Stainless Steel Coil Tube for Polyester Heat Medium Furnace Systems
Product Overview
The Stainless Steel Coil Tube (产品编号: 1498) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous length tubing product specifically designed for high-temperature heat transfer applications within polyester (PET) heat medium furnace systems. Unlike conventional straight-length seamless or welded pipes, coil tubes are supplied in the form of continuous, tightly wound coils, enabling seamless integration into complex heat exchanger geometries without the need for field welding or mechanical coupling joints.
This product has been subjected to rigorous failure analysis and stress evaluation, particularly addressing the critical issue of crack initiation and propagation in polyester heat medium furnace coil tubes. The design incorporates lessons learned from documented crack failure modes, including thermal fatigue, creep deformation, and stress corrosion cracking (SCC), to deliver a robust, long-service-life heat transfer component for demanding industrial environments.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their exceptional combination of high-temperature strength, thermal fatigue resistance, and oxidation resistance. The primary material grades include:
- 321 Stainless Steel (UNS S32100): Titanium-stabilized austenitic grade with superior resistance to intergranular corrosion and thermal stress cracking. Ti (0.10–0.30%) acts as a carbide scavenger, preventing chromium depletion at grain boundaries during prolonged exposure to temperatures between 425°C and 870°C.
- 310S Stainless Steel (UNS S31008): High-temperature austenitic grade with elevated Cr (25–30%) and Ni (19–22%) content, offering outstanding oxidation resistance up to 1150°C and excellent creep strength for sustained high-temperature service.
- 304 Stainless Steel (UNS S30408): General-purpose austenitic grade suitable for moderate-temperature heat medium service with good formability and corrosion resistance.
Mechanical Properties (Typical at Room Temperature)
| Property | 321 SS | 310S SS | 304 SS |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A5) | ≥ 40% | ≥ 35% | ≥ 40% |
| Hardness (HBW) | ≤ 200 | ≤ 200 | ≤ 200 |
| Maximum Service Temperature | 870°C | 1150°C | 870°C |
Chemical Composition (wt%)
| Grade | C | Cr | Ni | Ti | Si | Mn | P | S |
|---|---|---|---|---|---|---|---|---|
| 321 | ≤ 0.08 | 17.0–19.0 | 9.0–13.0 | 5×C to 0.70 | ≤ 1.00 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 |
| 310S | ≤ 0.08 | 24.0–26.0 | 19.0–22.0 | — | ≤ 1.50 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 |
| 304 | ≤ 0.08 | 18.0–20.0 | 8.0–10.5 | — | ≤ 1.00 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 |
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12.7 mm – 168.3 mm (½" – 6") | ASTM A213 / ASME SA-213 |
| Wall Thickness | 1.5 mm – 12.7 mm (0.059" – 0.500") | ASTM A213 / ASME SA-213 |
| Coil Winding Diameter | 1,500 mm – 3,000 mm | Company Standard |
| Coil Length | Up to 300 m per coil | Company Standard |
| Manufacturing Method | Hot-Formed Seamless (HFW / Hot-Finishing Mill) | ASTM A213 |
| Surface Finish | Mill Annealed (No. 1) / Pickled & Annealed (2B) / Ground | ASTM A403 |
| Temperature Range | -196°C to 1150°C (grade dependent) | — |
| Pressure Rating | Up to 30 MPa (PN300) | ASME B31.3 |
| Tolerance – OD | ±0.15 mm (for OD ≤ 50 mm); ±0.50 mm (for OD > 50 mm) | ASTM A213 |
| Tolerance – Wall | ±10% of nominal wall thickness | ASTM A213 |
Manufacturing Process
The production of the stainless steel coil tube follows a multi-stage manufacturing sequence optimized to minimize residual stresses and prevent the crack initiation mechanisms identified in failure analysis studies:
- Raw Material Selection and Inspection: High-purity austenitic stainless steel slabs or billets are procured and subjected to spectroscopic analysis (OES) to verify chemical composition within specified ranges. Incoming material undergoes ultrasonic (UT) and magnetic particle (MT) inspection to reject any sub-surface defects.
- Hot Rolling and Piercing: Billets are reheated to 1150–1250°C and hot-rolled through a multi-stand mill to produce hollow tube blanks with controlled dimensional tolerances.
- Pilot Rod Extrusion / Mandrel Drawing: For seamless tube production, the hot-rolled blank is extruded through a die using a pilot rod, ensuring uniform wall thickness and eliminating weld seams that could serve as crack initiation sites.
- Coil Winding: The continuous tube is wound onto precision-wound coils with controlled bending radii (minimum bend radius ≥ 3× OD) to avoid plastic deformation and micro-cracking at the inner curvature of the bend.
- Solution Annealing and Pickling: The coiled tube undergoes solution annealing at 1050–1100°C followed by rapid water quenching to dissolve carbides and restore full austenitic microstructure. Subsequent pickling in nitric/hydrofluoric acid mixtures removes surface scale and ensures a clean, corrosion-resistant surface finish.
