Stainless Steel Coil Tube — Hard Condition (H) | Fully Cold-Worked Specification
1. Product Overview
The Stainless Steel Coil Tube in Hard Condition (H) represents the most advanced mechanical state achievable through a process of full cold working (充分冷加工). This product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd. and is classified under the Hard Temper (H) designation within the mechanical condition hierarchy of coil tube specifications. The extensive cold deformation applied during production significantly enhances the yield strength and hardness of the base austenitic stainless steel matrix, resulting in a material that delivers maximum pressure resistance among all available mechanical conditions.
This grade is specifically engineered for applications demanding superior mechanical integrity, including prefabricated elbows, straight pipe sections, and high-pressure process piping systems where dimensional stability and resistance to deformation under load are critical performance criteria.
2. Material & Properties
The Hard Condition (H) coil tube is produced from high-quality austenitic stainless steel (typically Grade 304 or 304L) as the base material. The full cold working process induces severe plastic deformation in the crystalline microstructure, generating a high density of dislocations and work-hardening effects that fundamentally alter the mechanical behavior of the material.
2.1 Mechanical Properties
- Vickers Hardness (HV): ≥ 280 — indicating a substantially hardened microstructure resulting from full cold deformation
- Elongation (A): ≥ 10% — maintaining adequate ductility despite the significant cold work, ensuring the material retains sufficient formability for controlled fabrication operations
- Yield Strength: Significantly elevated compared to annealed (soft) condition, providing superior resistance to plastic deformation under operational loads
- Tensile Strength: Enhanced through strain hardening, contributing to maximum allowable working pressure ratings
2.2 Microstructural Characteristics
- High dislocation density within austenitic grains due to extensive cold work
- Potential for strain-induced martensitic transformation (α' phase) in susceptible grades, contributing to additional hardening
- Refined grain boundaries and increased grain boundary energy
- Residual compressive stresses on the outer surface, beneficial for fatigue resistance
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Name | Coil Tube (盘管) | — |
| Mechanical Condition | Hard (H) — Fully Cold-Worked | ASTM A213 / GB/T 12771 |
| Vickers Hardness | HV ≥ 280 | ASTM E92 / ISO 6507 |
| Elongation (Minimum) | ≥ 10% | ASTM E8 / ISO 6892-1 |
| Primary Application Limitation | Prefabricated elbows and straight sections only | ASME B31.3 / EN 10217 |
| Pressure Rating | Maximum among all mechanical conditions (H, 1/2H, 1/4H, S) | ASME B31.3 / GB 50316 |
| Base Material (Typical) | Austenitic Stainless Steel (Grade 304 / 304L) | ASTM A269 / ASTM A213 |
| Cold Reduction Ratio | Maximum (full cold working) | Internal Specification |
4. Manufacturing Process
4.1 Process Description
The Hard Condition (H) coil tube is produced through a rigorous full cold working process that involves maximum cold reduction from the annealed (soft) state. The manufacturing sequence is as follows:
- Material Preparation: High-purity austenitic stainless steel strip or seamless tube blanks are supplied in the fully annealed (soft/S) condition as the starting material.
- Sequential Cold Drawing/Reduction: The tube or strip undergoes multiple passes through precision cold-working dies or rollers, achieving the maximum practicable reduction ratio. This is the defining step that distinguishes the H condition from intermediate hardening levels (1/2H, 1/4H).
- Dimensional Control: Tight tolerances on wall thickness, outer diameter, and ovality are maintained throughout the cold working sequence to ensure uniform mechanical properties across the entire cross-section.
- Coiling: The finished cold-worked tube is wound into coils for efficient downstream processing and shipping.
- Quality Inspection: Each coil undergoes hardness testing (Vickers), tensile testing, dimensional verification, and surface quality inspection before release.
4.2 Comparison of Mechanical Conditions
| Condition | Cold Work Level | Typical HV | Typical Elongation | Pressure Resistance |
|---|---|---|---|---|
| Soft (S) — Annealed | None | 120–180 | ≥ 35% | Lowest |
| Quarter Hard (1/4H) | Low | 180–220 | ≥ 20% | Moderate |
| Half Hard (1/2H) | Medium | 220–260 | ≥ 15% | High |
| Full Hard (H) | Maximum | ≥ 280 | ≥ 10% | Maximum |
5. Applications
The Hard Condition (H) coil tube, with its maximum pressure resistance, is specifically suited for the following applications:
- Prefabricated Elbows: The enhanced mechanical strength allows for fabrication of elbows with thinner wall sections while maintaining required pressure ratings, reducing material costs and weight.
- Straight Pipe Sections: Used in high-pressure process lines where maximum allowable working pressure (MAWP) is a critical design parameter.
- High-Pressure Instrument Piping: Ideal for instrument connections and impulse lines in process plants where pressure cycling and elevated operating pressures are present.
- Hydraulic Systems: Suitable for hydraulic hose assemblies and high-pressure fluid conveyance applications.
- Structural Applications: Where elevated yield strength is required for load-bearing components.
5.1 Application Limitations
Important: Due to the significantly reduced ductility inherent in the full cold working process, the Hard Condition (H) coil tube is restricted to prefabricated elbows and straight sections only. It is not recommended for applications requiring complex forming operations such as deep drawing, tight-radius bending, or extensive field fabrication, as the limited elongation (≥ 10%) may lead to cracking or fracture during aggressive deformation.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. ensures that every coil of Hard Condition (H) tube meets or exceeds the following quality standards and certification requirements:
- Material Compliance: ASTM A269 (Welded Austenitic Stainless Steel Tubing), ASTM A213 (Tubes, Heat-Resisting, Iron-Chromium-Chromium-Nickel), and/or GB/T 12771 (Stainless Steel Seamless Tubes for General Purposes)
- Hardness Verification: Vickers hardness testing per ASTM E92 / ISO 6507, with results certified at HV ≥ 280
- Tensile Testing: Performed per ASTM E8 / ISO 6892-1, confirming minimum elongation of ≥ 10%
- Dimensional Inspection: 100% inspection of outer diameter, wall thickness, and coil dimensions per applicable standards
- Surface Quality: Visual and automated inspection for surface defects, scratches, and oxide scale
- Mill Test Reports (MTR): Comprehensive material test reports provided with each shipment, documenting chemical composition, mechanical properties, and traceability information
- Traceability: Full lot and heat number traceability from raw material through finished coil
7. Unique Selling Points
- Maximum Pressure Resistance: The Hard (H) condition delivers the highest pressure resistance of all available mechanical states, enabling thinner-wall designs and optimized material utilization in high-pressure applications.
- Superior Yield Strength: Full cold working significantly elevates yield strength, providing exceptional dimensional stability and resistance to plastic deformation under sustained loads.
- Enhanced Wear Resistance: The HV ≥ 280 hardness level provides improved resistance to mechanical wear and abrasion in service conditions.
- Cost-Effective Design: By achieving higher pressure ratings through cold work rather than increased wall thickness, the H condition offers a material-efficient solution for pressure-containing applications.
- Controlled Ductility: Despite maximum cold working, the material retains ≥ 10% elongation, providing sufficient formability for prefabricated elbow and straight section fabrication.
- Corrosion Resistance Retained: The cold working process does not compromise the inherent corrosion resistance of the austenitic stainless steel base material, ensuring long-term service life in aggressive environments.