means of exploring a lighter, cheaper and potentially more reliable solution. When the end user overhauled the crude oil pump, the Vanessa valves—which were operated by an actua- tor--were also deployed to manage the isolation of the pumps from the main oil header under full pressure. The test was so successful that these Vanessa valves were kept in service. Since then, Vanessa TOVs have been installed in numerous offshore applications around the world. Further developments in offshore Brazil Reducing weight while also maximizing space is a constant quest for EPCs and end users who are building platforms and FPSOs. To address these critical needs, a major oil and gas company oper- ating in fields off the coast of Brazil replaced all heavy top-side ball and high-performance butterfly valves with Vanessa triple offset valves on two of their FPSOs. This type of valve had been installed previously on the cargo tank piping system on the main deck and in the pump room, and proved diffi- cult to operate and disappointing in terms of long- term performance. As an alternative, Vanessa valves were adopted in these areas instead to address both isolation and ESD functions with a single prod- uct. Several years later, these Vanessa triple offset valves were in operation. Subsequently, because of the success of the first installation, this customer also chose Vanessa valves for installation on three additional FPSOs. New TOV applications in E&P In recent years, with the newest developments of FLNG (including floating storage regasification units or FSRUs) technology has leaped forward, and so has the TOV range of applications. While util- ities (including the ones used on topsides and float- ing units) have been easily handled by Vanessa valves for many years, there have been new groundbreaking adoptions within processing areas. To name a few, TOVs have been specified in separators (used to sep- arate oil from gas and other debris including sand), in vapor recovery units (where waste gas in a FLNG is recovered instead of being flared), HIPPS and as isolation valves in gas flaring systems. Furthermore, another important process in which TOV adoption is gaining traction is the dehydration and purification of gas through molecular sieving. Used in both gas FPSO and FLNG applications, molecular sieving has historically been handled by heavy rising stem ball valves. These valves on larger sizes and pressure classes are extremely heavy and have a large footprint, generating a number of direct (material use) and indirect (instal - lation and increased floating vessel weight) costs that engineers must account for during frontend engineering design (FEED) project phases. The tilting mechanism itself, a variant on a standard quarter-turn ball valve, is subject to wear and can degenerate over time. Although the valve sealing elements may not involve rubbing capabilities, fric- tion is transferred to both the shaft cam (towards core pins) and the S-shaped pin slot. This valve design requires specialized maintenance, includ- ing the use of costly spare parts, significant time and effort.

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