Stainless Steel Resistance Heating Furnace Coil Tube (Coiltube) — Technical Specification

1. Product Overview

The Stainless Steel Resistance Heating Furnace Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular heating element manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Catalog No. 1390). This product is specifically designed for integration into industrial resistance heating furnaces, where it serves as the primary heat-transfer medium by converting electrical energy into thermal energy through resistive heating. The coil tube is fabricated in continuous coil form (盘管 / Coil Form) to maximize surface area and thermal efficiency within confined furnace geometries.

This specification is informed by comprehensive failure analysis studies, particularly the engineering review documented in "Analysis of Failure Causes for Resistance Heating Furnace Coil Tubes", which provides critical insights into material degradation mechanisms, thermal fatigue behavior, and operational limits that directly influence product design, material selection, and quality assurance protocols.

2. Material & Properties

2.1 Base Material Composition

The coil tube is fabricated from high-grade austenitic stainless steel, selected for exceptional resistance to oxidation, scaling, and thermal fatigue at elevated operating temperatures. The primary material grades include:

2.2 Key Mechanical & Physical Properties

Property Specification / Value Test Standard
Tensile Strength (at room temperature) ≥ 520 MPa (310S); ≥ 515 MPa (309S) ASTM A213 / GB/T 12771
Tensile Strength (at 1000°C) ≥ 180 MPa (310S) ASTM A213
Yield Strength (0.2% offset) ≥ 205 MPa ASTM A213
Elongation ≥ 35% (minimum) ASTM A213
Thermal Conductivity (at 100°C) ~15.1 W/(m·K) ASTM E1461
Thermal Expansion Coefficient 16–18 × 10⁻⁶ /°C (20–1000°C) ASTM E228
Maximum Continuous Operating Temperature 1150°C (2100°F) for 310S grade Manufacturer datasheet
Resistivity (at 20°C) 0.30–0.40 Ω·mm²/m ASTM B193
Specific Heat (at 100°C) ~500 J/(kg·K) ASTM E1269

2.3 Chemical Composition (Typical — 310S Grade)

Element C Cr Ni Mn S P Si Fe
Maximum (%) 0.08 25.0 35.0 2.0 0.03 0.035 1.5 Balance
Minimum (%) — 19.0 24.0 — — — — —

2.4 Critical Failure Analysis Insights

Based on the engineering study "Analysis of Failure Causes for Resistance Heating Furnace Coil Tubes", the following degradation mechanisms have been identified and addressed in the design of this product:

  • Thermal Fatigue Cracking — Repeated heating and cooling cycles induce cyclic thermal stresses at the coil tube surface. Mitigation is achieved through optimized wall thickness, controlled carbon content (≤ 0.08%), and the use of titanium-stabilized grades (321/347H).
  • Internal Oxidation & Scaling — At elevated temperatures, oxygen diffusion leads to internal chromium depletion and scale spallation. High chromium (≥ 25%) and niobium stabilization inhibit this mechanism.
  • Creep Rupture — Prolonged operation near maximum service temperature causes time-dependent deformation and eventual rupture. HR310H/HR347H grades with Nb stabilization provide enhanced creep resistance.
  • Thermal Shock Fracture — Rapid temperature differentials between the inner and outer walls of the tube can cause catastrophic failure. The coil tube design incorporates sufficient wall thickness tolerance and material ductility to absorb transient thermal gradients.
  • Electrical Overload & Localized Hot Spots — Uneven current distribution or resistive joint failures can create localized overheating. Precision manufacturing tolerances and consistent resistivity control minimize this risk.

3. Specifications

Parameter Specification Notes
Product Name Resistance Heating Furnace Coil Tube (Coiltube) 盘管 / Coiltube
Catalog Number 1390 Wenzhou Jixing Metal Materials Co., Ltd.
Material Grade 310S / 309S / 321 / TP347H / TP310H Selectable per application
Outer Diameter (OD) Φ8 mm – Φ50 mm Custom sizes available
Wall Thickness 0.5 mm – 3.0 mm Typical: 1.0–2.0 mm
Coil Winding Diameter Φ100 mm – Φ500 mm Dependent on furnace geometry
Coil Length (per spool) 50 m – 500 m Customizable
Surface Finish Pickled and Passivated (P&P); Polished available Ra ≤ 0.8 μm for polished finish
End Condition Plain / Threaded / Flanged / Custom Per customer drawing
Resistivity Tolerance ± 5% Consistency across spool
Maximum Operating Temperature 1150°C (continuous); 1200°C (intermittent) 310S grade reference
Operating Atmosphere Air, Inert (N₂, Ar), Vacuum, Reducing Grade selection depends on atmosphere
Heat Treatment Solution Annealed (1050–1150°C) + Water Quench Full austenitic structure
Coiling Form Continuous spiral coil on spool 盘管形式
Standard Compliance ASTM A213 / A269; GB/T 12771; EN 10216-5 Multi-standard certified

4. Manufacturing Process

The production of the Resistance Heating Furnace Coil Tube follows a rigorous, multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and resistance to the failure modes identified in the engineering failure analysis study:

  1. Raw Material Selection & Incoming Inspection
    • Hot-rolled stainless steel strip or seamless tube blanks are sourced from certified mills with full mill test reports (MTRs).
    • Incoming inspection includes spectroscopic analysis (OES) for chemical composition verification, hardness testing, and visual surface inspection.
  2. Coil Winding & Forming
    • Flat strip is wound onto precision mandrels to form the desired coil geometry (盘管 winding).
    • Winding parameters (pitch, diameter, tension) are controlled by CNC winding machines to ensure uniformity and eliminate stress concentrations.
  3. Welding (if applicable)
    • Longitudinal seams (for strip-wound coils) are welded using Argon Arc Welding (TIG / GTAW) under inert gas shielding to prevent oxidation.
    • Weld joint quality is verified through X-ray radiography (RT) and dye penetrant testing (PT) per ASME Section IX.
  4. Solution Annealing
    • The formed coil tube is solution annealed at 1050–1150°C in a controlled atmosphere (vacuum or inert gas) to achieve a fully austenitic microstructure, dissolve carbides, and relieve residual stresses.
    • Quenching is performed rapidly (water or controlled air quench) to prevent chromium carbide precipitation at grain boundaries.
  5. Pickling & Passivation
    • Acid pickling removes oxide scale formed during annealing; passivation establishes a protective chromium oxide layer on the surface.
    • This step is critical for ensuring long-term oxidation resistance in furnace service environments.
  6. Dimensional & Electrical Testing
    • OD, wall thickness, and coil diameter are measured using calibrated micrometers and laser gauges.
    • Electrical resistivity is measured along the coil length to verify uniformity within ± 5% tolerance, ensuring consistent heat output.
  7. Final Quality Assurance & Packaging
    • Each spool undergoes final visual inspection, dimensional verification, and certification documentation.
    • Coils are wrapped in protective packaging (wooden spools with moisture barriers) to prevent mechanical damage and corrosion during transit.

5. Applications

The Stainless Steel Resistance Heating Furnace Coil Tube is widely employed across multiple industrial sectors where reliable, high-temperature resistive heating is required:

6. Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and