The main sealing parts of a valve include the mating surface between the opening and closing parts and the valve seat, the fit between the packing and the valve stem and packing box, and the connection between the valve body and the valve cover. The first leakage is called internal leakage, which directly affects the valve's ability to cut off the medium and the normal operation of the equipment. The leakage in the last two places is called external leakage, which means that the medium leaks from the inside of the valve to the outside of the valve. It directly affects safety production, causes losses to the working medium, economic losses to the enterprise, environmental pollution, and in severe cases, can cause production accidents. Especially for high temperature and high pressure, flammable and explosive, toxic or corrosive media, external leakage of the valve is not allowed at all, as its consequences are more serious than internal leakage. Therefore, the valve must have reliable sealing performance to meet the leakage requirements of its operating conditions.

Classification standard for valve sealing grades in China

At present, there are two commonly used classification standards for valve sealing levels in China.

1.1 Classification of Valve Sealing Grades in Chinese National Standards GB/T 13927 "Industrial Valve Pressure Testing".

1.2 Classification of Valve Sealing Grades in Chinese Machinery Industry Standard JB/T 9092 "Inspection and Testing of Valves".

2 International Classification Standards for Valve Sealing Grades

At present, there are five commonly used classification standards for valve sealing levels on the periphery.

2.1 Classification of valve sealing grades by the former Soviet Union

In order to select products based on the sealing degree of the valve and the specified purpose, valves were classified according to the sealing degree.

2.2 Classification of valve sealing grades by the International Organization for Standardization

The International Organization for Standardization standard ISO5208 "Pressure testing of metal valves for industrial valves".

2.3 Classification of Valve Sealing Grades by the American Petroleum Institute (APl) API 598-2004 "Inspection and Testing of Valves.".

2.4 Classification of Valve Sealing Grades by the Valve and Pipe Manufacturers Standardization Society (MSS) in the United States. The valve leakage requirements allowed by MSS SP61 in the American Valve and Pipe Manufacturers Standardization Society standard "Pressure Testing of Steel Valves" are as follows:

(1) When plastic or rubber is used as a sealing surface in the valve sealing pair, there should be no visible leakage during the duration of the sealing test.

(2) The maximum allowable leakage on each side when closed should be: 0.4 milliliters per millimeter and hour for the nominal size (DN) of the liquid; Gas is nominal size (DN) per millimeter and 120 milliliters per hour.

(3) The allowable leakage of the check valve can be increased by four times.

2.5 Classification of Control Valve Sealing Grades by American National Standards/American Instrument Institute Standards (ANSI/FCI)

The American National Standard is ANSI/FCI70-2 (ASME B16.104) for Control Valve Seat Leakage.

2.6 Classification of valve sealing grades according to EU standards

European Standard EN 12266-1 "Testing of Industrial Valves and Valves" Part 1. Pressure testing, testing methods, and acceptance criteria - mandatory requirements.

3.Selection of Sealing Grades for 3 Valves

3.1 Selection of Domestic Valve Sealing Grades

(1) The national standard GB/T13927 (Industrial Valve Pressure Testing), implemented on July 1, 2009, was developed based on the European standard ISO 5208. It is applicable to 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 and maximum allowable leakage of sealing tests are the same as those specified in ISO 5208. This standard is a revision of GB/T13927 (General Valve Pressure Testing), which adds six levels: AA, CC, E, EE, F, and G. The new version of the standard stipulates that "the selection of leakage level should be one of the strict requirements specified in the relevant valve product standard or purchase contract. If there is no special provision in the product standard or purchase contract, non-metallic elastic seal valves shall meet the requirements of Class A, and metal seal auxiliary valves shall meet the requirements of Class D.". ”Usually, Class D is suitable for general valves, and for more critical valves, it is recommended to choose a leakage level above Class D.

(2) The mechanical industry standard JB/T 9092 "Inspection and Testing of Valves" is a revision of ZB J16006. The maximum allowable leakage for the sealing test is based on the American Petroleum Institute standard API

Developed in 598-1996. Suitable for 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 sealing pairs, elastic sealing pairs, and non-metallic sealing pairs (such as ceramics). Currently, GB/T 9092 is under revision.

