Fig. 7 — Calibration graph for area F1. Fig. 8 — Calibration graph for area F2. Fig. 9 — The water wall of boiler #1 is shown zoomed out. It shows the area from elevation 70 ft (below burners) to elevation 99.5 ft (just below the superheater tubes). The dark area below the line showing the top of the burners was confirmed by ultrasonic readings to be 0.098 to 0.150 in. (black to yellow colors, respectively). The dark area to the right (south corner) is due to heavy scale that lifted the scanner away from the wall. Individual tube numbers are shown at the top, and the distance scale and elevation are shown to the left. odometer; E-PIT™ tool capable of inspecting five tubes simultaneously; E-PIT™ hand-held scanner for the inspection of individual tubes; Ferroscope™ 308, 16-channel RFT instrument; remote vision system; 200- ft umbilical; and an industrial laptop computer. Calibration. The equipment was calibrated on-site by taking ultrasonic thickness readings on at least two separate elevations of the same tube 26 Inspection Trends / April 2011 having both nominal thickness and known wall loss. In this instance, the thinned area of tubes on one of the walls at the burner elevation was used to produce the calibration curves shown in Figs. 7 and 8. Procedure. A datum line marked on the wall was where all measurements were taken. In this instance, the datum line was at an elevation of approximately 99.5 ft. The tool detectors were aligned with this datum for each of the scans performed. From the datum line, the RFT system descended the wall at a speed of approximately 10 ft/min while gathering data from the crowns of five tubes simultaneously. Depending on the frequency and sample rate, this can equate to (up to) 2000 thickness readings per foot. Once reaching target height, the crawler was stopped and the direction reversed. Data were also gathered on
Inspection Trends - April 2011 - Spring
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