The PN series standards of chemical industry flanges are an important standard system used to regulate the connection of flanges in the chemical industry. They mainly involve key parameters such as the size, pressure rating, material, and sealing surface form of the flanges. The following provides a detailed analysis of the PN series standards from five aspects: identification composition, nominal pressure (PN) grade, sealing surface form, material and structure, and application and selection:
1. Identification Composition
The identification of PN series flanges usually consists of the standard number, nominal pressure (PN), nominal diameter (DN), sealing surface form, material grade, etc. For example, the identification "HG/T 20592-2009 PN16 DN100 RF S30408" indicates:
HG/T 20592-2009: The standard is the chemical industry standard HG/T 20592-2009;
PN16: The nominal pressure is 16 bar;
DN100: The nominal diameter is 100 mm;
RF: The sealing surface form is raised face;
S30408: The material is 06Cr19Ni10 (304 stainless steel).
2. Nominal Pressure (PN) Grade
The PN series standards use nominal pressure (PN) as the pressure grade identifier, with the unit being bar. Common PN grades include:
PN2.5, PN6, PN10, PN16, PN25, PN40, PN63, PN100, PN160.
Pressure conversion relationship:
1 bar ≈ 0.1 MPa ≈ 14.5 psi.
For example, PN16 corresponds to a pressure of approximately 1.6 MPa.
Application scope:
Different PN grades are suitable for different pressure and temperature conditions. The selection of the appropriate grade should be based on process requirements.
3. Sealing Surface Form
The sealing surface form directly affects the sealing performance of the flange. Common sealing surface forms include:
Raised face (RF): Smooth surface, suitable for general media and pressure conditions.
Full plane (FF): Completely flat surface, suitable for low pressure, non-critical sealing occasions.
Eccentric face (MFM): One flange is concave, the other is convex, suitable for higher pressure and temperature conditions.
Screw groove face (TG): One flange is screw-shaped, the other is groove-shaped, suitable for high pressure, high temperature or flammable and explosive media.
Ring connection face (RJ): Metal ring sealing is used, suitable for ultra-high pressure and high temperature conditions.
4. Materials and Structures
1. Materials:
Carbon steel: Such as Q235, 20# steel, suitable for general media and temperature conditions.
Stainless steel: Such as 304 (S30408), 316 (S31608), suitable for corrosive media.
Alloy steel: Such as 16Mn, 15CrMo, suitable for high temperature, high pressure or special media.
2. Structures:
Plate flat welding flange (PL): The flange disc is directly welded to the pipe, suitable for low pressure, non-critical occasions.
Pipe with neck flat welding flange (SO): The flange has a short neck, with better rigidity and sealing performance than plate flat welding flange.
Pipe with neck butt welding flange (WN): The flange has a long neck, suitable for high pressure, high temperature or vibration-prone occasions.
Integral flange (IF): The flange is an integral structure with the equipment or pipeline, suitable for critical equipment.
Loose fitting flange: The flange is connected to the equipment or pipeline through flange lap or live fitting, suitable for occasions requiring disassembly.
5. Application and Selection
1. Application Areas:
Chemical, petroleum, pharmaceutical, food industries: Used for the connection of pipelines, valves, pumps, heat exchangers, etc. in equipment.
Special media: Such as corrosive media, high-temperature and high-pressure media, flammable and explosive media, etc., require the selection of appropriate materials and sealing surface forms.
2. Selection Key Points:
Pressure and temperature: Select the appropriate PN grade and material based on process conditions. Medium characteristics: Consider the corrosiveness, toxicity, flammability, and explosiveness of the medium, and select corrosion-resistant materials and sealing surface forms.
Installation and maintenance: Based on the installation space and maintenance requirements, choose the appropriate flange structure (such as butt-weld flanges are convenient for on-site welding, and loose-lipped flanges are convenient for disassembly).
Economy: Under the premise of meeting the process requirements, select materials and structures with lower costs.
VI. Comparison with Other Standards
1. Comparison with Class series standards:
PN series: Pressure grade is indicated by nominal pressure (PN), with units of bar, applicable to the European system.
Class series: Pressure grade is indicated by pound class (Class), with units of pounds per square inch (psi), applicable to the American system.
Conversion relationship: Class 150 ≈ PN 10, Class 300 ≈ PN 20, Class 600 ≈ PN 50.
2. Comparison with national standards (GB):
PN series: Chemical industry standards such as HG/T 20592-2009 are based on the PN series and applicable to the chemical industry.
GB standards: Such as GB/T 9112-2010, applicable to general industrial pipelines, some parameters differ from the PN series.
VII. Details of Identification
1. Standard number: Ensure that the implemented standard is consistent with industry requirements, such as the chemical industry should prefer HG/T 20592-2009.
2. Nominal diameter (DN): Match with the outer diameter of the steel pipe, avoiding confusion between A series (international standard series) and B series (domestic standard series).
3. Material grade: Clearly indicate the material composition and performance, such as 304 stainless steel should be labeled as S30408 or 06Cr19Ni10.
4. Sealing surface form: Select the appropriate sealing surface form according to the medium and pressure to ensure sealing reliability.
VIII. Summary
The PN series standard of chemical flanges through a unified identification system, standardizes the key parameters such as size, pressure, material, and sealing surface form of the flange, providing a reliable guarantee for the equipment connection in the chemical industry. In practical applications, it is necessary to reasonably select the type and specification of the flange based on process conditions, medium characteristics, and economy, to ensure the safety and stability of the system.
