Stainless Steel Fixed-Pitch Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Fixed-Pitch Coil Tube (Catalogue No. 1256) is a precision-wound tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is produced using a proprietary fixed-pitch long coil tube winding fixture (定螺距长盘管绕制工装), which ensures consistent helical geometry, uniform pitch distribution, and dimensional repeatability across production batches. The coil tube is engineered for demanding thermal exchange, fluid conveying, and structural applications where corrosion resistance, mechanical integrity, and geometric precision are critical.
Unlike conventional coil tubes with variable or hand-adjusted pitch, the fixed-pitch design eliminates cumulative geometric error, yielding a product with superior dimensional accuracy and interchangeability. The winding fixture employs a rigid guide mechanism with calibrated lead screws and tension-controlled feed systems to maintain a constant helix angle and pitch throughout the full coil length.
2. Material and Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their combination of corrosion resistance, formability, and weldability. The following material grades are typically available:
- SUS 304 / AISI 304 (1.4301) — General-purpose grade with excellent atmospheric and mild chemical corrosion resistance. Chromium content 18–20%, Nickel content 8–10.5%.
- SUS 304L / AISI 304L (1.4307) — Low-carbon variant (C ≤ 0.03%) suitable for welding applications requiring resistance to intergranular corrosion.
- SUS 316 / AISI 316 (1.4401) — Molybdenum-bearing grade (Mo 2–3%) offering enhanced resistance to pitting and crevice corrosion in chloride-containing environments.
- SUS 316L / AISI 316L (1.4404) — Low-carbon version of 316 for critical welded assemblies.
- SUS 321 / AISI 321 (1.4541) — Titanium-stabilized grade for elevated-temperature service up to 870 °C.
Mechanical Properties (Typical for 304 Grade, Annealed Condition):
- Tensile Strength (UTS): ≥ 515 MPa (75 ksi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (30 ksi)
- Elongation (at Break): ≥ 40%
- Hardness: ≤ 95 HRB
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Type | Fixed-Pitch Coil Tube (Helical Tubing) | — |
| Material Grade | SUS 304, 304L, 316, 316L, 321 | ASTM A270, ASTM A213, EN 10217-7 |
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2") | ASTM B304 / ISO 3505 |
| Wall Thickness | 0.5 mm – 3.0 mm | — |
| Coil Pitch (Fixed) | 10 mm – 150 mm (constant, ±0.5 mm tolerance) | Proprietary fixture calibration |
| Coil Diameter (Mean) | 50 mm – 1,200 mm | — |
| Coil Length | Up to 30 m (continuous winding) | — |
| Number of Turns | 10 – 1,500 turns | — |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, Mirror (Ra ≤ 0.4 μm) | ASTM A480 |
| End Preparation | Flat cut, beveled (37.5° ±1°), or threaded | ASME B1.20.1 |
| Dimensional Tolerance (OD) | ±0.05 mm (close tolerance available) | ISO 1128 |
| Dimensional Tolerance (Pitch) | ±0.5 mm over full coil length | — |
| Operating Temperature Range | −196 °C to +870 °C (grade-dependent) | — |
| Maximum Working Pressure | Up to 6.3 MPa (depending on OD and wall thickness) | ASME B31.3 |
4. Manufacturing Process
4.1 Tube Procurement and Inspection
Raw stainless steel tubes are sourced from certified mills conforming to ASTM A270 or EN 10217-7 specifications. Incoming material undergoes 100% dimensional verification and spectroscopic chemical analysis (OES) to confirm grade compliance. Tubes are inspected for surface defects, wall thickness uniformity, and straightness prior to coil forming.
4.2 Fixed-Pitch Winding Fixture Setup
The proprietary winding fixture is calibrated to the specified coil pitch, mean coil diameter, and number of turns. Key components include:
- Lead Screw Drive Mechanism — Provides constant axial feed synchronized with rotational motion to maintain fixed pitch.
