Abstract
Thirty eight cases of grooving corrosion that occurred in practice at the weld of electric resistance welded pipe were analyzed. Two types of grooving corrosion were observed; the continuous type was characterized by the uniformly grooved line over an appreciable length along the pipe and the discontinuous type was associated with tuberculation, deep penetration being limited to the welded area covered by tubercles. In 66% of the cases, perforation of the pipe occurred within 4 years. The maximum penetration rate was as high as 8.4mm/y in one case and 2.5mm /y in average. These corresponded 80 and 25 times respectively that of the overall corrosion rate of steel in waters. Grooving corrosion occurred most frequently in pipes of 80A (89.1mm OD) to 200A (216.3mm OD), which is presumably of no significance since they are most frequently used for water pipes. There was a general tendency that a high penetration rate was associated with water of low specific resistance. Thus, more than half of the cases were found in cooling waters cooled by recirculation through a spray or tray type tower. While most of grooving corrosion were found in water pipes, it also occurred on the outside surface in contact with soils or insulating materials soaked with water. The failed pipes had no singularity in chemical composition. Since differential microstructures are present practically in all commercial pipes manufactured by the electric resistance welding process, there is always a potential danger of grooving corrosion. On the other hand, its occurrence is relatively few considering a large amount of pipe used for water pipes. It is important to set up a safe-or-unsafe criterion with respect to environment, although further studies are needed to do so.
