Stainless Steel Coil Tube — Natural Curvature Release & Anti-Torsion Specification

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.  |  Catalogue No.: 215

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) supplied by Wenzhou Jixing Metal Materials Co., Ltd. is a continuous-length tubular product wound into a compact coil configuration for efficient storage, transportation, and downstream processing. This specification addresses a critical installation and maintenance consideration: the Natural Curvature Release principle applied during the coil unspooling (pay-out) operation.

The fundamental requirement is to allow the tube to rotate freely during pay-out without imposing external torsional loads. This ensures that residual elastic energy accumulated during the coiling process is released in a controlled manner, preserving the material's mechanical integrity and preventing microstructural degradation that could compromise subsequent forming operations.

2. Material & Properties

2.1 Base Material Grades

2.2 Mechanical Properties (Typical — Annealed Condition)

2.3 Metallurgical Considerations

Austenitic stainless steels possess a face-centered cubic (FCC) crystal structure that provides excellent ductility and work-hardening resistance. However, when torsional strain is introduced during improper coil handling, dislocation pile-up occurs at grain boundaries, creating localized stress concentrations. These stress concentrations serve as crack initiation sites during subsequent cold-forming operations such as bending, mandrel drawing, or roll bending.

3. Technical Specifications

Parameter Specification Standard Reference
Outer Diameter (OD) 3.0 mm – 108 mm ASTM A511 / EN 10217
Wall Thickness (WT) 0.3 mm – 3.0 mm ASTM A511 / EN 10217
Coil Inner Diameter (ID) 250 mm – 500 mm Manufacturer specification
Coil Length (Typical) 50 m – 500 m per coil —
Surface Finish Bright Annealed (BA) / Pickled & Passivated ASTM A478
Maximum Allowable Residual Torsion ≤ 0.5° per meter of tube length Wenzhou Jixing internal standard
Minimum Bend Radius (Post-Release) ≥ 3× OD (cold bend), ≥ 2× OD (hot bend) ASTM A999
Pay-out Speed (Recommended) ≤ 5 m/min (small OD); ≤ 2 m/min (large OD) Wenzhou Jixing handling guideline
Operating Temperature Range −196°C to +870°C (304); −196°C to +870°C (316) ASME Section VIII

4. Manufacturing Process & Natural Curvature Release Protocol

4.1 Production Sequence

  1. Hot Rolling: Billet is hot-rolled into seamless tube blanks
  2. Piercing & Elongation: Mandrel piercing establishes initial bore geometry
  3. Cold Drawing: Multi-pass cold drawing achieves dimensional precision and surface finish
  4. Solution Annealing: Heating to 1050–1150°C followed by controlled cooling to restore full annealed microstructure
  5. Pickling & Passivation: Acid pickling removes scale; passivation establishes protective chromium oxide layer (≥ 10 nm)
  6. Coiling: Continuous tube is wound onto precision-diameter pay coils

4.2 Anti-Torsion Measures — Natural Curvature Release

The coiling operation inevitably introduces elastic torsional strain into the tube wall. Upon unspooling, this strain energy must be released without transferring torsional moment into the tube body. The following protocol is mandated:

4.3 Consequences of Non-Compliance

Accumulated torsional strain, if not properly released during pay-out, propagates into subsequent forming operations. During cold bending, the superimposed torsional stress reduces the effective yield strength at the outer bend radius by up to 15–20%, leading to premature cracking. This manifests as intergranular or transverse fractures on the outer surface of the bend, particularly in wall thicknesses below 1.0 mm.

5. Applications

6. Quality Certifications & Compliance

Certification / Standard Scope
ISO 9001:2015 Quality Management System
ISO 14001:2015 Environmental Management System
ASTM A511 Standard Specification for Cold-Formed Austenitic Stainless Steel Seamless Tube
EN 10217-7 Non-ferrous metallic materials — Seamless tubes for pressure purposes — Part 7: Austenitic stainless steel tubes
GB/T 12771 Chinese National Standard — Stainless Steel Seamless Tubes for General Purposes
ASME B36.19M Welded and Seamless Wrought Stainless Steel Pipe
Mill Test Certificate (MTC) — EN 10204 3.1 Third-party inspection and material verification

7. Unique Selling Points

  1. Controlled Coiling Geometry: Wenzhou Jixing employs precision coil winding with calculated layer-to-layer contact pressure to minimize residual torsional energy, reducing the criticality of downstream release procedures.
  2. Pre-Release Condition Verification: Each coil batch is subjected to torsional strain measurement prior to dispatch, ensuring compliance with the ≤ 0.5°/m residual torsion threshold.
  3. Technical Support for Forming Integration: The manufacturer provides application engineering guidance for integrating the coil tube into customer bending, roll-forming, and mandrel-drawing lines with proper pay-out configurations.
  4. Full Traceability: Heat-number traceability from mill ingot through final coil ensures complete quality chain documentation for regulated industries.
  5. Wide Range Availability: Stocked diameters and wall thicknesses enable rapid supply for both prototyping and production-scale requirements.

8. Handling & Storage Recommendations