Stainless Steel Coil Tube for Ethylene Cracking Furnace Radiation Section
Product Code: 1502 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Classification: High-Temperature Process Tubing / Coil Tube
1. Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a specialized high-temperature process tube engineered for use in the radiation zone of ethylene cracking furnaces (ECF) within petrochemical and olefins production facilities. These coil tubes serve as the primary heat transfer elements through which hydrocarbon feedstocks are subjected to extreme thermal conditions (typically 800–1150 °C) to produce ethylene, propylene, and other valuable light olefins via thermal cracking reactions.
The design, fabrication, and selection of radiation coil tubes constitute one of the most critical engineering challenges in ethylene plant design. The tubes must simultaneously withstand:
- Extreme cyclic thermal loads with rapid temperature fluctuations (up to 50 °C/min during start-up and shutdown)
- Internal pressures of 0.1–0.3 MPa(g) at operating temperature
- Coking deposition on the inner wall surface requiring periodic decoking operations
- External radiant heat flux from furnace burners (up to 100–150 kW/m²)
- Thermal fatigue from repeated heating and cooling cycles (over 100,000 cycles in service life)
Wenzhou Jixing Metal Materials Co., Ltd. provides these coil tubes in pre-formed coil configurations, ready for installation into multi-tube configurations such as Multi-Tube Furnaces (MTF), Single-Tube Furnaces (STF), and Reformers, offering significant advantages in installation efficiency, flow uniformity, and thermal management.
2. Material Grades & Properties
2.1 Primary Material Grades
The coil tubes are fabricated from a range of austenitic stainless steel and specialty high-temperature alloys, selected based on the specific cracking severity, feedstock type, and furnace design parameters:
- SAE 310S / 310 (UNS S31008): General-purpose radiation coil tube material with excellent oxidation resistance up to 1150 °C and good thermal fatigue performance.
- SAE 309 / 309S (UNS S30908): Used where weldability and moderate creep strength are prioritized; suitable for less severe cracking conditions.
- SAE 316 / 316L (UNS S31608/S31603): Employed for lower-temperature sections or preheating zones requiring superior corrosion resistance.
- Incoloy 800H (UNS N08810): Premium selection for high-severity cracking service with superior thermal fatigue resistance and resistance to coking-induced degradation.
- Incoloy 625 (UNS N06625): Maximum-performance option for the most demanding cracking conditions, offering exceptional creep rupture strength and corrosion resistance.
- Haynes 230 (UNS N06230): Ultra-high-performance alloy for advanced furnace designs requiring operation above 1200 °C.
2.2 Key Mechanical & Physical Properties (Typical Values)
| Property | SAE 310S | Incoloy 800H | Incoloy 625 |
|---|---|---|---|
| Maximum Service Temperature (°C) | 1150 | 1200 | 1150 |
| Tensile Strength at 1100 °C (MPa) | ≈180 | ≈200 | ≈280 |
| Creep Rupture Strength at 1100 °C / 100,000 h (MPa) | ≈35 | ≈55 | ≈90 |
| Thermal Conductivity at 1000 °C (W/m·K) | ≈35 | ≈30 | ≈25 |
| Thermal Expansion Coefficient (20–1000 °C, ×10⁻⁶/K) | ≈19.5 | ≈18.5 | ≈13.5 |
| Density (g/cm³) | 8.0 | 8.87 | 8.44 |
| Oxidation Scale Growth at 1100 °C (μm/h) | ≈0.5 | ≈0.3 | ≈0.1 |
2.3 Chemical Composition Requirements
| Element | SAE 310S (%) | Incoloy 800H (%) | Incoloy 625 (%) |
|---|---|---|---|
| C (Carbon) | ≤0.08 | 0.05–0.10 | ≤0.10 |
| Cr (Chromium) | 24.0–26.0 | 19.0–21.0 | 20.5–23.0 |
| Ni (Nickel) | 19.0–22.0 | 30.0–35.0 | 58.0–65.0 |
| Mn (Manganese) | ≤2.00 | ≤1.00 | ≤0.35 |
| Si (Silicon) | ≤1.00 | ≤0.50 | ≤0.35 |
| Mo (Molybdenum) | — | — | 2.50–3.50 |
| Nb (Niobium) | — | — | 8.00–10.00 |
| N (Nitrogen) | — | — | 0.10–0.40 |
3. Specifications
3.1 Geometric & Dimensional Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 19.05 mm (3/4") to 168.28 mm (6-5/8") |
| Wall Thickness | 2.0 mm to 12.7 mm (standard); up to 19.0 mm for high-pressure applications |
| Coil Bending Radius | Minimum 3.0× OD (standard); down to 2.5× OD for specialty alloys |