- Rigid Guide Rings — Maintain tube alignment and prevent ovalization during bending.
- Tension Control System — Maintains consistent tensile force on the tube to prevent buckling or wrinkling at the inner coil diameter.
- Reference Datum System — Ensures repeatable starting and ending positions for each coil.
4.3 Coil Winding
The tube is fed through a forming die and wound around a mandrel or free-form coil former. The fixed-pitch mechanism ensures that each successive turn maintains a constant axial displacement relative to the previous turn. The winding process is performed at controlled speed to minimize residual stresses and springback effects.
4.4 Post-Winding Treatment
- Stress Relief Annealing — Heating to 1050–1150 °C followed by controlled cooling to eliminate cold-work hardening and residual stresses introduced during forming.
- Pickling and Passivation — Removal of oxide scale and formation of a protective chromium oxide passive film (per ASTM A967).
- Surface Finishing — Mechanical polishing or electropolishing to achieve specified surface roughness if required.
4.5 End Processing and Assembly
Coil ends are prepared according to customer specifications, including flat cutting, beveling, threading, or welding of fittings. Multi-coil assemblies may be joined by orbital TIG welding (GTAW) with helium backing gas to maintain internal surface quality.
5. Applications
The fixed-pitch coil tube finds extensive application across multiple industries:
- Heat Exchangers — Spiral heat exchangers, air-cooled condensers, and evaporator coils in HVAC and refrigeration systems.
- Chemical Processing — Reactor internals, heat transfer coils, and fluid distribution tubing in corrosive process environments.
- Pharmaceutical and Food Processing — Sanitary-grade coils for pasteurization, sterilization (SIP/CIP), and fluid transfer systems.
- Automotive Industry — Radiator coils, intercooler tubes, and turbocharger exhaust manifolds.
- Petroleum and Gas — Subsea production tubing, wellhead assemblies, and downhole heat exchangers.
- Power Generation — Boiler tubes, superheater elements, and condenser coil bundles.
- Medical Equipment — MRI gradient coils, autoclave heating elements, and dialysis fluid circuits.
6. Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product conformance:
- ISO 9001:2015 — Quality Management System certification for manufacturing processes.
- ISO 14001:2015 — Environmental Management System certification.
- ASME Section IX — Welding procedure and welder qualification compliance.
- EN 10204 3.1 — Third-party material certification for all supplied products.
- CE Marking — Compliance with applicable European Directives for pressure equipment (PED 2014/68/EU).
- ASTM / ASME — Product conformity to relevant American standards (ASTM A270, A213, A312; ASME B31.3).
Each production batch is accompanied by a Mill Test Certificate (MTC) documenting chemical composition, mechanical properties, dimensional measurements, and heat treatment records. Non-destructive testing (NDT) methods including ultrasonic testing (UT), dye penetrant inspection (DPI), and hydrostatic pressure testing are employed as applicable.
7. Unique Selling Points
Precision Fixed-Pitch Geometry: The proprietary winding fixture delivers a pitch tolerance of ±0.5 mm over coil lengths exceeding 30 meters, far surpassing conventional variable-pitch coil manufacturing capabilities.
- Dimensional Consistency: Fixed-pitch design eliminates cumulative geometric error, ensuring uniform heat transfer coefficients and flow characteristics throughout the coil length.
- Material Versatility: Available in multiple stainless steel grades (304, 304L, 316, 316L, 321) to address diverse corrosion and temperature requirements.
- Customization Capability: Flexible configuration of OD, wall thickness, pitch, coil diameter, number of turns, surface finish, and end preparation to meet specific engineering specifications.
- Full Traceability: Complete material and process documentation from raw tube mill certification through final product inspection.
- Cost-Effective Long-Run Production: The fixed-pitch fixture design enables high repeatability and reduced scrap rates in serial production, offering competitive pricing for volume orders.
- Engineering Support: Technical consultation available for coil design optimization, including pitch selection, coil diameter determination, and pressure drop calculations.