Stainless Steel Coil Tube (Coiltube) — Waste Heat Recovery Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for high-temperature waste heat recovery applications, including coil-type waste heat boilers (Waste Heat Boiler, WHB) and regenerative heat exchangers. This product is engineered to withstand extreme thermal cycling, corrosive flue gas environments, and sustained high-pressure steam generation conditions. The coil tube is formed into continuous helical or spiral configurations to maximize heat transfer surface area within compact installation footprints, making it an ideal solution for industrial energy recovery systems in oil and gas processing, petrochemical, and power generation facilities.
Derived from engineering experience in coal gasification and oil gasification waste heat boiler renovation projects, this coil tube product line integrates advanced metallurgical design with precision cold-forming techniques to deliver superior thermal efficiency, extended service life, and reduced maintenance intervals.
Material & Properties
Primary Alloy Grades
- 304 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance in oxidizing environments; suitable for moderate-temperature waste heat recovery up to 870°C (1600°F).
- 316 (UNS S31608) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion; recommended for sulfur-bearing flue gas applications.
- 321 (UNS S32108) — Titanium-stabilized grade with enhanced resistance to intergranular corrosion and thermal stress cracking; preferred for sustained temperatures above 500°C (932°F).
- 310S (UNS S31008) — High-temperature austenitic grade capable of continuous service up to 1150°C (2094°F); used in extreme-temperature gasification waste heat applications.
- TP347H (UNS S34709) — Stabilized austenitic grade with excellent creep resistance at elevated temperatures; suitable for pressure vessel and boiler applications per ASME standards.
Mechanical Properties (Typical for Grade 321)
| Property | Value | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa (74,700 psi) | ASTM A213 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa (29,700 psi) | ASTM A213 / EN 10216-5 |
| Elongation (% Elong.) | ≥ 40% | ASTM A213 |
| Hardness (HB) | ≤ 217 | ASTM A213 |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | ASM Handbook Vol. 6 |
| Linear Thermal Expansion (20–800°C) | 18.5 × 10⁻⁶ /°C | ASM Handbook Vol. 6 |
| Maximum Continuous Service Temperature | 870°C (1600°F) | Manufacturer Data |
Chemical Composition (Typical — Grade 321)
| Element | Specification (wt%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Chromium (Cr) | 18.00 – 21.00 |
| Nickel (Ni) | 9.00 – 12.00 |
| Titanium (Ti) | 5 × (C × 100) – 0.70 |
| Manganese (Mn) | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 |
| Sulfur (S) | ≤ 0.030 |
| Phosphorus (P) | ≤ 0.045 |
Specifications
Dimensional Parameters
| Parameter | Specification / Range | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ± 0.05 mm |
| Wall Thickness | 0.50 mm – 3.00 mm | ± 10% |
| Coil Winding Diameter | 150 mm – 1200 mm | ± 2.0% |
| Coil Pitch (Helical Spacing) | 15 mm – 80 mm | ± 0.5 mm |
| Coil Length (as-wound) | 3.0 m – 50.0 m | ± 0.1% |
| Number of Turns | Custom (up to 500 turns) | ± 0.5 turn |
| Straight Length (per segment) | 3.0 m – 12.0 m | ± 10 mm |
| End Condition | Plain, Beveled, or Threaded | Per drawing |
| Surface Finish | 2B (Mill), BA (Bright Annealed), or Electropolished | Ra ≤ 0.8 μm (electropolished) |
| Maximum Operating Pressure | Up to 4.0 MPa (580 psi) at 350°C | Per ASME VIII Div.1 |
| Maximum Operating Temperature | Up to 870°C (1600°F) | Grade-dependent |
| Heat Transfer Coefficient (gas side) | 30 – 150 W/(m²·K) | Application-dependent |
Coil Configuration Options
| Configuration Type | Description | Typical Application |
|---|---|---|
| Spiral Coil | Continuous helical winding with uniform pitch | Waste heat boiler tubes, air preheaters |
| Concentric Coil | Multiple concentric rings of decreasing diameter | Compact heat exchangers, evaporators |
| Double-Helix Coil | Interlaced dual-strand helical arrangement | High-capacity steam generators |
| Annular Coil | Flat ring configuration with radial support | Process heater internals |
Manufacturing Process
- Raw Material Selection and Incoming Inspection — High-purity stainless steel strip or seamless tube stock is procured from certified mills (e.g., Outokumpu, Posco, Tsingshan). Each batch undergoes spectrographic analysis (OES) for chemical composition verification and mechanical testing per ASTM A213 or EN 10216-5.
