How to Identify Markings on Flanges
author: www.qishine.com
2026-02-27
Decoding the "ID Card" on Flanges: Reading the Secrets of Industrial Piping from Their Markings
In the intricate world of industrial piping systems, flanges act as crucial "joints," responsible for connecting, sealing, and supporting components. Yet, the dense array of markings, symbols, letters, and numbers on flanges often causes confusion—what key information lies behind them? Mastering the interpretation of flange markings is not only an essential skill for professionals but also a fundamental requirement for ensuring the safe and efficient operation of piping systems. This article will guide you step-by-step in cracking the code of flange markings.
1. Company Logo: Tracing the Manufacturing Source
The manufacturer's logo or trademark on a flange is the starting point for tracing product quality responsibility. It represents the company's reputation and quality control standards. During procurement or maintenance, opting for products from reputable brands with clear markings adds an extra layer of security to the system.
The manufacturer's logo or trademark on a flange is the starting point for tracing product quality responsibility. It represents the company's reputation and quality control standards. During procurement or maintenance, opting for products from reputable brands with clear markings adds an extra layer of security to the system.
Flange Marking: Logo, Standard, Flange Type, Size, Pressure, Sealing face Type, Material, Heat Number
2. Standard Code: The Universally Understood Technical Language
The standards a flange adheres to form the foundation of its technical specifications. The most common standards include:
American Standard System: ASME/ANSI B16.5 (common pressure ratings and dimensions), such as the ASME B16.5 BL Flange, and API 6A (oil and gas wellhead equipment)
European Standard System: EN 1092-1 (common in Europe), DIN (German standard)
Other Important Standards: JIS (Japanese standard), GB/T (Chinese national standard)
The standard code is typically located near the logo and indicates the technical specifications governing the flange's dimensions, pressure ratings, facing types, etc.
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15985833169
3. Flange Type: Structure Determines Application
Flange type is usually indicated by abbreviations or symbols. Common types include:
- WN (Welding Neck Flange): For high-pressure and high-temperature applications.
Flange type is usually indicated by abbreviations or symbols. Common types include:
- WN (Welding Neck Flange): For high-pressure and high-temperature applications.
Weld Neck Flange
- SO (Slip-On): Easy to install; used for medium to low pressure.
Slip On Flange
- BL (Blind): Used to seal the end of a piping system.
Blind Flange: without holes, used for end sealing
- THD (Threaded): Connects to the pipe via threads.
Threaded Flange
- LJ (Lap Joint): Used with a stub end.
Lap Joint Flange: A stub end and a lap joint ring
- SW (Socket Weld): Socket weld flange，Suitable for high-pressure and high-temperature environments.
Socket Weld Flange
4. Size Parameters: Deciphering DN and OD
Size markings typically include:
- Nominal Diameter: e.g., DN150, NPS 6″, representing the universal size for the piping system.
- Outside Diameter and Thickness: Some flanges may indicate the actual OD and center thickness.
- Bolt Hole Information: Includes number of holes, hole diameter, and bolt circle diameter (BCD).
Size markings typically include:
- Nominal Diameter: e.g., DN150, NPS 6″, representing the universal size for the piping system.
- Outside Diameter and Thickness: Some flanges may indicate the actual OD and center thickness.
- Bolt Hole Information: Includes number of holes, hole diameter, and bolt circle diameter (BCD).
5. Pressure Rating: A Critical Safety Indicator
The pressure rating marking is vital. Common systems include:
- American Class Series: Class 150, 300, 600, 900, etc. The number represents pressure-bearing capacity (in psi) at ambient temperature.
- European PN Series: PN6, PN10, PN16, PN25, etc. The number represents the nominal pressure in bar.
The pressure rating marking is vital. Common systems include:
- American Class Series: Class 150, 300, 600, 900, etc. The number represents pressure-bearing capacity (in psi) at ambient temperature.
- European PN Series: PN6, PN10, PN16, PN25, etc. The number represents the nominal pressure in bar.
Note: Pressure rating is closely related to flange material and operating temperature. It must be used in conjunction with the standard temperature-pressure rating tables.
6. Facing Type: Key to Leakage Prevention
The flange facing marking determines its sealing performance and the type of gasket required:
- FF (Flat Face): For low-pressure, non-hazardous media.
- RF (Raised Face): The most common type, used with soft gaskets.
The flange facing marking determines its sealing performance and the type of gasket required:
- FF (Flat Face): For low-pressure, non-hazardous media.
- RF (Raised Face): The most common type, used with soft gaskets.
Comparison between FF Flange and RF Flange
- RTJ (Ring Type Joint): For high-pressure and high-temperature applications.
FF Flange VS RF Flange VS RTJ Flange
- TG (Tongue and Groove): For media prone to leakage.
Tongue & Groove Face (T & G)
7. Material Identification: Assurance of Corrosion Resistance and Strength
Material codes indicate the manufacturing material of the flange. Common ones include:
- Carbon Steel Series: A105 (forged carbon steel), WCB (cast carbon steel)
- Stainless Steel Series: 304/L, 316/L, 321 (corrosion-resistant, high-temperature)
- Alloy Steel Series: F11, F22 (high-temperature and high-pressure resistant)
- Special Materials: Monel, Inconel (resistant to extreme corrosion)
Material codes indicate the manufacturing material of the flange. Common ones include:
- Carbon Steel Series: A105 (forged carbon steel), WCB (cast carbon steel)
- Stainless Steel Series: 304/L, 316/L, 321 (corrosion-resistant, high-temperature)
- Alloy Steel Series: F11, F22 (high-temperature and high-pressure resistant)
- Special Materials: Monel, Inconel (resistant to extreme corrosion)
Material selection must be based on media characteristics, temperature, pressure, and environmental factors.
8. Heat Number / Lot Number: The Lifeline for Quality Traceability
The Heat Number or Lot Number is a unique identifier for material traceability. It can be used to query:
- The production batch of the raw material
- Chemical composition test reports
- Mechanical property test data
- Heat treatment records
The Heat Number or Lot Number is a unique identifier for material traceability. It can be used to query:
- The production batch of the raw material
- Chemical composition test reports
- Mechanical property test data
- Heat treatment records
During quality audits or incident analysis, the heat number is an indispensable traceability clue.
Conclusion: Small Markings, Significant Responsibility
Although small, the markings on a flange are an information hub connecting safety, efficiency, and responsibility. Mastering their interpretation means you can:
Although small, the markings on a flange are an information hub connecting safety, efficiency, and responsibility. Mastering their interpretation means you can:
1. Select Accurately: Choose the correct flange specifications based on operating conditions, avoiding mismatches.
2. Assess Safety: Evaluate usage risks through pressure and material markings.
3. Troubleshoot Quickly: Rapidly identify component parameters during maintenance, minimizing downtime.
4. Trace Responsibility: Pinpoint supply chain links through the logo and heat number.
2. Assess Safety: Evaluate usage risks through pressure and material markings.
3. Troubleshoot Quickly: Rapidly identify component parameters during maintenance, minimizing downtime.
4. Trace Responsibility: Pinpoint supply chain links through the logo and heat number.
There are no small matters in industrial safety. Whether you are an engineer, procurement specialist, or field operator, developing the professional competence to "read and identify markings" is a responsibility to your work and a commitment to safety. It is recommended to build a library or database of flange markings in daily work, accumulating experience to ensure every connection is reliable and every marking is clear.
Qishine is ideal choice for EPC companies and project contractors.
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15985833169
FF RF or RTJ Choose the Right Flange Face or Pay the Price Later
How to Choose the Marking Method for Fasteners
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