Detecting External High-Temperature Oxidation with the Cokebusters Smart Pig

During a scheduled maintenance turnaround, a major refinery engaged Cokebusters to carry out an in-line inspection of an 8-pass Vacuum Distillation Furnace, aiming to assess the condition of both the convection and radiant coils. The unit presented a challenge, featuring multiple nominal tube sizes (4″, 6″ and 8″) and complex geometry, including plugged headers (“mule ears”).

Thanks to our patented Intelligent Pigging system, Cokebusters delivered a complete geometric analysis across all eight passes helping the client detect a serious integrity threat they hadn’t anticipated.

Advanced Technology, Proven in the Field

We deployed the trusty Mark IV Smart Pig; a single-bodied, neutrally buoyant inspection tool that uses ultrasonic transducers to measure both wall thickness and internal radius. The device can navigate through concentric reducers and tight bends and its superior manoeuvrability enables it to carry out dual inspections in a single pass.

Despite the presence of plugged headers in the radiant coils, the Smart Pig successfully navigated all eight passes – something the client later acknowledged no other commercially available system had achieved.

Results: External Wall Loss in Radiant Tubes

The Smart Pig identified a consistent pattern of external wall loss in all 4″ radiant tube sections, with Pass G showing the most severe degradation. The damage was most concentrated in the central regions of each coil (Tubes 11 to 21).

Correlation between internal radius and wall thickness confirmed that the loss was predominantly external, which was an indication of External High-Temperature Oxidation (HTO).

Our mechanical decoking team noted these were also the areas with the heaviest internal coke contamination, reinforcing the hypothesis that elevated tube skin temperatures had played a key role.

The images below show a cross-sectional tube image taken from one of the affected areas. The data table below the image clearly identifies the extent and orientation of the wall loss at this particular axial location.

Identifying the Damage Mechanism

In consultation with the client’s Refinery Engineers, it was concluded that the damage likely stemmed from localised flame impingement, caused by burner misalignment. This misalignment led to localised overheating, accelerating coke build-up and further raising skin temperatures, creating ideal conditions for severe external oxidation.

Action Taken: A Data-Driven Maintenance Response

Following the Cokebusters report:

• Tubes identified as below the corrosion allowance were removed and replaced.

• All defect data was confirmed manually via UT by the client’s inspection team.

• Burner alignment was corrected to prevent recurrence.

• The client committed to regular mechanical decoking and intelligent pigging to avoid similar issues in the future.

Notably, the client praised Cokebusters’ Smart Pig as the only system capable of successfully inspecting tubes with this specific header configuration, reinforcing the value of our combined mechanical cleaning and inspection service.

Looking Ahead

As we expand our inspection services across the energy sector, Cokebusters remains committed to delivering high-quality data, proven technology, and real-world value whether it’s in a refinery heater, a fired heater or a pipeline system.