This article covers the key marking requirements for four major categories: steel pipes (ASME B36.10 & B36.19), flanges (ASME B16.5), butt-weld fittings (ASME B16.9), and forged fittings (ASME B16.11). All these standards follow the general marking principles defined in MSS SP-25.

About MSS SP-25 – General Marking Regulation

MSS SP-25 is the universal standard marking system for valves, flanges, fittings, and unions used in industrial piping systems. Published by the Manufacturers Standardization Society (MSS), this standard defines consistent rules for marking content, location, method, and durability. It is widely referenced by major ASME standards, including ASME B16.5, B16.9, and B16.11.

The main purpose of MSS SP-25 is to ensure clear product identification, material traceability, pressure rating recognition, and safe installation. It specifies mandatory items such as manufacturer identification, material grade, size, pressure class, standard number, and heat number.

In short, MSS SP-25 serves as the common foundation for marking all ASME B16 series piping products.

ASME B36.10 & B36.19 – Marking for Steel Pipes

ASME B36.10M (for carbon steel pipes) and ASME B36.19M (for stainless steel pipes) are dimensional standards. They only define outer diameter, wall thickness, tolerance, length, and bevel requirements. These two standards do NOT include any marking requirements.

Marking for steel pipes must follow the applicable material specification, such as:

• ASTM A53, ASTM A106, API 5L for carbon steel
• ASTM A312, ASTM A213 for stainless steel

Typical marking:

• Manufacturer’s logo or trademark  (Optional)
• Product Name
• Pipe Type (seamless or welded)
• Size
• Length
• Material grade
• Standard
• Heat number

For example: PIPE SMLS 1/2″ X 6MTR ASTM A106 GR.B SCH STD ASME B36.10 ZZ2570

ASME B16.5 – Flange Marking

ASME B16.5 is the standard for pipe flanges and flanged fittings. It includes clear and detailed marking requirements, based on MSS SP-25.

Typical marking contents:

• Manufacturer’s trademark (Optional)
• Flange Name
• Nominal size
• Pressure class
• Hub Thickness (for weld neck flange)
• Sealing Face
• Material
• Standard
• Heat number (mandatory for cast steel flanges)

Sequence of the marking do not have strict regulation.

For example: SHZC 4″ #2500 SCH40 RTJ WN FLANGE ASTM A350 LF2 ASME B16.5 ZZ0440

ASME B16.9 – Marking for Butt Weld Fittings

ASME B16.9 covers factory-made butt-weld fittings, including elbows, tees, reducers, and caps. Its marking requirements follow MSS SP-25.

Typical marking examples:

• Manufacturer’s identification mark (Optional)
• Fitting Name
• Fitting Type (seamless or welded)
• Material grade
• Nominal size
• Standard
• Heat number

A complete marking shows like: 90DEG LR SMLS 3IN SCH80 ASTM A234 WPB ASME B16.9 ZZ0188

ASME B16.11 – Forged Steel Fittings Marking

ASME B16.11 applies to socket-weld and threaded forged steel fittings. Marking rules are clearly defined and based on MSS SP-25.

Typical marking examples:

• Manufacturer’s mark (Optional)
• Fitting Name
• Fitting Type (SW or THD)
• Material
• Pressure rating
• Nominal size
• Standard
• Heat number

Such as: 90DEG DN20 3000# BSPT ASTM A105 ASME B16.11 ZZ0250

Conclusion

Understanding marking requirements for ASME B16 and B36 series products helps ensure correct material selection, quality control, and site compliance.

• ASME B36.10/B36.19 pipes: No marking requirements — follow material standards.
• ASME B16.5 flanges, B16.9 butt-weld fittings, B16.11 forged fittings: Follow their own standards plus MSS SP-25.

Correct marking improves traceability, reduces installation errors, and supports long-term reliability in industrial piping systems.

In short, we generally follow the formula below:

Manufacturer’s mark+Name+Type+Size+Material+Standard+Heat Number

Some parts of the marking contents can be deleted when the marking space is limited. And sequence of the marking do not have strict regulation. But below 5 parts cannot be omitted anytime.

Mandatory content: Type+Size+Material+Heat Number

Custom markings are also commonly applied as agreed with customers.

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