- Precision Sizing: The coil tube passes through a cold-drawing or rotary piercing sizing mill to achieve final dimensional tolerances on OD and wall thickness.
- Final Inspection and Testing: Each coil undergoes hydrostatic pressure testing (typically 2× working pressure), dimensional measurement, surface inspection, and spectroscopic verification. Optional non-destructive testing (NDT) includes eddy current testing (ECT) for surface and near-surface defect detection.
Crack Failure Mitigation Design Features
Informed by the documented crack failure analysis of polyester heat medium furnace coil tubes, the manufacturing process incorporates the following critical design controls:
- Stress-Relief Annealing: A dedicated low-temperature stress-relief cycle (600–700°C) is performed post-coil-winding to eliminate bending-induced residual stresses that could promote fatigue crack initiation.
- Controlled Bending Radius: The minimum coil winding radius is engineered to ensure that the maximum tensile strain at the inner curvature remains below the yield threshold, preventing work-hardening and micro-crack formation.
- Grain Size Control: Annealing parameters are optimized to produce a uniform, fine-grained austenitic microstructure (ASTM grain size ≥ 6), which enhances fatigue resistance and reduces susceptibility to intergranular cracking.
- Low Carbon Content: Carbon content is restricted to ≤ 0.08% to minimize chromium carbide precipitation (Cr₂₃C₆) at grain boundaries, thereby preventing sensitization-induced intergranular stress corrosion cracking (IGSCC).
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd is purpose-engineered for the following industrial applications:
- Polyester (PET) Heat Medium Furnaces: Primary application — the coil tube serves as the heat transfer element in indirect heating systems for polyester resin melting and extrusion processes, operating at sustained temperatures of 250–400°C with thermal medium (heat transfer oil or molten salt).
- Polymer Processing Systems: Heat transfer coils for nylon, polycarbonate, and other engineering polymer melt processing furnaces.
- Chemical Heat Exchangers: Continuous-length coil heat exchangers for chemical reaction vessels and distillation columns where weld-free construction is critical for pressure containment.
- Food and Pharmaceutical Processing: Sanitary-grade coil tubes for pasteurization, sterilization, and thermal processing systems where hygienic, crevice-free geometry is mandated.
- Power Generation: Coil-type economizers and superheaters in waste-heat recovery boilers and industrial steam generators.
- Textile Dyeing and Finishing: Heat transfer coils in continuous dyeing and finishing machines for polyester and polyamide fiber production.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring full traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System Certification
- ASTM A213 / ASME SA-213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel, Nickel Alloy, and Chromium-Nickel Alloy Boilers, Heat Exchangers, and Heat Transfer Equipment
- ASTM A403 — Standard Specification for Wrought Austenitic Chromium-Chromium-Nickel Alloy Steel Bars and Shapes
- EN 10216-5 — European Standard for Tubes for Heat Exchangers and Heat Transfer Equipment
- JIS G3459 — Japanese Industrial Standard for Stainless Steel Tubes for Heat Exchangers
- GB/T 14976 — Chinese National Standard for Cold-Rolled or Cold-Drawn Seamless Stainless Steel Tubes
- ASME B31.3 — Process Piping Design Code Compliance
- EN 13445 / PED 2014/68/EU — Pressure Equipment Directive Compliance (for pressure-containing applications)
Testing and Inspection Protocol
| Test Method | Standard | Purpose |
|---|---|---|
| Hydrostatic Pressure Test | ASTM A213 / ASME SA-213 | Verification of pressure integrity; minimum test pressure = 1.5× maximum working pressure |
| Spectroscopic Analysis (OES) | ASTM E415 | Chemical composition verification |
| Ultrasonic Testing (UT) | ASTM E213 / ASTM E127 | Detection of internal volumetric defects |
| Eddy Current Testing (ECT) | ASTM E309 | Detection of surface and near-surface longitudinal and transverse cracks |
| Magnetic Particle Inspection (MT) | ASTM E1444 | Detection of surface-breaking defects (for ferritic phases) |
| Tensile Testing | ASTM A370 / ASTM E8 | Verification of mechanical properties (Rm, Rp0.2, A5) |
| Charpy V-Notch Impact Test | ASTM E23 | Low-temperature toughness verification |
| Intergranular Corrosion Test | ASTM A262 (Practice E/A) | Verification of resistance to sensitization-induced IGSCC |
| Dimensional Inspection | ASTM A213 | OD, wall thickness, and straightness verification |
Unique Selling Points
- Failure-Informed Design: The coil tube design is directly informed by documented crack failure stress analysis of polyester heat medium furnace applications, incorporating validated mitigation strategies for thermal fatigue, creep, and SCC.
- Weld-Free Continuous Length: Supply in coil form eliminates field weld joints — the most common site of failure in heat exchanger tubing — dramatically improving system reliability and reducing maintenance intervals.
- Superior Thermal Fatigue Resistance: Titanium-stabilized (321) and high-alloy (310S) grades provide exceptional resistance to cyclic thermal loading inherent in start-stop furnace operations.