Stainless Steel Coil Tube for Cracking Furnace Convective Section

Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for deployment in the convective section of ethylene cracking furnaces and similar high-temperature petrochemical processing equipment. This coil tube is supplied in coiled form to facilitate efficient installation in serpentine tube configurations, where it serves as the primary heat exchange surface for transferring thermal energy from furnace flue gases to process fluids.

Coil tubes in cracking furnace convective sections are subject to a unique and demanding service environment characterized by cyclic temperature variations, exposure to corrosive combustion byproducts, and the critical threat of dew point corrosion (Dew Point Corrosion) when flue gas temperatures drop below the acid dew point. This product is engineered to mitigate these degradation mechanisms while maintaining structural integrity and dimensional accuracy over extended operational cycles.

Material & Properties

Material Grades

Key Mechanical Properties

Corrosion Resistance Characteristics

Specifications

Parameter Specification Standard/Reference
Outer Diameter (OD) 19.05 mm – 114.3 mm (3/4" – 4") ASTM A269 / ASME SA-213
Wall Thickness (壁厚) 1.5 mm – 6.35 mm (0.059" – 0.250") ASTM A213
Coil Length (盘管长度) Custom, typically 20 m – 100 m per coil Per project specification
Coil Inner Diameter (盘管内径) ≥ 1.5 × OD (minimum bend radius compliance) ASME B31.3
Surface Finish (表面状态) Pickled and Passivated (酸洗钝化); Ra ≤ 0.4 μm ASTM A380
Manufacturing Method (制造方法) Hot-Finished, Cold-Drawn, or Cold-Rolled (热轧、冷拔或冷轧) ASTM A269 / A213
Temperature Range (使用温度范围) −196°C to +1150°C (continuous service) Per grade-specific limits
Pressure Rating (压力等级) Up to 40 MPa (design, depending on wall thickness and temperature) ASME B31.3
Tolerance on OD (外径公差) ±0.03 mm (for OD ≤ 50.8 mm); ±0.05 mm (for OD > 50.8 mm) ASTM A269
Tolerance on Wall Thickness (壁厚公差) ±10% of nominal (cold-drawn); ±12.5% (hot-finished) ASTM A213
Delivery Condition (交货状态) Coiled (盘卷); Annealed and Pickled (固溶退火+酸洗) —
Applicable Standards (适用标准) ASTM A269, ASTM A213, ASME SA-213, EN 10216-5, GB/T 12771 —

Manufacturing Process

The production of high-quality stainless steel coil tubes for cracking furnace applications follows a rigorous multi-stage manufacturing workflow to ensure dimensional precision, metallurgical homogeneity, and superior surface integrity:

  1. Steel Billet Preparation (钢坯准备): Virgin or certified recycled stainless steel billets are produced via vacuum induction melting (Vacuum Induction Melting, VIM) or arc furnace (Arc Furnace) with Argon Oxygen Decarburization (AOD) refining to achieve ultra-low sulfur and carbon specifications.
  2. Hot Rolling (热轧): Billets are reheated to 1150–1250°C and hot-rolled into seamless tube blanks with controlled cooling rates to ensure uniform austenitic grain structure.
  3. Solution Annealing (固溶处理): Tubes are reheated to 1050–1150°C and rapidly quenched (water or air) to dissolve carbide precipitates and restore full corrosion resistance and ductility.
  4. Cold Drawing / Cold Rolling (冷拔/冷轧): For tight tolerance requirements, tubes undergo cold working to achieve precise OD and wall thickness specifications, followed by intermediate annealing to prevent work hardening.
  5. Coiling (盘卷成型): Tubes are precisely coiled using CNC-controlled coiling equipment to achieve uniform bend radii without ovality, kinking, or surface deformation. The minimum coil diameter is calculated based on the tube's material properties and desired service life to prevent fatigue initiation at bend regions.
  6. Pickling and Passivation (酸洗钝化): Tubes are immersed in a mixed acid bath (nitric acid + hydrofluoric acid, 硝酸+氢氟酸) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide passive film on the surface.
  7. Final Inspection (最终检验): Comprehensive non-destructive testing (Non-Destructive Testing, NDT) including eddy current (Eddy Current Testing, ECT), ultrasonic testing (Ultrasonic Testing, UT), and visual inspection ensures compliance with all dimensional and metallurgical requirements.

Applications

Primary Application: Ethylene Cracking Furnace Convective Section

The primary design application for this coil tube is the convective section of ethylene cracking furnaces (Ethylene Cracking Furnace, ECF) in petrochemical and olefins production facilities. In this service, the coil tube absorbs waste heat from high-temperature flue gases exiting the radiant section, preheating process streams such as feedwater, quench oil, and process gas.

Corrosion Environment Considerations

The convective section of a cracking furnace operates under conditions that promote acid dew point corrosion, a critical failure mechanism. When sulfur-containing feedstocks (e.g., naphtha, ethane) are combusted, the flue gas contains sulfur dioxide (SO₂) and sulfur trioxide (SO₃). At tube wall temperatures below the acid dew point (typically 120–180°C depending on SO₃ concentration), these species condense as dilute sulfuric acid (H₂SO₄), causing aggressive corrosion of unprotected or inadequately protected tube surfaces.

Key application scenarios include:

Additional Applications

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications to ensure the reliability and traceability of every coil tube produced:

Testing and Verification Protocols

Unique Selling Points

1. Anti-Dew Point Corrosion Engineering (防露点腐蚀工程设计)

This coil tube is specifically engineered with material selection and surface treatment strategies to address the acid dew point corrosion challenge inherent to cracking furnace convective sections. The selection of low-carbon (L-grade) austenitic stainless steels with optimized molybdenum content provides enhanced resistance to sulfuric acid attack at temperatures below the acid dew point. The pickled and passivated surface finish establishes a robust chromium oxide passive film that acts as a first line of defense against corrosive condensate.

2. Precision Coiling for Fatigue Resistance (精确盘卷抗疲劳设计)

Advanced CNC-controlled coiling technology ensures uniform bend radii with controlled ovality (≤ 1.5% of OD), minimizing stress concentration at coil bends. This reduces the risk of fatigue cracking at curved sections during thermal cycling, significantly extending service life compared to conventionally coiled products.

3. Full Traceability and Documentation (全追溯性与文件完整性)

Each coil tube is accompanied by comprehensive documentation including heat number traceability to the original steelmaking process, mill test certificates (Mill Test Certificate, MTC), and all non-destructive examination reports, ensuring full compliance with international quality standards and facilitating engineering verification.

4. Customization Capability (定制化能力)

Wenzhou Jixing Metal Materials Co., Ltd. offers fully customized solutions including:

5. Cost-Effective Lifetime Solution (全生命周期成本效益方案)

While the initial material cost of premium stainless steel coil tubes may exceed carbon steel alternatives, the significantly extended service life—typically 3 to 5 times longer in dew point corrosion-prone environments—results in superior total cost of ownership (Total Cost of Ownership, TCO). Reduced unplanned shutdowns, lower maintenance frequency, and elimination of costly tube replacement campaigns provide substantial economic advantages over the asset lifetime.

Dew Point Corrosion Protection Recommendations

For optimal performance in