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GB/T 12385-2025Standard test methods for sealability of gaskets for pipe flanges (English PDF)

管法兰用垫片密封性能试验方法

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Issued by

State Administration for Market Regulation; Standardization Administration of China

Level / Type

National · Recommended

Issue date

March 28, 2025

Implementation date

October 1, 2025

Scope

GB/T 12385-2025 is the English-translated version of 管法兰用垫片密封性能试验方法.

GB/T 12385-2025 is the Chinese national standard on standard test methods for sealability of gaskets for pipe flanges, in the field of fluid systems and general-purpose components. The /T suffix marks it as a recommended standard: it is not compulsory by itself, but it becomes binding as soon as a contract, a tender or a customer specification calls it up - which in practice is how most foreign buyers meet it. It was issued on 28 March 2025 by the State Administration for Market Regulation; Standardization Administration of China, and has been in force since 1 October 2025. Classification: ICS 23.040.60, CCS J15. This page is published from the official record of the standard held by the Chinese standards administration: the identification, the dates, the classification and the issuing body are taken from there. The clause text, the tables and the numeric limits are in the document itself, which is delivered complete in English translation.

Document preview — GB/T 12385-2025

National Standard of the People's Republic of China

ICS: 23.040.60
Classification: J15

Issued by: State Administration for Market Regulation; Standardization Administration of China

1 Scope
2 Normative References
3 Terms and Definitions
4 Leak Detection Cavity Pressurization Method (Method A)
4.2 Test Device
4.5.4 In accordance with the provisions of
4.7 Leakage Rate Calculation and Test Result
5 Pressure Drop Method (Method B)...
5.5 Test Procedures
6 Helium Mass Spectrometry Vacuum Leak Detection
6.5 Test Procedures
6.5.2 In accordance with the provisions of
6.5.3 Turn on the vacuum pump, vacuumize the pipeline to a gauge pressure below
7 Selection of Test Methods and Precautions
8 Test Report...

Foreword

This document was drafted in accordance with the rules provided in GB/T 1.1-2020 Directives for Standardization - Part

1.Rules for the Structure and Drafting of Standardizing Documents. This document serves as a replacement for GB/T 12385-2008 Standard Test Method for Sealability of Gaskets for Pipe Flanges. In comparison with GB/T 12385-2008, apart from structural adjustments and editorial modifications, the main technical changes are as follows:

a) The Scope is modified (see Chapter 1; Chapter 1 of Version 2008);

b) The asbestos rubber sheet is deleted (see Table 1 of Version 2008);

c) The provisions for specimens, dimensions and dimensional measurements are added (see 4.3.2,

d) The helium mass spectrometry vacuum leak detection method (Method C) is added (see Chapter 6). Please be noted that certain content of this document may involve patents. The institution issuing this document does not undertake the responsibility of identifying these patents. This document was proposed by China Machinery Industry Federation. This document shall be under the jurisdiction of National Technical Committee 237 on Piping Fittings of Standardization Administration of China (SAC/TC 237). The drafting organizations of this document. East China University of Science and Technology; Zhejiang CPS Cathay Packing & Sealing Co., Ltd.; Ningbo Tiansheng Sealing Parts Co., Ltd.; China Productivity Center for Machinery Co., Ltd.; Ningbo Yitiandi Xinyuan Sealing Technology Co., Ltd.; Cixi Hengli Sealing Materials Co., Ltd.; Special Equipment Safety Supervision Inspection Institute of Jiangsu Province; Guangzhou Dongshan South Seals Co., Ltd.; Wuxi Xixi Chemical Machinery Parts Co., Ltd.; Wenzhou Huahai Sealing Co., Ltd.; Taizhou Longjiang Chemical Machinery Technology Co., Ltd.; SINOPEC Engineering Incorporation; China Tianchen Engineering Corporation Ltd.; CNPC EastChina Design Institute Co., Ltd.; Beijing Branch of China Huanqiu Contracting & Engineering Co., Ltd.; Suzhou Nuclear Power Research Institute; Ningbo Auto Sealing Technology Co., Ltd.; Cixi AIFLON Sealing Parts Co., Ltd.; Zhejiang Zhengtong Pipes Co., Ltd.; Shenzhen Minle Pipe Industry Co., Ltd.; Zhejiang Bomeite Energy Equipment Co., Ltd.; Yanqi Lake Institute of Basic Manufacturing Technology Research Co., Ltd.; Nuclear Industry Research and Engineering Co., Ltd. The main drafters of this document. Zhang Lanzhu, Wu Yimin, Li Xinggen, Feng Feng, Lin Jianhong, Xu Shaohuan, Li Ke, Wu Kaijun, Hui Fuming, Zhang Yong, Xiong Conggui, Zhao Yong, Liu Hongfu, Liu Jianxin, Pang Dong, Han Chuanwei, Ye Xin, Ye Qiwei, Yang Xin, Xu Zhihua, Zhang Kemei, Wang Xiaojuan, Chang Haijun. Standard Test Methods for Sealability of Gaskets for Pipe Flanges

