Valve sealing grade standards

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1 Classification standards for valve sealing grades in China: At present, the two main classification standards for valve sealing grades commonly used in China are as follows. 1.1 Classification of valve sealing grades according to Chinese standards – Standard GB/T 13927 \"Pressure testing of industrial valves\". 1.2 Classification of valve sealing grades according to Chinese mechanical industry standards The mechanical industry standard JB/T 9092 \"Inspection and testing of valves\". 2 International classification standards for valve sealing grades At present, the five most commonly used international classification standards for valve sealing grades are as follows. 2.1 Classification of valve sealing grades in the former Soviet Union: To select products based on the degree of sealing of valves and their intended uses, valves were classified according to their sealing performance. 2.2 Classification of valve sealing grades by the International Organization for Standardization The International Organization for Standardization standard ISO 5208, \"Pressure testing of industrial valves – Metal valves\". 2.3 Classification of valve sealing ratings by the American Petroleum Institute (API). API Standard API 598–2004, \"Inspection and Testing of Valves\". 2.4 Classification of valve sealing grades by the Mechanical Society of the Valve and Pipe Industry (MSS) in the United States: The MSS standard \"Pressure Testing of Steel Valves\" MSS SP61 specifies the following requirements regarding allowable valve leakage: (1) When one of the sealing surfaces in the valve seal assembly is made of plastic or rubber, there shall be no visible leakage during the duration of the sealing test. (2) The maximum allowable leakage per side when closed shall be: 0.4 milliliters per hour per millimeter of nominal size (DN) for liquids ； The gas flow rate is 120 milliliters per hour per millimeter of nominal diameter (DN). (3) The allowable leakage amount of the check valve can be increased by 4 times. 2.5 Classification of control valve seal ratings according to American ** standards/ANSI/FCI standards. The American ** standard is ANSI/FCI 70-2 (ASME B16.104), \"Leakage of Control Valve Seats\". 2.6 Classification of valve sealing classes according to EU standards European standard EN 12266—1 \"Testing of industrial valves\" Part 1. Pressure testing, test methods, and acceptance criteria – mandatory requirements. 3 Selection of Valve Sealing Grades 3.1 Selection of Valve Sealing Grades in China (1) The standard GB/T 13927 «Pressure Testing of Industrial Valves», which came into effect on July 1, 2009, was formulated with reference to the European standard ISO 5208. Suitable for the inspection and pressure testing of industrial metal valves, including gate valves, globe valves, check valves, plug valves, ball valves, and butterfly valves. The classification of seal tests and the maximum allowable leakage amount are the same as those specified in ISO 5208. This standard is a revision of GB/T13927 (General Pressure Testing for Valves). Compared with GB/T13927, six new grades, namely AA, CC, E, EE, F, and G, have been added. The new standard specifies that \"the selection of the leakage level should be the most stringent one specified in the relevant valve product standards or required in the purchase contract.\" Unless otherwise specified in the product standards or order contracts, non-metallic elastic-sealed valves shall meet Class A requirements, while metal-sealed valve assemblies shall meet Class D requirements⋯ ”Generally, grade D is suitable for ordinary valves, while valves that are more critical should use a leakage rating higher than grade D. (2) The mechanical industry standard JB/T 9092 \"Inspection and Testing of Valves\" is a revision of ZB J16006. The maximum allowable leakage amount for the seal test is established with reference to the American Petroleum Institute standard API 598--1996. Suitable for the inspection and pressure testing of valves used in the petroleum industry, including gate valves, globe valves, plug valves, ball valves, check valves, and butterfly valves with metal seal pairs, elastic seal pairs, and non-metallic seal pairs (such as ceramics). Currently, GB/T 9092 is under revision. (3) In engineering design, it should be noted that: **Standard GB/T 19672 (Technical Requirements for Pipeline Valves) was formulated with reference to the European standard ISO 14313 and the American Petroleum Institute standard API 6D. **The standard GB/T 20173 \"Pipes and valves for pipeline transportation systems in the oil and gas industry\" was formulated with reference to the European standard ISO 14313. Both standards GB/T 19672 and GB/T 20173 specify acceptance criteria for valve leakage rates that are in line with the requirements of ISO 5208 grades A and D. Therefore, when higher leakage requirements than the standard are specified in the engineering design, they should be stated in the purchase contract. 