Stainless Steel Radiant Furnace Coil Tube (Coiltube) — Low-Temperature Superheated Steam Service
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1352) is a precision-engineered tubular component designed for continuous service in radiant furnace (一段炉) superheated steam low-temperature coil systems. These coil tubes serve as critical heat-exchange elements in metallurgical and petrochemical processing facilities, where they are subjected to sustained thermal cycling, high-temperature oxidation, and internal steam flow erosion. The product line has been rigorously developed and validated through extensive field damage analysis studies, incorporating lessons learned from real-world failure investigations to deliver superior durability, thermal efficiency, and operational reliability.
As a specialized product within the industrial heat-transfer tubing category, these coil tubes are engineered to withstand the demanding conditions of superheated steam environments, where temperatures can range from 200 °C to 650 °C, combined with aggressive oxidation and carburization risks. The design philosophy emphasizes failure prevention through optimized material selection, geometric configuration, and manufacturing precision.
Material & Properties
Primary Material Grades
The coil tubes are fabricated from high-performance austenitic stainless steel grades selected for exceptional resistance to high-temperature oxidation, thermal fatigue, and corrosion under superheated steam conditions:
- SAE 310S / UNS S31008 — Chromium-Nickel austenitic stainless steel with enhanced high-temperature strength and oxidation resistance up to 1150 °C continuous service.
- SAE 309S / UNS S30908 — A low-carbon variant of Type 309, offering excellent resistance to thermal cracking and oxidation in reducing and oxidizing atmospheres.
- SAE 321H / UNS S32109 — Columbium-stabilized austenitic stainless steel with superior resistance to intergranular corrosion and high-temperature scaling.
- SAE 347H / UNS S34709 — Niobium-stabilized austenitic grade providing enhanced resistance to sigma phase formation and thermal fatigue cracking.
Key Mechanical & Physical Properties (Representative — SAE 310S)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (RT) | ≥ 515 MPa | ASTM A213 / A269 |
| Tensile Strength (650 °C) | ≥ 280 MPa | ASTM A213 |
| Yield Strength (0.2% offset, RT) | ≥ 205 MPa | ASTM A213 |
| Elongation (RT, min.) | ≥ 35% | ASTM A213 |
| Thermal Conductivity (100 °C) | 16.3 W/(m·K) | ASTM E1461 |
| Coefficient of Thermal Expansion (20–1000 °C) | 17.0 × 10⁻⁶ /°C | ASTM E228 |
| Density | 8.0 g/cm³ | — |
| Maximum Continuous Service Temperature | 1150 °C | — |
Chemical Composition (SAE 310S, Typical %)
| C | Mn | P | S | Si | Cr | Ni | N | Fe (bal.) |
|---|---|---|---|---|---|---|---|---|
| ≤ 0.08 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | ≤ 1.00 | 24.0–26.0 | 19.0–22.0 | ≤ 0.10 | Balance |
Specifications
| Parameter | Specification / Range |
|---|---|
| Product Designation | Coiltube — Radiant Furnace Superheated Steam Low-Temperature Coil |
| Product Number | 1352 |
| Outer Diameter (OD) | 19.05 mm – 159.0 mm (¾" – 6") |
| Wall Thickness | 1.5 mm – 12.7 mm (⅛" – ½") |
| Coil Bend Radius | ≥ 5× OD (minimum); custom radii available |
| Tube Length (per coil) | 6 m – 120 m (custom lengths upon request) |
| Surface Finish | Pickled & Passivated (2B / No. 1 / BA finish options) |
| End Condition | Plain end, beveled end, or threaded (per customer specification) |
| Operating Temperature Range | 200 °C – 650 °C (continuous); peak transient up to 1150 °C |
| Internal Pressure Rating | Up to 2.5 MPa (design-dependent) |
| Applicable Standards | ASTM A213, ASTM A269, ASME B36.19M, EN 10216-5, GB/T 14976 |
| Packaging | Coiled on steel spools with moisture-proof wrapping; seaworthy packing available |
Manufacturing Process
The production of these coil tubes follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:
- Raw Material Selection & Inspection — Only certified ingots or billets from approved primary steelmakers are procured. Each heat lot undergoes full chemical analysis (per ASTM E1251) and ultrasonic testing (ASTM E165) to confirm absence of internal defects such as shrinkage cavities, inclusions, and segregation.
- Hot Rolling / Seamless Tube Production — Tubes are produced via the pilotless seamless tube manufacturing process (e.g., Mannesmann piercing, rotary piercing, or plug piercing). The hot-finished tubes are subsequently cold-drawn or cold-rolled to achieve precise dimensional tolerances (±0.05 mm OD, ±10% wall thickness).
- Heat Treatment (Solution Annealing) — Tubes are solution-annealed at 1050–1150 °C followed by rapid water quenching to dissolve carbides and restore full austenitic microstructure. This step is critical for ensuring maximum corrosion resistance and eliminating residual stresses from forming operations.
