Stainless Steel Coil Tube (盘管 / Coil Tubing) — Inverted Drawing Process

Wenzhou Jixing Metal Materials Co., Ltd. (温州继兴金属材料有限公司) presents its precision-engineered stainless steel coil tubing, manufactured through a proprietary inverted coil tube drawing process. This product line represents a convergence of advanced forming technology, rigorous metallurgical control, and adherence to international quality standards, delivering high-performance tubing solutions for demanding industrial applications worldwide.

Product Overview

The Stainless Steel Coil Tube (盘管) is a continuous-length tubular product wound into coil form, designed to provide seamless, uniform tubing suitable for a wide range of fabrication and assembly processes. Unlike straight-length tubing, coil tubing offers superior handling characteristics, reduced material waste, and enhanced production efficiency in downstream manufacturing environments.

The defining feature of this product line is its production via an Inverted Coil Tube Drawing Machine (倒立式盘管拉拔机), a specialized piece of equipment that reverses the conventional drawing orientation. In this configuration, the tube is drawn downward under the influence of gravity, which provides several critical advantages including improved dimensional accuracy, reduced surface defects, enhanced lubricant distribution, and more consistent reduction ratios throughout the drawing pass. This inverted geometry ensures that the tube's internal diameter (ID) and wall thickness (WT) maintain exceptional concentricity and uniformity along the entire coil length.

Coil tubing is available in both seamless and welded configurations, with seamless variants produced from hot-rolled or cold-rolled blanks and welded variants formed through electric resistance welding (ERW) or orbital welding processes. The coil form factor facilitates continuous processing, making it ideal for automated manufacturing lines in automotive, aerospace, energy, and chemical processing sectors.

Material & Properties

Available Grades

The stainless steel coil tube product line encompasses a broad spectrum of austenitic, ferritic, and duplex stainless steel grades, selected to meet specific corrosion resistance, mechanical strength, and temperature performance requirements:

Mechanical Properties

Mechanical properties are governed by the grade designation, wall thickness, and processing history. Typical values for cold-drawn austenitic stainless steel coil tubing are presented below:

Corrosion Resistance

The passive chromium oxide film formed on the surface of stainless steel coil tubing provides outstanding resistance to atmospheric corrosion, aqueous environments, and chemical media. Specific performance characteristics include:

Surface Finish Options

Specifications

Parameter Specification Standard / Reference
Outer Diameter (OD) 6.0 mm – 219.0 mm (¼" – 8½") ASTM A269 / ASTM A554 / EN 10217
Wall Thickness (WT) 0.5 mm – 12.0 mm ASTM A269 / ASTM A554
OD Tolerance ±0.10 mm (close tolerance); ±0.5% (standard) ASTM A269
WT Tolerance ±0.10 mm (close tolerance); ±10% (standard) ASTM A269
Coil Length 100 m – 500 m per coil (continuous) Manufacturing specification
Coil Weight 500 kg – 3,000 kg per coil Manufacturing specification
Coil Core Diameter 100 mm / 150 mm / 200 mm / 300 mm (custom available) Customer requirement
Coil Form Single coil / Double coil / Flat-pack coil Manufacturing specification
Tube Construction Seamless / Welded (ERW / Orbital) ASTM A269 / ASTM A554 / EN 10217
Heat Treatment Annealed (固溶退火) / Solution Treated ASTM A269
End Condition Plain / Beveled / Threaded / Flanged Customer specification
Maximum Operating Temperature Up to 870°C (304/304L); Up to 1100°C (310); Up to 300°C (Duplex) Grade-dependent
Minimum Operating Temperature Down to −196°C (Cryogenic applications) ASTM A269
Winding Direction CW (Clockwise) / CCW (Counter-Clockwise) Customer specification
Protective Packaging Plastic wrap / VCI paper / Wooden pallet / Export-grade crate ISO 9001 packaging standards

Manufacturing Process

The production of Wenzhou Jixing's stainless steel coil tubing follows a meticulously controlled multi-stage process, with the inverted coil tube drawing operation serving as the critical forming step. Each stage is subject to in-process inspection and statistical process control (SPC) to ensure consistent quality.

