Black spiral welded steel pipe

Professional Category Explanation and Complete Production Process

Black spiral welded steel pipe, also commonly known in the industry as black spiral pipe or black spiral tube, is officially called black spiral double-sided submerged arc welded steel pipe. It is a bare pipe product processed from hot-rolled steel strip as the core raw material. The product undergoes only basic rust removal treatment before leaving the factory, without galvanizing, anti-corrosion paint, 3PE protection, or other surface processing. The pipe body exhibits the original blackish-gray or blackish-brown appearance of the steel. Its production process follows mature spiral welded pipe standard technology, with full quality control throughout: First, the strip steel is uncoiled, leveled, and milled, with precise processing of the welding bevel; then, it is spirally coiled and formed, strictly controlling the roundness and ovality of the pipe body; subsequently, double-sided submerged arc welding technology is used to ensure a full and strong weld; all finished products undergo 100% ultrasonic and X-ray non-destructive testing and individual hydrostatic testing; finally, only end trimming and dust and rust removal are performed, without additional anti-corrosion coating, before warehousing. The entire set of process standards is in line with international standards, ensuring the stability of the basic quality of pipe materials from the source.

Multiple practical advantages, adapting to diversified procurement needs

Black spiral welded steel pipe, thanks to its process and product characteristics, possesses several outstanding advantages, making it highly recognized by engineering procurement clients. First, it is economical in price. By omitting the complete pre-finished anti-corrosion process, the price of the same specification product is 8%-15% lower than conventional anti-corrosion spiral pipes, making it a core choice for controlling procurement budgets in engineering projects. Second, it offers high flexibility in secondary processing. The bare pipe surface has no protective layer, allowing procurement parties to independently carry out processing such as painting, epoxy coating, 3PE anti-corrosion, and galvanizing according to site conditions and usage requirements, easily achieving personalized anti-corrosion customization. Third, it boasts excellent mechanical properties. Continuing the inherent structural characteristics of spiral pipes, it exhibits excellent ring stiffness, strong resistance to extrusion and foundation settlement, and fully meets pressure-bearing performance standards, satisfying the mechanical requirements of conventional infrastructure and pipeline construction. Fourth, it offers comprehensive specification coverage. From small diameters to large diameters and various wall thicknesses, it can be mass-produced, providing a one-stop solution for pipe selection needs of different projects.

Core Specifications

Outer Diameter: φ219mm～φ3620mm (DN200～DN3600), covering small, medium, and large diameters

Wall Thickness: 5～25mm, including thin-walled, standard-walled, and thick-walled varieties; extra-thick walls can be customized.

Main Materials: Q235B, Q355B, L245, L360

Standard Length: Standard 6m, 9m, 12m; custom lengths 6–18m supported.

Pressure Range: 0.6MPa～6.4MPa, suitable for low to medium-high pressure applications.

Standards: SY/T 5037, GB/T 9711, API 5L

Production Process

The process is the same as that of ordinary spiral welded pipes, except that the overall anti-corrosion process for the finished product is omitted:

1. Strip steel uncoiling, leveling, and edge milling; processing welding bevels.

2. Spiral coiling and forming, controlling roundness and ovality.

3. Double-sided submerged arc welding, ensuring full welds.

4. 100% ultrasonic and X-ray non-destructive testing; hydrostatic testing on each pipe.

5. Pipe end finishing, simple dust and rust removal; no overall anti-corrosion coating; finished products are directly put into storage.

Main Application Scenarios

1. Pile Foundation/Support Engineering: Bridges, buildings, foundation pit pile foundation casings, pipe jacking sleeves (mostly temporary components, no long-term corrosion protection required).

2. Indoor/Overhead Pipelines: Internal circulating water pipes, ventilation and dust removal ducts, workshop process pipelines (dry environment, no rain exposure).

3. Secondary Corrosion Protection Engineering: Buried pipelines, water conservancy pipelines, oil and gas branch lines with unified on-site corrosion protection after purchase.

4. Temporary Works: Temporary water supply and drainage on construction sites, temporary fencing columns, temporary steel structure supports.

5. Heavy Steel Structures: Factory columns, equipment bases, large supports (for use in dry indoor environments).

Corrosion Protection Recommendations & Service Life

1. Treatment Solutions for Different Scenarios

Dry Indoor Environment: No additional corrosion protection required; normal use is sufficient.

Damp Indoor Environment / Short-Term Outdoor Exposure: Apply anti-rust primer + topcoat for simple protection.

Long-Term Outdoor Exposure / Ordinary Buried Pipeline: Apply epoxy coal tar pitch and IPN8710 anti-corrosion coating.

High-Standard Buried Pipeline: Apply 3PE anti-corrosion layer on-site.

2. Estimated Service Life

Bare Pipe (Unprotected) Outdoor Exposure: Significant rust appears in 3–6 months; structural safety is affected in 1–2 years.

Apply ordinary anti-rust paint: 8–12 years indoors, 4–6 years outdoors.

After completing formal anti-corrosion treatment (epoxy/3PE): Service life is equivalent to that of finished anti-corrosion spiral pipes, reaching 15–30 years.

Selection Guidelines

1. Environmental Priority: For open-air, buried, or humid/corrosive environments, bare black pipes are not recommended; secondary corrosion protection must be planned in advance.

2. Temporary/Permanent Distinction: For temporary pile foundations and temporary pipelines, prioritize black spiral pipes to reduce costs; for permanent underground pipelines, prioritize pre-prepared anti-corrosion pipes.

3. Processing Capacity Matching: If the project site has professional anti-corrosion construction capabilities, black pipes can be purchased and processed in-house; if on-site construction capabilities are lacking, pre-prepared anti-corrosion pipes should be purchased directly.

4. Pressure and Wall Thickness: For medium-high pressure and heavy-load conditions, select thicker wall specifications according to requirements; do not simply reduce wall thickness to save money.

FAQ

Q1: Can black spiral pipes be buried directly underground?

A: No. Burying bare pipes will cause them to rust quickly and thin out, making them prone to leakage and collapse. A complete anti-corrosion layer must be applied first.

Q2: How to choose between black spiral pipes and black straight seam pipes?

A: For deep burial, pressure, and complex geological conditions, choose black spiral pipes, as they have better resistance to settlement and strength. For short, low-pressure indoor pipelines, black straight seam pipes are a better choice due to their lower cost.

Q3: Can they be used for greenhouse frames?

A: Not recommended. Bare pipes are prone to rust and have a large diameter and weight. Hot-dip galvanized round/elliptical pipes are preferred for greenhouses.

Q4: How well does paint adhere to black pipes after installation?

A: Pipes from reputable manufacturers have clean surfaces, and paint adhesion is good after rust removal, which is a common secondary anti-corrosion method used in engineering projects.