Spiral Stainless Steel Coil Tube (Coiltube)

1. Product Overview

The Spiral Stainless Steel Coil Tube (also designated as Coiltube) is a precision-engineered continuous tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product features a helical coil configuration formed from seamless or welded stainless steel tubing, designed to deliver maximum material utilization, superior flexibility in installation, and enhanced resistance to mechanical stress. The spiral geometry provides inherent spring-back characteristics, making it ideal for applications requiring compact storage, thermal expansion accommodation, and vibration damping.

Unlike conventional straight-length tubing, spiral coil tubes offer significant advantages in terms of space efficiency, reduced welding joints, and improved flow dynamics in heat exchanger and piping systems. The continuous coil form factor minimizes the number of connection points, thereby reducing potential leak paths and improving long-term system reliability.

2. Material & Properties

Spiral stainless steel coil tubes are fabricated from high-grade austenitic and duplex stainless steel grades, each selected for specific performance requirements:

• ASTM A269 / A312 Grade 304 (UNS S30400): General-purpose corrosion resistance with excellent formability. Chromium (Cr) content of 18–20%, Nickel (Ni) content of 8–10.5%.
• ASTM A269 / A312 Grade 316 (UNS S31600): Enhanced resistance to pitting and crevice corrosion due to Molybdenum (Mo) addition of 2–3%. Suitable for chemical and marine environments.
• ASTM A269 / A312 Grade 316L (UNS S31603): Low-carbon variant (C ≤ 0.03%) for superior weldability and resistance to intergranular corrosion.
• ASTM A312 Grade 321 (UNS S32100): Titanium-stabilized grade offering excellent resistance to sensitization at elevated temperatures up to 870°C.
• ASTM A312 Grade 347 (UNS S34700): Niobium-stabilized grade for high-temperature service applications.
• ASTM A312 Grade 904L (UNS N08904): Super-austenitic grade with high Ni and Mo content for extreme corrosion environments.

Mechanical Properties (Typical Values for Annealed Condition)

Grade	Tensile Strength (MPa)	Yield Strength (MPa, 0.2% Offset)	Elongation (%)	Hardness (HB Max)
304	≥ 515	≥ 205	≥ 40	≤ 201
316	≥ 515	≥ 205	≥ 40	≤ 201
316L	≥ 485	≥ 170	≥ 40	≤ 201
321	≥ 515	≥ 205	≥ 40	≤ 201
347	≥ 515	≥ 205	≥ 40	≤ 201
904L	≥ 550	≥ 220	≥ 35	≤ 201

Corrosion Resistance Characteristics

• Pitting Resistance: 316/316L grades exhibit a Pitting Resistance Equivalent Number (PREN) of approximately 24–26, significantly outperforming Grade 304 (PREN ≈ 19).
• Crevice Corrosion: Low-carbon grades (304L, 316L) demonstrate superior resistance in chloride-containing environments.
• Intergranular Corrosion: Stabilized grades (321, 347) and low-carbon variants resist sensitization in the 450–850°C temperature range.
• Stress Corrosion Cracking (SCC): All austenitic grades maintain resistance to SCC in non-chloride environments; duplex grades available upon request for chloride-rich conditions.

3. Specifications

Dimensional Specifications

Parameter	Specification	Standard Reference
Outside Diameter (OD)	6.0 mm – 219.1 mm (¼" – 8")	ASTM A269 / EN 10217-7
Wall Thickness (WT)	0.5 mm – 12.7 mm (0.020" – 0.500")	ASTM A269 / EN 10217-7
Coil Length (Continuous)	50 m – 1000 m (configurable)	Manufacturer Standard
Coil Diameter	300 mm – 1500 mm (configurable)	Manufacturer Standard
OD Tolerance	±0.10 mm (for OD ≤ 12.7 mm); ±0.05 × OD (for OD > 12.7 mm)	ASTM A269
Wall Thickness Tolerance	±10% of nominal	ASTM A269
Roundness	≤ 0.03 × WT	ASTM A269
Surface Roughness (Ra)	≤ 0.8 μm (standard); ≤ 0.2 μm (electropolished)	ASTM A269 / Custom
End Form	Plain, Beveled, Flanged, Threaded (upon request)	Custom
Delivery Condition	Annealed (Solution Annealed), Pickled & Passivated	ASTM A269

Available Surface Finishes

• 2B Finish: Standard cold-rolled, annealed, and pickled surface with a matte appearance.
• No. 4 Brushed Finish: Uniform directional grain pattern suitable for architectural and decorative applications.
• Mirror Polish (Ra ≤ 0.1 μm): Achieved through mechanical polishing followed by electropolishing.
• Electropolished (EP): Electrochemical finishing providing enhanced corrosion resistance and ultra-smooth surface (Ra ≤ 0.2 μm).
• Pickled & Passivated (P&P): Removal of scale and oxide layers with formation of a protective chromium oxide passive film.

4. Manufacturing Process

The production of spiral stainless steel coil tubes involves a meticulously controlled multi-stage manufacturing sequence, each phase engineered to ensure dimensional accuracy, metallurgical integrity, and surface quality:

Stage 1: Raw Material Selection and Incoming Inspection

1. Material Certification: Each heat lot of stainless steel strip or seamless tube blank is verified against mill test certificates (MTC) conforming to EN 10204 Type 3.1.
2. Chemical Analysis: Spectroscopic verification of Cr, Ni, Mo, C, N, and trace element composition within specified grade tolerances.
3. Physical Inspection: Visual examination for surface defects, dimensional measurement, and hardness spot-testing.

