A B S T R A C T Tension-compression and rotating-bending fatigue tests were carried out using aluminium alloy 2024-T3, in 3% NaCl solution. The corrosion pit growth characteristics, and also the fatigue crack initiation and propagation behaviour were investigated in detail. The results obtained are summarized as follows: (i) Most of corrosion fatigue life (60-80%) is occupied with a period of corrosion pit growth at low-stress amplitude. The corrosion pit growth law can be expressed as functions of stress amplitude σ a and an elapsed time t. (ii) The critical stress intensity factor for crack initiation from the corrosion pit was determined as 0.25 MPa √ m. This value is the same as the threshold stress intensity factor range for crack propagation. (iii) Corrosion fatigue life can be estimated on the basis of corrosion pit growth law and crack propagation law. The estimated fatigue lives agree well with the experimental data.

Tension-compression and rotating bending fatigue tests were carried out using aluminum alloy 2024-T3 in 3% sodium chloride solution. During corrosion fatigue process, many corrosion pits were initiated at the early stage, and cracks were initiated from the pits. The characteristics of the pit growth were investigated in detail. The critical condition for crack initiation from the corrosion pit was also studied. Crack initiation periods during corrosion fatigue were evaluated on the basis of the corrosion pit growth law.

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In Japan, generally, the lifetime of distribution pipes (ductile cast iron pipes) is considered to be 40-50 years. However, starting in 1973 in Sapporo, leakage incidents, owing to corrosion on external surface of pipes and joint bolts, started to be found in ductile cast iron pipes which had been laid for less than 10 years. Therefore we have covered the entire length of newly laid pipes with polyethylene sleeves as an anti-corrosion measure. However, leakage incidents caused by external corrosion occurred occasionally along a total of 856 km of distribution pipes laid before this measure started. Such a problem of widespread maintenance of externally corroded distribution pipes was quite rare in Japan. We investigated the cause of external corrosion and corrosion situations and derived the formula to predict depth of external corrosion. Consequently, we established an effective renewal method by building an externally corroded pipe danger map to give renewal priority to externally corroded distribution pipes depending on leakage possibility.