Stainless Steel Coil Tube — Wax Removal Machine Boiler Application (CO₂ Protected Automatic Welding)
1. Product Overview
The Stainless Steel Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchange component specifically designed for use in wax removal machine boilers (also referred to as de-waxing apparatus or wax extraction systems). These coil tubes are fabricated through continuous coiling processes and are subsequently welded using Carbon Dioxide (CO₂) Gas Shielded Arc Welding — an automatic welding technique that ensures uniform, high-integrity weld seams throughout the entire coil assembly.
Coil tubes serve as critical heat transfer elements within industrial boiler systems, where they facilitate the efficient exchange of thermal energy between the working fluid and the combustion medium. In the context of wax removal machinery, the coil tube must endure prolonged exposure to elevated temperatures, corrosive wax residues, and repeated thermal cycling — demands that necessitate a material solution combining superior corrosion resistance, thermal stability, and mechanical durability.
Key Insight: The adoption of CO₂ protected automatic welding for coil tube fabrication represents a significant advancement over traditional manual welding methods, offering repeatability, reduced human error, and consistent weld quality — all essential for maintaining the structural integrity of boiler heat exchange components under sustained operational stress.
2. Material Composition & Properties
Wenzhou Jixing Metal Materials Co., Ltd employs premium-grade stainless steel grades tailored to the demanding environment of wax removal boiler systems. The primary material specifications are as follows:
2.1 Primary Alloy Grades
- AISI 304 / UNS S30408 (18/8 Stainless Steel): The standard austenitic grade offering excellent general corrosion resistance, good weldability, and adequate high-temperature strength up to approximately 870°C (1600°F). Contains 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 / UNS S31608 (18/10/2 Stainless Steel): Enhanced version with 2–3% Molybdenum (Mo) addition, providing superior resistance to pitting and crevice corrosion — particularly advantageous in environments where chlorinated wax residues or acidic contaminants may be present.
- AISI 321 / UNS S32108 (Stabilized Austenitic): Titanium (Ti)-stabilized grade recommended for applications involving sustained temperatures above 425°C (800°F), where sensitization and intergranular corrosion risk must be mitigated.
2.2 Mechanical Properties (Typical Values for AISI 304, Annealed Condition)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) | ASTM A269 / A270 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (30 ksi) | ASTM A269 / A270 |
| Elongation (in 50 mm gauge length) | ≥ 40% | ASTM A269 / A270 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM E140 |
| Density | 7.93 g/cm³ (0.285 lb/in³) | — |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | ASTM E153 |
| Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
| Maximum Service Temperature | 870°C (1600°F) | — |
2.3 Corrosion Resistance Characteristics
- Pitting Resistance Number (PREN): 18–20 for AISI 304; 24–26 for AISI 316
- Carburization Resistance: Excellent below 800°C (1472°F) for Ti-stabilized grades
- Oxidation Resistance: Maintains protective chromium oxide film (Cr₂O₃) up to 1150°C (2094°F) in intermittent service
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) | — |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd | — |
| Product Code / Serial No. | 1638 | — |
| Form | Continuous coil / helical coil | — |
| Available Outer Diameters (OD) | Φ12 mm – Φ108 mm (custom sizes available) | ASTM A269 / A270 |
| Available Wall Thickness | 0.5 mm – 6.0 mm | ASTM A269 / A270 |
| Coil Inner Diameter (Diameter of Coil) | Φ200 mm – Φ2000 mm (application-specific) | — |
| Coil Pitch | 15 mm – 50 mm (adjustable per design) | — |
| Number of Turns | 5 – 500+ (custom fabrication) | — |
| Surface Finish | No. 4 Brushed / 2B / Mirror Polish (Ra ≤ 0.4 μm) | ASTM A480 |
| End Form | Plain / Beveled / Threaded / Flanged | ASME B1.20.1 |
| Welding Method | CO₂ Protected Automatic Welding (GMAW-S) | ASME Section IX / AWS D10.6 |
| Applicable Standards | ASTM A269, ASTM A270, EN 10216-5, GB/T 12771 | — |
| Packing | Wooden crate / Export-grade steel frame | — |
| Minimum Order Quantity (MOQ) | Negotiable | — |
4. Manufacturing Process
The fabrication of stainless steel coil tubes for wax removal machine boilers follows a rigorously controlled multi-stage process, each phase governed by strict quality assurance protocols:
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel seamless or welded tubes are verified for chemical composition (via Optical Emission Spectrometry, OES), mechanical properties, and dimensional conformity per ASTM A269/A270.
- Cutting & Straightening: Tubes are cut to required lengths using cold saw or plasma cutting, then straightened to eliminate residual curvature within ±0.5 mm/m tolerance.
- Coil Forming (Cold Bending): Straight tubes are passed through a precision coil forming machine that imparts the helical geometry. The bending process is executed at ambient temperature to preserve the metallurgical properties of the stainless steel. Tooling is calibrated to achieve the specified coil pitch, inner diameter, and turn count.
