Corrosion assessment in large aboveground storage tanks (LASTs)

Bruce W. Maxfield

doi:10.1117/12.302515

15 March 1998 Corrosion assessment in large aboveground storage tanks (LASTs)

Bruce W. Maxfield

Proceedings Volume 3398, Nondestructive Evaluation of Utilities and Pipelines II; (1998) https://doi.org/10.1117/12.302515
Event: Non-Destructive Evaluation Techniques for Aging Infrastructure and Manufacturing, 1998, San Antonio, TX, United States

Abstract

The top, wall and floor of a large aboveground storage tank (LAST) are all subject to corrosion. Of these, the floor is often the most critical part because access is limited to periods when the tank is taken out of service. Tank floor corrosion can be either top or bottom side. Bottom side corrosion and top side corrosion under a coating are the most difficult to quantify rapidly and economically. An instrument based upon magnetic flux leakage (MFL) has been developed that permits the rapid, quantitative evaluation of tank floor corrosion in the presence of a coating up to 3 mm thick. This instrument produces a map of the magnetic field distribution (normal component) in a fixed reference plane about 1 mm above the steel or coating surface. Under a variety of practical circumstances, this magnetic field map is highly reproducible. The resulting 'image' of corrosion can usually be interpreted in terms of pit depth with an accuracy of better than plus or minus 10% of the nominal plate thickness. This in normally adequate for any pitting less than 50% of the nominal plate thickness in depth. For deeper pits and in order to assess for general thinning, it is normally desirable to use a standard ultrasonic thickness gauge in order to have better measurement accuracy. Inspections performed with this instrument provide the tank owner with a permanent quantitative, reproducible paper and digital record of the tank floor corrosion that can be compared with subsequent inspection and repair records.

Citation Download Citation

Bruce W. Maxfield "Corrosion assessment in large aboveground storage tanks (LASTs)", Proc. SPIE 3398, Nondestructive Evaluation of Utilities and Pipelines II, (15 March 1998); https://doi.org/10.1117/12.302515

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