3.2 Selection of valve sealing grades abroad (1) The classification of valve sealing grades used in the former Soviet Union was primarily applied in the 1950s; with the dissolution of the former Soviet Union, most countries no longer use this classification system for sealing grades, opting instead for the classification systems established by European and American standards. The sealing grade classification of the European standard EN 12266—1 complies with the provisions of the International Organization for Standardization standard ISO 5208, but it lacks the grades AA, CC, and EE. Compared to the 1999 version, ISO 5208 has added six new grades: AA, CC, E, EE, F, and G. The ISO 5208 standard provides a comparison of several sealing grades with those in the API 598 and EN 12266 standards. ④. The comparison of seal ratings for other nominal sizes can be determined by calculating the leakage rate based on the diameter. (2) The American Petroleum Institute standard API 598 is the most commonly used inspection and pressure testing standard for American-standard valves. Manufacturer standard MSSSP61 is commonly used for the inspection of steel valves in the \"fully open\" and \"fully closed\" positions, but it is not applicable to control valves. American standard valves are usually not subject to MSS SP61 testing. API 598 is applicable to the sealing performance testing of valves manufactured in accordance with the following API standards: flanged, lug-type, wafer-type, and weld-connected check valves; API 594 – metal plug valves with flanged, threaded, and weld-connected connections; API 599 – steel gate valves, globe valves, and check valves for use in the oil and gas industry, with sizes up to DN100; API 602 – corrosion-resistant bolted valve covers and gate valves with flanged and weld-connected connections; API 603 – metal ball valves with flanged, threaded, and weld-connected connections; API 608 – double-flanged, lug-type, and wafer-type butterfly valves. Note for engineering design: Compared to the 1996 version, API 598–2004 eliminates the inspection and pressure testing requirements for API 600 (steel gate valves with bolted valve covers for use in the oil and gas industry). Standard API 600/2001 (ISO 10434–1998) specifies that the sealing performance tests for valves shall be carried out in accordance with ISO 5208; however, the leakage rates specified in Tables 17 and 18 of this standard follow the requirements of API 598–1996, rather than using the sealing class classification system of ISO 5208. The API 600 standard, implemented on September 11, 2009, corrected this inconsistency in the 2001 version by specifying that the sealing performance tests for valves should be conducted in accordance with API 598, without specifying a version, which in turn conflicts with API 598–2004. Therefore, when selecting API 600 and its sealing performance testing standard API 598 in engineering design, it is essential to specify the version of the standards to ensure consistency in their provisions. (3) The American Petroleum Institute standard API 6D (ISO 14313), \"Petroleum and Natural Gas Industries – Pipeline Systems – Pipeline Valves\", specifies the acceptance criteria for valve leakage as follows: The leakage rate of soft-sealed valves and oil-sealed plug valves shall not exceed Grade A of ISO 5208 (no visible leakage allowed); the leakage rate of valves with metal seats shall not exceed Grade D of ISO 5208 (1993). However, according to the sealing test described in B.4, their leakage rate shall not be more than twice that of Grade D of ISO 5208 (1993), unless otherwise specified. ”The standard states: “Special applications may require a leakage rate lower than Class D of ISO 5208(1993).” ”Therefore, any leakage requirements in engineering design that exceed the standard should be specified in the purchase contract. Appendix B of API 6D--2008, which outlines additional test requirements, specifies the additional test requirements for valves that the manufacturer must carry out when required by the purchaser. Sealing tests are divided into low-pressure and high-pressure gas sealing tests; the high-pressure sealing test, which uses inert gases as the testing medium, will replace the liquid-based sealing tests. The sealing test should be selected based on the type, diameter, and pressure class of the valve; the provisions of ISO 5208 standard can be referred to. For valves on long-distance pipelines GAl and industrial pipelines GCl, it is recommended to use a low-pressure sealing test, which can increase the rate of qualified valves. When selecting a high-pressure sealing test, it should be noted that elastic-sealed valves may experience a decrease in their sealing performance under low-pressure conditions after undergoing such a test. The requirements for valve seal testing should be selected appropriately based on the actual operating conditions of the medium; this can effectively reduce the production costs of valves. (4) The American **Standard Institute for Instrumentation standard ANSI/FCI 70-2 (ASME B16.104) applies to the specifications for the sealing ratings of control valves. In engineering design, considerations should be given to selecting either metal elastic seals or metal seals, based on factors such as the characteristics of the medium and the frequency of valve operation. The sealing grade of the metal-sealed control valve shall be specified in the purchase contract. Based on experience, for metal-sealed control valves, the requirements for grades I, II, and III are relatively low, and they are seldom chosen in engineering design. Generally, for ordinary metal-sealed control valves, grade IV is the minimum requirement, while for more critical control valves, grades V or VI are used. For the control valve design of the flare system in an ethylene plant, metal-sealed Class IV requirements were adopted, and it has operated well. (5) Additionally, it should be noted in engineering design that API 6D specifies that the chloride content in the water used for sealing tests of austenitic stainless steel valves must not exceed 30 ug/g, while both ISO 5208 and API 598 require that the chloride content in the water used for such tests must not exceed 100 ug/g. Due to the varying requirements of different standards, it is recommended that the chloride ion content of the water used in the seal test be clearly specified in the valve purchase contract. 