Stainless Steel Coiled Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coiled Tube (hereinafter referred to as "Coiltube") is a continuous, helically wound tubular product manufactured from austenitic, duplex, or super-austenitic stainless steel strip stock. Unlike conventional seamless or welded straight pipes, Coiltube is produced through a coiling (or helical winding) process that yields a long, continuous length of tubing wound into a compact spiral coil. This unique geometry provides exceptional flexibility in downstream fabrication, enabling seamless integration into complex heat exchanger, condenser, and process piping systems without the need for field welding or mechanical couplings.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the production and supply of high-grade stainless steel Coiltube, adhering to international standards including ASTM A269 (Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service Applications), ASTM A778 (Standard Specification for Stainless Steel Tubular Products for General Applications), and EN 10217-7 (Non-ferrous metal tubes and pipes — Technical delivery conditions — Part 7: Austenitic stainless steel tubes). The Coiltube product line is designed to deliver superior corrosion resistance, thermal conductivity, and mechanical integrity across a wide range of operating temperatures and chemical environments.
2. Material Grades & Properties
Coiltube products are available in multiple stainless steel grades, each selected to address specific service requirements. The following table summarizes the most commonly offered grades and their key metallurgical properties:
| Grade (UNS) | Designation | Cr (%) | Ni (%) | Mo (%) | Tensile Strength (MPa, min.) | Yield Strength (MPa, min.) | Corrosion Resistance Class |
|---|---|---|---|---|---|---|---|
| 304 (S30400) | Austenitic | 18–20 | 8–10.5 | — | 515 | 205 | General atmospheric & mild chemical |
| 304L (S30403) | Low-carbon Austenitic | 18–20 | 8–10.5 | — | 485 | 170 | Welded structures, low-temperature service |
| 316 (S31600) | Molybdenum-bearing Austenitic | 16–18 | 10–14 | 2–3 | 515 | 205 | Marine, chemical, pharmaceutical |
| 316L (S31603) | Low-carbon Mo-bearing Austenitic | 16–18 | 10–14 | 2–3 | 485 | 170 | Welded assemblies, aggressive chloride environments |
| 321 (S32100) | Titanium-stabilized Austenitic | 17–19 | 9–12 | — | 515 | 205 | High-temperature service (up to 870 °C) |
| 316Ti (S31635) | Ti-stabilized Mo-bearing Austenitic | 16–18 | 10–14 | 2–3 | 515 | 205 | High-temperature chemical processing |
| 310S (S31008) | High-temperature Austenitic | 19–22 | 24–30 | — | 205 | 115 | Extreme oxidation resistance (up to 1150 °C) |
| 2205 (S32205) | Duplex Austenitic-Ferritic | 22–23 | 4.5–6.5 | 3–3.5 | 550 | 450 | High-strength chloride environments |
| 904L (S39073) | Super-Austenitic | 19–23 | 23–28 | 4–5 | 485 | 220 | Extremely aggressive sulfuric acid environments |
Key Metallurgical Characteristics
- Crystal Structure: Predominantly face-centered cubic (FCC) austenitic phase, providing excellent ductility and formability. Duplex grades exhibit a balanced austenitic-ferritic microstructure for enhanced strength and stress corrosion cracking (SCC) resistance.
- Carbon Content: Strictly controlled at ≤ 0.08% for standard grades and ≤ 0.03% for "L" (low-carbon) variants to prevent intergranular corrosion during welding and heat treatment.
- Surface Finish: Available in 2B (cold-rolled, annealed, and bright-passed), BA (bright annealed), No. 4 brushed, No. 8 mirror, and custom matte finishes. Surface roughness (Ra) can be tailored from 0.4 µm to 1.6 µm depending on application requirements.
- Heat Treatment: Solution annealed at 1040–1120 °C followed by rapid water quenching to ensure a fully austenitic, strain-free microstructure with maximum corrosion resistance.
3. Dimensional Specifications
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 108.0 mm | ±0.15 mm | ASTM A269 / EN 10217-7 |
| Wall Thickness (WT) | 0.5 mm – 6.0 mm | ±10% of nominal | ASTM A269 / EN 10217-7 |
| Coil Length (per coil) | 5 m – 300 m (continuous) | ±1 m | Manufacturer specification |
| Coil Inner Diameter (Coil ID) | 150 mm – 500 mm | ±5 mm | Manufacturer specification |
| Coil Weight | 50 kg – 500 kg (per coil) | — | Manufacturer specification |
| End Form | Plain cut, beveled, or formed (U-bend ready) | ±0.5 mm | Customer requirement |
| Straightness (per coil loop) | ≤ 1.0 mm/m | — | Internal QC standard |
| Roundness (circularity) | ≤ 2% of OD | — | ASTM A269 |
| Temperature Range (operating) | −196 °C to +1150 °C (grade-dependent) | — | Grade-specific datasheet |
| Pressure Rating (typical) | Up to 40 bar (grade & dimension dependent) | — | ASME B31.3 |
Surface Treatment Options
- Pickling & Passivation (PP): Removal of mill scale and formation of a stable chromium oxide passive film for maximum corrosion resistance.
- Pickling & Passivation with Descaling (PPD): Additional mechanical descaling for heavily scaled surfaces.
- Acid Pickling (AP): Hydrofluoric-nitric acid blend immersion for surface cleaning without passivation.
- Electropolishing: Electrochemical surface refinement for hygienic and pharmaceutical applications (Ra ≤ 0.25 µm).
