Stainless Steel Coil Tube for Organic Heat Carrier Boilers (Coiltube)

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component designed specifically for use in Organic Heat Carrier Boilers (also referred to as Synthetic Fluid Boilers or Thermal Oil Heaters). These coil tubes serve as the primary heat exchange elements within the boiler system, facilitating the transfer of thermal energy from the combustion zone to the organic heat transfer fluid (typically synthetic hydrocarbon-based thermal oils such as LQ series or YD series fluids). The coil geometry maximizes the surface area-to-volume ratio, enabling efficient convective and radiative heat transfer within compact boiler configurations.

Wenzhou Jixing Metal Materials Co., Ltd. manufactures coil tubes that meet the demanding requirements of high-temperature, continuous-duty thermal fluid systems, where operating temperatures may reach 350°C (662°F) or higher. The integrity and reliability of these coil tubes are critical, as any leakage can result in catastrophic system failure, fluid loss, and potential safety hazards. Extensive failure analysis research on organic heat carrier boiler coil tubes has informed the design optimization and quality control processes employed in the manufacturing of these products.

Material & Properties

Coil tubes for organic heat carrier boiler applications are manufactured from austenitic stainless steel grades selected for their superior resistance to oxidation, thermal fatigue, and mechanical degradation under prolonged high-temperature exposure. The primary material grades include:

• SAE 304 / AISI 304 (UNS S30408) — Chromium-Nickel austenitic stainless steel with excellent general corrosion resistance and moderate high-temperature strength. Suitable for operating temperatures up to 320°C (608°F).
• SAE 316 / AISI 316 (UNS S31608) — Molybdenum-enhanced austenitic stainless steel offering superior resistance to pitting and crevice corrosion. Recommended for applications involving trace moisture or aggressive chemical environments within the heat transfer system.
• SAE 321 / AISI 321 (UNS S32108) — Titanium-stabilized austenitic stainless steel providing enhanced resistance to intergranular corrosion and thermal cracking at elevated temperatures. Preferred for sustained operation above 300°C (572°F).
• SAE 310S / AISI 310S (UNS S31008) — High-chromium, high-nickel austenitic stainless steel with outstanding oxidation resistance and thermal stability. Suitable for the highest temperature applications in organic heat carrier systems, up to 350°C (662°F) continuous service.

Key Mechanical Properties (at Room Temperature, Annealed Condition):

• Tensile Strength (UTS): 515–720 MPa (75,000–104,000 psi), depending on grade and wall thickness
• Yield Strength (0.2% offset): 205–310 MPa (29,700–45,000 psi)
• Elongation: 40–55% minimum in 50 mm (2 in) gauge length
• Hardness: ≤ 210 HB (Brinell) in annealed condition

High-Temperature Performance: The selected stainless steel grades maintain creep resistance and oxidation resistance at operating temperatures consistent with organic heat carrier boiler design parameters. At 350°C (662°F), SAE 310S retains approximately 85% of its room-temperature tensile strength, making it the optimal choice for high-temperature zones of the boiler.

Specifications

Parameter	Specification	Standard Reference
Outer Diameter (OD)	Φ32 mm – Φ114 mm (1.26 in – 4.50 in)	ASTM A213 / GB/T 14976
Wall Thickness	1.5 mm – 4.0 mm (0.059 in – 0.157 in)	ASTM A213 / GB/T 14976
Coil Diameter	500 mm – 2000 mm (19.7 in – 78.7 in)	Customer-specific / Project drawing
Coil Length (Straightened Equivalent)	Up to 500 m (1,640 ft) per coil	—
Dimensional Tolerance (OD)	±0.05D or ±0.15 mm, whichever is less	ASTM A213 / ASME B36.19M
Dimensional Tolerance (Wall)	±10% of nominal wall thickness	ASTM A213
Coiling Tolerance (Diameter)	±3% of nominal coil diameter	Manufacturer specification
Surface Finish	Pickled and passivated; Ra ≤ 1.6 μm (63 μin)	ASTM A380
Operating Temperature Range	−40°C to +350°C (−40°F to +662°F)	Manufacturer specification
Design Pressure	Up to 1.6 MPa (232 psi) working pressure	ASME Section IV / GB/T 17410
Heat Transfer Fluid Compatibility	LQ Series, YD Series, Therminol VP-1, Dowtherm A	Manufacturer specification
End Preparation	Plain end, beveled end (37° ± 2°), or threaded (NPT/BSP)	ASME B1.20.1 / ASME B36.19M
Welding Process (if applicable)	Orbital TIG (GTAW) or Pulse TIG welding	ASME Section IX / EN ISO 15614

Manufacturing Process

The production of stainless steel coil tubes for organic heat carrier boiler applications involves a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:

