Stainless Steel Coil Tube — Tensile Strength (Rm) Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product delivered in continuous coil form, designed for high-volume downstream processing including forming, cutting, welding, and heat treatment. This specification focuses specifically on the Tensile Strength (Rm) — defined as the maximum load-bearing capacity of the material before fracture — which is one of the most critical mechanical performance indicators governing the structural integrity, forming behavior, and service reliability of the coil tube in demanding industrial applications.
Tensile strength, denoted as Rm (from the German Reißfestigkeit), represents the highest stress the material can withstand under uniaxial tensile loading before necking and ultimate failure occur. For stainless steel coil tubes, Rm is intrinsically linked to the hardness state (annealed/soft condition vs. cold-worked/hard condition) of the material, with the hard state achieving tensile strength values of approximately 1.5 to 2 times that of the soft (annealed) state.
2. Material & Mechanical Properties
2.1 Material Grades
Stainless steel coil tubes are typically produced from austenitic, ferritic, and martensitic stainless steel grades conforming to international standards including ASTM A511, ASTM A269, EN 10217, and GB/T 12771. Common grades include:
- Austenitic grades: 304 (UNS S30408), 304L (UNS S30403), 316L (UNS S31603), 321 (UNS S32108)
- Ferritic grades: 430 (UNS S43000), 409 (UNS S40900)
- Martensitic grades: 410 (UNS S41000), 420 (UNS S42000)
2.2 Tensile Strength (Rm) — Core Performance Indicator
The tensile strength Rm is the maximum stress recorded on the engineering stress-strain curve during a standard uniaxial tensile test (per ASTM E8/E8M or ISO 6892-1). It is determined by dividing the maximum force applied (Fmax) by the original cross-sectional area (A0) of the test specimen:
Rm = Fmax / A0
For stainless steel coil tubes, Rm values vary significantly depending on the temper condition (hardness state) of the material:
- Soft (Annealed) Condition: Rm typically ranges from 515 MPa to 620 MPa (for austenitic grades such as 304/316L), corresponding to a hardness of approximately 90–120 HV (Vickers Hardness).
- Hard (Cold-Worked / Spring Temper) Condition: Rm can reach 770 MPa to 1240 MPa, achieving approximately 1.5× to 2.0× the tensile strength of the soft state, with corresponding hardness values of 200–350 HV.
This direct correlation between hardness state and tensile strength is the defining metallurgical characteristic that allows manufacturers and end-users to select the appropriate temper condition for specific load-bearing requirements while balancing formability, ductility, and fatigue resistance.
2.3 Additional Mechanical Properties
- Yield Strength (Rp0.2): Proportional limit stress at 0.2% plastic strain; typically 205–1000 MPa depending on temper.
- Elongation (A50): Reduction in ductility with increasing hardness; soft state ~40–50%, hard state ~10–15%.
- Elastic Modulus (E): ~193–210 GPa (relatively constant across temper conditions for austenitic grades).
- Impact Toughness: Measured per ISO 148; varies with grain structure and temper condition.
3. Technical Specifications
| Parameter | Specification / Value | Test Standard |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coil Tube) | — |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. | — |
| Key Property | Tensile Strength (Rm) — Maximum Load-Bearing Capacity Before Fracture | ASTM E8/E8M; ISO 6892-1 |
| Rm — Soft (Annealed) Condition | 515 – 620 MPa (Austenitic 304/316L) | ASTM A269; EN 10217-7 |
| Rm — Hard (Cold-Worked) Condition | 770 – 1,240 MPa (1.5× to 2.0× soft state) | ASTM A269; EN 10217-7 |
| Rm — Hardness Correlation | Directly proportional; Hard state achieves 1.5–2× the Rm of soft state | ASTM E92 (Rockwell); ISO 6507 (Vickers) |
| Yield Strength (Rp0.2) | 205 – 1,000 MPa (temper-dependent) | ASTM E8/E8M |
| Elongation (A50) | 10 – 50% (soft state higher; hard state lower) | ASTM E8/E8M |
| Outer Diameter (OD) | 1.5 mm – 100 mm (customizable) | ASTM A511 |
| Wall Thickness (WT) | 0.2 mm – 6.0 mm (customizable) | ASTM A511 |
| Coil Inner Diameter (ID) | Standard: 152 mm / 200 mm / 254 mm; Custom available | — |
| Surface Finish | No. 1, 2B, BA (Bright Annealed), No. 4, Mirror (8K) | ASTM A480 |
| Dimensional Tolerance | ±0.05 mm (OD); ±0.02 mm (WT) for precision grades | ASTM A511; EN 10217 |
| Applicable Standards | ASTM A269, ASTM A511, ASTM A213, EN 10217-7, GB/T 12771, JIS G3459 | — |
4. Manufacturing Process
The production of stainless steel coil tubes with controlled tensile strength (Rm) involves a multi-stage manufacturing process, each stage critically influencing the final mechanical properties:
- Raw Material Preparation: Stainless steel strips are sourced from certified mills, verified for chemical composition (including Cr, Ni, Mo, C, Si, Mn, P, S content) per the target grade specification.