Stage 1: Raw Material Preparation

High-purity stainless steel billets or hot-rolled coils are procured from certified suppliers and subjected to incoming inspection, including chemical composition analysis (via optical emission spectrometry), visual surface examination, and mechanical property verification. Material certificates (Mill Test Reports, MTR) are reviewed and archived for full traceability.

Stage 2: Tube Forming

For seamless tubing, the billet is heated to the appropriate temperature and pierced to form a hollow shell, which is then rolled to the desired intermediate OD and WT. For welded tubing, coil strip is fed into an ERW or orbital welding system, where the edges are precisely aligned, heated, and fused to create a continuous seam. The resulting tube blank is then cooled and straightened.

Stage 3: Inverted Coil Tube Drawing (倒立式盘管拉拔)

This is the signature process that distinguishes Wenzhou Jixing's product quality. The inverted coil tube drawing machine operates with the following principles:

  1. Inverted Geometry: The drawing die and cap are mounted in an inverted (upside-down) configuration, with the tube being pulled downward. Gravity assists in maintaining consistent contact between the tube and the drawing cap, reducing the risk of internal bulging and ensuring uniform wall thickness reduction.
  2. Cap Drawing (芯棒拉拔): A hardened, precision-ground drawing cap (plug) is inserted into the tube bore. As the tube is drawn through the die, both the OD and ID are simultaneously reduced, achieving precise dimensional control in a single pass.
  3. Multi-Pass Reduction: The tube undergoes multiple sequential drawing passes, each with progressively smaller reduction ratios (typically 10–25% per pass). This staged approach prevents excessive work hardening and maintains material ductility.
  4. Lubricant Application: A specialized drawing lubricant (typically a calcium stearate or polymer-based compound) is applied to both the internal and external surfaces. The inverted orientation promotes superior lubricant retention within the tube bore, reducing friction and wear on the die and cap.
  5. Coil-to-Coil Operation: The drawing process is performed continuously from a feed coil to a take-up coil, enabling high production rates while maintaining dimensional consistency along the entire coil length.
  6. Die Configuration: Tungsten carbide (WC) or cemented carbide dies with precision-ground bearing surfaces are used to minimize surface scratches and ensure dimensional accuracy. Die life is monitored and maintained through scheduled regrinding.

Stage 4: Annealing & Stress Relief

Following the cold drawing process, the tubing is solution-annealed (固溶退火) at temperatures between 1010°C and 1150°C, depending on the grade, followed by rapid quenching in air or water. This process relieves residual stresses, restores full ductility, homogenizes the microstructure, and re-establishes the protective passive oxide layer. The annealing cycle is precisely controlled using thermocouple-monitored furnaces with documented heat treatment charts.

Stage 5: Pickling & Passivation

The annealed tubing undergoes chemical pickling (using a nitric acid / hydrofluoric acid mixture or a proprietary eco-friendly pickling compound) to remove surface scale, discoloration, and residual drawing lubricant. This is followed by passivation with a dilute nitric acid or citric acid solution to activate and stabilize the chromium oxide passive film. The pickling and passivation process is verified through a ferrite inspection and a water droplet test (ASTM A967).

Stage 6: Final Inspection & Testing

Each coil of finished tubing undergoes comprehensive quality verification:

Stage 7: Coiling & Packaging

The finished tubing is coiled to the specified coil diameter and length, with the ends properly identified and labeled. Protective packaging is applied according to the customer's requirements, with options including plastic film wrapping, VCI (Vapor Corrosion Inhibitor) paper wrapping, wooden palletizing, and export-grade crate packaging with desiccant protection.

Applications

Automotive Industry (汽车行业)

Stainless steel coil tubing is extensively used in automotive exhaust systems, fuel lines, brake lines, turbocharger pipes, and catalytic converter substrates. The coil form facilitates high-speed automated tube-cutting and bending operations in automotive manufacturing lines, reducing scrap and improving throughput.

Aerospace Industry (航空航天行业)

Precision-drawn stainless steel tubing serves in hydraulic systems, fuel delivery lines, pneumatic actuator lines, and structural components. The high strength-to-weight ratio, excellent fatigue resistance, and dimensional accuracy achieved through the inverted drawing process make it ideal for aerospace applications where reliability is paramount.

Oil & Gas Industry (石油天然气行业)

Coil tubing is employed in downhole production systems, well completion operations, hydraulic fracturing lines, and surface piping for refineries and processing facilities. Duplex and super