Stainless Steel Coil Tube — Precision Seamless Sanitary Grade (GB/T 3639)
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a high-precision seamless tube product designed in strict accordance with the Chinese National Standard GB/T 3639 — Precision Seamless Steel Tubes for General Cold-Rolled Use. This product is specifically engineered to meet hygienic-grade requirements, making it suitable for applications demanding exceptional dimensional accuracy, superior surface finish, and rigorous cleanliness standards. The coil tube form factor offers the advantages of continuous-length processing, reduced welding joints, and improved material utilization compared to straight-length seamless tubes.
GB/T 3639 is a cornerstone standard in China's seamless steel tube industry, governing the technical specifications for cold-rolled and cold-drawn precision seamless steel tubes. This standard ensures consistent mechanical properties, tight dimensional tolerances, and reliable metallurgical quality across all production batches.
Material & Properties
Coiltube products are fabricated from high-purity austenitic and austenitic-ferritic stainless steel grades, primarily conforming to the following material specifications:
- 304 (06Cr19Ni10) — The most widely used austenitic grade, offering excellent corrosion resistance, weldability, and formability across a broad temperature range.
- 316 (06Cr17Ni12Mo2) — Enhanced resistance to pitting and crevice corrosion due to the addition of molybdenum, ideal for aggressive chemical and marine environments.
- 316L (06Cr17Ni12Mo2N) — Low-carbon variant of 316 with superior resistance to intergranular corrosion, preferred for hygienic and pharmaceutical applications.
- 321 (06Cr18Ni11Ti) — Titanium-stabilized grade providing excellent resistance to stress corrosion cracking at elevated temperatures.
Key Mechanical Properties
| Property | 304 / 304L | 316 / 316L | 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 520 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 217 |
| Operating Temperature Range | −196 °C to +870 °C | −196 °C to +870 °C | −196 °C to +900 °C |
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 500.0 mm | GB/T 3639 |
| Wall Thickness | 0.30 mm – 30.0 mm | GB/T 3639 |
| OD Tolerance | ±0.05 mm (precision grade) | GB/T 3639 |
| Wall Thickness Tolerance | ±0.02 mm (precision grade) | GB/T 3639 |
| Length / Coil Length | Up to 3,000 m per coil (customizable) | Manufacturer Spec. |
| Coil Inner Diameter | 300 mm / 500 mm / 600 mm (customizable) | Manufacturer Spec. |
| Surface Finish | No. 4 Finish / BA (Bright Annealed) / Electropolished | Hygienic Grade |
| Surface Roughness (Ra) | ≤ 0.4 μm (electropolished); ≤ 0.8 μm (BA) | Hygienic Grade |
| End Condition | Plain end / Beveled end (as specified) | Custom |
| Heat Treatment | Solution Annealed (1050–1100 °C) | GB/T 3639 |
| Coil Weight | Up to 3,000 kg per coil (typical) | Manufacturer Spec. |
Manufacturing Process
The production of hygienic-grade stainless steel coil tubes follows a rigorously controlled multi-stage manufacturing process to ensure compliance with GB/T 3639 and hygienic industry requirements:
- Steel Billet Preparation — High-purity stainless steel billets are sourced from certified suppliers and undergo spectrographic analysis to verify chemical composition within specified limits.
- Piercing — Billets are heated to 1,150–1,250 °C and pierced through a rotating mandrel to produce seamless hollow tubes, eliminating the need for welding.
- Hot Rolling / Hot Drawing — The pierced tubes are hot-rolled or hot-drawn to achieve the approximate final dimensions, establishing the initial microstructure.
- Pickle & Descale — Tubes are submerged in an acid pickling bath (nitric acid + hydrofluoric acid blend) to remove oxide scale and surface contaminants.
- Cold Drawing / Cold Rolling — Tubes are cold-worked through precision-die drawing or multi-pass cold rolling to achieve the tight dimensional tolerances required by GB/T 3639 (±0.05 mm OD tolerance).
- Solution Annealing — Tubes are heated to 1,050–1,100 °C in a protective atmosphere furnace and rapidly cooled to restore full solution-annealed microstructure, ensuring maximum corrosion resistance and ductility.
- Precision Cold Working — Final sizing is achieved through additional cold-drawing passes to meet exact dimensional specifications.
- Surface Treatment — Tubes undergo electropolishing or bright annealing (BA) processing in a sealed furnace under controlled atmosphere (argon or nitrogen) to achieve surface roughness values below 0.4 μm Ra, meeting hygienic-grade standards.
- Coil Winding — Finished tubes are carefully wound into coils on precision-controlled winding equipment to prevent mechanical damage, surface scratches, or deformation.
- Final Inspection & Packaging — Each coil undergoes comprehensive quality inspection including dimensional measurement, chemical analysis verification, surface inspection, and non-destructive testing (NDT). Approved coils are wrapped in protective film, strapped, and palletized for shipment.
