Stainless Steel Coil Tube — Technical Specification (No. 294)
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-formed continuous tubing product supplied in coiled configuration. This product category is fundamental to downstream applications requiring seamless, continuous-length tubing, particularly in welding, bending, and forming operations. The coil tube is distinguished by its consistent cross-sectional geometry, controlled surface finish, and uniform mechanical properties throughout the coil length.
A critical engineering consideration for coil tube products is the control of ovality (不圆度, Ovality) and warpage (翘曲, Warpage), as these geometric deviations directly impact welding quality, dimensional accuracy, and process reliability in subsequent manufacturing stages. Wenzhou Jixing Metal Materials adheres to stringent internal quality protocols to minimize these deviations, ensuring that the coil tube meets the exacting requirements of industrial fabrication.
2. Material & Properties
Stainless steel coil tubes are typically produced from austenitic stainless steel grades, with the following common material specifications:
- 304 (UNS S30400) — General-purpose austenitic grade with excellent corrosion resistance and formability
- 304L (UNS S30403) — Low-carbon variant optimized for welding applications and reduced sensitization risk
- 316 (UNS S31600) — Molybdenum-enhanced grade for superior resistance to pitting and crevice corrosion
- 316L (UNS S31603) — Low-carbon version of 316 for enhanced weldability
- 321 (UNS S32100) — Titanium-stabilized grade for elevated-temperature service
- SUS304J1 / SUS316L — Japanese Industrial Standard equivalents
2.1 Typical Mechanical Properties (Cold-Worked Condition)
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa (304); ≥ 515 MPa (316) | ASTM A270 / GB/T 228 |
| Yield Strength (屈服强度) | ≥ 205 MPa (304); ≥ 205 MPa (316) | ASTM A270 / GB/T 228 |
| Elongation (延伸率) | ≥ 35% (304); ≥ 30% (316) | ASTM A270 / GB/T 228 |
| Hardness (硬度) | ≤ 217 HBW (304); ≤ 217 HBW (316) | ASTM A270 / GB/T 231 |
| Corrosion Resistance (耐蚀性) | PASS — 48h 5% NaCl immersion | ASTM A967 / GB/T 10125 |
2.2 Chemical Composition (Typical, wt%)
| Element | 304 / 304L | 316 / 316L |
|---|---|---|
| Carbon (C) | ≤ 0.08 / ≤ 0.03 | ≤ 0.08 / ≤ 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.030 |
3. Specifications
3.1 Dimensional Parameters
| Parameter | Range / Tolerance | Standard Reference |
|---|---|---|
| Outer Diameter (外径, OD) | 6.0 mm – 168.3 mm | ASTM A269 / GB/T 12771 |
| Wall Thickness (壁厚, WT) | 0.5 mm – 12.0 mm | ASTM A269 / GB/T 12771 |
| OD Tolerance (外径公差) | ± 0.05 mm (≤ 32 mm OD); ± 0.10 mm (> 32 mm OD) | GB/T 14976 |
| Wall Thickness Tolerance (壁厚公差) | ± 10% (standard); ± 5% (close tolerance) | ASTM A269 |
| Ovality (不圆度, Ovality) | ≤ 2% of nominal OD (critical control parameter) | Internal QC standard |
| Coil Weight (盘重) | 1,000 kg – 5,000 kg per coil | Customer specification |
| Coil Inner Diameter (盘圈内径) | 150 mm – 500 mm | Customer specification |
| End Condition (端部状态) | Plain cut; beveled ends available on request | — |
3.2 Surface Finish Options
| Finish Designation | Ra (μm) | Description |
|---|---|---|
| Bright Annealed (BA, 光亮退火) | 0.05 – 0.20 | Highly reflective, mirror-like surface; suitable for food-grade and pharmaceutical applications |
| Pickled (酸洗, Pickle Finish) | 0.20 – 0.50 | Uniform matte finish; general industrial use |
| 2B Finish (2B 表面) | 0.20 – 0.50 | Intermediate finish with slight reflectivity |
| No. 4 Brushed (拉丝, Hairline) | 0.40 – 1.60 | Directional grain pattern; aesthetic and architectural applications |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, material integrity, and surface quality:
- Steel Coil Preparation (钢带准备) — Cold-rolled stainless steel strip (SS strip) is received and inspected for surface quality, chemical composition, and mechanical properties. The strip is slit to the required width using precision slitting lines.
- Forming (成型) — The strip is fed through a series of roll-forming stations that progressively bend the flat strip into a tubular shape. The number of forming stations and roll configuration is optimized for each tube diameter and wall thickness combination.