- Surface Preparation — The coil tube blank undergoes degreasing, pickling, and passivation treatment to remove scale, oxide, and organic contaminants, ensuring a clean surface for subsequent forming operations.
- Precision Cold Coiling / Helical Winding — The straight tube segment is fed through a CNC-controlled coiling machine equipped with synchronized servo-driven rollers. The winding diameter, pitch, and number of turns are controlled to within ± 0.5% accuracy. Real-time dimensional monitoring ensures geometric consistency throughout the coil length.
- Welding (if applicable) — For multi-segment coils, longitudinal or circumferential welds are performed using Gas Tungsten Arc Welding (GTAW) or Pulsed Gas Metal Arc Welding (GMAW) with inert gas shielding (Argon or Helium). Weld quality is verified via radiographic testing (RT) or ultrasonic testing (UT) per ASME Section IX.
- Solution Annealing and Stress Relief — The formed coil is heat-treated at 1050°C – 1150°C followed by rapid water quenching to restore full austenitic microstructure, eliminate residual stresses from cold forming, and maximize corrosion resistance. This step is critical for preventing stress corrosion cracking (SCC) in service.
- Precision Dimensional Verification — Post-heat-treatment coils undergo comprehensive dimensional inspection including OD measurement, wall thickness verification (ultrasonic), coil diameter checking, pitch uniformity assessment, and straightness measurement using laser scanning or coordinate measuring machines (CMM).
- Final Surface Treatment — Depending on the application requirement, the coil tube may receive additional bright annealing (BA), electropolishing, or passivation treatment to achieve the specified surface finish and enhanced passivation layer.
- Pressure Testing and Leak Detection — Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum design pressure, followed by helium or nitrogen leak detection to ensure zero-defect sealing integrity.
- Packaging and Shipping — Finished coils are wrapped in moisture-barrier protective film, padded with anti-corrosion paper, and secured on custom wooden pallets or crates for safe international shipment.
Applications
- Oil and Gas Waste Heat Boilers — Coil tubes serve as the primary heat transfer elements in waste heat boilers (WHBs) recovering thermal energy from coal/oil gasification syngas, with operating temperatures up to 870°C. The helical configuration provides compact heat exchange surfaces suitable for retrofit applications in existing gasification plants.
- Petrochemical Process Heat Exchangers — Used in reboilers, evaporators, and preheaters where resistance to sour gas (H₂S, CO₂) and cyclic thermal loading is critical.
- Power Generation — Applied in superheater tubes, economizers, and air preheaters within coal-fired and biomass-fired boilers.
- Chemical Processing — Suitable for heat exchangers handling aggressive chemical media including acids, alkalis, and halogenated compounds.
- Food and Pharmaceutical Industry — Electropolished coil tubes used in sanitary-grade heat exchangers and sterilization systems requiring hygienic surfaces.
- Marine and Offshore — Corrosion-resistant coil tubes for marine waste heat recovery systems and offshore platform heating applications.
Quality Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent manufacturing quality and process control.
- ISO 3834-2 — Requirements for quality documentation for fusion welding of metallic materials (if welding is involved).
- ASME Section IX — Compliance with qualification requirements for welding procedures and personnel.
- EN 10204 Type 3.1 — Inspection certificate confirming that test results are derived from specific inspection of the supplied product.
- Material Certification per ASTM A213 / EN 10216-5 — Full material traceability with mill test certificates (MTC) for every batch.
- NDT Testing per ASME Section V — Non-destructive testing including radiographic testing (RT), ultrasonic testing (UT), and dye penetrant testing (PT) as required by application codes.
- Pressure Vessel Compliance — Products suitable for use in ASME BPV Code Section I (Power Boilers) and Section VIII Division 1 (Pressure Vessels) applications.
- CE Marking (EU PED 2014/68/EU) — Conformity with European Pressure Equipment Directive for equipment within Category II and above.
Unique Selling Points
- Optimized for Waste Heat Recovery Retrofit — Designed based on engineering lessons from large-scale coal/oil gasification waste heat boiler renovation projects, ensuring proven performance in demanding industrial waste heat environments.
- Compact Heat Transfer Geometry — The helical coil configuration achieves 30–50% higher heat transfer surface density compared to conventional straight-tube bank arrangements, enabling significant space savings in retrofit installations.
- Superior Thermal Shock Resistance — Austenitic stainless steel grades selected for their