- Slitting: Master coils are slit into precise strip widths corresponding to the desired tube outer diameter, with edge quality controlled to prevent surface defects.
- Pipe Forming (Spiral Winding / Roll Forming): The strip is continuously formed into a tubular shape through precision roll-forming equipment. The degree of cold working applied during forming directly determines the hardness state and resulting Rm value.
- Welding: Longitudinal welds are created via TIG (Tungsten Inert Gas) welding or orbital welding, with shielding gas (Ar or He) ensuring weld integrity and corrosion resistance.
- Heat Treatment (Tempering):
- Soft (Annealed) Condition: Solution annealing at 1010–1150°C followed by controlled cooling to achieve maximum ductility and minimum Rm (~515–620 MPa).
- Hard (Cold-Worked / Spring Temper) Condition: Limited or no post-forming annealing; cold work hardening increases dislocation density, yielding Rm of 770–1,240 MPa (1.5–2× soft state).
- Surface Finishing: Pickling, passivation, and polishing to achieve the required surface finish grade (2B, BA, No. 4, Mirror).
- Quality Inspection: Tensile testing, hardness testing, dimensional measurement, hydrostatic testing, and visual/surface inspection.
- Coiling & Packaging: Finished tubes are wound onto coils, wrapped in protective film or paper, and packaged for shipment.
5. Applications
The tunable tensile strength (Rm) of stainless steel coil tubes enables their deployment across a broad spectrum of industrial applications:
- Automotive Industry: Exhaust systems, fuel lines, turbocharger pipes — requiring high Rm for structural integrity at elevated temperatures.
- Medical Devices: Surgical instrument tubing, endoscope shafts, implant components — utilizing soft-state Rm for precision forming and sterilization compatibility.
- Petroleum & Chemical Engineering: Process piping, heat exchanger tubes, reactor components — demanding corrosion-resistant hard-state Rm for high-pressure environments.
- Food & Beverage Processing: Hygienic piping, brewing equipment, dairy processing lines — leveraging BA/Mirror finish with adequate Rm for pressure service.
- Construction & Architecture: Structural decorative tubes, handrails, elevator components — where controlled hardness state balances aesthetics and load capacity.
- Aerospace: Hydraulic lines, fuel system tubing, engine exhaust components — requiring certified Rm values under strict aerospace standards (AMS).
- Electronics & Semiconductor: Vacuum chamber components, plasma etching chamber parts — utilizing precision-dimensioned coil tubes with specified mechanical properties.
- Spring & Wire Products: Automotive springs, appliance springs, tension elements — exploiting the high Rm of the hard (cold-worked) state for elastic energy storage.
6. Quality Certifications & Testing
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality assurance protocols to ensure that the tensile strength (Rm) and all associated mechanical properties of their stainless steel coil tubes meet or exceed international standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001 — Environmental Management System certification.
- Material Test Certificates (MTC): EN 10204 Type 3.1 / Type 3.2 certificates provided upon request, documenting chemical composition and mechanical properties including Rm, Rp0.2, and A50.
- Tensile Testing: Performed in accordance with ASTM E8/E8M and ISO 6892-1 using calibrated universal testing machines (UTM) with data logging for full stress-strain curve documentation.
- Hardness Testing: Conducted via ASTM E92 (Rockwell) and ISO 6507 (Vickers) to verify the hardness state correlation with Rm.
- Hydrostatic Testing: Performed per ASTM A269 to verify weld integrity and pressure-bearing capacity.
- Dimensional Inspection: Optical and ultrasonic measurement systems for OD, WT, and coil geometry verification.
- Third-Party Inspection: Available upon customer request through accredited inspection bodies (e.g., SGS, Bureau Veritas, TÜV).
7. Unique Selling Points
- Precision-Controlled Rm: The ability to deliver coil tubes in both soft and hard temper conditions, with hard-state Rm reaching 1.5× to 2.0× the soft-state value, provides end-users with precise mechanical property control tailored to specific application requirements.
- Continuous Coil Delivery: Enables high-throughput downstream processing with minimal material waste, reducing production costs and improving manufacturing efficiency.
- Multi-Grade Availability: Comprehensive range of austenitic, ferritic, and martensitic grades meeting ASTM, EN, GB, and JIS standards.
- Customization Capability: Flexible OD, wall thickness, surface finish, coil dimensions, and temper condition to meet bespoke engineering specifications.
- Full Traceability: Each coil batch is accompanied by detailed material test certificates and production traceability documentation ensuring complete supply chain transparency.