Hot-Dip Galvanized Seamless Steel Pipe

Seamless steel pipe with a hot-dip zinc coating of 30 to 700 g/m² on the outside and inside, combining no weld seam with full corrosion protection. From OD 18 mm to 530 mm in 20#, 45# and A106 Gr.B, for high-pressure lines exposed to weather, salt or chemical attack.

Product Overview

Galvanized seamless pipe combines two properties that are rarely needed at once: the pressure capability of a seamless wall and the corrosion protection of a zinc coating. The base pipe is pierced and rolled from a solid billet so it has no weld seam, and it is then pickled, fluxed and dipped in molten zinc so the coating forms on the outside surface and on the bore, including the cut ends.

The combination is specified where a line carries pressure and is also exposed to a corrosive environment — high-pressure water and process lines at coastal plant, chemical and petrochemical pipework, cooling and chemical dosing lines in power stations, marine and offshore systems, and oilfield injection and gathering lines. In these duties an uncoated seamless pipe corrodes from the outside in a marine atmosphere and from the inside wherever the fluid is aggressive, and painting cannot reach the bore.

We supply galvanized seamless pipe from OD 18 mm to 530 mm with wall thicknesses from about 2.7 mm to 11 mm in the standard range, in 20# quality carbon steel, 45# for higher-strength duty and A106 Gr.B where the elevated-temperature specification applies. Coating weight is chosen per order, and a high-build coating of about 300 g/m² and above is available for aggressive service.

Specifications & Size Range

Common outside diameters and wall thicknesses available galvanized, with the coating weight chosen per order. Because the coating is applied to a seamless base pipe, wall thickness and pressure capability are as for the uncoated pipe. Heavier walls and larger diameters are made to order.

Outside diameter	Common OD × wall (mm)	Coating (g/m²)	Standard length	Typical service
Small, OD 18 – 38 mm	18×3, 22×3, 25×3, 27×3, 32×3, 38×3	30 – 300	6 m, cut to order	Instrument and dosing lines, small pressure lines, marine fittings
Medium, OD 42 – 89 mm	42×3.5, 48×3.5, 57×4, 60×4, 76×4, 89×4.5	100 – 400	6 m, cut to order	Process pipework, cooling lines, chemical and seawater lines
Large, OD 108 – 219 mm	108×4.5, 114×5, 133×5, 159×6, 168×6, 219×7	200 – 500	6 m / 12 m	Water and process mains, power plant pipework, oilfield injection lines
Extra large, OD 245 – 530 mm	273×7, 325×8, 377×9, 426×10, 480×10, 530×10	275 – 500	6 m / 12 m, made to order	Large process and outfall lines, marine structures, plant headers
Heavy wall – high pressure	Any OD above, wall to 20 mm	as specified	to order	High-pressure chemical, hydraulic and offshore pipework

Tolerances

Base pipe dimensions follow the referenced seamless standard for the production route, with cold-drawn sizes held to a tighter diameter and wall tolerance than hot-rolled. Coating is applied and tested to GB/T 13912, ISO 1461, ASTM A123 and JIS H8641, quoted as coating mass in g/m² total on both surfaces, with about 7 µm of coating per 100 g/m². Hydrostatic testing and ultrasonic wall inspection are available on the base pipe before coating.

Steel Grades & International Equivalents

All grades below are supplied with a mill test certificate. The right-hand column shows the material type and the Chinese standard the grade is produced to; the middle columns give the nearest recognised equivalent in other national standards. Exact equivalence for a specific project should be confirmed on the enquiry.

GB (China)	ASTM / AISI (US)	EN (Europe)	JIS (Japan)	DIN (Germany)	Type / Standard
Q235B + hot-dip galvanized	A123 / A153 (ASTM)	EN ISO 1461	JIS H8641	DIN 50976	Hot-dip galvanized structural steel (GB/T 13912)
20# seamless (A106 Gr.B equivalent)	A106 Gr.B / A53 Gr.B	P235GH (EN 10216-2)	STPG370 (JIS G3454)	St37.0	Seamless carbon steel pipe (GB/T 8163 / GB/T 3087)
20# (20 carbon steel)	AISI 1020 / ASTM A29 1020	C22 (EN 10083)	S20C (JIS G4051)	CK22	Quality carbon structural steel (GB/T 699)

Grade Notes

• Q235B + hot-dip galvanized — Zinc coating of 30–700 g/m² gives 5–30+ years of atmospheric corrosion protection depending on thickness and environment.
• 20# seamless (A106 Gr.B equivalent) — High-temperature service seamless pipe for steam, water and process lines. Supplied with mill test certificate.
• 20# (20 carbon steel) — Low-carbon quality steel with good weldability and cold formability. Standard material for seamless pipes, boilers and machined parts.

Chemical Composition (%, ladle analysis)

Typical specification limits. Actual heat values are reported on the mill test certificate supplied with every shipment.

