What Is a Cracking Tube (Radiant Coil)?

A cracking tube, also known as a radiant coil, is a centrifugally cast heat-resistant alloy pipe installed inside the radiant section of an ethylene pyrolysis furnace. Process feedstock and steam pass through this coil while the furnace fires around it, and the tube wall transfers extreme heat into the flowing gas so that hydrocarbon molecules break apart into ethylene, propylene, and other lower-weight olefins. In short, the cracking tube is the physical reactor wall where thermal cracking actually happens.

Where the Radiant Coil Sits in a Cracking Furnace

An ethylene cracking furnace is generally divided into two zones: the convection section, where feed and steam are preheated by flue gas, and the radiant section, where the cracking tube is suspended vertically and exposed directly to burner flames. The radiant coil is bent into a serpentine or U-shaped configuration and connected by return bends, allowing a long reaction path to fit inside a compact firebox. Outlet temperatures at the coil exit typically reach 1050 to 1150 degrees Celsius, while the tube skin itself can run even hotter, which is why material selection is the single most important design decision for this component.

Materials and Structural Features That Define a Cracking Tube

Because the coil operates at the edge of what metal can withstand, cracking tubes are manufactured from centrifugally cast nickel-chromium alloys rather than standard carbon steel. The casting process produces a fine, dense grain structure that resists creep deformation over years of continuous service.

• High thermal and mechanical strength to endure repeated thermal cycling without bulging or sagging.
• Corrosion and coking resistance from premium alloy compositions that limit carbon deposition and scale build-up on the inner wall.
• Optimized tube geometry that promotes even temperature distribution and reduces localized hot spots.
• Tight dimensional tolerances so the coil integrates cleanly with existing furnace headers and hangers.
• Custom sizing in length, outer diameter, and wall thickness to match a specific furnace duty and feedstock type.

Cracking Tube (Radiant Coil) vs Convection Coil

It is easy to confuse the radiant coil with the convection section tubing, but the two components serve very different roles inside the same furnace.

Tuopu Cracking Tube and Related Furnace Tube Series

Beyond the radiant coil itself, a complete cracking furnace relies on several matched tubular components, from reformer tubes to tube sheets, all manufactured to the same alloy and dimensional standards for a consistent thermal system.

Explore the Furnace Tube Product Range

A selection of related centrifugally cast furnace components engineered for petrochemical, refining, and DRI applications.

Tube Sheet Furnace Parts Reformer Tube Reformer Tube DRI Reformer Tube DRI Industry Ethylene Cracking Furnace Chemical Industry Hydrocracking Fired Heater Oil Refining Industry

Typical Applications of Cracking Tubes

Radiant coils are not limited to a single process; they are used wherever hydrocarbons must be broken down under controlled high-temperature conditions.

• Ethylene and propylene production furnaces in petrochemical plants.
• Hydrocarbon pyrolysis units processing naphtha, ethane, or LPG feedstock.
• Chemical processing plants that require durable, high-performance cracking components.
• Large petrochemical projects where precise temperature control extends component life and protects downstream equipment.

How to Choose the Right Cracking Tube for a Furnace

Selecting a suitable radiant coil starts with the feedstock and the furnace's designed run length between decoking cycles. Lighter feedstocks such as ethane generally allow longer run lengths and can tolerate a narrower tube bore, while heavier feedstocks like naphtha produce more coke and often call for larger diameters and alloys with stronger anti-coking surface treatment. Wall thickness must also account for stress rupture life at the maximum design temperature, since even a small increase in skin temperature can significantly shorten service life. Buyers should confirm centrifugal casting quality, chemical composition certificates, and dimensional inspection reports before installation.

Maintenance and Service Life Considerations

Cracking tubes degrade primarily through carburization, creep, and coke-related stress rather than sudden failure, so scheduled inspection is essential. Regular decoking, whether by steam-air burn or mechanical pigging, keeps the inner surface clear and prevents excess coke from insulating the tube wall and forcing higher firing rates. Periodic wall-thickness measurement and metallurgical sampling help operators plan tube replacement before an unplanned shutdown occurs, protecting both safety and production continuity.