Inspecting Beyond the Curve with IRIS

To employ ultrasonic testing through an internal rotary inspection system to assess the straight sections of vertical boiler tubes that include elbows.

Boiler tubes are subject to high temperatures and the potential presence of sulfur oxides under normal operations. Over time, these conditions can lead to the development of damage mechanisms such as inner erosion or outer corrosion, which can pose significant problems. While internal rotary inspection system inspection is known for providing accurate thickness measurements, the shape of boilers that feature vertical tubes with bent sections limits the use of this technique. This makes them impossible to scan using conventional IRIS probes. Furthermore, the accessibility to the boiler tubes may be restricted, limiting the inspection to the lower end only. This presents a set of interconnected challenges that need to be addressed: negotiating the bends to inspect the straight sections of the tube, providing local immersion of the steam turbine during inspections from the lower end of the vertical tubes, and ensuring proper turbine centering to avoid signal loss caused by a misaligned IRIS probe.

A flexible internal rotary inspection system probe capable of passing through elbows with a specified bend radius for two specific tube lines.

To achieve the goal of inspecting the straight parts of the boiler tubes, a significant challenge is encountered when the probe needs to pass through sharp elbows. Not only does the new solution need to travel through these elbows, but it also must provide better coverage at the bend vicinities. The image provided demonstrates that only a 50-millimeter (2-inch) section before the bend is unable to be inspected because the turbine and centering device are shorter than standard components.

In response to these challenges, we developed a flexible internal rotary inspection system solution that incorporates a centering device integrated with the turbine. This petal-shaped centering device offers the rigidity necessary to keep the turbine properly centered while providing the flexibility required to negotiate bends smoothly. In addition to this feature, the shortened transducer and turbine head prevent the tips of the turbine from rubbing against the tube’s inner surface, ensuring better centering closer to the bends. The versatility of the flexible IRIS probe kit is enhanced by interchangeable centering devices, allowing the inspection of different inner diameter tubes. This probe has been designed to pass through two tube lines featuring a 120-mm (4.7-in) bending radius with a 75-degree elbow. More specifically, this probe can operate in a 31.8-mm (1.3-in) outer diameter (OD) tube with an inside diameter (ID) ranging from 19.8 to 21.2 mm (0.78 to 0.83 in) and a 38.1-mm (1.5-in) OD tube with an ID ranging from 26.1 to 27.5 mm (1.03 to 1.08 in).

Similarly, two interchangeable foam-loaded holders are used to retain water as the vertical tubes are inspected from their lower end. Just like a standard IRIS probe, the turbine spins as water flows through it. Because of the holders, water collects and floods the tube at the turbine’s location. This simple yet efficient design quickly immerses the probe head and further aids in centering the probe accurately.