To make corrosion rate of steel structures clear, we suggested the corrosion survey method including non-destructive survey, which measures steel thickness by means of an ultrasonic thickness meter provided with a monitor for underwater operation and destructive survey, which measures thickness and weight of steel pieces cut from steel structures. And, sheet-pile survey was conducted at Hirohata, Osaka, Shibushi and Sasebo Harbors, pipe-pile survey conducted at Shimonoseki Harbour, and tie-rod survey conducted at Toyama Harbour by the suggested method, and the following results were obtained:
(1)Sheet-pile thickness measured by means of an ultrasonic thickness meter was approximately equal to that of steel pieces obtained by means of a micro-meter or to that of steel pieces calculated from their weight. However, as the number of possible locations measured by means of an ultrasonic thickness meter ranged from 50% to 90% of the total, it is to be desired to execute both non destructive and destructive surveys.
(2)Corrosion rate of sheet-pile in the past survey was greater than several times that in this survey.
(3)Above H.W.L. corrosion rate of sheet-pile was 0.01 to 0.03 millimeters per year. at H.W.L. 0.10 to 0.12 millimeters per year, and between L.W.L. and mud line was 0.02 to 0.05 millimeters per year.
(4)Corrosion rate of pipe-pile between H.W.L and mud line was 0.02 to 0.05 millimeters per year.
(5)Corrosion rate of tie-rod covered by jute with pitch was 0 millimeter per year.