(3) In engineering design, it should be noted that the national standard GB/T19672 (Technical Conditions for Pipeline Valves) is formulated based on the European standard ISO 14313 and the American Petroleum Institute standard API 6D. The national standard GB/T 20173 (Pipeline Valves for Petroleum and Natural Gas Industries) is formulated based on the European standard ISO 14313. The acceptance criteria for valve leakage in GB/T 19672 and GB/T 20173 are the same as the Class A and Class D requirements of ISO 5208. Therefore, when there are leakage requirements higher than their standards in engineering design, they should be specified in the purchase contract.


3.2 Selection of Sealing Grades for Foreign Valves

(1) The classification of valve sealing grades in the former Soviet Union was mainly applied in the 1950s. With the disintegration of the former Soviet Union, most countries now do not choose this classification of sealing grades, but instead use the European and American standards for sealing

Classification of sealing levels. The classification of sealing levels according to the European standard EN 12266-1 complies with the provisions of the International Organization for Standardization standard ISO 5208, but lacks three levels: AA, CC, and EE. Compared to the 1999 version, ISO 5208 has added six levels: AA, CC, E, EE, F, and G. The ISO 5208 standard provides a comparison of several sealing levels with API 598 and EN 12266 standards.

4.Classification standard for sealing levels of low leakage valves

Low leakage valve refers to a small external leakage that cannot be determined by conventional water pressure and air pressure sealing tests, and requires more advanced methods and instruments to detect. The small leakage of a valve to the external environment is called low leakage. There are currently three commonly used standards internationally for detecting low leakage in valves:

(1) EPA method 21 "Volatile Organic Component Leakage Detection" by the United States Environmental Protection Agency.

(2) International Organization for Standardization ISO 15848 (Industrial valves: Low leakage measurement, testing, and qualification procedures).

(3) Shell MESC SPE 77/312 "Industrial Valves: Type Approval and Product Testing for Low Leakage Measurement, Classification Systems, Qualification Procedures, and Switching and Control Valves".

5.Selection of  Low Leakage Valves

Bellows sealed valve is a type of low leakage valve. In the past, for working conditions with special requirements for the external leakage level of valves, corrugated pipe sealed valves were generally selected. However, due to the high difficulty and technical requirements of the f-JJm corrugated pipe sealed valve, its corrugated pipe material cannot be fully localized, and the cost is too high, which restricts its widespread promotion and use in the petrochemical industry. At present, with the continuous enhancement of people's awareness of safety and environmental protection, the increase of technical cooperation with foreign countries, and the continuous strengthening of the technical strength of domestic valve manufacturers, the understanding of low leakage valves by domestic technicians is also constantly improving, leading to the continuous expansion of their application scope. If the valves selected for flammable and explosive media in petrochemical enterprises can meet the low leakage standard, it will undoubtedly greatly reduce the emission of toxic and explosive media in the device, and avoid accidents that endanger life safety such as fires, explosions, and poisoning caused by valve leakage. Compared with bellows valves, low leakage valves that meet ISO15848 and SHELL MESC SPE 77/31 standards have a simple structure, easy processing and manufacturing, and a cost that is about 10% to 20% higher than general valves. Based on the previous analysis and comparison of these two standard sealing grades, the leakage rate of Class B valves with tight grades can generally meet the low leakage requirements of certain special working conditions, and the machining accuracy requirements are relatively easy to achieve. The manufacturing cost does not increase much, and it can replace the use of some corrugated pipe valves. At present, low leakage valves have more practical significance for oil and gas field purification systems with high hydrogen sulfide content. Because hydrogen sulfide is a highly toxic and combustible gas, heavier than air, it can accumulate in low-lying areas. Inhaling a certain concentration of hydrogen sulfide can harm the body and even lead to death, so the requirements for leakage from such natural gas purification facilities are more stringent.