Classification of Valve Pressure Ratings in the Petrochemical Industry
Valve pressure ratings in the petrochemical industry are primarily categorized into three major systems: the American Standard (ANSI/ASME Class, or "Pound Class"), the European Standard / Chinese National Standard (PN, or "Nominal Pressure"), and the Japanese Standard (Class K). Among these, the American Standard is the dominant standard within the petrochemical sector.
I. Comparison of the Three Major Pressure Rating Systems
Table
American Standard (Class) | National/European Standard (PN) | Approximate Pressure (MPa) | Japanese Standard (JIS) | Applicable Conditions (Petrochemical)
150 | PN20 | 2.0 MPa | 10K | Low Pressure: General oil products, water, steam, and air pipelines
300 | PN50 | 5.0 MPa | 20K | Low-to-Medium Pressure: Hydrotreating, reforming, aromatics units, etc.
600 | PN100 | 10.0 MPa | 40K | Medium Pressure: Catalytic cracking, hydrocracking
900 | PN150 | 15.0 MPa | 65K | High Pressure: High-pressure hydrotreating, ethylene units
1500 | PN250 | 25.0 MPa | 110K | Ultra-High Pressure: Ammonia synthesis, urea production, deep-sea oil extraction
2500 | PN420 | 42.0 MPa | 180K | Extreme High Pressure: Special high-temperature and high-pressure conditions
II. Detailed Explanation of Core Systems
1. American Standard: ANSI/ASME Class (Pound Class)
Standards: ASME B16.34, B16.5
Characteristics: Pressure-Temperature Ratings. The numerical value does not represent a direct pressure figure; rather, it indicates the pressure resistance rating of the material at a specific reference temperature.
Class 150: Reference temperature of 260°C
Class 300–2500: Reference temperature of 454°C
Common in Petrochemicals: Class 150, 300, and 600 cover over 80% of typical operating conditions. 2. Chinese National Standard (GB) / European Standard (EN) PN (Nominal Pressure)
Standards: GB/T 1048, HG/T 20592
Characteristics: Based on the maximum allowable working pressure at **ambient temperature (20°C)**; units are in bar (PN16 = 16 bar = 1.6 MPa).
Commonly used in petrochemicals: PN16, PN25, PN40, PN63, PN100.
3. Japanese Standard (JIS) - K-Class
Standard: JIS B2238
Characteristics: Primarily used for matching with Japanese-manufactured equipment; 10K ≈ PN20, 20K ≈ PN50.
III. Classification and Selection of Pressure Ratings in the Petrochemical Industry
1. Classification by Pressure Range (Petrochemical Industry Convention)
Low Pressure
Class ≤300 (PN ≤50): ≤5.0 MPa
Applications: Atmospheric distillation columns, heat exchangers, cooling water systems, fuel gas lines, wastewater systems.
Medium Pressure
Class 600–900 (PN 100–150): 6.4–15.0 MPa
Applications: Atmospheric and vacuum distillation, catalytic cracking, hydrorefining, general compressor outlets.
High Pressure
Class 1500–2500 (PN ≥250): ≥25.0 MPa
Applications: Hydrocracking, reforming, ethylene production, synthesis gas, supercritical steam.
2. Key Selection Considerations
Temperature Correction: For the Class system, it is mandatory to consult pressure-temperature rating tables. As temperature increases, the allowable working pressure decreases significantly.
Example: Carbon steel (WCB) Class 300 has an allowable pressure of 5.0 MPa at ambient temperature; however, at 425°C, this drops to only approximately 2.1 MPa.
Material Selection/Matching:
Class 150/300: Carbon steel (WCB, LCB), 304 stainless steel.
Class 600+: Chrome-molybdenum steel (WC6, WC9), 316L stainless steel, duplex stainless steel. Mixing Prohibited: Class 150 and PN16 cannot be directly paired (due to differences in sealing faces and bolt hole patterns).
IV. Summary
Preferred Choice for Petrochemical Applications: The ANSI Class system (Class 150, 300, and 600 are the most commonly used).
Commonly Used in Domestic Projects: The PN system (PN16, PN25, and PN40).
Key Distinction: "Class" denotes a pressure-temperature rating, whereas "PN" denotes the nominal pressure at ambient temperature; therefore, material selection must be based on a comprehensive assessment that takes into account temperature, process media, and material properties.
