They are usually the result of moisture ingress between the floor and the pad (underside) or water in the product (topside). Lake and pipe types of corrosion are most commonly found in storage tank floors. It is interesting to note the steps or 'terraces' formed as the corrosion progressed. Figure 1 shows erosion whereas Figures 2 to 4 sketch corrosion shapes that have been given the terms "Lake Type", "Cone Type" and "Pipe Type".įigures 5 to 8 are photographs of erosion and typical corrosion of the lake and cone type. To help appreciate the difference we will illustrate erosion and some typical pit shapes. The ultrasonic means of detecting erosion in pipework was so successful during the 1960's that it has given a false impression of the accuracy that will be obtained with pitting type corrosion.
There are many types and mechanisms of corrosion but in this instance we deal exclusively with corrosion that is typical between the pad and the underside of tank bottoms or from water contamination inside the tank. This paper discusses the underlying principles of the methods and their effect on Probability of Detection (POD) and accuracy. Users and providers of these inspection services may have different perceptions and expectations of the sensitivity and accuracy of the methods.
#MAGNETIC FLUX LEAKAGE MANUAL#
Magnetic Flux Leakage (MFL) and manual Ultrasonics (UT) have been used extensively for the detection and sizing of corrosion pits in ferrous plates and pipes.
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