Stainless Steel Coil Tube (Coiltube) for Primary Reformer Applications — Humidification & Fuel Gas Preheating
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered bent tube product designed specifically for high-temperature, high-pressure process environments in the petrochemical and refining industries. This product is primarily deployed within Primary Reformer Furnaces (e.g., Unit 101B) to serve dual critical functions: (1) steam humidification of process gas streams entering the catalyst bed, and (2) fuel gas preheating to optimize combustion efficiency and thermal management within the furnace radiant zone.
Coiltubes are formed by cold-bending or hot-bending seamless stainless steel tubes into precise helical or serpentine geometries, enabling maximum heat transfer surface area within confined furnace volumes. These products represent a critical component in ammonia synthesis, methanol production, and hydrogen generation processes where temperature control and heat recovery are paramount to operational safety and energy efficiency.
Material & Properties
Base Material Grades
- AISI 310 / 310S (UNS S31008 / S31009) — Austenitic stainless steel with elevated chromium (24–26%) and nickel (19–22%) content, offering exceptional oxidation resistance at temperatures up to 1150°C. This is the preferred grade for humidification coil tubes operating directly in the radiant zone.
- AISI 304 / 304L (UNS S30400 / S30403) — General-purpose austenitic stainless steel suitable for fuel gas preheating coil tubes operating at moderate temperatures (up to 870°C).
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic stainless steel providing superior resistance to intergranular corrosion and thermal cycling fatigue, ideal for applications involving repeated heating and cooling cycles.
- Incoloy 800 / 800H (UNS N08800 / N08810) — Nickel-iron-chromium alloy offering outstanding resistance to carburization, sulfidation, and thermal fatigue in aggressive fuel gas environments.
Key Mechanical & Physical Properties (Typical for AISI 310S)
- Tensile Strength (Rm): ≥ 520 MPa
- Yield Strength (Rp0.2): ≥ 205 MPa
- Elongation (A5): ≥ 40%
- Density: 7.95 g/cm³
- Thermal Conductivity (20°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 16.5 × 10⁻⁶ /K
- Maximum Service Temperature: 1150°C (oxidizing atmosphere)
- Minimum Service Temperature: Cryogenic (no ductile-to-brittle transition)
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ25 mm – Φ89 mm (customizable) | ASTM A213 / GB/T 14976 |
| Wall Thickness | 1.5 mm – 6.0 mm | ASTM A213 / GB/T 14976 |
| Bend Radius (Centerline) | 3D – 15D (D = tube OD) | ISO 15497 / ASME B31.3 |
| Coil Length (Developed) | 5 m – 150 m per spool | Project-specific design |
| Maximum Operating Pressure | ≤ 4.0 MPa (fuel gas); ≤ 2.5 MPa (steam) | ASME B31.3 / EN 13480 |
| Maximum Operating Temperature | ≤ 1100°C (humidification); ≤ 650°C (fuel gas preheat) | Material grade-dependent |
| Surface Finish | Pickled & Passivated (Ra ≤ 1.6 μm) | ASTM A967 |
| Tolerance on OD | ±0.5% (Precision grade) | ASTM A213 |
| Tolerance on Wall Thickness | ±10% | ASTM A213 |
| Bend Tolerance | ±1° on angle; ±2 mm on radius | ISO 15497 |
| End Preparation | Plain end / Beveled (37°) / Threaded (NPT/BSP) | ASME B31.3 |
| Applicable Standards | ASTM A213, ASME SA-213, GB/T 14976, EN 10216-5 | — |
Manufacturing Process
Step 1: Raw Material Selection & Inspection
High-purity austenitic stainless steel seamless tubes conforming to ASTM A213 or GB/T 14976 specifications are procured from certified mills. Incoming materials undergo rigorous inspection including Positive Material Identification (PMI) via X-ray fluorescence (XRF) spectrometry, chemical composition verification by optical emission spectrometry (OES), and hydrostatic testing to ensure wall integrity.
Step 2: Straightening & Pre-Treatment
Coiled or straight lengths of tube are mechanically straightened using hydraulic or pneumatic straightening equipment. Surface contaminants, mill scale, and residual oils are removed through chemical pickling (mixed acid bath: HNO₃/HF) followed by passivation to establish a protective chromium oxide film.
Step 3: Tube Bending (Forming)
The core forming operation utilizes precision CNC-controlled bending machines with the following configurations:
- Cold Bending: For tubes ≤ Φ48 mm with bend radii ≥ 5D, performed at ambient temperature using mandrel-assisted or U-die bending to prevent ovalization and wrinkling.
- Hot Bending: For thicker-wall or tighter-radius applications, tubes are induction-heated to 900–1050°C and bent over a die to achieve the target geometry without work hardening or cracking.
- Forming Methods: Mandrel bending, U-die bending, rotary draw bending, and spiral coiling (for continuous helical geometries).
Step 4: Post-Forming Heat Treatment
Following bending, the coil tube spools undergo solution annealing at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure, eliminate residual stresses, and ensure maximum corrosion resistance and ductility. The resulting grain size shall be ASTM No. 4 or finer.
