Diametric Growth in Heater Coils: What It Tells You And How to Catch It Before It’s Too Late

When it comes to asset integrity in the energy sector, undetected tube deformation can lead to significant operational safety risks and costly unplanned downtime. At Cokebusters our mission is to ensure those risks are identified early and managed effectively – especially when the damage isn’t visible from the outside.

One such example involved a recent inspection carried out by Cokebusters USA at a facility in Texas, where our team was called in during a scheduled turnaround to assess a Reactor Charge Heater. What we found demonstrated not only the dangers of diametric growth in process coils but also the power of our inspection technology in detecting it.

The Hidden Threat of Diametric Growth

We used our patented Cokebusters Mark IV Smart Pig to perform an In-Line Inspection (ILI) and identified significant diametric abnormalities in the radiant coils of three out of four passes.

Most notably, in Pass 2, Tube 7, we measured a diametric growth of up to 4.7%. Unlike localised bulging or ovality, this deformation was uniform and circumferential; a strong indicator of short-term overheating rather than long-term creep damage.

These findings were visualised in our proprietary 3D C-scan data – a key advantage over traditional NDT methods – and confirmed through post-processing and graphical plotting. Without this level of diagnostic detail, the damage may well have gone unnoticed.

Understanding the Cause

Our Smart Pig doesn’t just flag defects, it helps us trace the root cause.

Following data analysis, a full Level III Fitness for Service (FFS) assessment was conducted in line with API 579-1/ASME FFS-1 standards.  Microstructural analysis and micro-hardness testing pointed to a heat-induced transformation in the tubing material: the presence of ferrite and martensite, coupled with plastic deformation and strain hardening, confirmed the tubes had been overexposed to temperatures above 750°C – likely during an operational shutdown.

Importantly, there was no evidence of long-term creep damage, thanks to historical operating data and proper burner alignment. The swelling was a result of short-term thermal stress, not chronic degradation.

Smart Pigging as a Proactive Integrity Strategy

Once the damaged tubes were removed, with locations and defect quantification confirmed by the client, the value of Smart Pig inspection became clear. The client acknowledged that conventional non-destructive testing (NDT) would not have detected this type of damage.

As a result, the facility has now adopted annual mechanical cleaning and tube inspection as part of their regular turnaround strategy.  This was a powerful step toward improving the reliability and safety of their heater assets.

Why Cokebusters?

Our patented Smart Pig technology offers:

• Precise, full-length coil inspection

• Detailed geometric assessment of internal tube condition

• Customisable 3D reporting for actionable insights

• Consultative post-inspection support, ensuring clients understand the implications of our findings and the best course of action

Whether it’s diametric growth, wall thinning or ovality, our inspections provide more than just data – they provide confidence in your assets.  Our trained inspection technicians can work alongside on site engineers to analyse results and share information.

Get Ahead of Hidden Damage

If you’re relying solely on conventional NDT to assess your fired heater tubes, you might not be seeing the full picture. Contact Cokebusters today to learn how our inspection solutions can help you uncover critical damage before it compromises your operation.