Stainless Steel Coil Tube (Coiltube) — Waste Heat Boiler Grade
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-formed tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. specifically designed for use in coil-type waste heat recovery boilers (WHRB) and related high-temperature heat exchange systems. The coil tube is supplied in continuous helical coil configuration, eliminating the need for field welding and significantly reducing installation complexity. This product leverages advanced metallurgical processing, including controlled cold forming and acid pickling, to deliver superior corrosion resistance, thermal performance, and mechanical integrity under demanding industrial operating conditions.
The coil tube is engineered to withstand cyclic thermal loading, corrosive flue gas environments, and high-temperature steam generation — making it an essential component in power generation, petrochemical, and industrial waste heat recovery applications.
Material & Properties
Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards, with the following typical chemical compositions:
- AISI 304 / SUS304 — Chromium (Cr): 18.0–20.0%, Nickel (Ni): 8.0–10.5%, Carbon (C): ≤0.08%
- AISI 316 / SUS316 — Chromium (Cr): 16.0–18.0%, Nickel (Ni): 10.0–14.0%, Molybdenum (Mo): 2.0–3.0%, Carbon (C): ≤0.08%
- AISI 321 / SUS321 — Chromium (Cr): 17.0–19.0%, Nickel (Ni): 9.0–12.0%, Titanium (Ti): 5×C, Carbon (C): ≤0.08%
- AISI 347 / SUS347 — Chromium (Cr): 17.0–19.0%, Nickel (Ni): 9.0–12.0%, Niobium (Nb): 6–10×C, Carbon (C): ≤0.08%
Mechanical Properties (Annealed Condition)
- Tensile Strength (UTS): ≥515 MPa (75 ksi)
- Yield Strength (0.2% Offset): ≥205 MPa (30 ksi)
- Elongation: ≥40%
- Hardness: ≤95 HRB (Brinell Hardness Number, BHN)
- Operating Temperature Range: −196 °C to +870 °C (depending on grade)
Corrosion Resistance Characteristics
The austenitic microstructure, stabilized by controlled cold work and subsequent solution annealing, provides excellent resistance to:
- General atmospheric and acid corrosion
- Pitting and crevice corrosion (particularly in 316 and 316L grades)
- Intergranular corrosion (sensitization resistance via Ti/Nb stabilization in 321/347 grades)
- Oxidation scaling at elevated temperatures up to 870 °C
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Coiltube — Stainless Steel Helical Coil Tube |
| Product Serial No. | 1628 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Tube Outer Diameter (OD) | 12 mm – 51 mm (0.5" – 2") |
| Wall Thickness | 0.5 mm – 3.0 mm (0.020" – 0.118") |
| Coil Diameter | 1,000 mm – 4,000 mm (adjustable per design) |
| Coil Length | Up to 300 m per continuous coil |
| Surface Finish | Pickled and Passivated (P&P) / 2B / No. 4 Brushed |
| Surface Roughness (Ra) | ≤0.4 μm (pickled and passivated finish) |
| Standard Reference | ASTM A213, ASTM A269, GB/T 12771, JIS G3459 |
| End Condition | Plain end / Beveled end / Threaded (per specification) |
| Heat Treatment | Solution Annealed + Acid Pickled + Passivated |
| Maximum Operating Pressure | Up to 16 MPa (2320 psi) — design dependent |
| Maximum Operating Temperature | 870 °C (AISI 321/347) / 815 °C (AISI 304/316) |
| Packaging | Wooden crate / Steel frame with moisture-proof wrapping |
Manufacturing Process
1. Raw Material Procurement
Virgin stainless steel strip or seamless pipe blanks are sourced from certified mills with full traceability documentation (Mill Test Certificate, MTC). Incoming material undergoes spectroscopic verification to confirm compliance with the specified chemical composition.
2. Cold Forming / Coil Winding
The flat strip or straight pipe is cold-formed into a helical coil configuration using precision CNC-controlled coiling machines. The forming process maintains dimensional accuracy within ±0.1 mm tolerance for coil diameter and ±0.5 mm for pitch. The cold work introduces beneficial work hardening while preserving the ductility of the austenitic matrix.
3. Welding (if applicable — welded coil tube)
For welded coil tube configurations, the strip edges are joined using continuous submerged arc welding (SAW) or gas metal arc welding (GMAW) with matching filler metal. The weld seam undergoes 100% visual inspection and periodic radiographic testing (RT) per ASTM E94.
