As natural gas use continues to increase in the U.S. and throughout the world, new markets, technologies and infrastructure have enabled companies to capitalize on the advantages delivered by this non-toxic, non-corrosive and relatively clean-burning fossil fuel.
With the increased focus on the benefits of LNG, however, global regulatory bodies and environmentalist groups are also increasingly focused on the impact of natural gas extraction and utilization. The hazardous effects of fugitive methane emissions are an ongoing source of scrutiny, with LNG producers and standards committees both acutely aware of the importance of mitigating the associated risks.
The United States Environmental Protection Agency has likewise…show more content… Unlike on/off valves, check valves are flow sensitive and rely on the line fluid to open and close. Rather than offering emergency shutoff or complete flow control, check valves are intended only to prevent reverse flow and the resultant damage to piping systems. Because of this, seat leakage rates for check valves differ from those imposed on other valve types, and should be evaluated within the appropriate constraints.
The industry has a large number of leak rate standards available (API-598, API-6D, MSS, BS6364, Shell MESC SPE 77/300, ISO 5208, ANSI to name a few), and there is confusion in the industry today about which requirements are the most appropriate to impose on check valves. This article will review the valve industry seat leak rate standards, the purpose of each standard, and ultimately how they relate to check valve selection and specifications. Furthermore, we will examine the purpose and operation of check valves within LNG systems and discuss why ultra-low leak rates are generally not appropriate for check valves.
Leak Rate Specifications: Purpose and Practicality
The daily demands placed on check valves, including their constant exposure to fluid mediums, make them highly-susceptible to wear and other operational challenges like sticking, jamming and