In addition to ECA and PAUT, another critical technology in Eddyfi Technologies’ portfolio is Pulsed Eddy Current (PEC). PEC is designed to evaluate wall thickness and detect corrosion through protective insulation, without the need for extensive stripping of insulation or weatherproofing. This capability is invaluable in industries where accessing components for inspection can be prohibitively expensive. PEC's adaptability and efficiency have made it a go-to solution for many refineries and chemical plants worldwide, where in-service inspections and productivity are critical.
PEC technology is also gaining traction in the nuclear and power generation sectors, offering significant cost savings by eliminating the need for extensive insulation/coating removal during inspections. Its widespread adoption is reflected in its inclusion in key industry standards like ISO 20669, API RP 583, and ASME Section V, Article 21, which was published in July 2021 and serves as a guide for inspection procedures in power generation environments.
This blog outlines the real-world applications of Eddyfi Technologies’ Lyft® system, a PEC-based solution that has been successfully field-tested in various power generation settings. Through case studies and customer feedback, we demonstrate how this innovative technology meets the unique challenges faced by asset owners, ultimately reducing costs and enhancing the efficiency of NDT inspections in the industry.
Corrosion in Pressure Vessels: A Serious Challenge
Pressure vessels are critical components in many industries, designed to contain liquids and gases under high pressure. Their construction involves thick walls, typically between 12.70 and 38.10 millimeters (0.5 to 1.5 inches), providing the strength needed to handle intense pressure and temperature fluctuations. These vessels must adhere to strict safety standards, such as the ASME Boiler and Pressure Vessel Code (Section VIII), ensuring their reliability and safety in operation.
Given their high-pressure applications, pressure vessels often operate at elevated temperatures. To maintain safe working conditions and prevent heat loss, they require substantial insulation—usually at least 50.80 millimeters (2 inches) thick. This insulation is secured with support rings that keep it in place and protect the vessel's exterior. However, these support rings can also create a vulnerability to corrosion.
One of the major risks in pressure vessel maintenance is corrosion under insulation (CUI). This occurs when moisture or condensation finds its way beneath the insulation, leading to corrosion, often near the support rings.
Figure 1: Typical Corrosion Mapping
The problem tends to be most severe just above the insulation support rings, as water tends to accumulate there. As shown in the ultrasonic technique map above, corrosion intensity generally increases the closer you get to these rings. Regular monitoring and inspection are crucial to ensure that pressure vessels remain safe and functional, as unchecked corrosion could lead to hazardous leaks, endangering both human health and the environment.
To manage the risk of CUI effectively, industries are turning to advanced inspection methods like the pulsed eddy current technique. This innovative solution allows for the detection of significant corrosion, particularly near the insulation support rings in pressure vessels. What makes this technique particularly valuable is that it can be conducted on in-service systems, eliminating the need for costly downtime and allowing for more efficient maintenance planning.
Figure 2: Example of a C-scan Showing Relative Remaining Wall Thickness Above an Insulation Support Ring on a Demo Plate
Using pulsed eddy current technology, inspectors can detect corrosion without removing insulation or shutting down operations. This not only reduces the cost and disruption associated with traditional inspection methods but also enhances the reliability of corrosion detection, allowing for proactive maintenance and reducing the risk of catastrophic failures.
Inspection of Cast Iron Piping Systems
Selective leaching in cast iron piping systems refers to the process where specific elements within the cast iron are preferentially dissolved or corroded, leading to changes in the material's structure and properties. This can result in a weakened piping system, with implications for both performance and safety.
Key Concepts of Selective Leaching:
- Dealloying: Selective leaching, often called dealloying, occurs when certain elements in an alloy, such as cast iron, are removed or corroded at a faster rate than others. This process leads to a change in the chemical composition of the metal.
- Graphitization: In cast iron, selective leaching often leads to graphitization. This occurs when the iron matrix corrodes, leaving behind a network of graphite. The presence of graphite doesn't provide the same structural integrity as iron, which can lead to weakened pipes.
Graphitization in cast iron creates crater-like defects on the pipe's surface, often undetectable without surface preparation like sandblasting. This type of damage can lead to sudden pipe ruptures with no warning signs.
Figure 3: Corroded Cast Iron Pipes
Traditional ultrasonic testing struggles with cast iron due to its high attenuation, but electromagnetic techniques like pulsed eddy current excel in this context. PEC's compatibility with cast iron, enhanced by a dedicated algorithm that accounts for its unique magnetic properties, allows for effective detection and accurate sizing of defects.