- Precision Coil Bending (Tube Coiling) — Using CNC-controlled mandrel-assisted bending machines, tubes are formed into the required coil geometry. The bending process employs a minimum bend radius of 5× OD to prevent ovality, wall thinning, or micro-cracking at the coil apex. Real-time dimensional monitoring ensures coil-to-coil consistency.
- Pickling & Passivation — The coiled tubes are subjected to acid pickling (nitric-hydrofluoric acid blend) to remove scale, oxide layers, and bending-induced surface discoloration. A final passivation treatment (citric acid or nitric acid immersion) establishes a protective chromium-oxide passive film, enhancing corrosion resistance.
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Final Quality Control & Testing — Each coil lot undergoes comprehensive inspection including:
- Dimensional verification (OD, wall thickness, coil radius) via laser scanning and caliper measurement
- Hydrostatic testing at 1.5× design pressure (per ASTM A213)
- Visual inspection of internal and external surfaces via borescope
- Positive Material Identification (PMI) via XRF spectrometry
- Hardness testing (Rockwell B scale) to confirm annealed condition
- Packaging & Dispatch — Coils are secured on steel spools with anti-condensation wrapping, desiccant packs, and protective end caps. Seaworthy export packing is available for international shipments.
Applications
These stainless steel coil tubes are purpose-engineered for the following critical industrial applications:
- Radiant Furnace Superheated Steam Systems — Primary application in metallurgical reheating furnaces, where coil tubes transport superheated steam through the furnace radiant zone for heat recovery and steam generation. The low-temperature coil configuration manages thermal gradients and prevents localized overheating.
- Petrochemical Steam Reforming — Used in secondary and tertiary superheating sections of steam reforming furnaces for natural gas and naphtha cracking processes.
- Coke Oven Heat Recovery — Employed in steam recovery coils within coke oven battery systems for waste heat utilization.
- Industrial Boilers & Waste Heat Boilers — Installed as economizer tubes and superheater elements in high-efficiency boiler systems.
- Power Generation Auxiliaries — Utilized in balance-of-plant steam lines, deaerator supply coils, and turbine exhaust steam recovery systems.
- Chemical Processing — Applied in exothermic reaction heat removal coils, distillation column reboilers, and high-temperature heat exchangers where corrosion resistance is paramount.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system aligned with international standards. The coil tube product line is certified and compliant with the following:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- CE Marking — Compliance with European Union directives for industrial pressure equipment (PED 2014/68/EU).
- EN 10204 3.1 — Manufacturer's test report certification providing full traceability from raw material to finished product.
- ASME Section IX — Welding procedure qualifications for field installation and repair of coil tube assemblies.
- GB/T 14976 — Chinese national standard for seamless steel tubes for fluid transport.
- ASTM A213 / A269 — Full compliance with American Society for Testing and Materials specifications for austenitic stainless steel tubing.
Unique Selling Points & Technical Advantages
The distinguishing value proposition of the Jixing Coiltube product line is rooted in a failure-driven engineering philosophy, informed by systematic analysis of field-damaged radiant furnace coil tubes.
- Failure-Informed Design Optimization — Product specifications have been refined through detailed post-mortem analysis of real-world coil tube failures (oxidation cracking, thermal fatigue, steam-side erosion, and creep rupture). This ensures that design margins, material selections, and manufacturing tolerances directly address known failure modes.
- Superior Thermal Fatigue Resistance — The solution-annealed austenitic microstructure with optimized grain size (ASTM E112, grain size 6–8) provides exceptional resistance to thermal cycling fatigue, extending service life beyond industry benchmarks by 30–50%.
- Precision Coil Geometry — CNC mandrel-bending ensures uniform bend radii and minimal ovality (<1.5%), reducing flow turbulence and erosion hotspots within the coil, which directly mitigates the internal surface damage observed in legacy designs.
- Full Traceability — Every coil tube is accompanied by a complete material traceability dossier including mill test certificates, heat numbers, chemical analysis reports, mechanical test results, and heat treatment records.
- Custom Engineering Support — Technical consultation and custom design services are available for specialized applications, including non-standard diameters, custom coil geometries, and alloy selections tailored to specific furnace operating conditions.
- Cost-Effective Lifecycle Value — While the initial material cost may be premium relative to carbon steel alternatives, the dramatically extended service interval (typically 2–3× longer than standard-grade tubes) and reduced unplanned shutdown costs deliver superior total cost of ownership (TCO).
Technical Note — Low-Temperature Coil Failure Analysis Context
The development of this product line was directly informed by a comprehensive technical study titled "Analysis of Damage to Low-Temperature Coil Tubes in Radiant Furnace Superheated Steam Systems" (一段炉过热蒸汽低温盘管损坏情况分析). This study identified the following primary damage mechanisms in superheated steam coil tubes:
- Internal Oxidation (Carburization)