ADVANCED MATERIALS & PROCESSES | OCTOBER 2024 16 to evaluate the condition of the pipe without causing any damage. To achieve this, various nondestructive techniques were employed, including visual examination, electrochemical potential measurements, magnetic flux measurements using the patented Zee Probe, hardness measurements, and onsite replication or field metallography replication (FMR) (Figs. 6-11). For a better understanding of the results, the test findings are tabulated and shown in Table 1. Both onsite replication and hardness measurements indicated the presence of graphitic corrosion. See the photo- micrographs in Figs. 12-14, and hardness measurements (Table 2). Field metallography clearly showed that the castiron pipe section is partially graphitized (Figs. 12 and 13), and the flange section is graphitized at the surface (Fig. 14). By conducting this comprehensive assessment of the cast-iron water main that was exposed to atmospheric conditions, the goal was to gain valuable insights into the condition of the castiron water main and identify any potential issues or areas that might exhibit accelerated corrosion. A nondestructive approach gathered crucial data without causing any harm to the pipe, ensuring its continued functionality and reliability. All indications from testing are that accelerated surface corrosion is occurring. There is a graphitic layer and graphitic corrosion present on this cast-iron pipe. It is essential to emphasize that if the cast-iron pipe, which is exposed to the atmosphere, is showing evident signs of graphitic corrosion, the buried section of the pipe exposed to corrosive soil and reducing conditions is likely experiencing even more severe external corrosion. The internal corrosion of the pipe section would be comparable in both the segments exposed to the soil and the atmosphere since the internal surface is exposed to the same water in both cases. To understand graphitic corrosion, it is essential to grasp the structure of cast iron. Cast iron is an alloy of iron, carbon, silicon, and other elements. The microstructure of cast iron consists of graphite flakes embedded in a matrix of iron. The presence of graphite imparts desirable properties to cast iron, such as improved machinability and damping capacity. However, when exposed to corrosive conditions, the iron (ferrite and or pearlite phase) in the cast-iron material can react with certain elements, most notably oxygen TABLE 1 — CAST-IRON PIPE INSPECTION DATA Cast-iron pipe section Visual Electrochemical potential readings, V Zee Probe readings Observations 1 Brown surface -0.13 7 Graphitic corrosion 2 Dark brown surface -0.032 9 Graphitic corrosion 2 Dark surface -0.031 8 Graphitic corrosion 2 Brown surface -0.140 7 Graphitic corrosion 3 Brown and dark surface -0.028 8 Graphitic corrosion TABLE 2 — VICKERS HARDNESS DATA Reading Location Hardness values, HV 1 Unaffected CI pipe 256 2 282 3 311 4 268 5 Graphitized area 161 6 108 Fig. 12 — Non-affected structure. Fig. 13 — Partial graphitization of the iron/ pearlite phase can be clearly seen. Fig. 14 — Flange graphitized at the surface.
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