Figure 4: C-scan of a Cast Iron Pipe
Buried Pipe System in Nuclear Power Plant
Buried pipe systems in nuclear power plants is critical infrastructure that transports water, steam, gas, or other fluids necessary for plant operations. These systems play a crucial role in safety, cooling, and general plant operations, often running underground to connect different parts of the facility. They support various functions such as circulating cooling water, conveying steam, or transporting fuel. These pipes are vital for plant safety and must meet stringent regulatory requirements. The reliability of buried pipe systems is crucial for the safe operation of nuclear power plants.
These systems support essential plant processes, and their failure could have serious safety and environmental implications. Therefore, maintaining the integrity of these pipes through regular inspection, maintenance, and appropriate protective measures is a top priority for nuclear power plant operators and regulators. Techniques like ultrasonic testing, magnetic flux leakage, and pulsed eddy current allow for inspection without excavation, providing insights into pipe conditions and detecting issues before they become critical.
Piping systems operating at near-ambient temperatures typically don't face high levels of thermal stress, but they can still exhibit issues related to cold work. This process can affect the metal's properties, which may not be immediately apparent but can influence the results of non-destructive testing methods like pulsed eddy current.
Recent advancements in PEC analysis tools have made it possible to distinguish between these "false positives" due to cold work and genuine indications of wall thinning or corrosion. These advanced tools can help technicians identify true wall losses from other misleading signals by analyzing the amplitude and other characteristics of the PEC signal.
Figure 5: False-Positive Indication Caused by the Cold Work (Pilgering)
Internal Corrosion or Wall Loss in Piping System
Detecting internal indications from the exterior of a carbon steel pipe has traditionally been a significant challenge, but pulsed eddy current technology offers a solution. PEC is a volumetric technique capable of detecting both external and internal wall loss, providing invaluable insights into the pipeline's condition. It's essential to acknowledge that while PEC is proficient at detecting wall loss, it cannot distinguish between internal and external corrosion. Various mechanisms, such as flow-accelerated corrosion, erosion and internal crevice corrosion, can lead to wall loss in pipelines.
Figure 6: Example of Internal Erosion
In the power generation industry, steam and water transport systems are prevalent, often insulated for operator safety and to optimize process efficiency. A frequently encountered issue in pipe elbows is Flow-Accelerated Corrosion (FAC). Carbon steel pipelines transporting deoxygenated water and wet steam are particularly susceptible to this phenomenon. Continuous fluid flow leads to the dissolution of the protective oxide layer, exposing the metal beneath to ongoing corrosion and resulting in gradual wall deterioration over time.
On the other hand, internal crevice corrosion is a mechanism that can be encountered in the piping system of nuclear power plants located near the ocean. The pipes are generally recovered with a thin coating to mitigate the risk of corrosion in this high-salinity environment. Nevertheless, when corrosion happens, the wall loss can be very localized and requires low-footprint sensors to reach the probability of detection required in such cases. The pulsed eddy current array probes developed over the years are ideal NDT tools to assess these challenges with high productivity.
Inspection of Pipes Through Coatings or Corrosion Blisters
Corrosion scabs and blisters have long posed challenges for asset owners and operators striving to maintain integrity and prolong the useful life of their assets. The removal of these corrosive products is not only hazardous but also makes it difficult to assess the remaining structural integrity accurately. Presently, there is no widely accepted method for precisely characterizing such damage, leaving asset owners reliant on risk-based inspections to mitigate unforeseen issues. The pulsed eddy current is a technique offering an undeniable solution to these challenges, especially with the advent of advanced sensors like the PECA-HR array probe.
This probe is ingeniously designed, featuring an array of dual sensors strategically arranged for optimal performance. Data from these sensors are synthesized through a sophisticated algorithm, enabling precise spatial triangulation and resulting in a footprint significantly smaller than that of traditional probes. This technology allows for enhanced detection capabilities, even in components ranging from 3 to 19 millimeters in wall thickness and up to 51 millimeters of liftoff. The illustration below shows the C-scans obtained using both the conventional G2 sensor and the high-resolution (HR) sensor. These scans vividly showcase the superiority of the HR sensor in this context, clearly delineating the severity of wall loss beneath the scan. In this context, PEC probes stand as a beacon of innovation in the realm of asset integrity monitoring, offering a precise and efficient solution to the challenges posed by corrosion scabs and blisters.
