Stainless Steel Coil Tube for Conversion Furnace Convection Section

1. Product Overview

The stainless steel coil tube (Coiltube) is a specialized process piping component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., engineered specifically for use in the convection section of catalytic reforming conversion furnaces within petrochemical and refinery applications. This product is designed to handle mixed process gases at elevated temperatures and pressures while maintaining structural integrity over extended operational cycles.

Coil tubes differ fundamentally from conventional straight-tube designs in that they are formed into continuous helical or serpentine configurations, which offer superior heat transfer efficiency, reduced thermal stress concentrations, and enhanced mechanical flexibility. The coil tube module is a critical component in the convection section of a reforming furnace, where it absorbs radiant and convective heat from combustion flue gases to preheat and vaporize process feedstocks before they enter the radiant section and reformer tubes.

This product is developed and manufactured in accordance with rigorous international standards, ensuring compatibility with modern catalytic reforming units and steam cracking facilities. The coil tube module replacement construction technique—encompassing modular fabrication, on-site installation, and commissioning—represents a proven methodology for minimizing unplanned downtime during maintenance and turnaround activities.

2. Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steels selected for their exceptional resistance to high-temperature oxidation, sulfidation, and thermal cycling fatigue. The following materials are available depending on service conditions:

Key Mechanical Properties (TP310S at 20°C / 68°F):

Chemical Composition (TP310S):

3. Specifications

Parameter Specification
Product Name Stainless Steel Coil Tube (Coiltube) Module
Product Code / Serial No. 775
Material Grade ASTM A312 TP310 / TP310S / TP304 / TP304L / TP321 / TP347
Tube Outer Diameter (OD) 50.8 mm (2.00 in) to 114.3 mm (4.50 in)
Wall Thickness 3.0 mm to 6.4 mm (0.118 in to 0.252 in)
Coil Pitch 150 mm to 400 mm (6.0 in to 15.8 in)
Coil Mean Diameter 300 mm to 1500 mm (11.8 in to 59.1 in)
Module Length Customized per project requirements (typically 3.0 m to 12.0 m)
Maximum Operating Temperature Up to 1150°C (2100°F) for TP310S
Maximum Operating Pressure Up to 10.0 MPa (1450 psi)
Heat Treatment Solution Annealing (1050–1150°C, water or air quench)
Surface Finish Pickled and Passivated (P&P), Ra ≤ 0.8 μm
Welding Process GTAW (Gas Tungsten Arc Welding) / Orbital Welding
Applicable Standards ASTM A312, ASME B31.3, API 579, GB/T 14976
Manufacturing Standard EN 10217-7, JIS G3459
Heat Exchanger Standard TEMA R, ASME BPV Section VIII Div. 1

4. Manufacturing Process

The coil tube module is produced through a rigorously controlled multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:

  1. Raw Material Inspection: Incoming stainless steel tubes undergo 100% chemical composition analysis (spectrometry), mechanical property testing, and hydrostatic pressure testing in accordance with ASTM A312 requirements. Each heat lot is traceable through mill test certificates (MTCs).
  2. Cold Bending / Coiling: Tubes are cold-formed into helical coil configurations using precision hydraulic bending machines. The bending process is carefully controlled to prevent wall thinning, ovality distortion, or work-hardening beyond acceptable limits. Bending radius is maintained at a minimum of 4× the tube outer diameter to avoid plastic deformation.
  3. Module Assembly: Individual coil sections are fabricated into complete modules with inlet/outlet headers, support brackets, and expansion loops. All welds are performed using GTAW (Gas Tungsten Arc Welding) with helium back-purging to prevent internal oxidation.
  4. Welding Procedure Qualification (WPQ/PQR): All welding procedures are qualified per ASME Section IX, with qualified welders holding valid certifications. Weld parameters—including current, voltage, travel speed, and gas flow rates—are documented and monitored throughout production.
  5. Non-Destructive Testing (NDT): Welds are subjected to 100% visual inspection (VT), dye penetrant testing (PT), and radiographic testing (RT) or ultrasonic testing (UT) as required by project specifications. Acceptance criteria follow ASME B31.3 and API 579 guidelines.
  6. Heat Treatment: Post-weld heat treatment (PWHT) or solution annealing is performed at 1050–1150°C followed by rapid quenching to restore full austenitic microstructure, eliminate residual stresses, and ensure uniform corrosion resistance.
  7. Pickling and Passivation: The finished module undergoes acid pickling (nitric-hydrofluoric acid mixture) and passivation to remove mill scale, heat tint, and weld contaminants, establishing a protective chromium oxide passive film.
  8. Pressure Testing: Each completed module undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure, with a minimum hold time of 30 minutes. Leak testing is also performed as required.
  9. Final Inspection and Documentation: Comprehensive dimensional verification, surface finish measurement, and final NDT are conducted. A complete quality dossier—including MTCs, WPQ/PQR documents, NDT reports, pressure test records, and dimensional drawings—is compiled and delivered with each shipment.

5. Applications

The stainless steel coil tube module is specifically designed for the following industrial applications:

The modular design of the coil tube facilitates rapid replacement during planned turnarounds, significantly reducing maintenance downtime. The overall module replacement construction technique enables pre-fabricated coil assemblies to be installed as complete units, minimizing on-site welding and alignment work.

6. Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following standards:

Unique Selling Points:

  • Full traceability from raw material heat lot through final delivery, supported by comprehensive digital documentation.
  • Modular coil tube design enabling rapid installation and minimal on-site fabrication during turnaround activities.
  • Capability to supply custom-engineered coil configurations tailored to specific furnace convection section layouts and process requirements.
  • Extensive experience in catalytic reforming furnace coil tube modules, with proven performance in multiple refinery projects.
  • Integrated manufacturing capability encompassing tube procurement, coil forming, welding, heat treatment, NDT, and final assembly under a single quality management system.
  • Competent engineering team with expertise in high-temperature alloy metallurgy, thermal fatigue analysis, and furnace convection section design.

7. Ordering Information

Customers are advised to provide the following information when placing an inquiry or order:

Wenzhou Jixing Metal Materials Co., Ltd. is committed to delivering high-quality stainless steel coil tube modules that meet the most demanding performance requirements of the petrochemical and refining industries.