1. Raw Material Selection and Inspection: Cold-rolled stainless steel strip or seamless tube stock is sourced from certified mills with full chemical composition verification (per ASTM A240 or ASTM A213) and mechanical property testing. Incoming material undergoes 100% visual inspection, dimensional verification, and sampling for spectroscopic analysis to confirm grade compliance.
2. Tube Forming: Seamless tubes are cut to required lengths and prepared for coiling operations. Alternatively, cold-rolled strip may be roll-formed into tubular geometry with longitudinal seam welding (Orbital TIG) for certain configurations. The forming process is controlled to prevent excessive work hardening and to maintain uniform wall thickness throughout the coil.
3. Coiling Operation: Tubes are coiled using precision-controlled coiling machinery that maintains consistent coil diameter, pitch, and alignment. The coiling process is performed at controlled temperatures to prevent cold work cracking and to maintain the annealed temper of the material. Multi-layer coil configurations are managed with inter-layer protective spacers to prevent tube-to-tube contact damage.
4. Heat Treatment (Solution Annealing): Where applicable, coiled tubes undergo solution annealing at 1040–1120°C (1904–2048°F) followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses, and ensure maximum corrosion resistance and ductility.
5. Pickling and Passivation: Surface oxide scale formed during heat treatment is removed through acid pickling (typically using a nitric-hydrofluoric acid mixture or proprietary non-toxic pickling paste). Subsequent passivation with a dilute nitric acid or citric acid solution establishes a stable chromium oxide protective film on the tube surface.
6. Quality Inspection and Testing:
   • Visual Inspection: 100% inspection of tube surfaces for defects, dents, or surface irregularities.
   • Dimensional Verification: Measurement of OD, wall thickness, coil diameter, and pitch at defined intervals.
   • Hydrostatic Pressure Testing: Each coil tube assembly is pressure-tested to 1.5× the maximum design pressure (typically 2.4 MPa / 348 psi) for a minimum hold time of 30 seconds to verify watertight integrity.
   • Non-Destructive Testing (NDT): Eddy current testing (per ASTM E309) and/or ultrasonic testing (per ASTM E747) performed on weld seams and tube walls to detect subsurface defects.
   • Chemical Composition Verification: Spectroscopic analysis (OES or XRF) to confirm alloy grade compliance.
7. Packaging and Shipping: Coiled tubes are wrapped in protective plastic film, secured with steel banding, and packed in wooden crates or on pallets for transport. Documentation including mill certificates, test reports, and material traceability records accompanies each shipment.

Applications

Stainless steel coil tubes manufactured by Wenzhou Jixing Metal Materials Co., Ltd. are integral components in a wide range of industrial thermal systems and process applications:

• Organic Heat Carrier (Thermal Oil) Boilers: Primary application — coil tubes serve as heating elements in both liquid-phase and vapor-phase organic heat carrier boilers used for indirect heating processes where precise temperature control is required.
• Chemical Processing Industry: Used in reactors, distillation columns, and heat exchangers requiring corrosion-resistant heating elements for processes involving acids, solvents, and reactive chemicals.
• Food and Pharmaceutical Industry: Employed in cooking, drying, pasteurization, and sterilization equipment where product contact surfaces must meet sanitary standards (FDA-compliant 316L grade available upon request).
• Petrochemical and Refining: Applied in heat trace systems, feed preheating coils, and process heating loops operating at elevated temperatures.
• Textile and Dyeing Industry: Used in dyeing vats, finishing machines, and drying systems requiring uniform, high-temperature heat distribution.
• Wood and Paper Industry: Applied in pressurized drying kilns, paper drying cylinders, and board pressing systems utilizing thermal oil as the heat transfer medium.
• Plastics and Rubber Processing: Heating elements for injection molding machines, extruders, and press systems requiring precise temperature regulation.
• Heat Trace Systems: Coil tubes integrated into pipe tracing systems for maintaining fluid temperatures in pipelines in cold environments.

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and ensures all coil tube products comply with internationally recognized standards and certifications:

• ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
• ISO 14001:2015 — Environmental Management System certification.
• ASME Section IV — Compliance with Boiler and Pressure Vessel Code requirements for organic heat carrier boiler components.
• ASTM A213 — Standard specification for seamless austenitic stainless steel boiler, heat exchanger, and heater tubes.
• ASTM A269 — Standard specification for seamless and welded austenitic stainless steel tubing (general purpose).
• GB/T 14976 — Chinese national standard for seamless stainless steel tubes for fluid transport.
• GB/T 17410 — Chinese national standard for organic heat carrier boilers (design, manufacture, and inspection).
• EN 10216-5 — European standard for seamless heat exchanger tubes of austenitic and austenitic-ferritic stainless steels.
• CE Marking — Conformity with European Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components.
• Mill Test Certificates (MTC) — EN 10204 Type 3.1 certificates provided with each shipment, including chemical analysis, mechanical properties, and heat treatment records.

Unique Selling Points

• Failure-Informed Design: Product specifications and quality control protocols are informed by extensive research on organic heat carrier boiler coil tube leakage failure modes, including thermal fatigue cracking, oxidation-induced wall thinning, and stress corrosion cracking, ensuring enhanced service life and reliability.
• Full Traceability: Every coil tube is traceable to its mill heat number, with complete documentation of chemical composition, mechanical properties, and manufacturing process parameters.
• Custom Coiling Geometry: Capability to produce custom coil diameters, multi-layer configurations, and special end preparations to meet specific boiler design requirements.
• Multi-Grade Availability: Full range of austenitic stainless steel grades (304, 316, 321, 310S, and 316L) available to match specific temperature and corrosion resistance requirements.
• Rigorous Testing Protocol: 100% hydrostatic testing and non-destructive examination ensure zero-defect delivery for safety-critical boiler applications.
• Technical Support: Engineering team provides application-specific material selection guidance, coil layout optimization, and failure analysis consulting for existing installations.

Note: This product description is based on the knowledge framework from the study of "Research on Leakage Failure Analysis of Coil Tubes in Organic Heat Carrier Boilers" (《有机热载体锅炉盘管泄漏失效分析研究》