Applications
The hygienic-grade stainless steel coil tube conforms to the stringent cleanliness and surface quality requirements of the following industries:
- Food & Beverage Processing — Dairy processing equipment, beverage filling lines, brewing systems, and food-grade piping where bacterial adhesion must be minimized.
- Pharmaceutical Manufacturing — CIP (Clean-in-Place) and SIP (Sterilize-in-Place) systems, bioreactor piping, and drug delivery infrastructure requiring pharmaceutical-grade cleanliness.
- Dairy & Beverage Industry — Milk processing plants, juice production lines, and carbonated beverage manufacturing requiring smooth, non-reactive surfaces.
- Chemical Processing — Corrosive chemical transfer lines, reactor internals, and heat exchanger tubing in aggressive environments.
- Semiconductor & Electronics — Ultra-clean process gas lines, vacuum systems, and high-purity fluid delivery where particulate contamination is unacceptable.
- Medical Devices — Tubing for medical gas delivery, dialysis equipment, and surgical instrument manufacturing.
- Optical & Precision Instrumentation — Components requiring high surface reflectivity and dimensional precision.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring product conformity with international and national standards:
- GB/T 3639 — Chinese National Standard for Precision Seamless Steel Tubes (primary governing standard)
- GB/T 14976 — Chinese National Standard for Cold-Rolled Seamless Stainless Steel Tubes
- GB 4805 — Chinese National Standard for General Cold-Rolled Stainless Steel Tubes
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001 — Environmental Management System Certification
- ISO 45001 — Occupational Health and Safety Management System Certification
- ISO 22000 / HACCP — Food Safety Management System (for food-grade products)
- 3-A Sanitary Standards — International Dairy Food & Beverage Equipment Sanitation Certification
- CE Marking — European Conformity for pressure equipment and safety standards
- PED (Pressure Equipment Directive) — 2014/68/EU compliance for pressure applications
- EN 10216-5 — European Standard for Stainless Steel Tubes for Pressure Purposes
- ASTM A213 / A269 — American Society for Testing and Materials reference standards
Unique Selling Points
- Superior Dimensional Precision — Outer diameter and wall thickness tolerances as tight as ±0.02–0.05 mm, enabling seamless integration into precision-engineered hygienic systems without post-fabrication machining.
- Hygienic-Grade Surface Quality — Surface roughness values as low as 0.4 μm Ra achieved through electropolishing, eliminating crevices and pits where microorganisms can accumulate, ensuring compliance with FDA and 3-A sanitary requirements.
- Continuous Coil Format — Up to 3,000 meters per coil dramatically reduces the number of weld joints in fabrication, minimizing contamination risk points and improving overall system integrity in hygienic applications.
- Full Traceability — Each coil is accompanied by a Mill Test Certificate (MTC) including chemical composition analysis, mechanical property reports, and heat treatment documentation, ensuring complete batch traceability.
- Customization Capability — Flexible customization of coil dimensions, surface finishes, end conditions, and packaging configurations to meet specific customer requirements and project specifications.
- Comprehensive NDT Coverage — Every production batch undergoes ultrasonic testing (UT), eddy current testing (ECT), and hydrostatic pressure testing to guarantee internal and external defect-free integrity.
Technical Note: GB/T 3639 specifies requirements for precision seamless steel tubes produced by cold rolling or cold drawing methods. The standard covers tubes with outer diameters from 6 mm to 500 mm and wall thicknesses from 0.3 mm to 30 mm. Tubes manufactured under this standard are classified into precision grades (Class A and Class B) based on dimensional tolerance and straightness requirements. For hygienic-grade applications, Class A tolerances with additional surface finish and cleanliness specifications are recommended.
Testing & Inspection Protocol
| Test Method | Standard | Requirement |
|---|---|---|
| Chemical Composition Analysis | GB/T 223 Series | Conformity to grade specification |
| Tensile Testing | GB/T 228.1 | Per grade mechanical property table |
| Hardness Testing | GB/T 231.1 | ≤ 217 HBW (annealed condition) |
| Hydrostatic Pressure Test | GB/T 241 | No leakage at 1.5× working pressure |
| Ultrasonic Testing (UT) | GB/T 19795 | No internal defects detected |
| Eddy Current Testing (ECT) | GB/T 19795 | No surface/sub-surface defects |
| Surface Roughness Measurement | GB/T 1031 | ≤ 0.4 μm Ra (electropolished) |
| Dimensional Inspection | GB/T 3639 | Within specified tolerance limits |
| Corrosion Resistance (Salt Spray) | GB/T 10125 | No pitting after 1,000+ hours (316L) |
| Intergranular Corrosion Test | GB/T 4334 | Pass (for L grades and stabilized grades) |