| Coil Length (Uncoiled) | 60 m to 500 m per coil (configurable based on furnace design) |
| Tubes per Coil | 1 to 12 tubes per coil configuration (typical: 4, 6, or 8) |
| Tube Pitch (Center-to-Center) | 45 mm to 200 mm (standard spacing for radiant heat transfer optimization) |
| Dimensional Tolerance (OD) | ±0.10 mm (precision); ±0.25 mm (standard) |
| Dimensional Tolerance (Wall) | ±0.05 mm (precision); ±0.15 mm (standard) |
| Straightness Tolerance | ≤ 1.0 mm per 1000 mm |
| Coil Diameter (Packaged) | 1200 mm to 3000 mm (based on OD and wall thickness) |
| End Preparation | Plain ends, beveled ends (37.5°), or threaded ends per customer specification |
3.2 Applicable Standards
| Standard | Description |
|---|---|
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tubing for High Temperature Service |
| ASTM A312 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe for High Temperature Service |
| ASTM A790 | Standard Specification for Seamless Ferritic and Austenitic Chromium-Nickel-Iron Alloy Tubing for High Temperature Service |
| ASME B36.19M | Welded and Seamless Wrought Stainless Steel Pipe |
| ASME B31.3 | Process Piping (design and installation code) |
| EN 10216-5 | Non-alloy and Alloy Steel Tubes — Technical Delivery Conditions — Part 5: Austenitic Stainless Steel Tubes |
| GB/T 14976 | Chinese National Standard for Seamless Stainless Steel Tubes for Fluid Transport |
| GB/T 13296 | Chinese National Standard for Seamless Stainless Steel Tubes for Heat Exchangers and Heat Sinks |
| JIS G3459 | Japanese Industrial Standard for Stainless Steel Tubes for General Purposes |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Steel billets or slabs sourced from certified primary producers (e.g., Outokumpu, Sandvik, Nippon Steel, or domestic certified mills). Incoming material subjected to spectroscopic analysis (OES), tensile testing, and hardness verification.
- Hot Rolling / Seamless Tube Manufacturing: Tubes produced via either the hot cross-rolling (HCR) process (e.g., Mannesmann), plug piercing and rolling, or Autoclave seamless technology depending on diameter and wall thickness requirements.
- Precipitation Heat Treatment: For precipitation-strengthened alloys (Incoloy 800H, Incoloy 625), a controlled solution treatment followed by age-hardening heat treatment is performed to optimize precipitation phases (γ' and γ'' for Ni-based alloys) for maximum creep strength.
- Precision Sizing & Cold Drawing: Tubes undergo cold drawing or cold rolling to achieve precise dimensional tolerances (±0.05 mm wall thickness). This process also improves surface finish to Ra ≤ 0.4 μm, critical for minimizing coking initiation sites.
- Coil Forming / Bending: Pre-sized tubes are cold-bent into coil configurations using CNC-controlled tube bending machinery. The bending process employs a combination of mandrel support and rotary draw bending to ensure:
- Uniform wall thickness distribution (no thinning beyond 5%)
- Consistent bend radius across all tubes in the coil
- No wrinkling, cracking, or ovality exceeding 1.5% of OD
- Stress Relief / Annealing: Post-bending stress relief annealing at 1050–1150 °C (alloy-dependent) for 1–4 hours followed by controlled air cooling. This eliminates residual bending stresses and restores full mechanical properties.
- Surface Treatment & Passivation: Final surface cleaning via acid pickling and passivation to remove oxide scale and establish a protective chromium oxide film. Optional internal polishing for reduced coking tendency.
- Non-Destructive Testing (NDT): Comprehensive inspection including:
- Eddy Current Testing (ECT) for surface and near-surface defects
- Magnetic Particle Testing (MT) for ferromagnetic materials
- Ultrasonic Testing (UT) for internal voids and inclusions
- Helium or Pressurized Hydrostatic Testing for leak integrity
- Dimensional verification via laser scanning or coordinate measurement
- Packaging & Dispatch: Coils packaged on steel drums with protective end caps, moisture barriers, and corrosion inhibitors. Each coil tagged with a unique heat number, traceability certificate, and dimensional inspection report.