BS 1387 Hot-Dip Galvanized Steel Pipe

What is BS 1387 Hot-Dip Galvanized Steel Pipe?

BS 1387 Hot-dip galvanized steel pipe refers to welded or seamless steel pipe that complies with British Standard BS 1387 and has been hot-dip galvanized. It is suitable for water, gas, and air transportation.

Standard Status: While it has been superseded by European standards such as EN 10255, it is still widely used and referenced in many older systems and specific regions. When replacing old pipes, measure the outside diameter to confirm the specification — a mismatch may cause threaded connections to leak.

This page covers hot-dip galvanized BS 1387 pipes, including the galvanizing process, zinc coating grades, and round/square/rectangular product specifications. ▶ For the BS 1387 standard itself, including Light/Medium/Heavy dimensions, see our [BS 1387 Steel Pipe].

Hot-Dip Galvanizing Process

Hot-dip galvanizing involves immersing clean steel pipe in a bath of molten zinc at approximately 450°C, forming a dense layer of zinc-iron alloy and pure zinc on the surface. The zinc layer acts as a sacrificial protective layer; even if the surface is scratched, the zinc will rust before the iron, thus protecting the pipe itself. 

The zinc coating provides corrosion protection, extending the service life of the pipe, especially in outdoor or harsh environments.

Key Properties of BS 1387 Hot-Dip Galvanized Pipe

1. Corrosion resistance: The zinc coating provides long-term protection against rust and corrosion, especially in outdoor, buried, or coastal environments.
2. Mechanical strength: BS 1387 galvanized pipes have higher mechanical strength than plastic pipes and are more impact-resistant.
3. Fire resistance: The steel pipe is non-flammable and suitable for fire protection systems, including fire sprinkler pipelines.
4. Connection methods: Threaded ends are machined with standard tapered pipe threads (BS 21 / ISO 7-1), allowing easy installation with elbows, tees, and unions — no welding required.
5. Temperature resistance: Suitable for low-pressure steam and hot water applications within standard operating limits.

Wall Thickness Grades

BS 1387 pipes are available in three wall thickness grades:
● Light — thinner wall, for indoor water pipes and less demanding applications
● Medium — standard wall thickness, the most common type for water, gas, and air systems
● Heavy — thicker wall, for buried pipelines and higher-strength applications

Coating Grades

BS 1387 galvanized pipes are available in two zinc coating grades:

● Class B — Lightly galvanized (zinc coating weight approximately ≥375 g/m²)
● Class C — Heavy galvanized (zinc coating weight approximately ≥475 g/m²), providing longer corrosion protection life.

▶ For the full Class B vs Class C comparison table, see our [BS 1387 Steel Pipe Class B/C & Applications].

BS 1387 Hot-Dip Galvanized Steel Pipe Specifications

BS 1387 Galvanized Pipe Size Range

Parameter	Range
Common Sizes	1/4" – 4" (hot-dip galvanized); 1/4" – 6" for Medium/Heavy
Outer Diameter	13.7mm – 114.3mm (1/4" – 4"); up to 168.3mm for 6"
Wall Thickness	2.0mm – 5.4mm (varies by class and size)
Process Type	Seamless pipe or welded
Shapes	Round, square, rectangular, etc.
Lengths	5.5m, 5.8m, 6m, 11.8m (commonly used for fire sprinkler pipes), 12m, or custom
Standards	ASTM, DIN, JIS, BS, GB

Round Galvanized Steel Tube Specification

BS 1387 covers round galvanized steel tubes in nominal sizes from DN15 to DN250. The table below shows common outer diameters, wall thickness ranges, and standard lengths. Wall thickness should be specified by BS 1387 Light, Medium, or Heavy grade.

Square Galvanized Steel Tube Specification

Square galvanized tubes are available in sizes from 15×15mm to 600×600mm. These are typically supplied under EN 10219 or equivalent standards, with hot-dip galvanized finish. Wall thickness range varies by size.

Rectangular Galvanized Steel Tube Specification

Rectangular galvanized tubes are available in sizes from 20×30mm to 500×450mm. These are typically supplied under EN 10219 or equivalent standards, with hot-dip galvanized finish. Wall thickness range varies by size.

Pipe End Treatment

Pipes can be supplied with plain, threaded, or socket ends to accommodate various connection methods.

Threaded Ends:
Pipe ends are typically machined with standard tapered pipe threads (such as BS 21, now ISO 7-1), facilitating installation with threaded fittings such as elbows, tees, and joints. This eliminates the need for welding and facilitates installation.

Strict Testing Requirements

The standard requires that each pipe undergo a hydrostatic test to ensure its leak-tightness and strength.

Flattening and flaring tests are also required to verify workmanship and ductility.

Applications:

1. Low-pressure liquid, water, and steam transportation in residential and commercial buildings, such as cold water pipes and fire sprinkler systems.
2. Gas Piping: Indoor and outdoor low-pressure gas distribution networks.
3. Suitable for indoor and outdoor construction applications requiring durable, corrosion-resistant piping.
4. Compressed Air Piping: Low-pressure compressed air transportation in factory workshops.

5. Building Structures: Widely used in scaffolding, greenhouses, fencing, and other structural applications.

Advantages and Disadvantages of BS 1387 Hot-Dip Galvanized Steel Pipe

Advantages:
1. Corrosion Resistance: The hot-dip galvanized layer provides long-term corrosion protection.
2. High Strength: Compared to plastic pipes, it has higher mechanical strength and is more impact-resistant.
3. Easy Installation: Threaded connections require fewer tools and are easy to install on-site.
4. Fire Resistance: It is non-flammable and suitable for fire protection systems.

Disadvantages:
1. Heavy: It is more labor-intensive to transport and install than plastic pipe.
2. High Internal Resistance: The inner wall is not as smooth as plastic pipe, and the zinc layer may peel or scale after long-term use, affecting flow.
3. Higher Cost: The material and installation costs are higher than many modern plastic pipes (such as PPR and PVC).

4. Superseded: As an older standard, its replacement is recommended for new projects.

FAQs

Q1: Can BS 1387 galvanized 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.

Q2: How much weight does hot-dip galvanizing add?
A: Hot-dip galvanizing adds approximately 3%–6% to the pipe weight, depending on zinc coating thickness (typically 50–100 μm).

Q3: What is the difference between BS 1387 and EN 10255?
A: BS 1387 has been superseded by EN 10255, but the two are technically harmonized. EN 10255 specifies thin-wall, medium-wall, and heavy-wall series similar to BS 1387. 

Looking for BS 1387 Hot-Dip Galvanized Steel Pipes?

We supply round, square, and rectangular galvanized tubes in Class B/C coating, sizes from 1/4" to 6". Contact our team for:

● Product specifications and samples
● Custom lengths and sizes
● Bulk pricing and delivery

📧 info@hu-steel.com

Further Reading
● BS 1387 Pipe Dimensions: Light vs Medium vs Heavy
● MS ERW Pipe Weight Chart (IS 1239) 

● Galvanized ERW Carbon Steel Pipe

● Hot-Dip Galvanizing vs Electro-Galvanizing: Which is Better?

● Guide for Selecting the Thickness of Galvanized Pipe