Stainless Steel Coil Tube (盘管) — Horizontal Drilling Application Specification
1. Product Overview
Stainless Steel Coil Tube, also known as Coil Pipe or Continuous-Length Tubing, is a precision-engineered cold-drawn or cold-rolled seamless pipe product supplied in continuous coiled form rather than in discrete lengths. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product No. 1518), this coil tube is specifically designed for high-performance applications in Horizontal Directional Drilling (HDD), oil and gas extraction, geothermal energy systems, and subsea pipeline deployment.
Unlike conventional straight-length seamless tubing, stainless steel coil tubes are produced through a continuous manufacturing process that eliminates butt welds and joints, thereby providing superior mechanical continuity, enhanced pressure resistance, and extended operational life. This product represents a critical advancement in modern drilling technology, enabling uninterrupted pipe advancement through long horizontal boreholes without the need for in-hole couplings or threaded connections.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic and duplex stainless steel grades, selected for their exceptional combination of corrosion resistance, tensile strength, and ductility under extreme downhole conditions.
- Primary Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), AISI 321 (UNS S32100), and Duplex 2205 (UNS S32205)
- Corrosion Resistance: Excellent resistance to chloride-induced pitting, crevice corrosion, and stress corrosion cracking (SCC), particularly in 316L and 2205 grades
- Mechanical Properties: Tensile strength ranging from 515 MPa (304) to 620 MPa (316L), with yield strength of ≥205 MPa for austenitic grades and ≥450 MPa for duplex grades
- Operating Temperature Range: −196 °C to +870 °C (austenitic grades); −50 °C to +350 °C (duplex grades)
- Surface Finish: Commercial polish, electropolished, or passivated surfaces with surface roughness Ra ≤ 0.4 μm upon request
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Type | Seamless Stainless Steel Coil Tube (Continuous Length) | — |
| Outer Diameter (OD) | 1/2" to 4" (12.7 mm – 101.6 mm) | ASTM A213 / ASTM A312 |
| Wall Thickness | 0.5 mm to 8.0 mm | ASTM A269 / ASME B36.19M |
| Coil Length | 50 m to 1,000 m per coil (continuous) | Manufacturer Specification |
| Coil Inner Diameter (ID) | 600 mm to 1,500 mm (adjustable per application) | — |
| Material Grade | 304, 304L, 316, 316L, 321, 347, Duplex 2205 | AISI / UNS Designation |
| Manufacturing Method | Cold Drawing / Cold Rolling (Seamless) | ASTM A213 / EN 10216-5 |
| Tolerance (OD) | ±0.05 mm (precision grade); ±0.15 mm (standard grade) | ASTM A511 |
| Tolerance (Wall Thickness) | ±10% (standard); ±5% (precision grade) | ASTM A511 |
| Surface Condition | Pickled & Passivated; Electropolished; Mirror Finish | ASTM A967 / ASTM A380 |
| End Preparation | Plain end; Beveled (45°); Threaded; Flanged | ASME B1.20.1 / ASME B16.5 |
| Heat Treatment | Solution Annealed (1050 °C – 1150 °C); Stress Relieved | ASTM A999 |
| Testing | Hydrostatic Test, Eddy Current, Spectrographic Analysis, PMI Verification | ASTM A999 / ASTM E165 |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and continuous length capability:
- Raw Material Preparation: High-purity stainless steel billets or rods are sourced from certified mills and subjected to incoming chemical composition verification via optical emission spectroscopy (OES) and Positive Material Identification (PMI).
- Hot Rolling / Extrusion: Billets are heated to forging temperature (1,100 °C – 1,200 °C) and hot-rolled or hot-extruded into seamless hollow bars, establishing the initial tubular geometry.
- Piercing & Elongation: The hot-formed tubes are pierced to achieve initial wall thickness and then elongated through multiple passes to reduce diameter and wall thickness to near-final dimensions.
- Cold Drawing / Cold Rolling: Tubes are cold-drawn through precision tungsten carbide or diamond dies to achieve final OD, wall thickness, and tolerance specifications. This process imparts favorable grain structure and enhanced mechanical properties through work hardening.
