Overview of Pressure Rating Systems for Instrumentation Process Connections
The pressure rating of instrument process connections directly determines the pressure-bearing capacity and sealing reliability of flanges, threads, and other interfaces. The mainstream global standards are divided into three major systems: American ASME/ANSI pound class (Class), European and international PN nominal pressure, and Japanese K grade. Different systems cannot be directly interchanged; when selecting, both pressure rating and flange standard must be considered.
I. American Standard (ASME/ANSI System, Pound Class "Class")
Based on pounds per square inch (psi), the flange standard is ASME B16.5, widely used in North America. The pressure ratings of pipes, valves, and instrument interfaces must match.
Common Class Ratings and Parameters
| Class Rating | Nominal Pressure (approximate) | Typical Application Scenarios |
|---|---|---|
| Class 150 | ≈1.03 MPa (150 psi) | Low-pressure systems, such as water and air pipelines |
| Class 300 | ≈2.07 MPa (300 psi) | Medium-pressure systems, such as chemical and petroleum |
| Class 400 | ≈2.76 MPa (400 psi) | Less commonly used, special working conditions |
| Class 600 | ≈4.14 MPa (600 psi) | Medium-high pressure systems, such as steam and oil products |
| Class 900 | ≈6.21 MPa (900 psi) | High-pressure systems, such as high-pressure gas pipelines |
| Class 1500 | ≈10.35 MPa (1500 psi) | Ultra-high pressure systems, such as refining and natural gas |
| Class 2500 | ≈17.25 MPa (2500 psi) | Extremely high pressure systems, such as wellhead equipment |
Note: The Class rating value is not directly equal to the working pressure; the actual allowable pressure decreases with increasing temperature, and the ASME B16.5 pressure-temperature rating tables must be consulted.
II. European and International Standards (PN System, Nominal Pressure "PN")
Based on megapascals (MPa), flange standards include EN 1092-1, GB/T 9113, HG/T 20592 (European system), etc., adopted by Europe, China, and most countries worldwide.
Common PN Ratings and Parameters
| PN Rating | Nominal Pressure | Typical Application Scenarios |
|---|---|---|
| PN 2.5 | 0.25 MPa | Low pressure, such as water supply and drainage, low-pressure gas |
| PN 6 | 0.6 MPa | Low pressure, such as low-pressure steam, compressed air |
| PN 10 | 1.0 MPa | Medium-low pressure, general industrial pipelines |
| PN 16 | 1.6 MPa | Medium pressure, commonly in chemical and power industries |
| PN 25 | 2.5 MPa | Medium pressure, such as medium-pressure steam |
| PN 40 | 4.0 MPa | Medium-high pressure, such as high-pressure liquid pipelines |
| PN 63 | 6.3 MPa | High pressure, such as high-pressure gas and hydraulic systems |
| PN 100 | 10.0 MPa | Ultra-high pressure, such as high-pressure reactor connections |
| PN 160 | 16.0 MPa | Extremely high pressure, special industrial scenarios |
| PN 250 | 25.0 MPa | Extremely high pressure, such as high-pressure hydrogenation units |
| PN 320 | 32.0 MPa | Extremely high pressure, very few special working conditions |
| PN 400 | 40.0 MPa | Extremely high pressure, military or aerospace fields |
The PN value usually refers to the maximum allowable working pressure at 20°C; at high temperatures, the rating must be reduced according to the material.
III. Japanese Standard (K Grade System)
Originating from the Japanese JIS B2220 standard, it uses "K" to denote pressure rating, with units approximately in MPa, mainly used in Japanese domestic projects.
Common K Grade Ratings and Parameters
| K Rating | Nominal Pressure (MPa) | Typical Application Scenarios |
|---|---|---|
| 5K | ≈0.5 MPa | Low pressure, such as ordinary water pipelines |
| 10K | ≈1.0 MPa | Medium-low pressure, general industry |
| 20K | ≈2.0 MPa | Medium pressure, such as chemical and marine |
| 40K | ≈4.0 MPa | High pressure, such as high-pressure gas pipelines |
| 63K | ≈6.3 MPa | High pressure, similar to PN 63 |
| 100K | ≈10.0 MPa | Ultra-high pressure, special working conditions |
Note: K-grade flange dimensions differ slightly from ASME/PN systems; when connecting across systems, compatibility must be confirmed, and adapters used if necessary.
IV. Other Regional Standards and Special High-Pressure Scenarios
1. Chinese National Standards (GB) and Chemical Industry Standards (HG)
- GB/T 9113: Basically consistent with the European PN system, such as PN6, PN10, PN16, etc., widely used in domestic industrial projects.
- HG/T 20615 (American system): Covers ASME Class 150/300 and other ratings, suitable for North American imported equipment.
- HG/T 20592 (European system): Corresponds to the PN series, commonly used in the chemical industry.
2. High-Pressure and Ultra-High-Pressure Scenarios
For pressure ratings exceeding PN400 (40 MPa) or Class 2500 (17.25 MPa), specially customized connections are usually used, such as threaded locking and welded high-pressure connectors.
- API 6A: Wellhead equipment standard, up to 15000 psi (≈103.5 MPa).
- High-pressure hydrogenation units: Commonly PN250~PN320, requiring special lens gaskets or metal ring seals.
V. Selection and Procurement Recommendations
- Confirm the project standard system: North American projects prioritize ASME Class, European/Chinese projects prioritize PN, and Japanese projects prioritize K grade.
- Verify flange standard and dimensions: Even if pressure ratings are similar, bolt hole spacing and sealing surfaces of different flange systems may be incompatible.
- Consider temperature derating: Both Class and PN are based on normal temperature; for high-temperature conditions, pressure-temperature rating tables must be consulted.
- Match pipes and valves: The pressure rating of instrument process connections should be consistent with adjacent pipes and valves to avoid weak points.
Summary: Correctly understanding the three major pressure rating systems—ASME Class, PN, and K grade—is the foundation for instrument selection, procurement, and installation, effectively avoiding leakage and flange mismatch risks.