Stainless Steel Coil Tube (Coiltube) — Technical Specification

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a continuous-length tubular product formed through precision cold-drawing or cold-rolling processes, supplied in coiled configurations to facilitate automated cutting, forming, and installation. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product series encompasses a wide range of wall thicknesses, outer diameters, and material grades, engineered to meet the demanding requirements of industrial piping systems, heat exchangers, refrigeration circuits, and specialized thermal storage applications.

Coil tube technology has gained significant traction in thermal energy storage systems, particularly in ice-storage tank applications where continuous, leak-free tubing with high thermal conductivity and corrosion resistance is paramount. The coil configuration eliminates weld seams along the tube length, thereby enhancing structural integrity, reducing failure points, and enabling rapid deployment in large-scale installations.

2. Material & Properties

2.1 Available Material Grades

AISI 304 / 1.4301 — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
AISI 304L / 1.4307 — Low-carbon variant suited for welding applications requiring reduced sensitization
AISI 316 / 1.4401 — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion in chloride environments
AISI 316L / 1.4404 — Low-carbon 316 variant for critical welding and cryogenic applications
AISI 321 / 1.4541 — Titanium-stabilized grade for high-temperature service up to 870°C
AISI 310S / 1.4845 — High-temperature austenitic grade for oxidizing atmospheres
AISI 317L / 1.4438 — Enhanced molybdenum content for aggressive chemical processing environments

2.2 Mechanical Properties (Typical for AISI 304)

Property	Specification	Test Standard
Tensile Strength (R_m)	≥ 520 MPa	ASTM A213 / EN 10216-5
Yield Strength (R_p0.2)	≥ 205 MPa	ASTM A213 / EN 10216-5
Elongation (A₅₀)	≥ 40%	ASTM A213
Hardness	≤ 217 HB (as delivered)	ASTM A213
Thermal Conductivity (25°C)	16.3 W/(m·K)	ASTM E1461
Thermal Expansion Coefficient (20–100°C)	17.3 × 10⁻⁶ /K	ASTM E228

2.3 Corrosion Resistance

The austenitic stainless steel microstructure, stabilized by chromium (Cr ≥ 18%) and nickel (Ni ≥ 8%) content, provides inherent resistance to atmospheric corrosion, weak acids, and alkaline solutions. The 316 and 316L grades, with 2–3% molybdenum addition, demonstrate significantly enhanced resistance to pitting and stress corrosion cracking in chloride-containing environments, making them the preferred choice for marine, chemical, and thermal storage applications involving brine or saltwater heat transfer media.

3. Specifications

Parameter	Specification Range	Standard Reference
Outer Diameter (OD)	3.0 mm – 108.0 mm	ASTM A213 / EN 10216-5
Wall Thickness	0.3 mm – 6.0 mm	ASTM A213
Coil Inner Diameter	150 mm – 600 mm	Manufacturer standard
Coil Length	Custom (typically 200 m – 5000 m)	Per customer requirement
Surface Finish	Bright Annealed (BA), No.4 Brushed, 2B, Mirror Polished (Ra ≤ 0.4 μm)	ASTM A479
End Condition	Plain, Beveled, Threaded (per request)	ASTM A213
Tolerance on OD	±0.1 mm (precision grade); ±0.3 mm (standard grade)	EN 10216-5 Class B
Tolerance on Wall Thickness	±10% (standard); ±5% (precision grade)	EN 10216-5 Class B
Temperature Range	−196°C to +870°C (grade-dependent)	ASME BPVC Section I
Maximum Working Pressure	Grade- and dimension-dependent (calculated per ASME B31.3)	ASME B31.3
Delivery Condition	Hot-rolled (HR), Cold-drawn (CD), Annealed (AN), Solution Heat Treated (SHT)	ASTM A213

4. Manufacturing Process

4.1 Process Flow Overview

Raw Material Procurement — Certified stainless steel strip or seamless tube blanks sourced from approved mills with full traceability documentation (Mill Test Certificate / EN 10204 Type 3.1).
Coiling and Straightening — Precision coiling equipment ensures uniform coil geometry with controlled tension to prevent springback and dimensional deviation.
Cold Drawing / Cold Rolling — Tubes are cold-formed through calibrated dies to achieve precise OD and wall thickness tolerances while inducing beneficial strain hardening.
Intermediate Annealing — Periodic solution annealing at 1050–1150°C followed by controlled cooling to restore ductility, dissolve carbides, and maintain austenitic microstructure integrity.
Final Cold Drawing — Final pass through precision tooling to achieve target dimensions within specified tolerance classes.
Final Annealing and Pickling — Full solution heat treatment (1050–1150°C) with rapid quench to achieve full austenitic structure; followed by acid pickling to remove oxide scale and restore passive chromium oxide layer.
Surface Finishing — Optional mechanical polishing, electropolishing, or passivation treatment to achieve specified surface roughness (Ra) values.
Non-Destructive Testing (NDT) — 100% eddy current testing (ECT) for wall thickness and surface defect detection; hydrostatic pressure testing (typically 1.5× working pressure) for leak integrity verification.
Coiling, Packaging, and Dispatch — Final coiling with protective paper wrapping, wooden or steel crating, and moisture-absorbent desiccant packs for export-grade shipments.

