What are the differences between the pressure rating and temperature rating of American standard gate valves and national standards?

2025-04-18 09:47:34

There are significant differences between American standard gate valves (following ASME, API and other standards) and national standard Gate valves (following GB, JB and other standards) in terms of pressure rating and temperature rating systems, mainly reflected in system architecture, representation methods, applicable scope and material matching. The specific comparison is as follows:

Pressure temperature relationship

American standard:

The pressure rating should be determined based on the material group and temperature to determine the actual allowable pressure, for example:

The A105 carbon steel valve of Class 300 has an allowable pressure of 4.8MPa at 260 ℃, which decreases to 3.8MPa at 370 ℃.

national standard:

Provide the maximum working pressure of different materials at a specific temperature directly according to the nominal pressure temperature rating table.

3. Testing pressure requirements

American standard (API 598):

Shell test: 1.5 times the rated pressure (Class corresponds to the maximum working pressure at room temperature);

Sealing test: 1.1 times the rated pressure (low pressure sealing test is 0.4~0.7MPa).

National standard (GB/T 13927):

Shell test: 1.5 times nominal pressure;

Sealing test: 1.1 times nominal pressure (soft seal allows low pressure test of 0.6MPa).

2、 Differences in temperature classification

1. Temperature range and material compatibility

American standard:

Subdivide temperature levels by material type, for example:

Carbon steel (A105):- 29 ℃~425 ℃ (graphitization risk needs to be considered at high temperatures);

Stainless steel (316): -254 ℃~650 ℃ (depending on the heat treatment state and sealing surface material);

Low temperature conditions (such as -196 ℃) must comply with API 607 (fire protection) and ASME B16.5 low temperature rating (such as LC3, LC4).

national standard:

Provide an upper temperature limit based on nominal pressure and material, for example:

WCB carbon steel (PN ≤ PN40): -29 ℃~425 ℃;

CF8 stainless steel (PN ≤ PN16):- 196 ℃~200 ℃ (refer to manufacturer's data for practical application, high temperature strength is lower than American standard equivalent materials).

2. Temperature units and accuracy

The American standard temperature is commonly marked in Fahrenheit (° F) (such as 450 ° F ≈ 232 ℃), but it is also converted to Celsius in technical documents;

The national standard directly adopts Celsius (℃), with thicker temperature segments (such as 50 ℃ intervals), while the American standard is refined to intervals of 25 ℃ or 10 ℃ (such as 200 ° F, 250 ° F, etc. in ASME tables).

3、 Material standards and performance differences

1. Corresponding material grades

Differences in equivalent material properties between American standard materials and national standards (taking high temperature strength as an example)

A105 ZG230-450 A105 has a lower carbon content (≤ 0.35%), and the allowable stress at 425 ℃ is 15% higher than ZG230

WCB (ASTM A216) WCB (JB/T 2640) American standard WCB has higher impact toughness (≥ 27J) than the national standard (≥ 20J) and better low-temperature performance

316 (ASTM A351) 06Cr17Ni12Mo2 American standard 316 carbon content ≤ 0.08%, high temperature intergranular corrosion resistance slightly better than the same material in the national standard

2. Matching of sealing surface materials

The American standard hard seal (such as Stellite overlay) maintains good sealing performance above 600 ℃, while similar valves in the national standard (such as overlay cobalt based alloy) are usually marked with a temperature resistance of ≤ 550 ℃ (actually limited by welding processes and testing standards).

4、 Application scenarios and selection considerations

1. International project compatibility

American standard valves are widely used in foreign-related projects such as petrochemicals and LNG (following API and ASME standards), while national standard valves are mainly used in domestic municipal and heating projects (following GB and JB standards).

The actual allowable pressure of American standard Class 150 valves at high temperatures may be lower than the national standard PN20 (such as at 350 ℃, the allowable pressure of Class 150 for A105 is about 2.8MPa, while the allowable pressure for PN20 carbon steel valves is 3.2MPa), which needs to be accurately converted through a pressure temperature gauge.

2. Conversion Misconceptions

Prohibition of direct numerical conversion: Class 300 ≠ PN40 (Class 300 ≈ PN50 at room temperature, and may be lower than PN40 at high temperatures due to the decrease in allowable stress of the material);

Material grade needs to be verified: American standard valves need to specify the material group (such as Grade A105, Grade 316), and national standards need to specify the implementation standard (such as the material code in GB/T 12224).

Selection suggestion: In cross standard projects, it is necessary to use a pressure temperature conversion table (such as the comparison table between ASME B16.34 and GB/T 12224) combined with specific materials and working conditions for verification, to avoid directly matching based on nominal pressure or Class value, and ensure the safety and sealing of the valve at design temperature and pressure.