Stainless Steel Coiled Tube (Coiltube) — Ethylene Cracker Radiant Coil Tube

1. Product Overview

The Stainless Steel Coiled Tube (Coiltube), catalog reference No. 1502, is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use as a radiant coil tube within ethylene cracking furnaces (Ethylene Cracker Radiant Coil), where it serves as the primary heat transfer medium in the pyrolysis of hydrocarbons. The coiled configuration maximizes surface area within a compact furnace radiant section, enabling efficient thermal energy transfer at extreme operating temperatures.

Coiled tubes differ fundamentally from straight pipe assemblies in that they are cold-formed into a continuous helical geometry, eliminating the need for weld joints in the tube body. This seamless coiling process provides superior resistance to thermal fatigue, creep, and hot corrosion — critical advantages in the demanding environment of ethylene cracker furnaces operating at temperatures exceeding 800°C (1,472°F) with continuous thermal cycling.

Industry Context: The design of ethylene cracker radiant coil tubes is governed by stringent engineering considerations including heat flux distribution, metallurgical stability at elevated temperatures, mechanical integrity under cyclic loading, and long-term resistance to sulfur- and carbon-based corrosion. This product represents the culmination of advanced metallurgical science and precision manufacturing technology.

2. Material & Properties

2.1 Material Grades

The coiled tube is available in a range of high-temperature austenitic stainless steel and alloy grades, selected based on service conditions:

2.2 Mechanical Properties (Typical — Grade 310S, Solution Treated)

Property Unit Value (at 20°C / 68°F) Value (at 800°C / 1,472°F)
Tensile Strength (UTS) MPa ≥ 520 ≥ 140
Yield Strength (0.2% offset) MPa ≥ 205 ≥ 55
Elongation (50 mm gauge) % ≥ 30 —
Creep Strength (100 hr, 800°C) MPa — ≥ 100
Density g/cm³ 7.93 —
Thermal Conductivity (at 800°C) W/(m·K) — 25.0
Linear Thermal Expansion (20–800°C) μm/(m·K) — 18.5

2.3 Chemical Composition (Typical — Grade 310S, wt%)

Element C Mn Si P S Cr Ni N
Specification ≤ 0.08 ≤ 2.0 ≤ 1.5 ≤ 0.035 ≤ 0.030 24.0–26.0 19.0–22.0 ≤ 0.10

3. Specifications

3.1 Geometric Dimensions

Parameter Range / Value Notes
Outer Diameter (OD) 19.0 mm – 159.0 mm (3/4" – 6") Custom diameters available upon request
Wall Thickness (WT) 1.5 mm – 10.0 mm (5/80" – 13/32") Selected per thermal duty and pressure rating
Coil Diameter (Mean) 150 mm – 2,000 mm (6" – 80") Dependent on furnace geometry
Coil Length (per bundle) 50 m – 500 m (164 ft – 1,640 ft) Continuous helical configuration
End Preparation Plain end, beveled (37°/30°), or flanged Per ASME B16.25 or customer drawing
Surface Finish Mill finish, pickled & passivated (Ra ≤ 1.6 μm) Internal passivation for fluid handling
Dimensional Tolerance ± 0.15 mm (OD), ± 0.10 mm (WT) Per ASTM A213 / EN 10216-5

3.2 Performance Parameters

Parameter Specification
Maximum Operating Temperature 1,150°C (2,094°F) continuous
Design Pressure Up to 15 MPa (2,175 psi)
Thermal Cycling Endurance ≥ 10,000 cycles (ΔT = 400°C)
Design Service Life 15–25 years (continuous duty)
Heat Flux Tolerance Up to 600 kW/m² (radiant section)

3.3 Applicable Standards

4. Manufacturing Process

4.1 Process Flow

  1. Raw Material Selection & Inspection: Vessel steel or ingot-grade stainless steel billets are sourced from certified suppliers. Each heat is subjected to spectrographic analysis (OES), sulfur and phosphorus determinations, and mechanical property verification prior to acceptance.
  2. Hot Rolling & Seamless Tube Formation: Billets are heated to forging temperature (1,150–1,250°C) and processed through a piercer mill to form seamless tubes. Alternatively, the Autoclave Annealed (AA) or Mannesmann process may be employed depending on diameter and wall thickness requirements.
  3. Cold Drawing / Cold Rolling: Hot-rolled tubes are further reduced through multi-pass cold drawing or cold rolling to achieve precise dimensional tolerances, improved mechanical properties, and enhanced surface finish. For thicker-wall tubes, hot sizing alone may suffice.
  4. Solution Annealing: Tubes are heated to 1,050–1,150°C and rapidly quenched (air or water) to achieve a fully austenitic microstructure, dissolve carbides, and maximize corrosion resistance and ductility.
  5. Coiling (Cold Forming): The straight tube is fed through a precision coiling machine equipped with forming rolls and a mandrel system. The tube is progressively bent into the target helical geometry at controlled strain rates to avoid work hardening, ovality, or thinning. This is the critical differentiating step from straight pipe products.
  6. Post-Coil Stress Relief (Optional): For applications requiring minimal residual stress, the coiled tube may be subjected to a controlled heat treatment cycle (900–1,000°C, 1–2 hours, furnace cool) to relieve forming-induced residual stresses.
  7. Pickling & Passivation: The coiled tube is immersed in a mixed acid solution (HNO₃ + HF or HNO₃ + HCl) to remove surface scale and contamination, followed by passivation to establish a protective chromium oxide film.
  8. Final Inspection & Testing: Comprehensive dimensional, visual, and non-destructive testing (NDT) is performed. This includes hydrostatic pressure testing (typically 2× design pressure, held for minimum 30 seconds), eddy current testing for internal/external surface defects, and dimensional verification of coil geometry.
  9. Packaging & Dispatch: Tubes are protected with end caps, wrapped in moisture-barrier material, and packaged for transport with appropriate handling documentation.

4.2 Quality Control Milestones

5. Applications

5.1 Primary Application: Ethylene Cracker Furnaces

The primary application domain for this coiled tube product is as a radiant coil tube (Radiant Section Coil) in ethylene cracking furnaces. In these units, hydrocarbon feedstocks (naphtha, ethane, propane, or mixed C₃/C₄ streams) are subjected to severe pyrolysis conditions — typically 800–900°C at pressures of 0.1–0.4 MPa — to produce ethylene, propylene, and other olefins. The coiled tube functions as the reaction vessel through which the feedstock flows, absorbing radiant heat from furnace burners.

5.2 Detailed Application Scenarios

5.3 Operating Environment Characteristics

Parameter Typical Range Engineering Challenge
Tube Wall Temperature 800 – 1,050°C Oxidation, creep, carburization
Internal Gas Temperature 750 – 900°C Carbide precipitation, grain growth
Operating Pressure 0.1 – 0.4 MPa (gauge) Creep rupture, thermal fatigue
Thermal Cycling Startup/shutdown cycles; 2–4 times per year Low-cycle fatigue, thermal shock
Internal Corrosion Carbon deposition (coking), sulfur compounds Wall thinning, stress corrosion cracking
External Corrosion Oxidation, ash deposition Scale spalling, heat transfer degradation

6. Quality Certifications

6.1 Manufacturer Certifications

6.2 Product Testing & Certification