ISSN:
1662-8985
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Among the specialized electrical surveys to search for coating faults, assess possible externalcorrosion conditions and verify Cathodic Protection effectiveness, DCVG (Direct Current VoltageGradient) survey, and in particular the Transverse DCVG is usually considered the most effectivetechnique for finding coating faults on transport pipelines for oil, gas, and water.In this paper some preliminary results are reported that show that using a.c. current instead of directcurrent the localization of the coating faults can be much more precise and simple to be performedat the same time. Compared with the DCVG, the ACVG has many advantages among which: it doesnot need ON/OFF cycles since the OFF conditions are almost constant in the absence of alternatingstray currents, it can be carried out with economic and simple instrument, the use of unpolarizablereference electrodes (SCE) is not necessary and furthermore, it locates the faults and quantifies theirimportance with much more accuracy.Besides, the method needs shorter times and less manpower: one only operator is sufficient toperform the survey and it is therefore cheaper than performing DCVG.The results of the experiments carried out at the Training and Research Centre of Riyadh bycomparing the results of the two methods using the same current densities, clearly show thedifferent behaviour of the two techniques, in the presence of simulated / calibrated coating faults.Further researches are in course with this quite new technique as the localisation of coating faults isbeing made in terms of impedance rather than in terms of resistance. This has quite a hugeimplication when corrosion conditions of real coating faults are concerned. In case of a.c.interference (e.g. due to a.c. fed railways or electricity power lines) this could be a unique methodable to locate corroding coating faults on a buried, interfered metallic pipeline.The method is being patented not only as a new technique for coating fault location, but also for itspromising further developments still under investigation, as capable of finding corroding faults incase of a.c. interference
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/40/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.38.113.pdf
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