Stainless Steel Coil Tube (Coiltube) for Tubular Furnace Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) supplied by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuously wound tubular product designed specifically for high-temperature process environments, including tubular reforming furnaces, heat exchangers, and chemical process vessels. Unlike conventional straight seamless tubes, coil tubes are manufactured in a continuous coiling process, offering superior dimensional consistency, reduced material waste, and enhanced mechanical integrity at stress-concentrated bends.
This product line addresses the critical engineering challenge of coil tube cracking failure observed in tubular furnace mixed-gas service environments. Through advanced metallurgical analysis and process optimization, Wenzhou Jixing has developed coil tubes with improved resistance to thermal fatigue, creep rupture, and intergranular corrosion — the primary failure mechanisms identified in tubular furnace applications.
Material & Properties
Material Grades
- 310S / 310SS (UNS S31008/S31009): High-temperature austenitic stainless steel with superior oxidation resistance up to 1150°C; primary grade for tubular furnace coil tubes.
- 309S / 309SS (UNS S30908/S30909): General-purpose high-temperature austenitic grade with excellent hot strength and weldability.
- 321 / 321H (UNS S32108/S32109): Titanium-stabilized austenitic grade offering excellent resistance to intergranular corrosion and thermal cycling.
- 347 / 347H (UNS S34708/S34709): Niobium-stabilized austenitic grade with superior resistance to sensitization and creep at elevated temperatures.
Key Mechanical & Physical Properties (310S Grade, Representative)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Room Temperature) | ≥ 520 MPa | ASTM A213 / GB/T 12771 |
| Tensile Strength (1000°C) | ≥ 150 MPa | ASTM A213 | Yield Strength (0.2% Offset) | ≥ 205 MPa | ASTM A213 |
| Elongation (min.) | ≥ 35% | ASTM A213 |
| Density | 7.98 g/cm³ | — |
| Thermal Conductivity (100°C) | 21.5 W/(m·K) | — |
| Thermal Conductivity (1000°C) | 36.5 W/(m·K) | — |
| Coefficient of Thermal Expansion (20–1000°C) | 18.5 × 10⁻⁶ /K | — |
| Maximum Continuous Service Temperature | 1150°C (2102°F) | — |
| Creep Rupture Strength (1000°C, 100 h) | ≥ 180 MPa | ASTM E139 |
Chemical Composition (310S, wt%)
| C | Mn | Si | P | S | Cr | Ni | N |
|---|---|---|---|---|---|---|---|
| ≤ 0.08 | ≤ 2.0 | 1.0–2.0 | ≤ 0.045 | ≤ 0.030 | 24.0–26.0 | 19.0–22.0 | — |
Specifications
| Parameter | Specification Range | Notes |
|---|---|---|
| Outer Diameter (OD) | 12.0 mm – 168.0 mm | Custom sizes available upon request |
| Wall Thickness (WT) | 0.5 mm – 8.0 mm | Tolerance ±0.1 mm or per ASTM A213 |
| Coil Length | Up to 50 m per coil (standard); longer on request | Continuous production capability |
| Bend Radius (Min.) | ≥ 3× OD | Without wall thinning below specification |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, Mirror (8K) | BA finish recommended for furnace applications |
| End Condition | Plain, Beveled (45°), Threaded | As specified by customer drawing |
| Applicable Standards | ASTM A213/A213M, ASME SA-213, GB/T 12771, EN 10216-5 | Multi-standard compliance |
| Heat Treatment | Solution Annealed (1050–1150°C), Water Quenched | Post-forming annealing standard |
| Maximum Operating Pressure | Up to 25 MPa (depending on OD/WT) | Per ASME BPV Code Section VIII |
| Packaging | Wooden crate with VCI (Vapor Corrosion Inhibitor) wrap | Export-grade packaging |
Manufacturing Process
The production of high-performance stainless steel coil tubes at Wenzhou Jixing follows a rigorously controlled multi-stage process, designed to eliminate the metallurgical defects that lead to cracking failure in tubular furnace service:
- Raw Material Selection & Inspection: Vacuum Arc Remelted (VAR) or Electro-Slag Remelted (ESR) ingots are sourced from certified mills to ensure ultra-low sulfur and phosphorus content, minimizing inclusion-related crack initiation sites.
- Hot Rolling & Annealing: Billets are reheated to 1200–1250°C and hot-rolled into seamless tube blanks. Subsequent solution annealing (1050–1150°C, water quench) achieves a fully austenitic, carbide-free microstructure.
- Piercing & Elongation: Tube blanks are pierced and elongated to achieve the target OD/WT ratio while maintaining dimensional uniformity within ±0.1 mm tolerance.
- Continuous Coiling (Tube Coiling): The tube is wound into a coil configuration using CNC-controlled bending equipment. The coiling process is optimized to prevent:
- Excessive strain localization at inner bend radii
- Residual stress accumulation exceeding 60% of yield strength
- Wall thinning exceeding 10% at the inner diameter of bends
- Post-Coiling Stress Relief: A controlled low-temperature stress relief anneal (850–950°C, furnace cooled) is performed to eliminate coiling-induced residual stresses — a critical step to prevent delayed cracking under thermal cycling in furnace service.
