Stainless Steel Coil Tube — First-Tier Domestic Leader Specification
This document presents a comprehensive technical specification for Stainless Steel Coil Tubes (SSCT) sourced from the First-Tier Domestic Supplier Leader (第一梯队 国产龙头) within the Chinese stainless steel coil tube supply chain. The reference supplier entity, Baofeng Clean (宝丰洁净), is recognized for possessing industry-leading production capacity (产能), output value (产值), and quality certifications (认证). This specification is intended for procurement professionals, materials engineers, and supply chain managers evaluating premium-grade stainless steel coil tube materials for industrial and commercial applications.
Product Overview
Stainless steel coil tubes are continuous-length tubular products wound into coils for efficient storage, transportation, and downstream processing. Unlike straight-length (cut-length) pipes, coil tubes are delivered in coiled form, enabling seamless feeding into automated manufacturing lines, roll-forming operations, and continuous welding processes. The coil configuration minimizes material waste, reduces cutting losses, and enhances production throughput in high-volume fabrication environments.
The First-Tier Domestic Leader designation indicates that the supplying entity occupies the highest echelon within the Chinese stainless steel coil tube industry hierarchy. This tier is characterized by superior production scale, advanced metallurgical capabilities, rigorous quality management systems, and a proven track record of serving both domestic and international OEM (Original Equipment Manufacturer) customers across critical industries.
Material Composition and Metallurgical Properties
Grade Options
Stainless steel coil tubes available from first-tier domestic suppliers typically span the following major grade families, each selected based on the target application's mechanical, corrosion resistance, and thermal requirements:
- Austenitic Grades — 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603), 321 (UNS S32100), 310S (UNS S31008)
- Duplex Grades — 2205 (UNS S32205), 2507 Super Duplex (UNS S32750)
- Ferritic Grades — 430 (UNS S43000), 409 (UNS S40900)
- Martensitic Grades — 410 (UNS S41000), 420 (UNS S42000)
- Precipitation-Hardening Grades — 17-4PH (UNS S17400), 15-5PH (UNS S15500)
Typical Chemical Composition (Austenitic 304 Grade — Reference)
| Element | Symbol | Composition (% by mass) |
|---|---|---|
| Carbon | C | ≤ 0.08 |
| Chromium | Cr | 18.0 – 20.0 |
| Nickel | Ni | 8.0 – 10.5 |
| Manganese | Mn | ≤ 2.0 |
| Silicon | Si | ≤ 0.75 |
| Phosphorus | P | ≤ 0.045 |
| Sulfur | S | ≤ 0.030 |
| Nitrogen | N | ≤ 0.10 |
| Iron | Fe | Balance |
Mechanical Properties (Annealed Condition — 304 Reference)
| Property | Designation | Minimum / Typical Value | Test Standard |
|---|---|---|---|
| Tensile Strength | UTS (Ultimate Tensile Strength) | ≥ 515 MPa | ASTM A269 / GB/T 12771 |
| Yield Strength (0.2% Offset) | YS (Yield Strength) | ≥ 205 MPa | ASTM A269 / GB/T 12771 |
| Elongation | EL | ≥ 40% | ASTM A269 / GB/T 12771 |
| Hardness | HB (Brinell) | ≤ 217 HBW | ASTM E10 |
| Density | — | 7.93 g/cm³ | — |
| Thermal Conductivity | k | 16.3 W/(m·K) @ 100°C | ASTM E1225 |
| Modulus of Elasticity | E | 193 GPa | ASTM E111 |
| Thermal Expansion | α | 17.3 × 10⁻⁶ /°C (20–100°C) | ASTM E228 |
Dimensional Specifications
Coil Tube Geometric Parameters
| Parameter | Designation | Typical Range / Options | Standard Reference |
|---|---|---|---|
| Outer Diameter | OD | 3.0 mm – 108.0 mm | ASTM A554 / GB/T 12770 |
| Wall Thickness | WT | 0.3 mm – 6.0 mm | ASTM A554 / GB/T 12770 |
| Inner Diameter | ID | 2.0 mm – 100.0 mm (derived from OD and WT) | — |
| Coil Length | CL | Continuous; typically 1,000 m – 5,000 m per coil | Supplier Specification |
| Coil Inner Diameter | CID (Coil ID) | 300 mm – 600 mm | Supplier Specification |
| Coil Outer Diameter | COD (Coil OD) | 1,000 mm – 1,500 mm | Supplier Specification |
| Coil Weight | — | Up to 10,000 kg per coil (typical) | Supplier Specification |
| Surface Finish | — | No. 1 (Pickled), 2B (Cold Rolled & Annealed), BA (Bright Annealed), 2D (Matte) | ASTM A480 / GB/T 4237 |
| Surface Roughness | Ra | 0.4 – 1.6 μm (2B finish); ≤ 0.1 μm (BA/polished) | ISO 4287 |
| Dimensional Tolerance | — | ± 0.10 mm (OD); ± 10% (WT) | ASTM A554 / GB/T 12770 |
| Hardness Tolerance | — | ± 10 HV (Vickers) | ASTM E92 |
