GDD Metal supplies galvanized round steel pipe, also called GI round pipe or zinc-coated steel tube, for fence posts, greenhouse frames, outdoor supports and fabricated components. Our enquiry process separates the pipe specification from the coating specification: the steel grade and dimensions determine the required mechanical performance, while the zinc system addresses corrosion exposure. Send your size list and application to request a matched quotation.
Galvanized pipe is normally carbon steel pipe with a zinc coating. It therefore belongs to the carbon steel family; galvanizing describes its surface protection rather than a separate structural grade. Zinc forms a barrier between the steel and the environment. It also provides sacrificial protection: in suitable conditions, zinc corrodes preferentially and can protect small exposed areas near the coating. The zinc is gradually consumed, so coating thickness, moisture, salts and the service environment affect performance. No universal rust-free service life can be assumed.
For a typical ERW product, steel strip is formed into a round tube and its longitudinal edges are joined by electric resistance welding. The pipe is sized and inspected before galvanizing. Cleaning, pickling, rinsing and fluxing prepare the steel, which is then immersed in molten zinc, typically around 450°C. Zinc reacts with the clean steel to form bonded iron-zinc layers and an outer zinc-rich surface.
When the process allows cleaning solutions and zinc to flow through the tube, both outside and inside surfaces, including the accessible weld area, can be coated. Confirm inner-wall coverage, drainage, coating acceptance criteria and the required galvanizing standard in the order. Closed fabricated assemblies need a separate venting and drainage review.
In this route, steel strip is zinc-coated before being formed and welded into the tube. It can suit light frames, furniture components and greenhouse fabrication where the specified coating meets the exposure requirement. Welding affects the zinc near the seam; external seam repair and internal seam protection must be confirmed separately. Zinc on the strip does not establish uninterrupted protection inside the finished tube.
Both routes can involve hot-dip galvanizing. The useful purchasing distinction is when galvanizing occurs, which surfaces are protected and how the weld is treated. Surface brightness alone cannot identify the route or prove the coating thickness.
| Parameter | Order specification |
|---|---|
| Product | Galvanized round carbon steel pipe / GI steel tube |
| Pipe construction | ERW for the quoted size range; seamless options assessed separately when requested |
| Outside diameter | Exact OD in mm or NPS / DN with its dimensional standard; size availability confirmed at quotation |
| Wall thickness | Base-steel wall thickness in mm or the applicable schedule, with tolerances specified |
| Length | 5,800 / 6,000 / 11,800 / 12,000 mm or agreed cut length; confirm packing and transport limits |
| Grade and product standard | Examples: ASTM A500 structural tubing, EN 10219 structural hollow sections, or ASTM A53 / EN 10255 / GB/T 3091 pipe where appropriate. Exact grade, edition and tests follow the contract. |
| Galvanizing route | Post-weld hot-dip galvanizing or pre-galvanized strip tube, stated in the quotation |
| Coating requirement | Agreed zinc thickness in µm or coating mass on a defined surface basis; internal coverage and weld treatment specified separately |
| Pipe ends | Plain, beveled, threaded or grooved, subject to pipe specification and processing confirmation |
| Inspection | Agreed dimensional, surface, coating and weld checks; hydrostatic or NDT requirements according to the ordered standard |
| Packing and documents | Identified steel-strapped bundles; end protection, MTC, COO and agreed export documents |
| MOQ and lead time | Confirmed by dimensions, coating route, processing, quantity and shipment plan |
Options describe enquiry routes, not a claim that every dimension, grade and coating combination is available or certified. Structural tube is not automatically qualified for pressure service.
Zinc-coated carbon steel is often a practical choice for fencing, agricultural frames, sign supports and other exposed components. It combines the selected steel grade with corrosion protection and can reduce repainting needs compared with untreated steel. Coastal salts, chemical exposure and standing water still require an application-specific protection review.
Black carbon steel pipe can suit indoor machinery frames, welded assemblies and projects receiving paint or another coating after fabrication. It often has a lower initial material cost, but outdoor service usually needs additional protection. Compare the final coated assembly and maintenance cost. See our carbon steel welded pipe options.
Stainless steel relies on a chromium-rich passive surface film instead of a sacrificial zinc layer. Suitable grades and finishes are used in hygienic equipment, architectural tube and process systems. Grade 304 suits many mild environments; 316 is often considered where greater chloride resistance is needed, but neither grade is immune to corrosion. Material, fabrication and finishing costs can be higher than carbon steel alternatives. View our stainless steel pipe range.
Use the actual dimensions: DN and NPS are nominal designations, not a direct measurement of outside diameter. A schedule also does not mean one fixed wall thickness at every size. Provide OD × base-steel wall thickness × length wherever possible.
Define the coating basis: A strip designation such as Z275 commonly describes total zinc mass on both faces of the sheet. It is not the same as 275 g/m² on each finished pipe surface. Confirm outside, inside and seam requirements, together with the coating test method and applicable standard.
Separate calculated and delivered weight: For carbon steel with a density of approximately 7,850 kg/m³, theoretical bare-pipe mass is approximately 0.02466 × wall thickness × (OD − wall thickness) kg/m, using mm. An illustrative 48.3 mm OD × 3.2 mm wall × 6 m tube weighs about 21.35 kg before zinc. Actual supplied weight includes dimensional variation and coating; this example is not a stock or load-capacity specification.
A buyer orders posts and rails in several diameters. The enquiry specifies clamp fit, cut lengths, coating exposure and whether welding occurs before or after galvanizing. Any coating disturbed during subsequent cutting or welding is repaired using the agreed method.
A fabricator requests tubes for bending into arches. Besides zinc coverage, the sample review checks forming performance, ovality, seam condition and coating damage after bending. Humidity and contact with agricultural chemicals are considered when selecting the protection system.
A buyer submits the approved tube dimensions, grade and system requirements. The enquiry includes thickness tolerance, straightness, fitting compatibility and traceable test documentation. Galvanizing provides surface protection; it does not replace the structural specification or system approval.
These are illustrative buyer scenarios, not claims about completed GDD customer orders or published reviews.
Inspection can cover OD, base-steel thickness, length, straightness, weld condition, zinc coverage, surface condition, pipe ends and bundle quantity. Inner-wall or seam checks and coating measurements are agreed before production. A coating inspection report complements the steel MTC; the MTC alone does not prove complete internal zinc coverage.
GDD Metal supports traceable MTCs, EN 10204 3.1 inspection certificates when agreed, certificates of origin, commercial invoices, packing lists, customs and transport documents. Export licenses or exporter qualification documents can be supplied where applicable. The document set is confirmed against the contract and destination to support compliant export.
Bundles can be identified by size and batch, with end caps or thread protection as required. Shipping and storage arrangements should keep the pipes dry and avoid prolonged trapped moisture. Request bundle dimensions, pieces per bundle and total weight for your loading plan.
No. Internal protection depends on the manufacturing route and specification. Confirm inner-wall zinc coverage and internal weld protection separately, particularly for tubes made from pre-galvanized strip.
Galvanizing is a corrosion-protection process, not a steel grade. Required strength and mechanical tests must be specified through the base material and product standard.
Only a pipe specified and approved for that service should be used. Confirm the product standard, grade, pressure requirements, testing, connection system and destination approvals; a general outdoor GI tube is not automatically suitable.
Send the application, standard and grade, OD, wall thickness, length, galvanizing route, zinc requirement, internal protection, pipe ends, quantity, destination port and inspection documents. We will confirm feasible supply options, packing, MOQ and lead time.