4.2 Key Process Controls

Grain Size Control — Annealing cycles are optimized to maintain grain size between ASTM No. 5–8, ensuring a balance between ductility and mechanical strength.
Carbide Precipitation Prevention — For low-carbon grades (304L, 316L), carbon content is maintained below 0.03% to minimize chromium carbide precipitation during welding, preserving corrosion resistance in the Heat-Affected Zone (HAZ).
Dimensional Consistency — In-process laser measurement systems monitor OD and wall thickness in real time, with automated feedback to drawing equipment for continuous quality assurance.

5. Applications

5.1 Thermal Energy Storage Systems

Coil tubes are extensively employed in ice-storage tank systems for latent heat thermal energy storage (LTES). In these systems, stainless steel coil tubes serve as heat transfer media, circulating chilled water or brine to freeze or melt ice within the storage tank. The seamless coil configuration provides:

Elimination of longitudinal weld seams, reducing leak risk in cryogenic conditions
High surface-area-to-volume ratio, maximizing heat exchange efficiency
Resistance to thermal cycling fatigue, extending service life in repeated freeze-thaw cycles

5.2 Additional Application Domains

Automotive Industry — Fuel lines, brake lines, exhaust system components, and turbocharger feed lines
Medical and Pharmaceutical Equipment — Autoclave tubing, dialysis fluid lines, and bioreactor instrumentation
Food and Beverage Processing — Hygienic transfer lines, CIP (Clean-in-Place) compatible piping, and refrigeration coils
Petrochemical Industry — Crude oil transport, refined product distribution, and catalytic converter feed lines
Construction and Architecture — Decorative handrails, structural bracing, and HVAC (Heating, Ventilation, and Air Conditioning) ductwork
Heat Exchangers and Condensers — Tubular heat exchanger elements, evaporator coils, and condenser circuits
Cryogenic Systems — Liquefied natural gas (LNG) transfer lines and cryogenic storage tank internals

6. Quality Certifications and Standards Compliance

6.1 Manufacturing Certifications

ISO 9001:2015 — Quality Management System
ISO 14001:2015 — Environmental Management System
ISO 45001:2018 — Occupational Health and Safety Management System
EN 10204 Type 3.1 — Inspection Certificate with independent verification of test results
NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking (for applicable grades)
ASTM A270 / A269 — Compliance for wrought austenitic stainless steel tubing
EN 10216-5 — European standard for welded stainless steel tubes for pressure purposes
ASME SA-213 / SA-219 — American Society for Mechanical Engineers standards for heat exchanger tubing

6.2 Testing and Inspection Protocol

Test Type	Method	Frequency
Chemical Composition	Optical Emission Spectroscopy (OES) / Inductively Coupled Plasma (ICP)	Per heat lot
Dimensional Verification	Laser micrometer / ultrasonic thickness gauge	100% in-line monitoring
Surface Defect Detection	Eddy Current Testing (ECT)	100% of production length
Leak Tightness	Hydrostatic pressure test (1.5× MAWP)	100% of coils
Mechanical Properties	Tensile test, hardness test, impact test (Charpy V-notch)	Per heat lot / per batch
Corrosion Resistance	Potentiodynamic polarization / Salt spray test (ASTM B117)	Per heat lot / periodic
Intergranular Corrosion	ASTM A262 Practice E (acid solution test)	For L-grade and stabilized grades

7. Unique Selling Points

Seamless Integrity: The continuous coil configuration eliminates longitudinal weld seams, providing superior leak resistance and structural homogeneity compared to welded alternatives — a critical advantage in cryogenic and high-pressure applications.

Thermal Cycling Durability: Engineered for repeated freeze-thaw cycles in ice-storage and cryogenic applications, with proven performance exceeding 10,000 thermal cycles without degradation of mechanical properties.

Full Traceability: Every coil is accompanied by a complete material traceability package including heat number, mill test certificate, dimensional report, and NDT results, ensuring full compliance with international regulatory frameworks.

Customization Capability: Flexible manufacturing capacity enables tailored OD, wall thickness, coil dimensions, surface finish, and end-condition specifications to meet project-specific engineering requirements.

Weldability: All grades are optimized for excellent weldability, supporting TIG (Gas Tungsten Arc Welding), orbital welding, and resistance welding processes without preheating or post-weld heat treatment for standard wall thicknesses.

8. Packaging and Logistics

Each coil is individually wrapped in moisture-proof kraft paper with polyethylene film overwrap
Coils are crated in export-grade wooden pallets or steel skids with steel banding
Desiccant packs (silica gel, ≥500g per crate) are included to prevent condensation during transit
Maximum coil weight per unit: up to 3,000 kg (subject to OD and wall thickness)
Stacking height: up to 2 layers with proper load distribution

9. Technical Consultation

For detailed engineering support, material selection guidance, or custom specification development, Wenzhou Jixing Metal Materials Co., Ltd maintains a dedicated technical engineering team capable of providing:

Application-specific