Fig. 11 — Ultrasonic test results of the same tubes evaluated in Fig. 10 (wall loss detected). Inspection Trends / Spring 2011 27 the way up and were used to confirm any indications of wall loss detected. Results. The software semiautomatically generated a detailed report (spreadsheet) for each wall. In additon, field notes and a collage of the “color map” of the full-scan data from each wall was made — Fig. 9. Confirmations. The inspection results were backed up using ultrasonics — Figs. 10, 11. Summary • The VertiScan system proved effective in identifying general and local thinning near the welds at elevation 90.5 ft. Thinning was confirmed by ultrasonic thickness readings. • The scaffold gap must be a minimum of 10 in. from the crown of the tubes to allow the system to pass by. • For future inspections, it would help to have a fourth person doing on-site data analysis only. The operation of the RFT system when scaffolds are present is a three-person job (two people if no scaffolds are present). • The system provides the best value when there is no scaffold in the boiler. • Generally, one full water wall can be scanned per shift if just one system is in use. Capabilities. The technique is sensitive to all types of wall thinning, including the following: • Hydrogen damage, • Underscale pitting and graphitization, • Flame and soot blower erosion, • Blister and local overheating, • Creep damage (thermal fatigue), • Elephant skin and rhino hide, • Dents and gouges, and • Internal pitting. Works Consulted 1. MacLean, W. R. 1951. Apparatus for magnetically measuring thickness of ferrous pipe. U.S. Patent 2573799. 2. Schmidt, T. R. 1989. History of the remote-field eddy current inspection technique. Materials Evaluation 47(1): pp. 14, 17, 18, 20–22. Columbus, Ohio: American Society for Nondestructive Testing. 3. Atherton, D. L., and Czura, W. M. 1994. Finite element calculations for eddy current interactions with collinear slots. Materials Evaluation 52(1): 96–100. Columbus, Ohio: American Society for Nondestructive Testing. 4. Hoshikawa, H., Koyama, K., Koidoand, J., and Ishibashi, Y. 1989. Characteristics of remote-field eddy current technique. Materials Evaluation 47(1): 93–97. Columbus, Ohio: American Society for Nondestructive Testing. 5. Schmidt, T. R. 1984. The remote field eddy current inspection technique. Materials Evaluation 42(2): 225–230. Columbus, Ohio: American Society for Nondestructive Testing. 6. Lord, W., Sun, Y.-S., Udpa, S. S., and Nath, S. 1988. A finite element study of the remote-field eddy current phenomenon. IEEE Transactions on Magnetics Vol. 24, pp. 435–438. New York, N.Y.: Institute of Electrical and Electronics Engineers. 7. Mackintosh, D. D., Atherton, D. L., and Puhach, P. A. 1993. Throughtransmission equations for remote-field eddy current inspection of small-bore ferromagnetic tubes. Materials Evaluation 51(6): 744–748. Columbus, Ohio: American Society for Nondestructive Testing. 8. Sun, Y.-S., Udpa, L., Udpa, S., Lord, W., Nath, S., Lua, S. K., and Ng, K. H. 1998. A novel remote-field eddy current technique for inspection of thick walled aluminum plates. Materials Evaluation 56(1): 94–97. Columbus, Ohio: American Society for Nondestructive Testing. 9. Kilgore, R. J., and Ramachandran, S. 1989. Remote field eddy current testing of small-diameter carbon steel tubes. Materials Evaluation 47(1): 32–36. Columbus, Ohio: American Society for Nondestructive Testing. 10. Atherton, D. L., Macintosh, D. D., Sullivan, S. P., Dubois, J. M. S., and Schmidt, T. R. 1993. Remote field eddy current signal representation. Materials Evaluation 51(7): 782–789. Columbus, Ohio: American Society for Nondestructive Testing. 11. ASTM E 2096-00, Standard Practice for In Situ Examination of Ferromagnetic Heat-Exchanger Tubes Using Remote Field Testing. 2000. West Conshohocken, Pa.: ASTM International. ANKIT VAJPAYEE (avajpayee@russelltech.com) is with Russell NDE Systems, Inc., Edmonton, Alb., Canada. Fig. 10 — Butt joint weld with possible loss below (east wall 62–66).
Inspection Trends - April 2011 - Spring
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