Stainless Steel Coiltube — Ovality (Ellipticity) Dimensional Specification
Product Overview
The Stainless Steel Coiltube manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product supplied in continuous coil form, designed for high-performance applications in fluid conveyance, instrumentation, and structural assembly. Ovality, also referred to as ellipticity, is a critical geometric quality parameter that defines the deviation of the tube's cross-sectional profile from a perfect circle. This specification governs the maximum permissible deviation expressed as the ratio of the difference between the maximum and minimum diameters to the nominal diameter, calculated as follows:
Ovality (%) = (Dmax − Dmin) / Dnom × 100%
where Dmax is the maximum outer diameter, Dmin is the minimum outer diameter, and Dnom is the nominal outer diameter of the coil tube. This geometric parameter is recognized as the primary cause of ferrule-type (compression fitting) seal failure in downstream applications, making its control essential for system integrity and long-term reliability.
Material & Properties
Wenzhou Jixing Metal Materials Co., Ltd produces coiltube products from a range of austenitic stainless steel grades, each selected to meet specific corrosion resistance, mechanical strength, and formability requirements:
- 304 / 304L (UNS S30400 / S30403): The most widely used austenitic grade, offering excellent general corrosion resistance, good weldability, and outstanding cold-forming characteristics. The low-carbon 304L variant minimizes intergranular sensitization during welding.
- 316 / 316L (UNS S31600 / S31603): Enhanced molybdenum content (2.0–3.0%) provides superior resistance to pitting and crevice corrosion in chloride-containing environments, making it ideal for chemical processing and marine applications.
- 321 (UNS S32100): Stabilized with titanium to prevent chromium carbide precipitation at elevated temperatures, suitable for high-temperature service up to 870 °C.
- 310S (UNS S31008): High-temperature grade with excellent oxidation resistance, capable of sustained service in oxidizing atmospheres up to 1150 °C.
- Duplex 2205 (UNS S32205): Austenitic-ferritic microstructure providing approximately twice the yield strength of 304/316 with exceptional resistance to chloride stress corrosion cracking (SCC).
Typical mechanical properties for cold-worked coiltube include yield strengths ranging from 205 MPa (annealed) to over 600 MPa (cold-worked), with elongation values of 35–55% depending on the processing condition and grade.
Specifications — Ovality Tolerance Requirements
| Parameter | Precision Grade (精密级) | Ordinary Grade (普通级) | Test Method / Standard Reference |
|---|---|---|---|
| Ovality (Ellipticity) | ≤ 3% | ≤ 5% | ASTM A213 / ASTM A554 / EN 10217 |
| Measurement Formula | (Dmax − Dmin) / Dnom × 100% | ISO 4427 / GB/T 14976 | |
| Nominal OD Range (typical) | Φ3.0 mm – Φ108 mm | — | |
| Wall Thickness Range (typical) | 0.10 mm – 6.00 mm | — | |
| Coil Inner Diameter | ≥ 150 mm (standard); custom available | — | |
| Coil Length | Continuous coil; typical 200 m – 3,000 m per coil | — | |
| Surface Finish | Pickled & passivated; Ra ≤ 1.6 μm (standard); Ra ≤ 0.4 μm (electropolished) | ASTM A967 / ASTM B923 | |
| Temperature of Measurement | 20 ± 5 °C (ambient) | ISO 1 / GB/T 3193 | |
Grade Classification Criteria
- Precision Grade (≤ 3% Ovality): Intended for applications requiring high concentricity, such as instrumentation tubing, capillary tubes, semiconductor gas delivery lines, and critical hydraulic/pneumatic circuits where ferrule or compression fitting integrity is paramount.
- Ordinary Grade (≤ 5% Ovality): Suitable for general-purpose fluid conveyance, structural applications, heat exchangers, and non-critical process piping where moderate geometric tolerance is acceptable.
Manufacturing Process
The production of Wenzhou Jixing coiltube follows a rigorous multi-stage manufacturing sequence designed to maintain dimensional accuracy and minimize geometric deviations:
- Ring Cutting & Coil Forming: Stainless steel strip (slit from hot-rolled coil or cold-rolled strip) is fed into a forming station where it is progressively shaped into a tubular cross-section via a series of roll passes.
