Stainless Steel Coil Tube for Coal-to-Hydrogen Rotary Gasifier Water-Cooled Walls
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd | Catalog No.: 992
Product Overview
The stainless steel coil tube (Coil Tube / Coiltube) supplied by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered, continuously wound tubular component designed specifically for high-temperature, high-pressure water-cooled wall (Water-Cooled Panel, WCP) assemblies in coal-to-hydrogen rotary gasifier furnaces. Unlike conventional straight-segment piping, coil tubes are manufactured in a continuous spiral configuration, eliminating longitudinal butt-weld joints and significantly reducing the number of potential leak paths within the water-cooled structure. This design feature is critical in coal gasification service, where the tube is simultaneously subjected to extreme thermal gradients, mechanical vibration from rotating internals, and aggressive chemical environments produced by coal pyrolysis and hydrogenation reactions.
The product line encompasses both as-supplied coil tubes and field-repairable assemblies, with particular engineering focus on welding repair protocols for in-service water-cooled wall coil tubes exposed to thermal fatigue and slag erosion.
Material & Properties
Base Material Grades
- SAE 304 / S30408 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability; suitable for moderate-temperature water-cooled wall sections where oxidizing conditions prevail.
- SAE 316 / S31608 (UNS S31608) — Molybdenum-bearing austenitic grade offering superior resistance to chloride-induced stress corrosion cracking (SCC) and pitting, preferred for zones exposed to sulfur and chloride-containing syngas by-products.
- SAE 310S / S31008 (UNS S31008) — High-temperature austenitic grade with elevated chromium (≥24%) and nickel (≥19%) content; employed in the hottest regions of the gasifier where tube wall temperatures may exceed 900 °C.
- SAE 321 / S32108 (UNS S32108) — Titanium-stabilized austenitic grade providing enhanced resistance to intergranular corrosion (IGC) during welding repair operations and prolonged high-temperature service.
Mechanical & Physical Properties (Typical Values)
| Property | SAE 304 | SAE 316 | SAE 310S | SAE 321 |
|---|---|---|---|---|
| Yield Strength (0.2% Offset), min. (MPa) | 205 | 170 | 205 | 205 |
| Tensile Strength, min. (MPa) | 515 | 485 | 515 | 515 |
| Maximum Continuous Service Temperature (°C) | 870 | 870 | 1150 | 925 |
| Thermal Expansion Coefficient (×10⁻⁶ /K, 20–100 °C) | 17.3 | 16.0 | 18.5 | 17.3 |
| Thermal Conductivity (W/m·K, 100 °C) | 16.3 | 16.3 | 26.2 | 16.3 |
| Density (kg/m³) | 8000 | 8000 | 8030 | 8000 |
| Carbon Equivalent (Ceq, max. %) | 0.08 | 0.08 | 0.08 | 0.08 |
Chemical Composition Requirements (ASTM A213 / A269)
| Element | SAE 304 | SAE 316 | SAE 310S | SAE 321 |
|---|---|---|---|---|
| C (Carbon), max. % | 0.08 | 0.08 | 0.08 | 0.08 |
| Si (Silicon), max. % | 1.00 | 1.00 | 1.00 | 1.00 |
| Mn (Manganese), max. % | 2.00 | 2.00 | 2.00 | 2.00 |
| P (Phosphorus), max. % | 0.045 | 0.045 | 0.045 | 0.045 |
| S (Sulfur), max. % | 0.030 | 0.030 | 0.030 | 0.030 |
| Cr (Chromium), % | 18.0–20.0 | 16.0–18.0 | 24.0–26.0 | 17.0–19.0 |
| Ni (Nickel), % | 8.0–10.5 | 10.0–14.0 | 19.0–22.0 | 9.0–12.0 |
| Mo (Molybdenum), % | — | 2.0–3.0 | — | — |
| Ti (Titanium), % | — | — | — | 5 × C – 0.40 (min.) |
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 25.0 mm – 57.0 mm (typical); custom sizes available up to 114.3 mm | ASTM A213 / A269 |
| Tube Wall Thickness | 1.5 mm – 6.0 mm (standard); up to 10.0 mm on request | ASTM A213 |
| Coil Winding Diameter | 1.2 m – 6.0 m (configurable per gasifier geometry) | Custom / Project-Specific |
| Coil Length (Unwound) | Up to 300 m per continuous coil (no longitudinal butt welds) | — |
| Surface Finish | Hot-rolled (HR) or Cold-worked / Pickled & Polished (P&H); Ra ≤ 0.8 μm for P&H | ASTM A270 |
| End Condition | Plain cut, beveled (37.5°), or threaded per ASME B1.20.1 | ASME B1.20.1 |
| Operating Pressure (Design) | Up to 6.5 MPa (gasifier-side); water-side up to 4.0 MPa | Project Specification |
| Operating Temperature | Water-side: 250–450 °C; Gas-side: up to 1,200 °C (SAE 310S) | — |
| Heat Treatment | Solution annealing at 1050–1150 °C followed by water quench | ASTM A213 |
| Corrosion Allowance | ≥ 0.5 mm (integrated into wall thickness) | Project Specification |
| Weld Repair Limit | Maximum 3 repairs per 300 mm tube length; total repair volume ≤ 10% of weld volume | ASME Section IX, QW-403 / API 579 |
Manufacturing Process
The production of stainless steel coil tubes for coal-to-hydrogen gasifier water-cooled walls follows a rigorously controlled multi-stage manufacturing sequence:
- Strip Preparation & Inspection: Cold-rolled stainless steel strip is received from certified mills and subjected to 100% visual inspection, ultrasonic testing (UT) for internal laminations, and spectrographic analysis (PMI — Positive Material Identification) for chemical composition verification.
