When it comes to eddy current testing (ECT) for heat exchangers, the complexity of the task dictates the size and expertise of the team involved. Smaller scope inspections, such as those performed on air chillers, offer a straightforward introduction to tubing examinations. However, as the scale and importance of the heat exchangers increase, so does the need for a more robust and specialized team.
Small-Scale Inspections: Chillers
Chillers are among the simplest heat exchanger systems to inspect. These inspections are often carried out by a single technician using a small, handheld eddy current tester. This type of equipment is designed for on-the-fly analysis and typically does not permanently record tube data. The technician evaluates each tube in real time, identifying any defects that might compromise efficiency. If a defective tube is found, it is either plugged or replaced, but detailed records of which tubes were tested (and the inspection results) are not required to be kept. Mistakes in this context have relatively low consequences, as they primarily impact the efficiency of the unit rather than safety or operational reliability.
For these smaller scope inspections, the data management aspect—keeping track of which tubes are completed, which tubes have defects, and which tubes remain to be tested—is often performed by the operator.
Scaling Up: Larger Heat Exchangers
As we move into the realm of larger heat exchangers, such as feedwater heaters, condensers, and steam generators, the stakes and complexities rise significantly. Balance of Plant (BOP) heat exchangers in power plants, for example, may contain anywhere from dozens to over 10,000 tubes, per heat exchanger. This scale requires not only advanced equipment but also a well-coordinated team.
For these larger inspections, specialized eddy current testers are indispensable. These devices are equipped with:
Mixing capabilities: To suppress signals from tube supports, allowing for clearer defect detection.
Multi-frequency operation: Whether through simultaneous broadband signals or sequential multiplexing, these features enable thorough and precise evaluations.
Integrated storage: Ensuring all tube data is recorded for later analysis, which is critical for trending and comparisons in future inspections.
Historical Data Compare: Allowing a quick visual presentation of the same indication from several different historical inspections (at the same time on the same screen), to determine if flaw is changing over time.
The introduction of such advanced equipment necessitates the involvement of additional team members to manage the data, operate the equipment effectively, and maintain quality control.
When probe handling is performed manually at the heat exchanger tubesheet, at least two people are required. One team member locates the probe guide tube to the appropriate tubes, while another operates the data acquisition software. In many cases, the Level II operator is responsible not only for performing the test but also for evaluating the results and reporting the findings. Verbal communication between the probe handler and the operator is crucial to coordinate operations, such as moving the probe, inserting it, advancing to the next tube, or performing a retest.
When heat exchangers contain many thousands of tubes, the team size increases further. Inspections are often performed within a fixed and tight timeframe, requiring efficient operations to meet the planned schedule. To ensure timely completion, dedicated data analysts are incorporated into the team. This allows the operator to focus solely on collecting and recording data, while the data analysts evaluate the recorded information and identify defects. This division of labor optimizes both the speed and accuracy of the inspection process, ensuring that the inspection meets both quality and scheduling requirements.
Another important team consideration is the availability of trained data analysts. Since there are only so many qualified analysts in the world, the number needed for a large project can sometimes exceed those available to be physically present at the job site. In such cases, remote data analysts are often utilized to supplement the on-site team. This is achieved by transmitting data back and forth over dedicated communication lines, ensuring that even with limited on-site resources, the inspection can proceed without delay.
For large-scale heat exchangers, the sheer volume of data management can quickly become overwhelming for the operator alone. In these cases, dedicated data managers are brought in to handle the workload. Depending on the size of the project, one data manager may suffice, but in some instances, two or more data managers per shift are required to ensure smooth operations. These data managers play a critical role in organizing and maintaining the data, freeing the operator and analysts to focus on their respective tasks.
Critical Inspections: Steam Generators in Nuclear Plants
For simple heat exchanger exams like air chillers, accurate inspection results are less critical. However, for critical heat exchangers such as steam generators in nuclear plants, accuracy of results is paramount. In these cases, relying on a single team of data analysts is not the norm. Since the results must be as accurate as possible with minimal room for error, redundancy is a necessity.
Typically, two teams of data analysts, referred to as Primary and Secondary teams, are utilized. The data analysis results from both teams are compared by resolution analysts, who typically have Level III certification. These resolution analysts review discrepancies, resolve any conflicts, and determine the final results. This layered approach ensures the highest level of accuracy and reliability for these critical inspections, where even minor errors can have significant consequences.
Due to the importance of accurate results, independent oversight by an Independent Qualified Data Analyst (iQDA) is often required. This additional step ensures that the data analysis process is being performed correctly, providing an extra layer of verification and confidence in the results.
Additionally, for nuclear steam generator examinations, tube integrity assessments must be performed by engineers. Unlike simpler inspections where processes and exam variables are closely monitored and controlled, critical exams require detailed assessments to determine the types of degradation that already exist or have the potential to occur. This "degradation assessment" outlines the necessary test techniques required to identify both existing and potential degradation, ensuring the most effective and comprehensive evaluation of the heat exchanger’s condition.
Tube integrity engineers also perform condition monitoring. This involves assessing the results from an inspection, conducting historical look-backs of reported indications (such as wear fretting), and evaluating growth and trending of these indications. Such analyses are essential for predicting potential future issues and ensuring the ongoing safety and reliability of the system.
Furthermore, tube integrity engineers perform operational assessments to determine the allowable operating interval before the next inspection is required. These assessments take into account inspection results, historical trends, and degradation mechanisms to ensure the system operates safely and efficiently within the established parameters.
In some cases, tube integrity engineers may also require an in-situ pressure test to validate that tubes can remain intact during accident conditions, as required by regulatory bodies such as the USNRC. This additional testing step is crucial for ensuring the safety and integrity of critical heat exchangers under extreme scenarios.
Finally, when a tube is found to contain a defect requiring repair or plugging, a specialized tube repair and plugging team is brought in. These teams are responsible for processes such as sleeving, re-rolling, or installing plugs to address defective tubes. Their expertise ensures that the defective tubes are properly repaired or removed from service, maintaining the overall integrity and functionality of the heat exchanger system.
Recap: Why Each Team Member Is Crucial
Probe Handlers or Fixtures: Must locate the tubes with precision to ensure each tube is correctly encoded (e.g., Row 1, Column 5).
Operators: Crucial for recording good quality data for the right tubes to the correct extent, with the appropriate test parameters (e.g., frequencies, mode of operation, number of channels).
Data Analysts: Responsible for accurate data evaluation, ensuring tube integrity engineers can perform calculations based on reliable results.
Data Managers: Ensure the correct tubes are inspected with the right techniques and confirm that all required examinations are completed. They also collaborate with clients and tube integrity engineers to issue plug/repair lists.
Tube Integrity Engineers: Address all degradation issues effectively and ensure long-term reliability through comprehensive assessments.
Plugging/Repair Crews: Ensure defective tubes are properly repaired or plugged using the correct processes, maintaining the heat exchanger's overall functionality.
Clients: Bring insights into additional programs such as foreign object management, tube leakage, and contractor oversight. They help ensure all inspection aspects align with broader operational goals.
Summary: It Takes a Village
Eddy current testing of heat exchangers is a complex, collaborative process that requires the expertise and coordination of many specialized team members. From probe handlers ensuring precision at the tubesheet to data analysts interpreting critical inspection results, each role is essential. Data managers, tube integrity engineers, plugging crews, and even the clients themselves all contribute to the overall success of the inspection. Much like a village working together to achieve a common goal, the strength of the process lies in the collaboration and expertise of every individual. The inspection is only as strong as its weakest link, and every team member plays a vital role in ensuring the safety, efficiency, and reliability of the heat exchanger system.
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