Standard Sizing Reference (Select Configurations)
| OD (mm) | WT (mm) | ID (mm) | Weight (kg/m) | Typical Application |
|---|---|---|---|---|
| 6.0 | 0.5 | 5.0 | 0.071 | Medical tubing, instrumentation |
| 10.0 | 1.0 | 8.0 | 0.223 | Automotive exhaust, fuel lines |
| 19.05 | 1.65 | 15.75 | 0.740 | HVAC, refrigeration |
| 25.4 | 2.11 | 21.18 | 1.260 | Hydraulic systems, fluid transfer |
| 38.1 | 2.77 | 32.56 | 2.200 | Structural supports, process piping |
| 50.8 | 3.05 | 44.7 | 3.650 | Chemical processing, food & beverage |
| 76.2 | 3.96 | 68.28 | 6.970 | Industrial process piping |
| 108.0 | 4.0 | 100.0 | 10.400 | Large-bore process lines, desalination |
Manufacturing Process
The production of stainless steel coil tubes from a first-tier domestic supplier follows a rigorously controlled multi-stage process designed to ensure metallurgical homogeneity, dimensional accuracy, and surface integrity. The process chain is outlined below:
1. Raw Material Preparation and Melt Refining
High-purity stainless steel ingots or continuous-cast slabs are produced via AOD (Argon Oxygen Decarburization) or VOD (Vacuum Oxygen Decarburization) metallurgical routes to achieve precise control over carbon, nitrogen, and sulfur content. First-tier suppliers maintain in-house melting operations with advanced process control, including real-time spectroscopic analysis and computerized alloying, to ensure chemical composition consistency across heat lots.
2. Hot Rolling and Pickling
The prepared slabs are reheated to 1,100–1,200°C and hot-rolled into strip or coil form. The hot-rolled product is subsequently subjected to acid pickling (typically a mixed HNO₃/HF or HNO₃/HCl bath) to remove mill scale and restore the passive chromium oxide layer essential for corrosion resistance.
3. Cold Rolling
The hot-rolled pickled strip is cold-rolled in multiple passes through precision roll mills to achieve the target thickness and surface finish. Cold rolling introduces work hardening (strain hardening), which increases yield strength and hardness while reducing ductility. The reduction ratio per pass is carefully controlled to prevent localized thinning or surface defects.
4. Annealing and Surface Treatment
Cold-rolled coils are annealed in controlled-atmosphere furnaces (typically nitrogen or hydrogen-protected, or vacuum) at 1,050–1,150°C to:
- Relieve residual stresses introduced during cold rolling
- Restore ductility and formability
- Promote recrystallization and grain uniformity
- Re-establish the protective chromium oxide passive film
Post-annealing surface finishing options include 2B (cold-rolled, annealed, and skin-passed), BA (Bright Annealed), and 2D (matte/gray) finishes, each selected according to the downstream application's aesthetic and functional requirements.
5. Seamless Tube Forming
The annealed coil strip is fed into a seamless tube forming line (also referred to as an ERW — Electrical Resistance Welded — or laser-welded coil tube mill, depending on the specific process). The forming sequence typically involves:
- Coil uncoiling and straightening — Removal of coil set and introduction of the flat strip into the forming station
- Edge trimming and beveling — Precision edge preparation to ensure uniform weld quality
- Multi-stand roll forming — Progressive bending of the flat strip through a series of forming rolls to achieve the target circular cross-section
- Welding — ERW or laser welding of the longitudinal seam to achieve full-penetration, metallurgically sound joints
- Weld heat-affected zone (HAZ) treatment — Induction heating or annealing of the weld zone to homogenize microstructure and restore corrosion resistance
- Expansion and sizing — Mechanical expansion to achieve precise OD and WT tolerances, followed by final sizing in mandrel-die stations
- Coil re-winding — Finished tube is wound onto a coil pay-off reel for delivery
6. Heat Treatment (Post-Forming)
Depending on the grade and application, post-forming heat treatment may include:
- Solution Annealing — Heating to 1,050–1,150°C followed by water quenching to dissolve precipitates and maximize corrosion resistance (austenitic and super-austenitic grades)
- Precipitation Hardening — Solution treatment followed by aging at 480–550°C for 4 hours (17-4PH, 15-5PH grades)
- Stress Relief — Low-temperature annealing at 425–550°C to relieve forming stresses without sensitization