- Forming & Welding (Seam Welding): The strip is formed into a tubular cross-section and longitudinally seam-welded using submerged arc welding (SAW) or orbital automatic gas tungsten arc welding (GTAW). Weld parameters are optimized to achieve a single-pass, full-penetration weld with minimal heat-affected zone (HAZ) distortion.
- Solution Annealing: The continuously welded tube is passed through a continuous annealing furnace at 1050–1150 °C under protective nitrogen atmosphere, followed by rapid water quenching. This eliminates cold-work hardening, dissolves carbides, and restores full austenitic microstructure and ductility.
- Pickling & Passivation: The annealed tube is pickled in a citric acid or nitric-hydrofluoric acid (HNO₃/HF) solution to remove the mill scale oxide layer, followed by passivation treatment to establish a stable chromium-rich passive film (Cr₂O₃) on the surface.
- Coil Winding: The prepared straight tube is wound onto a precision coil-winding mandrel using a CNC-controlled winding machine. Tension is uniformly applied to prevent ovalization, kinking, or plastic deformation at the bend radius. The minimum bend radius is maintained at ≥ 3 × OD to avoid localized stress concentration.
- Dimensional Inspection: Post-winding inspection includes measurement of coil diameter, pitch accuracy, tube ovality (≤ 2% of OD), and visual examination of the entire coil surface for wrinkles, dents, or weld seam misalignment.
- Non-Destructive Testing (NDT): 100% eddy current testing (ET) and/or ultrasonic testing (UT) is performed along the entire coil length to detect seam weld defects, wall thinning, or internal discontinuities. Radiographic testing (RT) is applied to sample welds and all repair locations.
Welding Repair Protocol for In-Service Coil Tubes
A defining feature of this product line is the documented and validated welding repair methodology for water-cooled wall coil tubes in rotary gasifier furnaces. When in-service coil tubes develop wall thinning, slag-induced erosion, or thermal fatigue cracking, the following repair protocol is applied:
- Damage Assessment: Ultrasonic thickness mapping identifies the extent of wall loss; radiographic or penetrant testing (PT) delineates crack boundaries.
- Defect Removal: The damaged zone is machined or ground to expose sound base metal, with a minimum 3 mm margin beyond visible defect boundaries. A radiographic inspection of the prepared groove confirms complete removal of all damaged material.
- Welding Execution: Repair welding is performed using GTAW (Gas Tungsten Arc Welding) with matched or slightly enriched filler metal (e.g., ER309L for S30408 base metal; ER316L for S31608; ER310 for S31008). Pre-heat temperature is controlled at 100–150 °C to minimize thermal shock. Interspass temperature is maintained below 150 °C. A minimum of two passes is applied: a root pass for full penetration and a cap pass for surface integrity.
- Post-Weld Heat Treatment (PWHT): Localized solution annealing at 1050 °C for a minimum of 10 minutes per 25.4 mm of wall thickness, followed by air cooling, is applied to relieve residual stresses and homogenize the microstructure in the repair zone.
- Post-Repair Verification: 100% RT and PT inspection of the repaired area; dimensional verification to confirm no out-of-roundness exceeding 2% of OD; and hydrostatic pressure testing at 1.5 × design pressure for a minimum dwell time of 30 minutes.
Applications
- Coal-to-Hydrogen Rotary Gasifier Furnaces: Primary application — the coil tube forms the water-cooled wall panels that line the interior of the gasifier vessel, absorbing radiant heat from the coal combustion zone while maintaining structural integrity under temperatures up to 1,200 °C and pressures up to 6.5 MPa.
- Coal Gasification (IGCC / CGLS): Water-cooled wall coil tubes in integrated gasification combined cycle (IGCC) and coal gasification liquid synthesis (CGLS) plants.
- Coal-Direct-Liquid (CDL) Systems: High-temperature water-cooled panels in direct coal liquefaction reactors.
- Petrochemical Reformers: Water-cooled panels in steam methane reformer (SMR) tubesheets and radiant sections.
- Fuel Cells & Hydrogen Production: Balance-of-plant water-cooled components in PEM and SOFC fuel cell systems.
- Power Generation: Water-cooled wall tubes in supercritical and ultra-supercritical (USC) boiler units.
Quality Certifications & Standards Compliance
| Category | Standard / Certification | Scope |
|---|---|---|
| Material Specification | ASTM A213 (Seam |