GB/T 3091 Q235B Epoxy Coal Tar Anticorrosive Pipe 6 Inch for Underground Cooling Water

Engineered for high cost-efficiency and long-term subterranean reliability, this GB/T 3091 Q235B Epoxy Coal Tar Anticorrosive Pipe is an ideal piping solution for industrial underground cooling water systems. Utilizing a compact 6-inch nominal diameter (168.3mm OD) welded carbon steel base manufactured under the GB/T 3091 standard, Q235B steel offers excellent ductility, high weldability, and reliable low-to-medium pressure fluid containment.
The exterior (and optional interior) is protected by a high-build Epoxy Coal Tar (Coal Tar Epoxy) coating system. This dense, moisture-impermeable liquid barrier effectively defends the subterranean line from soil moisture, chemical degradation, and continuous cooling water immersion, providing a 30+ year maintenance-free service life for factory cooling loops, thermal power plant facilities, and commercial HVAC networks.

GBT-3091-Q235B-Epoxy-Coal-Tar-Anticorrosive-Pipe-6-Inch-for-Underground-Cooling-Water-1.

Features & Advantages

Economical & Practical Steel Base: GB/T 3091 Q235B carbon steel provides superior cost-performance for low-to-medium pressure fluid delivery without sacrificing structural weld integrity.

Superior Water Immersion Defense: Coal tar epoxy forms a dense, hydrophobic matrix that excels in continuously submerged or damp subterranean environments.

Agile 6-Inch Compact Size: The 168.3mm OD size is highly versatile and maneuverable for tight facility piping layouts, plant cooling loops, and industrial trench installations.

Microbial & Soil Acid Resistance: Protects the steel substrate against subterranean soil bacteria, bio-fouling, and organic acid degradation in damp backfill conditions.

Technical Specifications

Specification Item	Detailed Description
Product Name	Epoxy Coal Tar Coated Welded Steel Pipe
Base Pipe Standard	GB/T 3091 (Welded steel pipes for low-pressure fluid delivery)
Steel Grade	Q235B (Yield Strength ≥235 MPa, Tensile Strength 370–500 MPa)
Manufacturing Process	ERW (Electric Resistance Welding) / Welded
Nominal Pipe Size (NPS)	6 Inch (DN150)
Outer Diameter (OD)	6.625 inches (168.3 mm)
Wall Thickness (WT)	Typical 4.5 mm to 7.11 mm (Schedule 40 equivalent: 7.11 mm / 0.280 in, or customizable)
Anti-Corrosion Coating	High-Build Epoxy Coal Tar (Coal Tar Epoxy) Liquid System
Coating Standards	SY/T 0447, AWWA C210, SSPC-Paint 16
Typical Dry Film Thickness (DFT)	300 to 500 microns (12 to 20 mils)
Pipe Ends	Plain ends or Beveled ends (30°~35°) with a factory bare steel cutback for welding
Standard Length	5.8m, 6.0m, 11.8m, 12.0m, or customized

Product Applications

Underground Industrial Cooling Water Mains: Subterranean cooling loops in manufacturing plants, steel mills, and chemical facilities.

Commercial HVAC Systems: Underground chilled water and condenser water circulation lines.

Power Facility Infrastructure: Subterranean auxiliary cooling water supply and drainage networks in thermal power plants.

General Utility Lines: Subterranean industrial fire water loops and low-pressure non-potable water conveyance.

Rigorous Quality Control & Manufacturing Process

Our 6-inch GB/T 3091 pipes undergo a systematic manufacturing and coating protocol to ensure zero field failures:

Weld Seam Scarfing & Inspection: ERW weld beads on the Q235B base pipe are scarfed flush to ensure a perfectly smooth outer surface profile.

Surface Blasting to SA 2.5: The steel surface undergoes aggressive abrasive grit blasting to SA 2.5 cleanliness, creating the precise anchor pattern required for liquid epoxy adhesion.

Controlled Liquid Coating Pass: High-build liquid coal tar epoxy is applied in uniform passes to achieve the target 300–500 micron dry film thickness (DFT).

Pressure & Pinhole Inspection: 100% hydrostatic testing confirms pressure containment. Electronic Holiday testing ensures the coal tar epoxy layer is 100% pinhole-free before dispatch.

Frequently Asked Questions (FAQ)

Q1: What are the mechanical characteristics of Q235B steel under GB/T 3091?

A: Q235B is a widely specified low-carbon structural steel grade (comparable to ASTM A53 Grade A/B or European S235JR). Under the GB/T 3091 standard for low-pressure fluid delivery, Q235B offers an optimal balance of yield strength (≥235 MPa), high ductility, and superb field weldability, making it a highly cost-effective choice for industrial cooling loops.

Q2: Why is epoxy coal tar recommended for underground cooling water pipes?

A: Underground cooling lines face continuous exposure to internal water flow and damp subterranean soil. Coal tar epoxy is famous for its ultra-low water absorption rate, high chemical stability, and ability to prevent internal rust tuberculation and external soil corrosion, ensuring long-term, low-maintenance operations.

Q3: How do you weld 6-inch Q235B pipes on-site without damaging the coating?

A: Pipes are supplied with precision-beveled ends and a factory bare steel “cutback” (50mm–100mm). After field butt-welding and weld inspection, the joint area is cleaned and wrapped with cold-applied coal tar tape or coated with liquid epoxy coal tar paint to maintain continuous corrosion protection.

Q4: Can this 6-inch pipe be supplied with grooved or threaded ends?

A: Yes. While beveled ends for field welding are standard, GB/T 3091 Q235B pipes can also be supplied with grooved ends for mechanical roll-grooved couplings or threaded-and-coupled (T&C) ends if required by your specific facility layout.