-
Welding (焊接) — The formed tube is joined along the longitudinal seam using one of the following welding methods:
- Frequency Welding (高频焊, HFW) — High-frequency induction heating melts the edges for rapid, high-quality seam fusion
- Laser Welding (激光焊, LW) — High-energy laser beam achieves precise, narrow weld beads with minimal heat-affected zone (HAZ)
- MIG/TIG Welding (MIG/TIG 焊接) — Shielded metal arc welding for specific diameter and thickness ranges
- Internal & External Sizing (内外定径) — The welded tube passes through internal and external sizing rolls to achieve precise OD and wall thickness tolerances. This step is critical for controlling ovality and eliminating warpage.
- Weld Bead Removal (焊道处理) — Internal grinding or laser trimming removes the internal weld bead, while external grinding or brushing achieves the desired surface finish.
- Heat Treatment (热处理) — Solution annealing (固溶处理) at 1010–1150 °C followed by rapid water quenching restores full austenitic microstructure, eliminates cold-work stresses, and maximizes corrosion resistance.
- Pickling & Passivation (酸洗钝化) — Chemical pickling removes oxide scales formed during heat treatment. Passivation treatment establishes a protective chromium oxide layer on the surface.
- Coiling (盘卷) — The continuous tube is coiled onto a coil former at controlled tension to prevent additional warpage or deformation. Coil ends are secured with steel strapping and protective wrapping.
- Quality Inspection (质量检验) — Comprehensive inspection including dimensional measurement, surface inspection, ultrasonic testing (UT, 超声波检测), and hydrostatic pressure testing (水压试验) is performed prior to packaging.
5. Ovality & Warpage Control — Key Engineering Focus
Technical Insight: Ovality and warpage are among the most critical geometric parameters governing the welding quality of stainless steel coil tubes. Excessive ovality leads to uneven weld penetration, inconsistent bead geometry, and potential porosity or lack-of-fusion defects. Warpage causes tube misalignment during downstream welding operations, resulting in angular distortion and reduced joint strength.
5.1 Impact of Ovality on Welding Quality
- Uneven Heat Distribution: Non-uniform cross-sections cause asymmetric heat input during welding, leading to uneven weld bead profiles and potential undercutting on the thinner wall section.
- Weld Penetration Variability: Ovality exceeding 2% of nominal OD results in wall thickness variation along the circumference, compromising consistent penetration depth.
- Residual Stress Concentration: Geometric irregularities act as stress concentrators, increasing susceptibility to stress-corrosion cracking (SCC) in corrosive environments.
- Fit-Up Challenges: Downstream fabrication requires additional machining or grinding to compensate for ovality, increasing production costs and cycle time.
5.2 Impact of Warpage on Welding Quality
- Angular Misalignment: Tube warpage along the longitudinal axis causes misalignment during butt-welding or socket-welding operations, requiring corrective fixtures.
- Weld Geometry Deviation: Warped tubes produce weld joints with inconsistent throat thickness, reducing structural integrity.
- Process Parameter Instability: Automated welding systems require consistent tube geometry; warpage disrupts torch-to-workpiece distance, causing arc instability and weld defects.
- Downstream Machining Waste: Straightening operations consume additional material and introduce cold-work hardening, reducing formability.
5.3 Improvement Measures
- Optimized Roll Forming Sequence: Progressive forming angles are calculated using finite element analysis (FEA) to minimize residual elastic springback and geometric deviation.
- Precision Sizing Stations: Post-weld sizing rolls with hydraulic adjustment ensure ovality remains within ± 1% of nominal OD.
- Controlled Coiling Tension: Coiling is performed at tension levels calibrated to the tube's springback characteristics, preventing coiling-induced warpage.
- Online Geometric Monitoring: Laser-based diameter and ovality measurement systems provide real-time feedback for closed-loop process control.
- Material Selection Optimization: Strip flatness and edge quality are verified at incoming inspection to prevent upstream defects from propagating through the forming process.
- Post-Annealing Straightening: Light cold-straightening passes after solution annealing correct any residual warpage introduced during heat treatment.
6. Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials are widely employed across multiple industries due to their combination of corrosion resistance, formability, and dimensional precision:
- Food & Beverage Industry (食品饮料工业) — Hygienic piping systems, CIP (Clean-in-Place) compatible tubing for dairy, brewing, and processing facilities
- Pharmaceutical Industry (制药工业) — GMP-compliant process piping, autoclavable tubing systems requiring electropolished or BA finishes
- Chemical Processing (化工处理) — Transfer lines, reactor feed piping, and containment