Internal and External Epoxy Coal Tar Paint Welded Steel Pipe DN500 for Drainage

Engineered for high-capacity gravity flow and pressurized runoff systems, this Internal and External Epoxy Coal Tar Paint Welded Steel Pipe is a premier pipeline solution for heavy-duty municipal and industrial drainage. Utilizing a DN500 (508mm OD) welded carbon steel base, this pipe offers outstanding load-bearing capacity, making it perfect for installation under busy roadways, railways, and deep embankments.
Both the inner and outer surfaces are coated with a high-build Epoxy Coal Tar (Coal Tar Epoxy) paint. This dual-sided protective barrier provides complete shield protection: the external coat resists aggressive soil chemistry, moisture, and microbes, while the internal coat prevents chemical attack from acidic rain runoff, organic debris, and abrasive silt. It represents an exceptionally durable, high-flow, and cost-effective structural asset for critical drainage networks.

Features & Advantages

Dual-Sided Total Protection: Coated internally and externally to simultaneously combat aggressive soil environments on the outside and corrosive or abrasive drainage fluids on the inside.

High Structural Stiffness: Fabricated from high-strength welded carbon steel, providing superior ring stiffness to withstand deep burial depths and heavy traffic overburdens without cracking or collapsing.

Smooth Internal Hydraulic Flow: The internal coal tar epoxy cures to a uniform, low-friction finish that prevents sediment buildup, minimizes head loss, and optimizes gravity drainage efficiency.

Highly Cost-Effective Asset: Outperforms unlined steel and concrete in corrosive soils, offering a significantly longer service life at a fraction of the cost of premium polymer coatings.

Technical Specifications

Specification Item	Detailed Description
Product Name	Internal & External Epoxy Coal Tar Coated Welded Steel Pipe
Base Pipe Material	Welded Carbon Steel Pipe (SSAW or ERW to ASTM A53, API 5L, or GB/T 3091)
Nominal Diameter (DN)	DN500
Outer Diameter (OD)	20.00 inches (508.0 mm)
Wall Thickness (WT)	Typical 6.0 mm to 12.7 mm (8.0 mm / 0.315 inches standard, or custom)
Anti-Corrosion Coating	Liquid Epoxy Coal Tar (Coal Tar Epoxy) Paint on both internal and external surfaces
Coating Standards	AWWA C210, SSPC-Paint 16, SY/T 0447
Coating Thickness	Standard 300 to 500 microns Dry Film Thickness (DFT) per side, or custom multi-layer configs
Pipe Ends	Beveled ends (30°~35°) with internal and external bare steel cutbacks for field joint welding
Standard Length	5.8m, 6.0m, 11.8m, 12.0m, or customized

Product Applications

Municipal Stormwater Drainage: High-volume rainwater collection, urban runoff mains, and subterranean highway culverts.

Industrial Gravity Runoff Lines: Underground routing of process water, factory discharges, and mildly acidic chemical runoff.

Agricultural Land Drainage: High-capacity water diversion and irrigation mainlines buried in damp or marshy soils.

Subterranean Drainage Mains: Infrastructure pipelines crossing through highly corrosive, wet, or swampy terrains.

Rigorous Quality Control & Manufacturing Process

Our DN500 dual-coated drainage pipes are manufactured and coated under strict, modern quality control protocols:

Double-Sided Blast Cleaning: Both internal and external surfaces of the DN500 welded steel pipe undergo aggressive abrasive shot blasting to SA 2.5 cleanliness, creating a clean, consistent anchor profile.

Synchronized Liquid Coating Application: Liquid epoxy coal tar is applied via automated internal spray booms and external rotary spray nozzles. The multi-pass application ensures uniform thickness across both the parent metal and the weld seam area.

Controlled Curing Process: Coated pipes are placed in a dust-free curing chamber to allow the chemical-resistant coal tar epoxy matrix to fully cross-link.

Dual-Surface Integrity Testing: 100% dry film thickness measurement and electronic Holiday testing are performed on both the inner and outer surfaces to guarantee a pinhole-free, continuous barrier.

Frequently Asked Questions (FAQ)

Q1: What are the engineering benefits of applying epoxy coal tar internally AND externally for drainage?

A: Drainage water is rarely pure; it often carries acidic rainwater, chemical runoff, silt, and organic waste. The internal coating protects the steel from corrosion caused by stagnant water and mechanical abrasion from silt. The external coating protects against damp subterranean soil, microbial attack, and stray currents, ensuring 360-degree, dual-barrier protection.

Q2: Is a DN500 welded steel pipe suitable for deep burial under roadways?

A: Yes. Unlike plastic or concrete drainage pipes, DN500 (508mm OD) welded steel pipe possesses exceptional mechanical yield strength and high ring stiffness. It can withstand heavy traffic overburdens, high impact, and deep soil loads without cracking or losing structural shape.

Q3: How are the weld seams on the inside of the pipe coated uniformly?

A: During base pipe production, the internal weld beads of the ERW or spiral seam are trimmed or strictly monitored. During the coating process, specialized internal spray booms with rotating heads are used. This ensures the liquid coal tar epoxy completely and evenly encapsulates the internal weld seam without leaving thin spots or runs.

Q4: How do we protect the joints in the field without damaging the dual coating?

A: The pipes are delivered with precision-beveled ends and bare steel cutbacks on both the inner and outer ends (typically 50-100mm). After field butt-welding and weld inspection, the joint area is cleaned. The external joint is wrapped with cold-applied coal tar tape or liquid epoxy coal tar, and the internal weld joint is coated using specialized joint-coating tools or manual application to match the main pipe’s protective profile.