The PN series standards for chemical flanges are an important standard system used in the chemical industry to regulate flange connections, mainly involving key parameters such as the size, pressure rating, material, and sealing surface form of flanges. The following is a detailed analysis of the PN series standards from five aspects: identification composition, nominal pressure (PN) grade, sealing surface form, material and structure, application and selection:

I. Logo Composition

The marking of PN series flanges is usually composed of standard number, nominal pressure (PN), nominal diameter (DN), sealing surface form, material grade and other parts. For example, the identification "HG/T 20592-2009 PN16 DN100 RF S30408" indicates:

HG/T 20592-2009: The implemented standard is the chemical industry standard HG/T 20592-2009;

PN16: The nominal pressure is 16 bar;

DN100: Nominal diameter is 100 mm;

RF: The sealing surface form is a raised surface;

S30408: Material is 06Cr19Ni10 (304 stainless steel).

Ii. Nominal Pressure (PN) Grade

The PN series standards use the nominal pressure (PN) as the pressure rating 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, the pressure corresponding to PN16 is approximately 1.6 MPa.

Application scope:

Different PN grades are suitable for different pressure and temperature conditions, and the appropriate grade should be selected according to the process requirements.

Iii. Sealing surface Form

The form of the sealing surface directly affects the sealing performance of the flange. Common forms of sealing surfaces include:

Raised surface (RF) : Smooth surface, suitable for general media and pressure conditions.

Full flat surface (FF) : The surface is completely flat and suitable for low-pressure, non-critical sealing applications.

Concave-convex surface (MFM) : One flange is concave and the other is convex, suitable for higher pressure and temperature conditions.

Tenon groove surface (TG) : One flange is tenon and the other is groove, suitable for high-pressure, high-temperature or flammable and explosive media.

Ring connection surface (RJ) : It adopts metal ring sealing and is suitable for ultra-high pressure and high-temperature conditions.

Iv. Materials and Structures

Materials:

Carbon steel: such as Q235 and 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.

Structure

Plate flat welding flange (PL) : The flange plate is directly welded to the steel pipe and is suitable for low-pressure and non-critical applications.

Necked flat welding flange (SO) : The flange has a short neck, and its rigidity and sealing performance are superior to those of the plate flat welding flange.

Necked butt-weld flange (WN) : The flange has a long neck and is suitable for high-pressure, high-temperature or highly vibrating applications.

Integral flange (IF) : The flange is an integrated structure with the equipment or pipeline and is suitable for critical equipment.

Loose flange: The flange is connected to the equipment or pipeline through flanging or loose fitting, and is suitable for occasions where disassembly is required.

V. Application and Selection

Application field:

Chemical, petroleum, pharmaceutical, food and other industries: It is used for the connection of equipment such as pipelines, valves, pumps and heat exchangers.

For special media such as corrosive media, high-temperature and high-pressure media, flammable and explosive media, etc., appropriate materials and sealing surface forms need to be selected.

Key points for selection:

Pressure and temperature: Select the appropriate PN grade and material based on the process conditions.

Medium characteristics: Considering the corrosiveness, toxicity, flammability and explosiveness of the medium, etc., select corrosion-resistant materials and sealing surface forms.

Installation and maintenance: According to the installation space and maintenance requirements, select the appropriate flange structure (for example, butt-weld flanges are convenient for on-site welding, and loose flanges are easy to disassemble).

Economy: Under the premise of meeting the process requirements, select materials and structures with lower costs.

Vi. Comparison with Other Standards

Comparison with the Class series standards:

PN series: The pressure rating is indicated by nominal pressure (PN), with the unit being bar, and it is suitable for the European system.

Class series: Pressure grades are indicated in pounds (Class), with the unit being pounds per square inch (psi), and are suitable for the American system.

Conversion relationship: Class 150 ≈ PN 10, Class 300 ≈ PN 20, Class 600 ≈ PN 50.

Comparison with the national standard (GB) :

PN series: Chemical industry standards such as HG/T 20592-2009 are based on the PN series and are applicable to the chemical industry.

GB standards: such as GB/T 9112-2010, applicable to general industrial pipelines, and some parameters are different from those of the PN series.

Vii. Points to Note for Logo Details

Standard number: Ensure that the implemented standard is consistent with industry requirements. For example, HG/T 20592-2009 is preferred in the chemical industry.

Nominal diameter (DN) : Match the outer diameter of the steel pipe to avoid confusion between Series A (internationally recognized series) and Series B (domestically used series).

Material grade: Clearly specify the material composition and properties. For example, 304 stainless steel should be marked as S30408 or 06Cr19Ni10.

Sealing surface form: Select the appropriate sealing surface form based on the medium and pressure to ensure sealing reliability.

Viii. Summary

The PN series standards for chemical flanges, through a unified identification system, standardize key parameters such as the size, pressure, material, and sealing surface form of flanges, providing reliable guarantees for equipment connections in the chemical industry. In practical applications, the type and specification of flanges should be reasonably selected based on factors such as process conditions, medium characteristics and economy to ensure the safety and stability of the system.