1 Scope

This document describes three methods for determining the sealability of gaskets used for pipe flanges. the leak detection cavity pressurization method (Method A), the pressure drop method (Method B) and the helium mass spectrometry vacuum leak detection method (Method C). This document is applicable to the determination of the sealability of non-metallic flat gaskets, spiral wound gaskets, polytetrafluoroethylene coated gaskets, metal coated gaskets, flexible graphite composite reinforced gaskets, metal toothed combination gaskets and metal corrugated composite gaskets. Other types of gaskets may take this as a reference.

2 Normative References

This document does not have normative references.

3 Terms and Definitions

This document does not have terms or definitions that need to be defined.

4 Leak Detection Cavity Pressurization Method (Method A)

4.1 Overview It is applicable to the sealability test of gaskets for pipe flanges with the medium being nitrogen or helium, and the leakage rate ranging from 105 cm3/s (standard state) to 101 cm3/s (standard state) (hereinafter referred to as "the gaskets").

4.2 Test Device

4.2.1 The test device consists of a gasket loading system, a test medium supply system, a leak detection system and a test flange, as shown in Figure 1.

4.2.2 The gasket loading system shall be able to provide the specified gasket pre-tightening specific pressure and be able to control constant loading and unloading speeds. During the test, the fluctuation of the gasket pre-tightening specific pressure shall be 2% of the specified value. When the gasket pre-tightening specific pressure is less than or equal to 35 MPa, the loading speed and unloading speeds shall be

0.2 MPa/s; when the gasket pre-tightening specific pressure is greater than 35 MPa, the loading and unloading speeds shall be

0.5 MPa/s. PC

---the absolute pressure of the test medium introduced into the leak detection cavity, expressed in (MPa).

4.5.4 In accordance with the provisions of

4.2.3 and Table 1, introduce the test medium, and after the medium pressure reaches the specified value, maintain it for 10 minutes.

4.5.5 Start leak detection and record the pressure and temperature in the leak detection cavity at the beginning of the leak detection. Start timing and record the pressure and temperature in the leak detection cavity at the end of the measurement. The measurement time depends on the leakage rate and is usually 2 minutes ~ 10 minutes.

4.6 Number of Tests Select several specimens from the same sample and randomly select no less than 3 specimens for testing.

4.7 Leakage Rate Calculation and Test Result

4.7.1 The leakage rate calculation is based on the ideal gas law and is calculated in accordance with Formula (2). Where, LNV

---when nitrogen is the medium, the volume leakage rate under the standard state, expressed in (cm3/s) (the standard state); LHV

---when helium is the medium, the volume leakage rate under the standard state, expressed in (cm3/s) (the standard state); Tst

---the absolute temperature of the atmosphere under the standard state, expressed in (K) (Tst = 273.16); Pst

---the atmospheric pressure under the standard state, expressed in (MPa) (Pst = 0.101325); VC

