[ID] => 9876
[post_author] => 5714
[post_date] => 2018-07-24 12:19:46
[post_date_gmt] => 2018-07-24 11:19:46
[post_content] => The importance of heat recovery steam generators (HRSGs) in a combined-cycle power plant should not be understated. Acting as a thermodynamic link between gas and steam turbines, they play a crucial operational role. Experience industry-wide has shown that HRSGs are used well beyond their intended life and suffer from a variety of defects as a result.
One of the most destructive defects is corrosion at the tube’s inner diameter (ID). Commonly, inspection of ID corrosion is performed inside the tubes themselves, however the design of many HSRGs makes it very difficult to access these areas without cutting open a header and using complex robotics. The tubes are normally finned with carbon steel, spaced tightly together and quite often covered with iron oxide, which adds to the difficulty.
There is a strong desire on the part of the industry to find a non-destructive method that could detect ID corrosion from the outer diameter (OD), over the fins. One solution is pulsed eddy current (PEC) technology. Having been around for a long time, it has demonstrated its capability to detect wall thinning from corrosion from the outer diameter, often over thick insulation and weather jackets. Eddyfi Technologies, a global leader in surface inspection in the oil and gas, nuclear, and power generation industries, set out to demonstrate that detecting defects in HRSGs with PEC was a cost effective non-disruptive method of assessing the state of HSRG tubes.
THE RESULTS ARE IN
Eddyfi Technologies used an HSRG tube sample in an experiment. The tube was 1.1 m (43 in) long and had a 3.18 cm (1.25 in) ID and a 7.09 cm (2.79 in) OD, including its fins. The tube also had a normal wall thickness of 3.38 mm (0.13 in) and featured lime and iron oxide build-up as well as some bent fins.
All the PEC scans were performed in eight lines across the circumference at an axial rotation of 12.7 mm (0.5 in). As this is a high resolution for PEC, it made it possible to evaluate the minimum acceptance resolution for detection. Given these parameters, scans were performed at approximately 127-152 mm/s (5-6 in/s).
Driving the PEC probe was the Eddyfi Technologies Lyft® system which is able to instantly display scan results for analysis. The Lyft software itself uses advanced algorithms that make it possible to provide unique resistance to interference such as fins and iron oxide.
The initial scans with PEC managed to assess a roughly 813 mm (32 in) stretch of smooth uncorroded tube. Generalised corrosion was detected in an approximately 178 mm (7 in) stretch and the remaining tube featured heavier corrosion; the results were corroborated with a bore scope.
The demonstration went on to then detect the smallest defect that could be located with the probe. Defect A, positioned at 6 o’clock was 152.4 mm (6 in) with an approximate depth of 1.7 mm (0.067 in). Defect B was manufactured to be half the volume of the probe’s estimated smallest detectable defect. It was positioned at 12 o’clock, was 152.4 mm (6 in) and 0.84 mm (0.33 in) deep. Results of the scans showed both defects A and B were detected but B was at the detection limit, whereas defect A was always clearly visible.
While PEC technology has been used in the past, it has been with limited success. The combination of Eddyfi Technologies’ PEC probe and unique Lyft algorithm successfully demonstrated the technology’s ability to screen for wall thinning from the OD. As a result, this method is able to offer HRSG owners a better insight into the state of their assets in a non-destructive way, significantly decreasing the complexity and cost of inspections, with a high degree of confidence.
[post_title] => Eddyfi: Exploring new depths
[post_status] => publish
[comment_status] => open
[ping_status] => open
[post_name] => eddyfi-exploring-new-depths
[post_modified] => 2018-07-24 12:23:04
[post_modified_gmt] => 2018-07-24 11:23:04
[post_parent] => 0
[guid] => https://www.hcblive.com/?p=9876
[menu_order] => 0
[post_type] => post
[comment_count] => 0
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Eddyfi: Exploring new depths
Eddyfi Technologies tested its Lyft system with PEC technology to prove that it is able to detect wall thinning from corrosion in a non-destructive way