Stainless Steel Coil Tube (Coiltube) — Elongation (A%) Technical Specification
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a high-performance continuous-length tubular product supplied in coiled form, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed for applications demanding exceptional formability, ductility, and corrosion resistance. The coil format enables efficient downstream processing through automated forming, bending, and cutting operations, minimizing material waste and production cycle time.
The defining metallurgical characteristic of this product is its Elongation (A%) — a quantitative measure of the material's plastic deformation capacity prior to fracture. Elongation serves as the primary indicator of ductility and is a critical quality parameter governing the tube's suitability for cold-working operations such as deep drawing, mandrel bending, hydroforming, and swaging.
Material & Properties
The stainless steel coil tube is typically fabricated from austenitic grades including 304 (AISI 304 / UNS S30400) and 316 (AISI 316 / UNS S31600), which are characterized by a face-centered cubic (FCC) crystal structure that inherently provides superior ductility and work-hardening behavior. The material exhibits the following key properties:
- Corrosion Resistance: Chromium oxide passive layer (Cr₂O₃) provides resistance to atmospheric corrosion, acids, and chloride-containing environments.
- Plastic Deformation Capacity: High elongation values ensure extensive uniform deformation without necking or fracture.
- Work Hardening: Progressive increase in yield strength during cold deformation, enabling post-forming mechanical strengthening.
- Non-Magnetic (Austenitic Grades): Suitable for electromagnetic interference-sensitive applications.
- Weldability: Low carbon variants (e.g., 304L, 316L) offer excellent weldability with minimal sensitization risk.
Elongation (A%) — Detailed Specification
Elongation (A%), also known as Percent Elongation or Reduction in Length at Fracture, is defined as the ratio of the increase in gauge length after fracture to the original gauge length, expressed as a percentage. It is measured in accordance with ASTM E8/E8M or ISO 6892-1 standard tensile testing procedures.
The elongation value is directly influenced by the temper condition (heat treatment state) of the coil tube. Wenzhou Jixing Metal Materials provides three distinct temper grades, each engineered for specific downstream processing requirements:
| Temper Condition | Designation | Minimum Elongation (A%) | Typical Application |
|---|---|---|---|
| Soft Annealed (SA) | Full Anneal / Annealed & Pickled (AP) | ≥ 40% | Deep drawing, complex bending, hydroforming, severe cold forming |
| Semi-Hard (SH) | Half Hard / Quarter Hard | ≥ 25% | Moderate forming, structural tubing, automotive components |
| Hard (H) | Full Hard / Cold Worked Hard | ≥ 15% | High-stress applications, wear-resistant parts, spring-like behavior |
Manufacturing Process
The production of stainless steel coil tube with controlled elongation properties follows a rigorous multi-stage manufacturing sequence:
- Hot Rolling: Slab or strip is hot-rolled to the target dimensions at temperatures above the recrystallization point (~1100°C for austenitic grades), producing a fully recrystallized, equiaxed grain structure that maximizes ductility.
- Acid Pickling & Descaling: The hot-rolled product undergoes pickling in a mixture of nitric acid (HNO₃) and hydrofluoric acid (HF) to remove oxide scale and restore the passive chromium oxide layer.
- Hot Continuous Tube Milling or ERW/Welded Forming: The strip is formed into a tubular cross-section via a hot continuous tube mill or electric resistance welding (ERW) process, followed by seamless welding where required.
- Cold Reduction / Cold Drawing: The tube passes through multi-stand rolling mills or drawing dies to achieve precise dimensional tolerances. The degree of cold reduction directly governs the temper condition and corresponding elongation value.
- Intermediate Annealing (if required): For semi-hard temper, a controlled partial annealing cycle is applied at reduced temperatures (~800–900°C) to partially recover ductility while retaining some work-hardened strength.
- Coiling: The finished tube is wound into coils of specified diameter and weight for logistics and downstream processing convenience.
Quality Certifications & Testing Standards
All stainless steel coil tube products are manufactured and tested in compliance with the following international standards:
- ASTM A554: Standard Specification for Seamless and Welded Austenitic Stainless Steel Electric-Resistance-Welded Pipe
- ASTM A213: Standard Specification for Seamless Ferritic and Austenitic Stainless Steel Tubing for Heat-Exchanger and Similar Applications
- ASTM A778: Standard Specification for Seamless and Welded Austenitic and Ferritic Stainless Steel Pipe
- ISO 6892-1: Metallic Materials — Tensile Testing — Part 1: Method of Test at Room Temperature
- EN 10217-7: Heat-Resistant Stainless Steel Tubes — Part 7: Seamless Tubes
- JIS G3459: Seamless Austenitic Stainless Steel Tubes
Each production lot undergoes tensile testing to verify elongation (A%), yield strength (Rp0.2), and ultimate tensile strength (Rm). Additional quality assurance measures include:
- Hydrostatic Testing (per ASTM A554) to verify structural integrity
- Spectroscopic Chemical Analysis (OES/SEM) for composition verification
- Dimensional Inspection using automated laser measurement systems
- Surface Quality Assessment for pickling finish, scale-free surfaces
- Third-Party Inspection available upon request (SGS, BV, TUV)
Applications
The controlled elongation properties of Wenzhou Jixing Metal Materials' stainless steel coil tube make it suitable for a wide range of industrial applications:
- Automotive Industry: Exhaust system tubing, fuel lines, and structural brackets (semi-hard and hard tempers)
- Petrochemical & Oil/Gas: Heat exchanger tubes, process piping, and high-pressure transport lines
- Medical & Pharmaceutical: Surgical instrument tubing, dialysis equipment, and pharmaceutical processing piping (soft annealed)
- Food Processing: Sanitary-grade piping, mixing vessels, and hygienic transfer lines
- Construction & Architecture: Structural tubing, handrails, and decorative elements
- Electronics: Heat sinks, shielding enclosures, and precision components
- Aerospace: Hydraulic tubing, fuel lines, and structural components
Unique Selling Points
- Grade-Specific Elongation Guarantee: Wenzhou Jixing Metal Materials provides three distinct temper grades with precisely controlled minimum elongation values (≥40%, ≥25%, ≥15%), enabling customers to select the optimal balance of ductility and strength for their specific forming requirements.
- Coil Format Efficiency: Continuous coil supply eliminates butt-weld joints, reduces material waste by up to 15%, and enables high-speed automated downstream processing.
- Full Traceability: Every coil is accompanied by a mill test certificate (MTC) documenting chemical composition, mechanical properties, and heat treatment history.
- Customization Capability: Tailored temper conditions, wall thicknesses, and outer diameters available to meet project-specific requirements.
- International Standard Compliance: Products conform to ASTM, ISO, EN, and JIS standards, ensuring global market compatibility and regulatory acceptance.
Technical Summary
The Elongation (A%) property of Wenzhou Jixing Metal Materials' stainless steel coil tube represents a critical engineering parameter that directly determines the material's suitability for plastic deformation processes. With guaranteed minimum elongation values of ≥40% (Soft Annealed), ≥25% (Semi-Hard), and ≥15% (Hard), the product line offers versatile formability across a broad spectrum of manufacturing applications. Combined with the inherent corrosion resistance of austenitic stainless steel, this product delivers a reliable, high-performance solution for demanding industrial environments.