Stainless Steel Coil Tube (Coiltube) — Resistance-Heated Solution-Annealed

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a high-performance austenitic stainless steel tubing product supplied in continuous coil form. This product line is distinguished by its proprietary Resistance Heating Solution Treatment (RHST) process, which enables precise, uniform, and energy-efficient annealing of coiled tubing without the need for conventional furnace-based batch processing. The coil tube is engineered for demanding applications requiring superior corrosion resistance, mechanical integrity, and consistent microstructural homogeneity.

Unlike traditional solution annealing methods that rely on radiant or convection heating in batch furnaces, the resistance heating approach directly passes an electric current through the stainless steel coil itself, leveraging the inherent electrical resistance of the material to generate heat. This technique eliminates thermal gradients between the coil surface and core, achieving exceptional uniformity in the final annealed condition across the entire coil length.

2. Material & Properties

2.1 Applicable Grades

2.2 Key Mechanical Properties (Post-Solution Annealing, Grade 304 Reference)

2.3 Corrosion Resistance

3. Specifications

Parameter Specification Standard Reference
Outer Diameter (OD) 6.0 mm – 219.1 mm (¼" – 8⅝") ASTM A269 / A213
Wall Thickness 0.5 mm – 12.7 mm (0.020" – 0.500") ASTM A269 / EN 10216
Coil Length 10 m – 120 m (continuous, customizable) —
Coil Weight Up to 2,500 kg (5,500 lbs) per coil —
Dimensional Tolerance (OD) ±0.05 mm to ±0.5 mm (per grade and size) ASTM A269 Table 2
Dimensional Tolerance (Wall) ±10% of nominal wall thickness ASTM A269 Table 2
Surface Finish Pickled & Passivated (P&P), Mirror (Ra ≤ 0.25 µm), BA (Bright Annealed) ASTM A478 / EN 10204
Solution Treatment Temperature 1,010°C – 1,150°C (1,850°F – 2,100°F), grade-dependent ASTM A240 / A269
Quench Medium Controlled water spray or air cool (per application) —
Heat Treatment Method Resistance Heating (Direct Current, Inductive, or Combined) Proprietary Process

4. Manufacturing Process

4.1 Process Flow

  1. Coil Uncoiling & Inspection: Incoming cold-rolled stainless steel coil is inspected for surface defects, dimensional accuracy, and chemical composition verification via optical emission spectrometry (OES).
  2. Coil Forming (Cold Pilgering or Cold Drawing): The coil is formed into tube geometry through precision cold pilgering or capstan drawing, maintaining controlled strain distribution for optimal mechanical properties.
  3. Resistance Heating Solution Treatment: The coiled tube is passed through a specialized resistance heating station where direct current (DC) or controlled AC current is applied directly to the tube body. The electrical resistance of the stainless steel generates uniform volumetric heating, achieving the target solution treatment temperature (typically 1,050°C for 304/316 grades) with minimal thermal gradient between the outer and inner surfaces of the coil.
  4. Controlled Quenching: Upon reaching the solution temperature, the coil is rapidly quenched using controlled water spray or forced air, depending on the grade and application requirements. The quench rate is precisely calibrated to ensure complete solid solution formation without inducing residual stresses or distortion.
  5. Pickling & Passivation: The coil undergoes acid pickling (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation to restore the chromium oxide protective layer.
  6. Final Inspection & Testing: Comprehensive testing includes hydrostatic pressure testing, dimensional verification, chemical analysis, mechanical property testing, and intergranular corrosion testing.
  7. Coiling & Packaging: The finished coil is wound onto a standard or custom core, wrapped in protective material, and packaged for shipment.

4.2 Resistance Heating Technology — Technical Advantages

The Resistance Heating Solution Treatment process employed by Wenzhou Jixing Metal Materials Co., Ltd offers several critical advantages over conventional furnace annealing:

5. Applications

5.1 Primary Application Sectors

5.2 Unique Selling Points

6. Quality Certifications & Standards Compliance

6.1 Applicable Standards

6.2 Quality Management & Certifications

6.3 Inspection & Testing Protocol

  1. Chemical composition analysis (OES + spark emission)
  2. Hydrostatic pressure testing at 1.5× working pressure (minimum 30 seconds hold)
  3. Dimensional inspection (OD, wall thickness, straightness) at 100% coverage
  4. Mechanical property testing (tensile, hardness, elongation) per ASTM A370
  5. Intergranular corrosion testing per ASTM A240 Section 11 (600°C × 15 min)
  6. Surface quality verification (visual + profilometry for mirror finish)
  7. Eddy current or ultrasonic flaw detection (100% length coverage)
  8. Optional: Charpy impact testing, ferrite content measurement (for duplex grades)

7. Ordering Information

Customers are advised to specify the following when placing orders:

Wenzhou Jixing Metal Materials Co., Ltd — Leveraging advanced resistance heating solution treatment technology to deliver premium stainless steel coil tubes with exceptional metallurgical quality, dimensional precision, and corrosion performance for the world's most demanding industrial applications.