Introduction
Flanges are crucial components in piping systems, providing secure connections between pipes, valves, pumps, and other equipment. To ensure proper identification and compliance with industry standards, manufacturers mark flanges with specific details. These markings provide critical information about the flange’s specifications, including material, pressure rating, dimensions, and manufacturing details. This guide will explore the different types of markings found on flanges and their significance.
Common Flange Markings
Flange markings are typically stamped, engraved, or printed onto the flange’s surface, commonly found on the outer rim or the face of the flange. Below are the primary types of markings and what they indicate:
1. Standard or Specification
Flanges are manufactured according to specific international and national standards that determine their dimensions, tolerances, pressure ratings, and material properties. Some of the most widely used standards include:
ASME B16.5 – American standard for pipe flanges and flanged fittings.
ASME B16.47 – Standard for large-diameter flanges (Series A & B).
EN 1092-1 – European standard for steel flanges.
DIN 2501 – German flange standard.
JIS B2220 – Japanese Industrial Standard.
GB/T 9119-2010 – Chinese standard for steel pipe flanges.
For example, a flange marked ASME B16.5 indicates compliance with the American standard for pipe flanges and flanged fittings.
2. Nominal Diameter (DN/NPS)
The nominal diameter of a flange refers to the inner bore diameter, which corresponds to the size of the pipe it connects to. The marking can appear in two forms:
DN (Diameter Nominal, in millimeters) – Used in metric systems, such as DN100 (nominal diameter of 100mm).
NPS (Nominal Pipe Size, in inches) – Used in ANSI/ASME systems, such as NPS 4” (nominal pipe size of 4 inches).
3. Pressure Rating (PN/Class)
The pressure rating of a flange is a crucial parameter that determines its ability to withstand internal pressure. Pressure ratings are commonly expressed in two systems:
PN (Pressure Nominal, in bar or MPa) – Used in European and metric standards.
PN10, PN16, PN25, PN40, PN100, etc.
Class (in psi or lb) – Used in American standards.
Class 150, 300, 600, 900, 1500, 2500.
For example, a flange marked PN40 means it has a pressure rating of 40 bar, while Class 600 means it can withstand up to 600 psi.
4. Material Specification
Flanges are made from various materials to suit different industrial applications, and the material specification is usually stamped on the flange. Some common materials include:
Carbon Steel:
A105 (for forged carbon steel flanges)
A350 LF2 (for low-temperature carbon steel flanges)
Stainless Steel:
304, 316, 321 (common stainless-steel grades)
A182 F304, A182 F316 (for forged stainless steel)
Alloy Steel:
A182 F11, A182 F22 (for high-temperature and pressure applications)
For example, a marking A182 F316 means the flange is made from forged stainless steel grade 316.
5. Face Type and Finish
The face type of a flange determines how it seals with a gasket. Common types include:
RF (Raised Face) – Most common, used with various gaskets.
FF (Flat Face) – Used when full contact with the gasket is required.
RTJ (Ring Type Joint) – Used for high-pressure applications.
Additionally, the finish is often specified:
Stock Finish (125-250 micro-inch roughness) – Standard for most raised face flanges.
Spiral Serrated (30-55 grooves per inch) – Enhances gasket grip.
For example, a marking RF 125 AARH means the flange has a raised face with a 125 micro-inch roughness.
6. Manufacturer Identification and Heat Number
Flanges must be traceable to their manufacturer for quality assurance. Common markings include:
Manufacturer’s logo or name – Identifies the company that produced the flange.
Heat Number (Heat Code) – A unique code linking the flange to a specific batch of raw material used in manufacturing.
Lot Number – Assigned to track production batches for quality control.
For example, a marking H12345 indicates that the flange belongs to heat number 12345, which can be used to trace the material’s origin and composition.
7. Additional Information
Other optional markings may be found on a flange, such as:
Country of Origin – Indicating where the flange was manufactured.
Year of Manufacture – Some flanges have a year stamped for tracking purposes.
Coatings or Treatments – Such as PTFE-Coated, Galvanized, or Epoxy-Coated to indicate corrosion resistance treatments.
Example Flange Marking Interpretation
Consider the following marking on a flange: ASME B16.5 4″ 150LB A105 RF 125 AARH H12345 This means:
ASME B16.5 – Manufactured according to ASME standard.
4″ – Nominal Pipe Size is 4 inches.
150LB – Pressure rating is 150 psi.
A105 – Material is forged carbon steel.
RF – Raised Face.
125 AARH – Surface roughness is 125 micro-inch.
H12345 – Heat number for traceability.
Conclusion
Understanding flange markings is essential for ensuring compatibility, compliance with standards, and safe operation in piping systems. Each marking provides key details about the flange’s specifications, from size and pressure rating to material composition and manufacturing data. Proper identification helps engineers, procurement teams, and maintenance personnel select and install the correct flange for their applications, reducing the risk of failures and ensuring the integrity of industrial piping systems.