- Coiling: The continuously drawn tube is wound onto a large-diameter mandrel reel, maintaining constant tension to prevent deformation, ovality, or spring-back. Automated coil forming systems ensure uniform winding with controlled inter-layer pressure.
- Heat Treatment (Solution Annealing): Coiled tubes are solution-annealed at 1,050 °C – 1,150 °C followed by controlled cooling (air cool or water quench depending on grade) to restore full ductility, eliminate residual stresses, and precipitate-free austenitic microstructure.
- Pickling & Passivation: Chemical pickling removes oxide scale and surface contaminants; subsequent passivation treatment forms a stable chromium oxide (Cr₂O₃) protective layer, enhancing corrosion resistance.
- Non-Destructive Testing (NDT): Every coil undergoes 100% automated inspection including hydrostatic pressure testing, eddy current flaw detection, and ultrasonic thickness measurement to verify internal and external integrity along the entire coil length.
- Final Inspection & Packaging: Dimensional verification, surface quality assessment, and mechanical property certification are completed. Coils are protected with VCI (Vapor Corrosion Inhibitor) wrapping and wooden or steel-reinforced packaging for shipment.
5. Applications
The unique continuous-length characteristic of stainless steel coil tubes enables applications that are impractical or economically prohibitive with discrete-length tubing:
5.1 Horizontal Directional Drilling (HDD)
Coil tubes serve as the primary conduit pipe in HDD operations, allowing continuous pipe advancement through horizontal boreholes of up to several kilometers without in-ground connections. This eliminates the risk of connection failure, reduces installation time by up to 60%, and minimizes surface disruption. The seamless construction ensures hydraulic integrity under sustained borehole pressure.
5.2 Oil & Gas Industry
- Subsea pipeline deployment and umbilical lines
- Well completion tubing in high-pressure, high-temperature (HPHT) environments
- Chemical injection lines and sour service applications (H₂S-containing formations)
- Flow lines in offshore platforms
5.3 Geothermal Energy Systems
Continuous coil tubes are ideal for closed-loop geothermal heat exchangers and enhanced geothermal system (EGS) wellbores, where long uninterrupted lengths and high-temperature resistance are critical.
5.4 Chemical Processing & Pharmaceutical
- CIP (Clean-In-Place) piping systems requiring weld-free continuous runs
- High-purity fluid transfer in semiconductor manufacturing
- Food and beverage processing where hygiene and corrosion resistance are paramount
5.5 Marine & Offshore Engineering
Ballast water systems, fire suppression lines, and structural reinforcement in marine environments where chloride resistance and continuous pipe integrity are essential.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring full traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management
- API Q1 (ISO 9001-2015) — Quality Management System for Oil & Gas Industry
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- NACE MR0175 / ISO 15156 — Compliance for sour service applications
- EN 10204 3.1 — Material Test Certificates per lot/batch
- Mill Test Reports (MTR) — Full chemical composition, mechanical properties, and NDT results provided per coil
7. Unique Selling Points
Continuous-Length Advantage: Elimination of butt welds and threaded couplings provides a monolithic pressure boundary with zero leak points — a critical safety and reliability advantage in horizontal drilling and subsea applications.
Precision Engineering: Tight dimensional tolerances (±0.05 mm OD) and uniform wall thickness ensure consistent hydraulic performance and compatibility with precision fittings and connectors throughout the coil length.
Grade Versatility: Availability across multiple stainless steel grades — from cost-effective 304 to super-duplex 2507 — allows engineers to optimize material selection for specific service conditions including chloride exposure, temperature extremes, and mechanical loading.
Full Traceability & Testing: Every coil is individually traceable with comprehensive mill test documentation, 100% NDT coverage, and hydrostatic testing records, ensuring full quality assurance from raw material to final delivery.
Custom Coiling Configuration: Adjustable coil inner diameter, length, and winding tension accommodate diverse downstream processing requirements including automated pipe cutting, bending, threading, and direct deployment systems.