Grade	C	Si	Mn	P max	S max	Other elements
20# seamless (A106 Gr.B equivalent)	≤0.30	≥0.10	0.29–1.06	≤0.035	≤0.035	—
20# (20 carbon steel)	0.17–0.24	0.17–0.37	0.35–0.65	≤0.035	≤0.035	—

Mechanical Properties

Minimum values at room temperature unless stated. ReL = yield strength; Rp0.2 = 0.2% proof stress; Rm = tensile strength; A = elongation after fracture.

Grade	Yield (ReL)	Proof (Rp0.2)	Tensile (Rm)	Elongation A	Impact / others
Q235B + hot-dip galvanized	—	—	—	—	—	Coating 30–700 g/m² (both sides), made to order Adhesion per GB/T 13912 bend test
20# seamless (A106 Gr.B equivalent)	≥240 MPa	—	≥415 MPa	≥22%	—	—
20# (20 carbon steel)	≥245 MPa	—	≥410 MPa	≥25%	—	—

Standards & Documents

• GB/T 8163 — seamless steel pipes for liquid service
• GB/T 3087 — seamless steel pipes for low and medium pressure boilers
• ASTM A106 Gr.B — seamless carbon steel pipe for high-temperature service
• GB/T 13912 — hot-dip galvanized coatings on fabricated iron and steel articles
• ISO 1461 / ASTM A123 — hot-dip galvanized coating specifications, international
• Testing: hydrostatic pressure test, ultrasonic or eddy-current wall inspection, coating mass report, EN 10204 3.1 mill certificate

Typical Applications

Industry / Application	Typical use
Coastal & marine process lines	Seawater and cooling lines, jetty and offshore pipework and dockside systems, where salt spray attacks an uncoated pipe within months.
Chemical & petrochemical pipework	High-pressure process lines, dosing and transfer lines and plant piping exposed to chemical attack on the outside as well as the inside.
Power station & water treatment	Cooling water, chemical dosing, demineralised water and firefighting lines at power and desalination plants.
Oilfield & injection service	High-pressure injection and gathering lines, wellhead piping and surface pipework in corrosive field conditions.
High-pressure water systems	Hydrant and deluge mains, hydro-power and penstock auxiliary lines and pressure lines installed in wet or buried conditions.
Outdoor & buried pipework	Any pressure line installed above ground in aggressive weather or buried without additional wrapping, where a coated seamless pipe removes the need for site painting.
Structural high-pressure assemblies	Jacking, piling and structural tubular members that also carry internal pressure or must resist external corrosion without maintenance.

Common Problems Buyers Face — and How We Prevent Them

These are the issues that most often cause claims on steel imports. Each one is controlled in our process before shipment.

Our Supply & Manufacturing Advantages

• Pressure capability plus corrosion protection — A seamless wall for high-pressure duty with a coating that protects the outside and the bore, so no site painting or wrapping is needed.
• Coating inside and outside — The bore and the cut ends are coated as well as the outer surface, which is what protects a high-pressure line carrying aggressive fluid.
• Three grades for different duties — 20# for general pressure service, 45# for higher strength, and A106 Gr.B for elevated-temperature lines.
• Coating weight to your specification — 30 to 700 g/m² quoted on the enquiry, with a high-build coating of 300 g/m² and above available for aggressive service.
• Tested before coating — Hydrostatic pressure testing and ultrasonic or eddy-current wall inspection are performed on the base pipe, so a defect is found before the coating is applied.
• Complete documentation — Mill test certificate for the heat, hydrostatic test report and coating mass report issued as a matched set for the same pipe.

Packaging, Delivery & Payment

• Packing: loose in bulk vessel, or bundled and containerised to your requirement. Galvanized and coated products get VCI paper, waterproof wrapping and edge protection. See our export packaging methods.
• Availability: both stock and custom production. Tell us the specification and we will confirm the route.
• MOQ: no strict minimum — one ton can ship.
• Lead time: stock dispatched to port within 3 days; orders needing export packaging about 1 week; custom production quoted per product.
• Payment: stock — 10% deposit, balance before shipment; custom production — 50% deposit, balance before shipment.
• Documents: EN 10204 3.1 mill test certificate with every shipment; third-party inspection (SGS / BV) on request.

Frequently Asked Questions

Request a Quotation Export Packaging

Live Stock & Indicative Price

The table below lists live stock at the time of publication, with indicative EXW China reference prices in USD per tonne (converted at 6.70 CNY/USD). Steel prices move with the mill market every week — send us your size, quantity and destination and we will confirm availability and issue a firm FOB or CIF quotation.

Showing 98 of 98 listed sizes. Price range USD 681–1,239 per tonne (EXW China). MOQ from 1 tonne; stock dispatched to port within 3 days. Mill test certificate (EN 10204 3.1) and third-party inspection available on request.

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