4. Solution Annealing
The formed coil is subjected to solution annealing at 1,050–1,150 °C followed by rapid water quenching. This process:
- Relieves residual stresses from cold forming
- Restores full ductility and corrosion resistance
- Dissolves carbides to prevent sensitization
- Establishes a uniform austenitic grain structure
5. Acid Pickling
The annealed coil tube undergoes a rigorous acid pickling process — a critical step for waste heat boiler applications. The pickling procedure involves:
- Pre-cleaning: Removal of surface oils, scale, and contaminants via alkaline degreasing
- Acid immersion: Immersion in a mixed acid solution (typically HNO₃/HF or HNO₃/HCl) at controlled temperature (60–80 °C) for a specified duration
- Scale removal: Complete elimination of oxide scale formed during annealing
- Rinsing: Thorough deionized water rinsing to neutralize residual acid
6. Passivation
Following pickling, the tube surface is passivated using a nitric acid (HNO₃) or citric acid solution to form a thin, stable chromium oxide (Cr₂O₃) passive film. This film provides the essential barrier against corrosion in service. Passivation effectiveness is verified via ferrite particle test (ASTM A967) and red drop test.
7. Quality Inspection & Testing
- Dimensional inspection: OD, wall thickness, coil diameter, and pitch verification
- Visual inspection: 100% surface examination for defects, pitting, or discoloration
- Magnetic particle testing (MT): For welded joints per ASTM E1444
- Eddy current testing (ET): For detection of internal wall thickness variations
- Hydrostatic pressure testing: Performed at 1.5× maximum operating pressure
- Chemical analysis: Spark OES (Optical Emission Spectrometry) verification
- Metallographic examination: Grain size and microstructure confirmation
8. Packaging & Dispatch
Finished coil tubes are wound on protective wooden spools, wrapped with anti-corrosion moisture-proof film, and secured in export-grade wooden crates or steel-framed containers for global distribution.
Applications
Primary Applications
- Waste Heat Recovery Boilers (WHRB): The coil tube serves as the primary heat absorption element in fired-tube and coil-type waste heat boilers, recovering thermal energy from flue gases in power plants, cement kilns, and steel mills
- Industrial Furnace Heat Exchangers: Superheaters, economizers, and air preheaters in petrochemical and refining processes
- Power Generation: Steam generation systems in combined cycle gas turbines (CCGT) and cogeneration plants
- Oil & Gas Processing: Flue gas heat recovery in process heaters and catalytic cracking units
Secondary Applications
- Chemical processing heat exchangers
- Food and pharmaceutical sanitary processing systems
- Marine boiler systems
- Geothermal energy extraction systems
- Hydrogen production fuel cells
Quality Certifications & Compliance
Product Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 10204 — Type 3.1 Mill Test Certificates (MTC) per batch
- ASTM A213 / A269 — Seamless and welded stainless steel tube standards
- GB/T 12771 — Chinese national standard for stainless steel welded tubes
- ASME SA-213 — Boiler and heat exchanger tubes (where applicable)
Third-Party Verification
- TÜV Rheinland material certification
- Bureau Veritas (BV) inspection and certification
- SGS chemical composition and mechanical property verification
- API Monogram Program (for oil and gas applications)
Unique Selling Points
1. Integrated Pickling & Passivation Expertise: Drawing from extensive operational experience with coil-type waste heat boilers, Wenzhou Jixing Metal Materials applies a proprietary pickling and passivation protocol that ensures surface integrity exceeding industry norms — delivering a passive film thickness of 2–5 nm with verified corrosion potential ≥ +200 mV (SCE).
2. Continuous Coil Configuration — Zero Field Welding: The helical coil design eliminates the need for in-situ welding during installation, reducing installation time by up to 60% and eliminating potential leak points that compromise long-term reliability.
3. Superior Thermal Performance: The smooth pickled surface (Ra ≤ 0.4 μm) minimizes fouling and maintains optimal heat transfer coefficients throughout the service life, reducing overall system efficiency degradation by up to 15% compared to standard finish alternatives.
4. Full Traceability & Documentation: Each coil is accompanied by comprehensive documentation including chemical analysis reports, mechanical test data, heat treatment records, pickling and passivation logs, and dimensional inspection certificates — ensuring complete supply chain transparency.
5. Customizable Coil Geometry: Flexible manufacturing capability allows coil diameter, pitch, tube OD, and wall thickness to be tailored to specific boiler design requirements, enabling optimized thermal performance for each application.
Technical Notes & Recommendations
- For applications exceeding 650 °C continuous service, recommend AISI 321 or 347 grades to prevent sensitization and intergranular corrosion
- For chloride-containing environments (marine, chemical), specify AISI 316 or 316L grades
- Post-installation, avoid carbon steel contact to prevent galvanic contamination and localized corrosion
- Recommended inspection interval: 12 months for visual and dimensional; 24 months for eddy current wall thickness survey
- Storage: Maintain in original packaging in a dry, ventilated environment; avoid stacking coils beyond manufacturer-specified load limits