Fixed-Pitch Long Stainless Steel Coil Tube (Coiltube) — Technical Specification

1. Product Overview

The Fixed-Pitch Long Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product represents a specialized form of stainless steel tubing that is cold-formed into a helical coil configuration with a strictly controlled, uniform pitch (helix spacing). The manufacturing process employs a proprietary Fixed-Pitch Winding Fixture (定螺距绕制工装), which ensures dimensional consistency across the entire coil length, distinguishing this product from conventional coil tubes produced by standard bending equipment.

The Coiltube is designed for applications requiring high surface-area-to-volume ratios, efficient heat transfer, and compact installation footprints. Its fixed-pitch geometry provides predictable fluid dynamics, uniform stress distribution, and enhanced mechanical integrity under cyclic thermal loading conditions.

2. Material & Properties

The Coiltube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, mechanical strength, and formability under cold-working conditions.

• Material Grades: SUS304 (UNS S30400), SUS316L (UNS S31603), SUS321 (UNS S32100), and custom alloys upon request
• Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion in aggressive chemical environments
• Temperature Range: Continuous service from cryogenic temperatures (−196 °C) to elevated temperatures (up to 870 °C for SUS304; up to 925 °C for SUS321)
• Mechanical Properties (Annealed Condition):
  • Tensile Strength: ≥ 520 MPa (SUS304), ≥ 515 MPa (SUS316L)
  • Yield Strength (0.2% Proof): ≥ 205 MPa
  • Elongation: ≥ 40%
  • Hardness: ≤ 92 HRB
• Surface Finish: Electropolished, pickled, or mechanically polished (Ra ≤ 0.8 μm available upon request)
• Formability: Cold-wound without cracking or excessive work-hardening due to controlled strain rates during the fixed-pitch winding process

3. Specifications

Parameter	Specification / Range	Standard Reference
Outer Diameter (OD)	Φ3.0 mm – Φ50.8 mm	ASTM A213 / EN 10216-5
Wall Thickness	0.3 mm – 3.0 mm	ASTM A213 / EN 10216-5
Coil Diameter	Φ100 mm – Φ3000 mm	Custom per customer drawing
Pitch (Helix Spacing)	Fixed pitch, tolerance ±0.5 mm	Proprietary fixture design
Coil Length (Uncoiled)	Up to 200 m per continuous coil	Custom
Number of Turns	Up to 5,000 turns (continuous)	Custom
End Forming	Butt end, threaded end, or flanged connection	ASME B1.20.1 / EN 10226
Surface Treatment	Pickled & Passivated (P&P), Electropolished, Bead Blasted	ASTM A967 / AMS 2700
Dimensional Tolerance	±0.05 mm (OD), ±0.02 mm (pitch)	ISO 4621 / ASME B36.19M
Testing	Hydrostatic test, Eddy Current (ET), Visual Inspection (VT)	ASTM E309 / EN 10204 3.1
Material Certification	EN 10204 Type 3.1 / 3.2 Mill Test Certificate	ISO 9001:2015

4. Manufacturing Process

The production of the Fixed-Pitch Long Coiltube follows a rigorously controlled multi-stage process, each step subject to in-process quality inspection:

1. Raw Material Selection & Incoming Inspection:

   Stainless steel seamless or welded tubes are procured from certified mills (e.g., Outokumpu, voestalpine, Taiyuan Iron & Steel). Each batch undergoes spectral analysis (PMI verification), dimensional inspection, and mechanical property testing prior to acceptance.

2. Pre-Treatment & Annealing:

   Where required, incoming tubes are solution-annealed at 1050–1100 °C followed by rapid water quenching to restore full austenitic microstructure and maximize ductility for subsequent cold-forming operations.

3. Fixed-Pitch Winding Fixture Setup:

   The proprietary winding fixture is calibrated according to the target coil diameter, pitch, and turn count. The fixture incorporates precision guide rollers and a programmable drive system that maintains constant angular velocity, ensuring uniform pitch throughout the coil length. Fixture alignment is verified using laser interferometry prior to production.

4. Tube Straightening & Feeding:

   Raw tube is fed through a multi-roller straightener to eliminate any residual curvature, ensuring consistent contact with the winding fixture throughout the forming process.

