HEAT EXCHANGERS | NDE, INSPECTION & CONDITION MONITORING


several hours; a final report was completed off-site and required another week or more. “There was a 10- to 14-day lag from when the data was collected until it was analysed and they had a final report in hand,” he says. The plant managers endured these delays because they felt their personnel did not have the experience to manually analyse and validate the inspection results on site. “Automated analysis software produced results at the


rate of acquisition, or around 15 seconds per tube,” Bipes explains. “Instead of a two-week turnaround, the inspection team had preliminary reports within an hour of completion.” Furthermore, the process required one person whereas


Efficiency and consistency Brown describes a public utility with a BWR where the condensers have roughly 12,000 titanium tubes in each water box — around 50,000 tubes in total. Each tube is 55 feet long and has 15 support plates, with a stake evenly spaced between them to help stiffen the tube bundle. “We believed that some of these stakes were slipping out of position and sliding close to the support plate, putting circumferential stress on the tubes,” Brown says. “Under high-cycle vibration, tubes will relieve this stress by cracking axially or longitudinally.” Brown’s team created a plan to map each stake’s location and monitor any movement from its original position as a way to identify high-risk tubes. “All told, we needed to map roughly 800,000 stake locations between two reactor units,” Brown says. He estimated doing the work manually would take at least 2000 person-hours, with a large error factor. “Each inspector is going to measure a little differently, and the accuracy and approach of each individual is going to vary over thousands of measurements,” Brown says. “With automated acquisition and analysis, we could inspect 12 tubes at a time in about three seconds, looking for high-risk indications. In a matter of hours, we were able to give the customer a map of what we considered high-risk tubes caused by stakes that were not properly inserted or had moved. That’s impressive, and it added no time to our schedule or required nothing in the way of special skills or equipment.”


At a time when utilities are examining ways to reduce


operating and maintenance costs, they have to balance trying to improve heat exchanger inspection data confidence with making an efficient operation run better. “Automation allows us to perform high volumes of tube inspections quickly with better accuracy and consistency,” Brown explains. “The savings from plant uptime alone translate to millions of dollars for our customers.”


Eliminating repetitive tasks Zetec’s Tom Bipes recalls being contacted by an oil and gas processor about using automation to improve the efficiency, probability of detection and consistency of heat exchanger inspections at a remote refinery in Southeast Asia. “Normally the plant operator’s inspection team would


collect eddy current data, save it on one computer and then move to a different computer where another analyst would make a determination whether or not a tube should be taken out of service,” Bipes says. These steps typically took


previously there were three. “Qualified, experienced technicians and analysts are in high demand right now,” Bipes says. “Automated analysis allows them to focus on what they do best. It enhances the analyst’s abilities to identify potential indications and perform more inspections in the same amount of time without increasing costs.”


Historical comparisons Traditionally, analysts compare eddy current inspection data with historical benchmarks so they can recognise and interpret changes in signals over time. This process is often a manual effort, requiring the analyst to recall files from various campaigns and look for signals of interest. Automation can dramatically streamline this workflow.


Integrated with eddy current inspection analysis software, an automated historical data comparison tool can retrieve two or more independent data files and perform the correction of data slewing, alignment of signals and subtraction to create a “delta” process channel that highlights variations and potential discontinuities. This delta channel can be used with auto analysis software or as a standalone indicator of change for a manual process. NDE uses Zetec RevospECT HX Pro with HDC, or Historic


Data Compare, to monitor changes over time. “HDC can take data from a previous inspection, overlay


it on top of data you’re currently collecting, or any other data set, and then tell you what’s different about those two data streams,” Tom Bipes says. “The ability to compare data from one outage to another, without the variations and inconsistencies that come from manual analysis, gives asset owners confidence in their decisions about whether a flaw or defect has changed over time and needs to be addressed.”


NDE deployed HDC for its stake-mapping project. “We’ve done eddy current inspections at this particular power plant for three years straight,” says Brown. “HDC made it possible for us to quickly process and identify which stakes were moving and potentially putting tubes at risk. We could never have done the job manually.” At the end of the day, the effectiveness of historical


data comparisons increases with each inspection. “The more eddy current data you can collect and run through the system, the more beneficial and valuable automated analysis and comparisons can be,” Bipes says. “One analyst with an automated system can be far more efficient and focused on the critical aspects of the inspection compared to multiple analysts performing manual inspections.” “With our power-industry clients, the inspection windows


are narrow and specific: one eight-week period in the spring, and another in the fall,” Brown adds. “Automated analysis helps make my people available to do more work during those periods.” ■


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Left: A technician conducts a steam- generator tubing inspection at the Embalse power plant in Argentina. Typically it takes a crew of two to manage eddy current inspection data: one to acquire data in the vessel and another to compile the files. Automation software can combine both tasks Photo credit: Nucleoeléctrica Argentina S.A.


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