- Seam Welding: The formed tube is welded at the seam using TIG (Tungsten Inert Gas) or laser welding technology with argon shielding on both the inside and outside to ensure a high-integrity, corrosion-resistant weld.
- Post-Weld Heat Treatment: Solution annealing (1050–1150 °C followed by rapid water quench) restores the austenitic microstructure and relieves welding-induced residual stresses.
- Pickling & Passivation: The tube is cleaned via acid pickling (nitric/hydrofluoric acid mixture) to remove the heat-affected scale, followed by passivation to restore the protective chromium oxide layer.
- Cold Drawing / Sizing: Precision cold-drawing through calibrated dies refines the outer diameter, wall thickness, and ovality to meet the specified tolerance class. Multiple drawing passes may be employed for tighter tolerances.
- Coiling & Packaging: The finished tube is coiled onto a mandrel with controlled tension to prevent deformation, then packaged with protective wrapping and moisture barriers.
The cold-drawing stage is particularly critical for ovality control, as it directly determines the roundness of the tube cross-section. Wenzhou Jixing employs high-precision multi-roll drawing equipment with real-time diameter monitoring to ensure consistent ovality performance throughout the coil length.
Applications
Given the critical importance of controlled ovality for sealing integrity, Wenzhou Jixing coiltube products are deployed across a wide spectrum of industries:
- Instrumentation & Process Control: Pressure tubing, capillary lines, and impulse lines in control valve assemblies where ferrule fittings are standard.
- Hydraulic & Pneumatic Systems: High-pressure fluid lines requiring reliable compression-joint seals under cyclic loading.
- Semiconductor Manufacturing: Ultra-clean gas delivery tubing (316L electropolished) where even minor ovality can compromise vacuum-tight joints.
- Automotive & Aerospace: Fuel lines, brake lines, and hydraulic circuits demanding precision geometry for crimp or ferrule connections.
- Chemical & Pharmaceutical Processing: Sanitary-grade tubing (316L, electropolished) for CIP/SIP processes requiring leak-tight hygienic fittings.
- Food & Beverage Industry: Process piping with sanitary tri-clamp or ferrule connections.
- Medical Devices: Tubing for medical gas systems, infusion equipment, and analytical instruments.
- Energy & Petrochemical: Downhole instrumentation, instrument well tubing, and offshore platform piping.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains an integrated quality management system and holds the following certifications and compliances:
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality and process control.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 3.1 Certificate — Material test certificates providing third-party verified chemical composition, mechanical properties, and dimensional compliance data.
- ASTM / ASME Compliance — Products manufactured in accordance with ASTM A213, ASTM A554, ASME B36.19M, and related international standards.
- GB/T 14976 / GB/T 12771 — Chinese national standards for seamless and welded stainless steel tubes.
- EU PED 2014/68/EU — Pressure Equipment Directive compliance for pressure-rated applications.
- CE Marking — Conformity with European health, safety, and environmental protection standards.
- 3-A Sanitary Standards — Available for food, dairy, and pharmaceutical-grade tubing applications.
- CRN (Canadian Registration Number) — Available upon request for Canadian pressure equipment applications.
Unique Selling Points
- Industry-Leading Ovality Control: Precision-grade coiltube with ovality ≤ 3% significantly reduces the risk of ferrule seal failure, ensuring long-term system reliability and minimizing maintenance downtime.
- Full-Spectrum Grade Availability: Comprehensive material range from 304/304L to duplex 2205 and high-temperature 310S, enabling single-source procurement for diverse application requirements.
- Continuous Coil Supply: Uninterrupted coil lengths minimize splice points and installation labor, improving overall system integrity.
- Traceable Quality Documentation: Every coil is accompanied by a complete traceability package including mill test certificates, chemical analysis reports, dimensional inspection records, and heat number documentation.
- Customization Capability: Flexible manufacturing capacity supports non-standard diameters, wall thicknesses, coil configurations, and surface finishes tailored to specific customer specifications.
- Geometric Integrity for Critical Sealing: By directly addressing the root cause of compression fitting failures—tube ovality—Wenzhou Jixing coiltube provides a fundamentally more reliable sealing solution than products with uncontrolled or loosely specified geometric tolerances.