PSI - Issue 64

Pat Rajeev et al. / Procedia Structural Integrity 64 (2024) 523–530 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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the U.S. were utilized, with exposure times extending beyond 17 years. The results of this experimental series were published in 1957, offering a valuable insight into the rate of corrosion in soils at that particular period ( Romanoff, 1957 ). This report also proposed power law functions to predict maximum pit depth, (inch) and weight loss, (oz/ft 2 ) at a given time, (years) for different metals as follows. = = ′ (1) (2) where , ′ , and are constants, which were found separately for different metals using the obtained experimental observations. This study compared the measured actual corrosion depths of cable stays with the predictions of the Romanoff corrosion models. In addition to power law functions, recent studies have developed bi-modal corrosion models specially to address the complex long-term corrosion loss of mild and low alloy steels. These models are specially developed for steels in coastal environments and steels in contact with sea water. Thus, these models are not with in the scope of this study and comprehensive details of these models can be found elsewhere (Melchers, 2018). 3. Corrosion assessment of cable stays In collaboration with an industry partner, 25 in-service cable stays in utility poles in various locations across Victoria, Australia, were uprooted. Throughout the excavation and uprooting process, photographs were captured to closely examine the soil conditions and the state of the bed logs. Fig. 4 illustrates the excavation process to uproot steel rods in cable stays anchored to ground. The information of drawings and design specifications were examined to to ascertain the proof load capacities of the different types of stay systems being inspected. Identification discrepancies were found in two cable stays where pole identifications did not align with the existing database information, and the installation year was unspecified in another two cable stays. As a result, the information and results of the visual inspection were documented only for the remaining 21 anchor rods of cable stays. Visual inspection for corrosion was carried out for the specimens mainly to identify the level and extent of corrosion. Locations of the corrosion were identified to check whether ~300-400mm proposed inspection depth of the specimen from the ground level could represent the actual condition of the specimen. Inspected specimens were categorized into three groups, namely: • Category 1 - Significant corrosion at the bottom of the specimen without signs of corrosion within ~300-400 mm inspection depth of the specimen from the ground level. • Category 2 - Significantly corroded mostly throughout the length of the specimen below the ground level including ~300-400 mm inspection depth. • Category 3 - Slightly corroded some with signs of corrosion within ~300-400mm inspection depth of the specimen from the ground level. In order to assess the remaining capacity of the anchor rods, diameter measurements were taken at three locations namely; within the above ground region, within ~300-400 mm inspection depth of the specimen from the ground level and in the bottom part of the specimens. These data were compared to check whether which locations of the specimens were subjected to significant degradation. In order to eliminate the effects of corrosion on the diameter measurements, corrosion was removed in the sections where diameter was measured. Further, Galvanised coating thickness was measured using Elcometer® 345 coating thickness measurement device. Measurements were taken at the above ground region of the specimens (two average values for coating thickness were recorded with the use of measurements at different locations above ground). Moreover, the coating thickness was measured at degraded locations, however, the presence of corrosion created difficulties in interpreting these measurements. When measuring the coating thickness, surface of the specimen was smoothened manually using sand-paper in order to mitigate the effects of surface roughness for the resulting coating thickness measurements. Table 1 provides a summary of the cable stay anchor rod information. The installation years of the cable stays ranged from 1964 to 1993, indicating a maximum service life of approximately 49 years and a minimum of 30 years. The anchor rods were of either 24 mm or 19 mm in size with different anchor mechanisms. The aboveground galvanised coating thicknesses of the rods were ranging from 106 µm to 134 µm. Table 1 further denotes the corrosion category specified for each anchor rod after performing the visual corrosion inspection. From this categorization, it can be observed that some specimens showed significant corrosion at the bottom of the specimen without signs of corrosion within ~300-400 mm inspection depth of the