Corrosion of Spiral Rib Aluminized Pipe.

摘要

Aluminized steel pipes are expected to have a long service life, e.g., 75 years. Spiral ribed aluminized pipes (SRAP) have been widely specified and used by the Florida Department of Transportation (FDOT) for drainage of runoff water. Confidence in the long-term durability of SRAP has been challenged by recent unexpected early corrosion failures in various Florida locations. SRAP premature corrosion incidents have occurred in two modalities. Mode A has taken place in near-neutral soil environments and has been often associated with either gross manufacturing defects (i.e., helical cuts) or corrosion concentration at or near the ribs. Mode B tool place in pipes in contact with limestone backfill, and corrosion damage was in the form of perforations, not preferentially at the ribs and not necessarily associated with other deficiencies. These failures motivated initial research as well as the continuation investigation reported here. The objectives of the work were to establish to what extent the Mode A corrosion incidents can be ascribed to manufacturing defects that can be rectified by appropriate quality control, as opposed to an intrinsic vulnerability to corrosion of regularly produced SRAP due to ordinary forming strains, and to determine the mechanism responsible for Mode B corrosion, including the role that limestone backfill played in that deterioration. To achieve those objectives, laboratory experiments were conducted to replicate the conditions for Mode A and Mode B. Overall, the findings of this and previous work suggest that much of the corrosion damage observed in the Mode A incidents was promoted more by manufacturing deficiencies and less by any possible inherent susceptibility of corrosion at the ribs of SRAP that is produced following appropriate quality control. Experiments to explore the causes of Mode B corrosion showed that high pH values, sufficient to cause dissolution of the passive film on aluminum, can develop under exposure of limestone to flowing natural water. The findings substantiate for the first time an important vulnerability of aluminized steel in limestone soils and provide an explanation for the onset of rapid deterioration observed in the field under Mode B. The findings also provide strong evidence in support of service guidelines to disallow the use of limestone bedding for aluminized steel pipe, including SRAP.