Step 5: Dimensional Inspection & Quality Control
Finished coil tubes are inspected using:
- CMM (Coordinate Measuring Machine) for dimensional accuracy of bend geometry
- Eddy current testing (ECT) for wall thickness verification and defect detection
- Visual and penetrant testing (PT) at all bend locations for surface integrity
- Hydrostatic pressure testing at 1.5× design pressure for leak-tightness verification
Step 6: Final Passivation, Packaging & Marking
All spools receive a final passivation treatment, are wrapped in protective film, and packaged in wooden crates or steel containers with desiccant for moisture protection during transit. Each spool is marked with a unique heat number, product code, and traceability documentation.
Applications
Primary Application: Primary Reformer Furnace (Unit 101B)
The primary reformer is the heart of a steam methane reforming (SMR) process used in hydrogen production, ammonia synthesis, and methanol manufacture. Within this furnace, coil tubes serve two distinct process functions:
- Humidification Coil Tubes (增湿盘管): These tubes are installed in the radiant zone of the primary reformer to introduce controlled quantities of superheated steam into the process gas stream. The steam serves to maintain the appropriate H₂O/C ratio (typically 2.8–3.5 mol/mol) for the reforming reaction (CH₄ + H₂O → CO + 3H₂), suppress carbon deposition on catalyst surfaces, and stabilize the reaction temperature profile. Operating conditions: 800–1100°C, 2.0–3.5 MPa.
- Fuel Gas Preheating Coil Tubes (燃料气预热盘管): These tubes are positioned in the waste heat recovery section or convection zone to preheat fuel gas prior to combustion in the furnace burners. By recovering heat from flue gases or hot process streams, these coils improve overall furnace thermal efficiency by 3–5%, reduce fuel consumption, and ensure stable flame characteristics. Operating conditions: 400–650°C, 0.5–4.0 MPa.
Additional Applications
- Secondary Reformer Furnaces: Coil tubes for quench water injection and process gas temperature control
- Shift Converters: Heat exchange coil tubes in high-temperature shift (HTS) and low-temperature shift (LTS) reactors
- Reforming Furnace Convective Sections: Economizer tubes and air preheater coil elements
- Ammonia Synthesis Loops: Hot effluent gas coolers with internal coil configurations
- Hydrocracker Heaters: Fired heater transfer coil tubes in hydrotreating units
- Chemical Process Reactors: Jacketed reactor internal cooling/heating coils for exothermic/endothermic reactions
Quality Certifications & Compliance
Manufacturing Certifications
- ISO 9001:2015 — Quality Management System certification for consistent product quality
- ISO 14001:2015 — Environmental Management System for sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management System
- NACE SP0107 / ISO 21809-1 — Standard practice for inspection and cleaning of carbon steel surfaces prior to coating
Product Testing & Certification Standards
- ASTM A213 / ASME SA-213 — Standard specification for austenitic stainless steel tube for high-temperature service
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes for fluid transport
- EN 10216-5 — European standard for non-ferrous metal tubes for pressure purposes
- ASME B31.3 — Process piping code compliance for design, fabrication, and installation
- ISO 15497 — Tubes and pipes — Bending of tubes and pipes — General rules and verification
- ASTM E165 — Standard practice for liquid penetrant testing
- ASTM E309 — Standard practice for eddy-current testing of nonferromagnetic metal tubing
Traceability & Documentation
Each coil tube spool is accompanied by a comprehensive Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1, providing full traceability from raw material heat number through all manufacturing operations. Documentation includes chemical analysis reports, mechanical test results, bend test data, and dimensional inspection records.
Unique Selling Points
1. Application-Specific Engineering: Coil tubes designed and manufactured with deep domain knowledge of primary reformer furnace operations, ensuring optimal thermal performance, mechanical integrity, and service life in the most demanding process environments.
2. Precision Bending Capability: CNC-controlled bending equipment with ±1° angular accuracy and ±2 mm radius tolerance, producing repeatable geometries that ensure proper furnace fit-up and minimize installation labor.
3. Multi-Grade Material Expertise: Capability to supply coil tubes in multiple austenitic stainless steel and nickel alloy grades, enabling engineers to select the optimal material balance between cost, temperature capability, and corrosion resistance for each specific application.
4. Full Traceability & Quality Assurance: End-to-end traceability from mill heat number to finished spool, supported by comprehensive testing protocols (PMI, ECT, PT, hydrostatic) and EN 10204 3.1 certification documentation.
5. Energy Efficiency Contribution: Fuel gas preheating coil tubes contribute 3–5% improvement in overall furnace thermal efficiency, directly reducing fuel consumption and CO₂ emissions — aligning with global decarbonization objectives in the petrochemical sector.
6. Customization & Flexibility: Full customization of tube dimensions, bend geometries, coil configurations, end preparations, and material grades to meet project-specific design requirements, with engineering support from concept through commissioning.