5. Cold Winding / Coiling Operation:

   The tube is progressively wound around the fixture core at a controlled strain rate. The fixed-pitch mechanism prevents pitch variation, which is a common defect in conventional coiling methods. Real-time monitoring of forming forces detects any anomalies in tube properties or fixture alignment.

6. Post-Forming Stress Relief:

   Wound coils are subjected to a controlled stress-relief anneal (typically 400–500 °C for austenitic grades) to minimize residual stresses introduced during cold forming, without altering the fixed-pitch geometry.

7. End Processing:

   Tube ends are cut to precise lengths using CNC sawing or laser cutting, followed by end-forming operations (beveling, threading, or flange welding) as specified.

8. Surface Treatment:

   Final surface preparation includes pickling and passivation (acid immersion in nitric/hydrofluoric acid mixture), or electropolishing for critical applications requiring ultra-low surface roughness.

9. Final Quality Inspection:

   Each coil undergoes 100% dimensional verification (pitch, coil diameter, OD, wall thickness), eddy current testing for wall integrity, hydrostatic pressure testing, and visual inspection. A comprehensive traceability record is maintained per EN 10204.

5. Applications

The Fixed-Pitch Long Coiltube finds extensive use across multiple high-demand industrial sectors:

• Heat Exchangers: Spiral-wound heat exchangers, shell-and-tube exchangers with coiled bundle configurations, and air-cooled heat exchangers where compact surface area is critical
• Chemical Processing: Reactor internals, catalyst support coils, and heat transfer elements in corrosive chemical environments (petrochemicals, pharmaceuticals, fertilizer production)
• Food & Beverage Industry: Pasteurization coils, sterilization equipment, and hygienic heat transfer systems (compliant with 3-A Sanitary Standards)
• Energy Sector: Solar thermal collectors, geothermal heat exchangers, nuclear reactor coolant loops, and hydrogen fuel cell heat management systems
• Pharmaceutical Industry: Clean-in-place (CIP) compatible coils for bioreactors, fermentation vessels, and ultrafiltration systems
• Automotive & Aerospace: Compact heat exchangers for electric vehicle battery thermal management, aircraft environmental control systems, and hydraulic circuits
• Cryogenic Applications: LNG (Liquefied Natural Gas) transfer coils, superconducting magnet cooling circuits, and cryogenic storage systems

6. Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring full traceability and regulatory compliance:

• ISO 9001:2015 — Quality Management System certification covering all manufacturing processes
• ISO 14001:2015 — Environmental Management System
• EN 10204 Type 3.1 / 3.2 — Material Test Certification with full traceability to mill heat numbers
• ASME Stamp — Available for pressure vessel applications (upon request)
• CE Marking — Compliance with European Pressure Equipment Directive (PED 2014/68/EU)
• API 5L / API 5CT — Available for oil and gas sector applications
• 3-A Sanitary Standards — For food-grade and pharmaceutical applications

7. Unique Selling Points

Fixed-Pitch Precision: Unlike conventional coil tubes produced by standard winding machines where pitch variation is inevitable over long coil lengths, the proprietary Fixed-Pitch Winding Fixture guarantees pitch uniformity within ±0.5 mm tolerance across coils exceeding 200 meters in uncoiled length. This eliminates the need for post-forming correction and ensures consistent hydraulic performance.

• Long Continuous Coil Capability: Ability to produce single-continuous coils up to 200 m without weld joints, minimizing leak points and improving flow uniformity
• Custom Pitch Engineering: Tailored pitch configurations to optimize heat transfer coefficients, pressure drop, and mechanical resonance characteristics for specific applications
• Full Traceability: Each coil is linked to raw material mill certificates, process parameters, and final inspection data through a digital traceability system
• Multi-Material Flexibility: Production capability across SUS304, SUS316L, SUS321, duplex stainless steels (SUS2205), and specialty alloys (Inconel 625, Hastelloy C-276)
• Integrated Post-Processing: In-house capability for surface treatment, end forming, and pressure testing reduces supply chain complexity and lead times

8. Packaging & Delivery

Coils are individually wrapped in VCI (Vapor Corrosion Inhibitor) film, secured on custom wooden pallets with anti-slip bracing, and labeled with unique serial numbers, material specifications, and test certificates. Export packaging complies with ISPM 15 (International Standards for Phytosanitary Measures) for wooden materials. Delivery terms available: EXW, FOB, CIF, DDP (Incoterms 2020).