---the volume of the leak detection cavity, expressed in (cm3); t

---the leakage detection time, expressed in (s); P1

---the absolute pressure in the leak detection cavity at the beginning of leak detection, expressed in (MPa); T1

---the absolute temperature of the leak detection cavity at the beginning of leak detection, 4

---simulated flange (upper); 13

---buffer tank; 5

---pressure source; 6

---simulated flange (lower); 15

---sealed cavity; 7

5 Pressure Drop Method (Method B)...

5.5 Test Procedures

5.5.1 Use solvent (for example, acetone) to clean the flange sealing surface and install the gasket in the center.

5.7.1 The leakage rate calculation is based on the ideal gas law and is calculated in accordance with Formula (4). Where, LNV

---when nitrogen is the medium, the volume leakage rate under the standard state, expressed in (cm3/s) (the standard state); LHV

---when helium is the medium, the volume leakage rate under the standard state, expressed in (cm3/s) (the standard state); Tst

---the absolute temperature of the atmosphere under the standard state, expressed in (K) (Tst = 273.16); Pst

---the atmospheric pressure under the standard state, expressed in (MPa) (Pst = 0.101325); VS

---the volume of the sealed cavity, expressed in (cm3); t

---the leakage detection time, expressed in (s); P3

---the absolute pressure in the sealed cavity at the beginning of leak detection, expressed in (MPa); T3

---the absolute temperature of the sealed cavity at the beginning of leak detection, expressed in (K); P4

---the absolute pressure in the sealed cavity at the end of leak detection, expressed in (MPa); T4

---the absolute temperature of the sealed cavity at the end of leak detection, expressed in (K).

5.7.2 The final test result shall be the arithmetic mean of all calculated values and rounded to two significant figures.

6 Helium Mass Spectrometry Vacuum Leak Detection

Method (Method C)

6.1 Overview It is applicable to the sealability test of gaskets with the medium being helium with purity not lower than 99.9%, and the leakage rate LV ranging from 108 cm3/s (standard state) to 103 cm3/s (standard state). The specimen preparation, specimen size and specimen size measurement shall be carried out in accordance with 4.3.

6.4 Test Conditions The test conditions are in accordance with 4.4.

6.5 Test Procedures

6.5.1 Use a soft cotton cloth dipped in solvent (for example, acetone) to clean the surfaces of the upper and lower simulated flanges, and place the gasket between the simulated flanges in the center.

6.5.2 In accordance with the provisions of

6.2.2 and Table 1, apply the pre-tightening specific pressure to the gasket, and after reaching the specified value, maintain it for 15 minutes.

6.5.3 Turn on the vacuum pump, vacuumize the pipeline to a gauge pressure below

0.1 MPa, and introduce helium to replace the gas in the pipeline and the sealed cavity. Repeat this process twice, and then, turn off the vacuum pump and its pipeline valve.

6.5.4 Open the helium cylinder and introduce the test medium into the sealed cavity. Utilize a pressure reducing valve to adjust the helium medium pressure to the specified test medium pressure. Use the helium mass spectrometer to start the leak detection. After 15 minutes, when the leakage rate value becomes stable, record the leakage rate value.

6.5.5 Close the valve of the helium cylinder, turn off the helium mass spectrometer, release the helium in the sealed cavity, and stop the test.

6.6 Number of Tests Select several specimens from the same sample and randomly select no less than 3 specimens for testing.

6.7 Leakage Rate Calculation and Test Result The final test result is the arithmetic mean of all calculated values and rounded to two significant figures.

7 Selection of Test Methods and Precautions

7.1 Based on the leakage rate test range of the three test methods and the estimated leakage rate range of the test object, select the appropriate test method.

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This preview omits tables, figures, formulas and parts of the technical clauses. The complete document — 20 pages — is available in the English PDF.

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Editions of GB/T 12385

Edition	Title	Revision	Status
GB/T 12385-2025	Standard test methods for sealability of gaskets for pipe flanges	current edition	Current
GB/T 12385-2008	Standard test method for sealability of gaskets for pipe flanges	previous edition	Superseded

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