BS 1387 Pipes: Dimensions, Class B/C & Applications

What is BS 1387?

BS 1387:1985 is a crucial British standard that specifies requirements for steel pipes (including both galvanized and non-galvanized steel pipes). Its full title is "Specification for Screwed and socketed steel tubes and tubulars and for plain end steel tubes suitable for welding or for screwing to BS 21 pipe threads."

It defines three wall thickness series: Light (thin-wall), Medium (medium-wall), and Heavy (thick-wall). The standard has been superseded by EN 10255, but is still widely referenced in existing projects and Commonwealth markets.

Common Names: In the market, steel pipes that meet BS 1387 standards are often referred to as "gas pipes" or "water-gas pipes."

Key Features:

Material: Specified steel pipe, available in either galvanized or black (non-galvanized) versions.

Manufacturing Process:
BS 1387 steel pipes are manufactured using processes including high-frequency welding (HFW) and seamless hot rolling. These pipes undergo pre-treatment, grinding, and spray coating to ensure a uniform and leveling coating.

Hot-Dip Galvanizing:

BS 1387 steel pipes can be hot-dip galvanized to enhance corrosion resistance and service life. Hot-dip galvanizing is a process in which molten metal reacts with an iron matrix to create an alloy layer, bonding the base and coating. 

▶ For detailed galvanizing specifications (round, square, and rectangular), see our [BS 1387 Hot-Dip Galvanized Steel Pipe].

End Types:
Screwed and Socketed: Pipes with screwed ends and sockets for connection.

Plain End: Pipes with plain ends suitable for welding or screwing to BS 21 pipe threads.

BS 1387 Dimensions & Weights

The table below shows BS 1387 dimensions and theoretical weights for the Light, Medium, and Heavy series. Medium and Heavy weights are identical to IS 1239 Medium/Heavy.

Notes:
BS 1387 equivalence: IS 1239 Medium/Heavy weights are identical to BS 1387 Medium/Heavy. Buyers in the Middle East and Commonwealth markets can use this table directly for IS 1239 orders — no conversion needed.
Galvanized pipes: Hot-dip galvanizing adds approximately 3%–6% to the weight, depending on zinc coating thickness (typically 50–100 μm).
Length: Standard 5.5m, 5.8m, 6m, 11.8m, or 12m. Custom lengths available on request.

▶ For full IS 1239 weight data, see our [MS ERW Pipe Weight Chart].

BS 1387 Class B vs Class C

BS 1387 Class B and Class C refer to the zinc coating weight, not to wall thickness or pressure rating.

The purpose of galvanizing is to form a protective layer on the steel surface to prevent rust and corrosion. Class C requires a thicker zinc layer than Class B, thus providing longer-lasting, more durable corrosion protection.

Comparison	Class B (Light Galvanizing)	Class C (Heavy Galvanizing)
Zinc coating weight (≥g/m²)	375	475
Approx. thickness (μm)	~55	~67
Corrosion resistance	Moderate	Stronger
Suitable environment	Indoor, mild corrosion	Outdoor, buried, coastal, industrial
Typical applications	Indoor water pipes, compressed air pipes	Railings, scaffolding, buried pipes, high-salt areas
Surface appearance	Smoother, more uniform	Rougher, more visible zinc spangles
Cost	Slightly lower	Higher

Relationship with Light/Medium/Heavy: 

Light/Medium/Heavy refers to wall thickness (mechanical strength). Class B/C refers to zinc coating weight (corrosion resistance). They are independent — you can order a "Medium Duty, Class C" pipe.

Types and Classifications of BS 1387 Standards:

BS 1387 standard classifies steel pipes based on their manufacturing process, wall thickness, and coating:

1. Classification by Type and Wall Thickness

Light (Thin-Wall): Suitable for applications with relatively high working conditions, such as indoor water pipes. 

Medium (Medium Wall): The most commonly used type, suitable for general water, gas, and air systems.

Heavy (Thick Wall): Suitable for applications requiring more demanding conditions and higher mechanical strength, such as buried pipelines or areas subject to external impact.

2. Classification by Coating

Galvanized Steel Pipe (GI): Hot-dip galvanizing is applied to both the inner and outer surfaces of the pipe, providing excellent rust and corrosion resistance. This is the most common type and has a silver-gray color.

Black Steel Pipe: Ungalvanized steel pipe has a black oxide scale on the surface. It has poor corrosion resistance and usually requires anti-corrosion treatment such as painting before use.

BS 1387 Mechanical Properties & Testing

BS 1387 specifies clear mechanical and testing requirements to ensure pipes can withstand fluid pressure and mechanical stress in service.

