Exploring the standard difference and application of flange sealing face defect tolerance size

Exploring the standard difference and application of flange sealing face defect tolerance size

This paper provides a comparative analysis of the provisions on flange sealing face defect tolerance dimensions in ASME PCC-1-2019, HG/T 20592, HG/T 20615 and GB/T 38343-2019, describes the differences and analogies between the standards, and provides references for the plant owner and the person in charge of maintenance in the practical application.

1. Introduction

The allowable size of flange sealing surface defects is a key factor to ensure the sealing performance of flange connection. Different standards have different regulations on the allowable size of flange sealing surface defects. Understanding the differences and similarities between these standards will help us to choose and apply the standards correctly in practice and ensure the safe operation of the equipment.

2. Comparison of standard requirements

(1). ASME PCC-1-2019

Appendix D of ASME PCC-1-2019 specifies the permissible depth and width of defects on the flange face. Among them, local defects are allowed to exist a certain depth and width of pits, bumps, etc., but cracks or gaps through the entire flange are not allowed. Specific size limitations are: depth up to 0.8mm, width up to 25mm.

(2). HG/T 20592 and HG/T 20615

HG/T 20592 and HG/T 20615 standards stipulate the permissible dimensions of flange sealing surface defects for different types of flange surfaces (protruding surface, concave/convex surface, fully flat surface). Specific requirements are as follows:

- Protruding surface: defects with depth and width less than 0.8mm are allowed.
- Concave/convex surface: the depth of less than 0.8mm, the width is less than 1/4 of the width of the flange surface defects.
- Full plane: defects with depth and width less than 0.8mm are allowed.

(3). GB/T 38343-2019

GB/T 38343-2019 specifies the requirements for flange sealing surface roughness, which need to meet the provisions of HG/T 20592 and HG/T 20615. At the same time, for gaskets of different thicknesses, it specifies the requirements for surface unevenness of flange sealing surface:

- Gaskets with thickness ≤3mm: the surface unevenness of the flange sealing surface in the circumferential direction and the radius direction shall be less than 0.25mm.
- Thickness > 3mm gasket: the provisions of the more relaxed, the specific need to refer to the relevant standards.

3. The standard differences and similarities

(1). Differences

- ASME PCC-1-2019 differs from HG/T 20592 and HG/T 20615 in the type of defects, the former allows localised defects, the latter is not explicitly mentioned.
- HG/T 20592 and HG/T 20615 specify different defect size limits for different types of flange faces, while ASME PCC-1-2019 and GB/T 38343-2019 do not make a distinction.
- GB/T 38343-2019 focuses on the surface roughness and unevenness of flange sealing surfaces, which are not covered by other standards.

(2) Similarities

- Each standard puts forward restrictions on the depth and width of flange sealing surface defects.
- Each standard requires the defect size to be within a certain range to ensure the sealing performance of the flange connection.

4. Conclusion

The plant owner and maintenance person in charge should select the appropriate standard for reference according to the type of flange and gasket thickness actually used in the actual application. At the same time, the application of highly compensated gasket materials (e.g. GYLON EPIX®) can make up for the defects on the flange surface, improve the availability of the flange and reduce maintenance costs. Understanding the differences and similarities between the standards helps us to better grasp the allowable dimensions of flange sealing surface defects to ensure the safe and reliable operation of equipment.