4 Classification standards for the sealing performance of low-leakage valves. Low-leakage valves are those that have an extremely low actual leakage rate; conventional water or air pressure sealing tests are insufficient to determine their sealing quality, and more advanced methods and instruments are required to detect any minor external leakage. This slight leakage of the valve to the external environment is known as low leakage. Currently, the three most commonly used international standards for detecting low leakage in valves are as follows: (1) U.S. Environmental Protection Agency EPA Method 21 \"Detection of Volatile Organic Compound Leaks\". (2) International Organization for Standardization ISO 15848 (Industrial valves – Procedures for measurement, testing and qualification of low leakage). (3) SHELL MESC SPE 77/312 by Shell Petroleum Company, \"Industrial Valves: Low Leakage Measurement, Classification Systems, Qualification Procedures, and Type Approval and Product Testing for On/Off and Control Valves.\" The EPA Method 21 standard in the United States specifies only the testing methods without defining any leakage levels; it is a local standard and is therefore used less frequently. Both standards, International Organization for Standardization ISO 15848 and Shell Petroleum Company’s SHELL MESC SPE 77/312, evaluate the performance of valves based on three aspects: tightness grade, durability grade, and temperature grade. The tightness grades, which relate to leaks at the seal between the valve stem and the valve body, are divided into three levels: A, B, and C. According to the ISO 15848 standard, the leakage at the valve body seal is required to be ≤50 em3/m3, while the leakage at the valve stem is calculated based on the diameter of the valve stem in both standards. ISO 15848 has the highest sealing grade at Class A, while the sealing grades of Classes B and C are in line with the SHELLMESC SPE 77/312 standard. Typically, the sealing rating of low-leakage valves is below class B, while bellows-sealed valves have a sealing rating lower than class A due to the use of metal bellows for sealing at the valve stem area. 5 Selection of low-leakage valves: Bellows-sealed valves are one type of low-leakage valve. In the past, for applications with special requirements regarding external leakage levels of valves, bellows-sealed valves were generally chosen. However, due to the high difficulty in manufacturing bellows-sealed valves and the stringent technical requirements involved, as well as the fact that the materials used for these bellows cannot yet be fully produced domestically, their cost is too high, which limits their widespread use in the petrochemical industry. Currently, as people’s awareness of safety and environmental protection continues to grow, along with increased technical cooperation abroad and the improvement of the technical capabilities of domestic valve manufacturers, domestic technicians’ understanding of low-leakage valves is also advancing, which is expanding their range of applications. If the valves used for flammable, explosive, and toxic fluids in petrochemical enterprises can meet low-leakage standards, this will undoubtedly **reduce the release of such toxic, flammable, and explosive substances within the facilities, thereby preventing accidents that could lead to fires, explosions, poisoning, and other threats to human life due to valve leaks. Low-leakage valves that meet the ISO15848 and SHELL MESC SPE 77/31 standards have a simpler structure and are easier to manufacture compared to bellows valves; their cost is approximately 10% to 20% higher than that of conventional valves. Based on the previous analysis and comparison of these two standard sealing grades, valves with a tightness grade of B generally meet the low-leakage requirements in certain special operating conditions. The required precision for manufacturing is relatively easy to achieve, and the manufacturing cost increases only slightly; as a result, such valves can replace some bellows valves. Currently, low-leakage valves are of greater practical significance for the purification systems in oil and gas fields with high hydrogen sulfide content. Since hydrogen sulfide is a highly toxic and flammable gas that is heavier than air and can accumulate in low-lying areas, inhaling certain concentrations of it can harm the body or even lead to death; therefore, stricter requirements are imposed on leaks from such natural gas purification facilities. 6 Conclusion: When selecting the sealing class and the specified allowable leakage rate, it should be noted that in high-pressure valves, leakage of the medium between the sealing surfaces can cause surface erosion. If a corrosive medium leaks, the metal at the leakage site will be corroded. As the leakage gap widens, the amount of leakage increases rapidly, eventually leading to the destruction of the valve. Therefore, for valves operating in high-pressure or corrosive media environments, higher requirements must be placed on ensuring sealing performance. In pipelines transporting flammable, explosive, and toxic substances, leakage of the medium between the valve sealing surfaces can cause personal injury, financial losses, and even accidents. Therefore, for valves used to transport flammable, explosive, and toxic media, the sealing requirements should be established appropriately based on the hazard level of the media.