1. Tensile strength: The standard specifies a minimum tensile strength of approximately 320 MPa for Medium and Heavy series pipes. This ensures the pipe wall can resist internal pressure without deformation.
2. Flattening test: A ring cut from the pipe is flattened between two parallel plates to a specified distance. The weld and pipe wall must show no cracks or signs of failure. This verifies ductility and weld quality.
3. Bend test: A specimen is bent through a specified angle. No cracking is allowed on the outer surface. This confirms the pipe can be bent or formed on site without fracturing.
4. Hydrostatic test: Every pipe undergoes a hydrostatic test at a specified pressure before leaving the factory. This is a mandatory test for all BS 1387 pipes to ensure leak-tightness and wall strength.

5. Threaded ends: Pipe ends are machined with standard tapered pipe threads (BS 21, now ISO 7-1), allowing connection with pipe elbows, tees, and unions without welding. When replacing old BS 1387 pipes, always measure the outside diameter to confirm the specification — a mismatch may cause threaded connections to leak.

Typical Applications of BS 1387:

1. Building water supply and drainage systems: Particularly cold water pipes.
2. Gas distribution pipelines: Low-pressure indoor and outdoor gas networks.
3. Structural applications: Scaffolding, framing, fencing, railings, and supporting structures.
4. Fire protection pipe: BS 1387 galvanized pipes for fire sprinkler systems, fire protection piping, and red fire pipe applications. For sizes and specifications, see our [BS 1387 Hot-Dip Galvanized Steel Pipe Sizes & Specifications].
5. Industrial piping: General low-pressure industrial piping.

Current Status and Replacement Standards:

Standard Status: BS 1387 vs EN 10255

BS 1387 has been superseded by EN 10255 ("Non-alloy steel welded pipes suitable for threaded and compression fittings"). EN 10255 is the most direct successor and also specifies thin-wall, medium-wall, and heavy-wall series. Dimensions and applications are very similar, and the two standards are technically harmonized.
Other related standards:
EN 10305 series: Steel pipes for precision purposes
ISO 65: Carbon steel pipes suitable for ISO 7-1 threads

Important Note: Although BS 1387 has been superseded, it is still encountered in the following situations:

1) Maintenance and renovation of existing, older facilities. 

2) Some countries and regions still use the British Standards system.

3) Out of habit, users still refer to steel pipes that comply with newer standards such as EN 10255 as BS 1387 pipes.

BS 1387 Round Tube Sizes:

Purchasing Tips:

When ordering or replacing BS 1387 galvanized pipe, you will need to specify:

Nominal diameter: e.g., 1/2", 1", 2"
Wall thickness: Light, Medium, or Heavy
Coating: Galvanized (Class B or C) or Black
End type: Plain, threaded, or socketed
Length: 5.5m, 6m, 12m, or custom

If your environment presents a high corrosion risk (outdoor, buried, coastal) or pipe replacement is difficult, we strongly recommend Class C (heavy galvanized) for a longer service life. For general indoor applications, Class B is generally sufficient.

FAQs

Q1: What is the difference between BS 1387 Class B and Class C?
A: Class B = light galvanizing (zinc ≥375 g/m², ~55μm). Class C = heavy galvanizing (zinc ≥475 g/m², ~67μm). Class C offers longer corrosion protection for outdoor, buried, or coastal environments.

Q2: What is the difference between BS 1387 Light/Medium/Heavy and Class B/C?
A: Light/Medium/Heavy refers to wall thickness (mechanical strength). Class B/C refers to zinc coating weight (corrosion resistance). They are independent specifications.

Q3: Can BS 1387 pipes be used for fire sprinkler systems?
A: Yes. BS 1387 galvanized pipes (Class B or C) are commonly used for fire sprinkler systems. For exposed or corrosive environments, Class C is recommended.

Q4: Where can I find the BS 1387 PDF?
A: The full standard is available from BSI. This page provides a summary of the key dimensions and Class B/C requirements.

Conclusion:

BS 1387 is a classic standard for threaded steel pipes used for low-pressure fluid transportation. Its reliable performance, convenient threaded connections, and wide applicability have left a deep impression worldwide, particularly in Commonwealth countries and regions heavily influenced by the UK. Although it has been superseded by more modern EN standards, its technical requirements and product form factors continue to be preserved in the newer standards. When purchasing or discussing products, be sure to confirm whether strict compliance with the older BS 1387 standard is required or whether products complying with modern equivalents (such as EN 10255) are acceptable.

Read more:

●  BS 1387 Hot-Dip Galvanized Steel Pipe

●  MS ERW Pipe Weight Chart (IS 1239) – Indian Standard

●  Galvanized ERW Carbon Steel Pipe 

●  Guide for Selecting the Thickness of Galvanized Steel Pipe