- Internal Brushing: Mechanical internal surface finishing for food-grade and sanitary piping.
4. Manufacturing Process
The production of stainless steel Coiltube involves a multi-stage manufacturing sequence that integrates metallurgical processing with precision mechanical forming. The following process flow outlines the key stages:
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Raw Material Selection & Inspection:
High-purity stainless steel strip or wire rod is procured from certified mills. Incoming material undergoes spectroscopic analysis (OES) for chemical composition verification, ultrasonic testing (UT) for internal defect detection, and visual inspection for surface quality. Material certificates (Mill Test Reports, MTR) are reviewed for conformity with specified standards.
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Heat Treatment (Solution Annealing):
The strip stock is solution annealed at temperatures between 1040 °C and 1120 °C, followed by rapid quenching (water or controlled atmosphere). This process dissolves carbide precipitates, restores full austenitic phase homogeneity, and relieves internal residual stresses, ensuring maximum ductility and corrosion resistance.
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Pickling & Passivation:
Post-annealing, the strip is immersed in a mixed acid bath (typically HNO₃ + HF) to remove oxide scale and form a protective chromium oxide passive layer. Passivation is verified via ferric chloride (FeCl₃) spot testing or redox potential measurement.
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Cold Rolling & Dimensional Control:
The strip is cold-rolled to precise thickness and width tolerances. Tension-controlled rolling ensures uniform wall thickness and minimal variation in cross-sectional geometry. In-line laser measurement systems provide real-time dimensional feedback.
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Tube Forming (Hedman / Cross-Roll Method):
The flat strip is fed through a series of progressive forming rolls (Hedman process) that gradually shape the strip into a tubular cross-section. The cross-roll (or roll-bending) method is employed for seamless helical tube formation without longitudinal seams. This technique is critical for producing Coiltube with uniform wall thickness and excellent mechanical properties throughout the coil length.
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Welding (if applicable):
For welded Coiltube configurations, the formed tube is seam-welded using high-frequency induction welding (HF welding) or orbital TIG (Tungsten Inert Gas) welding. Weld parameters are optimized to minimize heat-affected zone (HAZ) width and prevent sensitization. Post-weld annealing may be applied for critical applications.
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Coiling (Helical Winding):
The formed tube is wound onto a coiling mandrel using a precision coiling machine. The coiling process involves controlled tension, diameter stepping, and layer indexing to ensure uniform coil geometry and prevent inter-layer contact damage. The helical pitch is maintained within specified tolerances to ensure consistent tube curvature.
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Post-Coiling Inspection & Testing:
Each coil undergoes comprehensive quality verification including:
- Hydrostatic Pressure Testing: Internal pressure test at 1.5× working pressure for a minimum hold time of 30 seconds to verify weld integrity and detect leaks.
- Eddy Current Testing (ECT): Non-destructive testing of the weld seam (if applicable) for detection of surface and subsurface defects.
- Dimensional Inspection: OD, wall thickness, and coil diameter measurements using calibrated gauges and laser profilometers.
- Chemical Composition Analysis: Spectroscopic verification of grade conformity.
- Surface Quality Inspection: Visual and magnetic particle inspection (MPI) for surface defect detection.
- Hardness Testing: Vickers or Rockwell hardness verification against grade-specific ranges.
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Packaging & Dispatch:
Coils are wrapped in moisture-proof polyethylene film, secured with steel strapping, and palletized for transport. Each coil is tagged with a unique identification number, grade designation, heat number, and dimensional data. Shipping documentation includes Mill Test Reports, Certificate of Conformance, and relevant CE/UKCA declarations where applicable.
5. Applications
Stainless Steel Coiltube finds extensive application across multiple high-demand industries owing to its corrosion resistance, thermal performance, and fabrication flexibility:
5.1 Heat Exchangers & Condensers
- Shell-and-tube heat exchangers in power generation, petrochemical, and chemical processing plants.
- Air-cooled condensers (ACC) for oil & gas refineries, where Coiltube's continuous length minimizes joint count and reduces leak risk.
- Plate-fin heat exchangers for cryogenic LNG (Liquefied Natural Gas) applications operating at temperatures as low as −162 °C.
5.2 Chemical & Petrochemical Processing
- Process piping for handling aggressive chemical media (acids, alkalis, halide-containing solutions) in chemical reactors, distillation columns, and storage systems.
- Reactor coil internals for polymerization, hydrogenation, and catalytic conversion processes.
- Evaporator tubes and crystallizer internals in fertilizer and specialty chemical manufacturing.
5.3 Food & Beverage Industry
- Sanitary process piping for dairy, brewing, and pharmaceutical manufacturing, utilizing electropolished and internally brushed finishes to meet FDA and 3-A Sanitary Standards.
- Plate heat exchanger tubes for pasteurization, sterilization, and UHT (Ultra-High Temperature) processing.
5.4 Marine & Offshore Engineering
- Ballast water system piping, seawater cooling circuits, and fire suppression systems on ships and offshore platforms, utilizing 316L and duplex 2205 grades for chloride resistance.
- Desalination plant (RO and MED) tubing and heat exchanger components.
5.5 Power Generation & Renewable Energy
- Steam generator tubes and feedwater piping in nuclear and fossil-fuel power plants.
- Geothermal energy systems and solar thermal collectors requiring high-temperature corrosion-resistant tubing.
- Fuel cell bipolar plate channels and hydrogen energy system piping (31