Stage 2: Tube Forming

1. Slitting: Precision slitting of stainless steel coil to exact blank width with controlled edge quality (no burrs, no cracks).
2. Forming: Progressive roll-forming of the strip into a helical tube profile using a series of matched forming rolls with tight geometric tolerances.
3. Welding (for welded tube): Continuous longitudinal welding via Automatic Submerged Arc Welding (ASAW) or Plasma Arc Welding (PAW) with inert gas (Argon) shielding to ensure a high-quality weld bead with full penetration.

Stage 3: Heat Treatment and Annealing

1. Solution Annealing: Heating to 1050–1150°C in a controlled atmosphere furnace (protective gas or vacuum) to dissolve carbides and restore full austenitic microstructure.
2. Quenching: Rapid cooling via air or water quench to lock in the solution-treated microstructure.
3. Stress Relief: Optional intermediate annealing at 850–900°C to relieve residual stresses from forming operations.

Stage 4: Surface Treatment

1. Pickling: Immersion in a mixed acid solution (HNO₃ + HF) to remove oxide scale and welding discoloration.
2. Passivation: Treatment with a citric acid or nitric acid solution to regenerate the protective chromium oxide passive film (minimum 10 μm thickness).
3. Optional Finishing: Electropolishing or mechanical polishing for applications requiring ultra-smooth surfaces.

Stage 5: Coiling and Winding

1. Continuous Coiling: The formed and heat-treated tube is wound into a spiral coil configuration using a precision coiler with controlled tension and alignment.
2. Coil Protection: Inter-layer protective film application and outer wrapping to prevent mechanical damage during storage and transportation.
3. End Sealing: Secure banding and end-cap installation to maintain coil integrity.

Stage 6: Final Quality Control

1. Dimensional Verification: Full-length OD and wall thickness measurement using ultrasonic thickness gauges and laser diameter sensors.
2. Hydrostatic Testing: Pressure testing at 1.5× the maximum working pressure for a minimum hold time of 10 seconds to verify weld integrity and absence of leaks.
3. Non-Destructive Testing (NDT): Eddy current testing (ECT) or ultrasonic testing (UT) for subsurface defect detection; Magnetic Particle Inspection (MPI) for surface-breaking defects on ferromagnetic materials.
4. Surface Inspection: Visual and dye penetrant examination (PT) for surface defects.
5. Chemical Composition Verification: Spot-check by Optical Emission Spectroscopy (OES) on finished product.

5. Applications

Spiral stainless steel coil tubes find extensive application across multiple high-performance industrial sectors:

• Heat Exchangers and Condensers: Spiral coil geometry provides enhanced heat transfer efficiency and thermal expansion accommodation in shell-and-tube heat exchangers, condensers, and evaporators.
• Petrochemical and Chemical Processing: Piping systems for transporting aggressive chemical media (acids, alkalis, solvents) where 316L and 904L grades provide superior corrosion resistance.
• Pharmaceutical and Bioprocessing: Hygienic-grade tubing (electropolished, 316L) for CIP/SIP-compatible piping systems, reactor internals, and fluid transfer lines.
• Food and Beverage Industry: Sanitary-grade tubing for milk processing, brewing, and food-grade fluid conveyance systems (compliant with 3-A Sanitary Standards).
• Power Generation: Boiler tubes, superheater coils, and feedwater systems in coal-fired, nuclear, and renewable energy plants.
• Marine and Offshore Engineering: Seawater cooling systems, ballast water piping, and subsea production systems utilizing duplex and super-austenitic grades.
• Automotive and Aerospace: Exhaust systems, fuel lines, and high-temperature components requiring thermal stability and corrosion resistance.
• Architectural and Decorative: Structural and decorative elements, handrails, and facade systems utilizing mirror-polished or brushed finishes.
• Spring and Damping Applications: Utilizing the inherent spring characteristics of the spiral coil form for vibration isolation and load-bearing spring assemblies.

6. Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications:

• ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
• ISO 14001:2015 — Environmental Management System certification for environmentally responsible manufacturing practices.
• ISO 45001:2018 — Occupational Health and Safety Management System certification.
• EN 10204 Type 3.1 — Mill Test Certificate (MTC) issued for each production lot, providing full traceability of chemical composition and mechanical properties.
• CE Marking — Conformity with European standards for pressure equipment and construction products.
• ASME Stamp (U/U1/U2) — For pressure vessel and piping components manufactured to ASME Boiler and Pressure Vessel Code.
• NSF/ANSI 61 — For drinking water system components (where applicable).
• 3-A Sanitary Standards — For food-grade applications (where applicable).

Governing Standards

Standard	Description
ASTM A269	Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe, Tube, and Fittings for Chemical and Similar Severities of Service
ASTM A312	Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Pipes
EN 10216-5	Non-Alloy and Alloy Steel Tubes for Technical Purposes — Heat Resistant Stainless Steel Tubes
EN 10217-7	Non-Alloy and Alloy Steel Tubes for Technical Purposes — Heat Resistant Stainless