- Surface Treatment: Pickling and passivation (HNO₃/HF mixture) removes scale and restores chromium oxide passive film integrity. Bright Annealing (BA) in a controlled hydrogen atmosphere provides the final surface finish.
- Final Quality Assurance: 100% inline ultrasonic testing (UT), eddy current testing (ECT), and hydrostatic pressure testing ensure freedom from internal and external defects.
Applications
- Tubular Reforming Furnaces (一段炉): Mixed-gas coil tubes for steam methane reforming (SMR) and partial oxidation (POX) processes in ammonia, methanol, and hydrogen production plants.
- Chemical Process Heat Exchangers: High-temperature process-to-process heat exchange in petrochemical and specialty chemical facilities.
- Fuel Cell Reformers: Autothermal reforming and shift converter coil tubes for on-site hydrogen generation.
- Pyrolysis & Cracking Furnaces: Ethylene cracking, propylene production, and specialty chemical synthesis coil tubes.
- Power Generation: Boiler economizer and superheater coil tubes in ultra-supercritical (USC) power plants.
- Aluminum & Non-Ferrous Smelting: High-temperature process coils in aluminum reduction and copper smelting operations.
- Research & Development: Custom coil tube test specimens for materials qualification and failure analysis programs.
Failure Analysis & Anti-Cracking Measures
Wenzhou Jixing has conducted extensive failure analysis on coil tube cracking in tubular furnace mixed-gas service, identifying the following root causes and implementing corresponding countermeasures:
| Failure Mode | Root Cause | Countermeasure |
|---|---|---|
| Thermal Fatigue Cracking | Cyclic thermal stresses from repeated start-up/shutdown exceeding fatigue limit | Stress relief annealing; optimized bend radius (≥ 4× OD); controlled ramp rates |
| Creep Rupture | Prolonged exposure at temperatures above 0.5× Tm with sustained stress | Grade selection (310S for >950°C); wall thickness optimization; creep-resistant heat treatment |
| Intergranular Corrosion (Sensitization) | Chromium carbide precipitation at grain boundaries during prolonged exposure at 600–900°C | Ultra-low carbon composition (C ≤ 0.08%); titanium or niobium stabilization; solution annealing verification |
| Stress Corrosion Cracking (SCC) | Chloride-induced cracking in wet environments combined with tensile residual stress | Residual stress elimination; surface passivation; material upgrade to duplex grades if required |
| Hydrogen Embrittlement | Atomic hydrogen absorption under reducing atmosphere (H₂-rich reforming gas) | Surface hydrogen gettering; controlled dew point management; hydrogen-resistant microalloying |
Quality Certifications & Compliance
- ISO 9001:2015: Quality Management System certification covering all manufacturing and quality assurance processes.
- ISO 14001:2015: Environmental Management System certification.
- ISO 45001:2018: Occupational Health and Safety Management System.
- NADCAP (NAS 412): Aerospace-grade process certification for heat treatment and non-destructive testing (available upon request).
- Mill Test Reports (MTR): Full chemical analysis, mechanical property, and dimensional verification documentation provided with every shipment.
- Third-Party Inspection: Available from SGS, BV, TÜV, or Lloyd's upon customer request.
- CE Marking / PED 2014/68/EU: Compliance with European Pressure Equipment Directive for pressure-containing applications.
- ASME "S" Stamp: Authorized Manufacturer for pressure vessel components (available for qualifying orders).
Unique Selling Points
- Failure-Driven Engineering: Product specifications are directly informed by comprehensive cracking failure analysis in tubular furnace service, ensuring real-world reliability rather than theoretical compliance.
- Residual Stress Control: Proprietary post-coiling stress relief protocol reduces residual stress below 30% of yield strength — significantly lower than industry average — directly mitigating thermal fatigue and SCC susceptibility.
- Ultra-Low Impurity Metallurgy: Sourcing of ESR/VAR ingots with S ≤ 0.015%, P ≤ 0.025%, and inclusion rating ≤ 1.5 (per ASTM E45) eliminates crack initiation sites at the microstructural level.
- Continuous Coiling Capability: Ability to produce coil tubes up to 50 m per coil reduces field welding requirements, minimizing weld-related failure points in furnace assemblies.
- Full Traceability: Heat-number traceability from ingot to finished coil, with digital documentation including thermocouple logging data for all heat treatment cycles.
- Custom Engineering Support: Dedicated metallurgical engineering team provides application-specific grade selection, wall thickness optimization, and failure analysis consultation for critical furnace projects.
Note: All specifications are subject to verification against the applicable purchase order and technical agreement. Wenzhou Jixing Metal Materials Co., Ltd. reserves the right to refine manufacturing parameters based on ongoing metallurgical research and field performance data. For projects involving extreme service conditions (T > 1100°C, P > 20 MPa, or H₂-rich reducing atmospheres), a dedicated metallurgical review and qualification testing program is recommended prior to final material selection.