- CO₂ Protected Automatic Welding (Gas Metal Arc Welding — Solid Wire, GMAW-S):
- Shielding Gas: 100% CO₂ (or 80% Ar / 20% CO₂ mixed gas, depending on wall thickness)
- Wire Electrode: ER308L or ER316L solid wire, matching or exceeding the base metal alloy composition
- Welding Parameters: Current 120–280 A, Voltage 18–28 V, Travel Speed 200–600 mm/min (adjusted per wall thickness)
- Joint Types: Butt welds at coil ends, fillet welds at U-bend connections, and socket welds at inlet/outlet ports
- Automated Control: CNC-controlled welding heads ensure consistent bead geometry, penetration, and fusion — critical for eliminating stress concentrations in heat exchange applications
- Post-Weld Treatment:
- Stress Relief Annealing: Heating to 1050–1100°C followed by controlled air cooling to relieve residual welding stresses and restore full annealed condition
- Pickle & Passivate: Immersion in nitric acid / hydrofluoric acid mixture to remove weld discoloration (heat tint) and restore the passive chromium oxide film
- Pressure Testing: Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the design working pressure (typically 1.5 MPa for wax removal boiler applications) held for a minimum of 30 minutes with zero leakage tolerance.
- Final Inspection & Dimensional Verification: Visual inspection, dye penetrant testing (DPT) per ASTM E165, and dimensional measurement of coil geometry.
4.2 CO₂ Protected Automatic Welding — Technical Rationale
The selection of CO₂ gas shielded arc welding for coil tube fabrication in wax removal boiler applications is driven by several engineering considerations:
- Deep Penetration: CO₂ shielding produces a deeper arc penetration compared to argon-based shielding, ensuring full fusion across the tube wall thickness — essential for pressure-retaining weld joints.
- Cost Efficiency: CO₂ is significantly less expensive than argon or mixed gas blends, making it economically viable for large-scale coil tube production.
- Automated Compatibility: CO₂ GMAW-S processes are highly amenable to robotic and CNC automation, enabling consistent weld quality across hundreds of identical coil assemblies.
- Weld Metallurgy: When using low-carbon filler metals (ER308L/ER316L), the carbon from CO₂ decomposition does not significantly compromise the corrosion resistance of the weld zone.
5. Applications
The stainless steel coil tubes produced by Wenzhou Jixing Metal Materials Co., Ltd are engineered for the following primary and secondary applications:
5.1 Primary Application — Wax Removal Machine Boilers
- Textile Industry De-Waxing: Coil tubes serve as the heating element within wax removal apparatus used to strip paraffin wax coatings from textile fibers, particularly in the production of silk and synthetic filament yarns.
- Beeswax Processing: Industrial-scale wax purification systems where coil tubes provide controlled steam generation for wax melting and filtration.
- Cosmetic & Pharmaceutical Wax Processing: High-purity wax melting and purification where stainless steel's non-reactive surface prevents product contamination.
5.2 Secondary Applications
- Industrial boiler heat exchangers
- Chemical processing reactors and heat transfer systems
- Food and beverage processing equipment (sanitary grade 316L)
- Geothermal energy systems
- Marine engineering heat exchange components
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring that all stainless steel coil tube products meet international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and service processes |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ASME Section IX | Welding qualification procedures and welder performance qualifications for pressure vessel components |
| AWS D10.6M/D10.6 | Qualification standard for welders in pipe and tubing welding applications |
| EN 10204-3.1 | Third-party inspection certificate — independent verification of material compliance |
| CE Marking (PED 2014/68/EU) | Conformity with European Pressure Equipment Directive for boiler and heat exchange components |
| MTC (Mill Test Certificate) | Full chemical and mechanical test data provided with each batch shipment |
| NACE SP0169 | Corrosion prevention requirements for materials in oilfield and chemical service |
7. Unique Selling Points
- Application-Specific Engineering: Coil tubes are designed and fabricated specifically for the unique thermal and chemical demands of wax removal machine boilers — not generic boiler components adapted for the application.
- Automated CO₂ Welding Integration: The use of CNC-controlled CO₂ protected automatic welding eliminates the variability inherent in manual welding, producing coil assemblies with uniform weld quality, consistent penetration, and minimal distortion — directly translating to extended service life and reduced maintenance intervals.
- Full Traceability: Each coil tube batch is accompanied by complete mill test certificates, welding procedure specifications (WPS), welder qualification records, and non-destructive testing (NDT) reports.
- Custom Fabrication Capability: Wenzhou Jixing Metal Materials Co., Ltd offers fully customizable coil geometry — including non-standard pitches, diameters, and turn counts — to match specific boiler design requirements.
- Material Versatility: Availability in multiple stainless steel grades (304, 316, 321, and custom alloys) allows customers to optimize the material selection for their specific operating environment and corrosion exposure.
- Integrated Pickle & Passivation: Post-weld passivation treatment ensures the full surface area — including weld zones — is protected by a stable chromium oxide film, preventing premature corrosion initiation at weld heat-affected zones (HAZ).