Extensive research was conducted on prestressed ASTM A648 Class II steel wire to identify the fracture morphology. Hydrogen embrittlement results when this prestressed steel wire, embedded in concrete cylinder pipe, is cathodically overprotected. From this study, a correlation was established between the environmental variables (pH, cathodic potential) and the type of failure. These experiments demonstrated that hydrogen embrittlement occurred in both environments (pH 2 and pH 12) and affected the fracture behavior of the wires. The wires subjected to cathodic potentials above-1.2 VSCE showed moresusceptibility to hydrogen embrittlement than the other samples. The SEM fractographic analyses showed a specific fracture morphology for the hydrogen embrittled regions of the charged samples. The SEM analysis of the fracture surface showed a thin rim (about 20-50 microns in thickness) on the outer surface that contrasts with the rest of the fracture morphology. In summary, the ASTM A648 steel /
prestressed wire showed high susceptibility to hydrogen embrittlement at cathodic potentials above -1.2
VSCE, resulting in severe loss of toughness and catastrophic failure under sudden action of force (water hammering). Therefore, it is extremely important to avoid overprotecting these prestressed wires when using a cathodic protection system to improve life expectancy.
Prestressed concrete cylinder pipes (PCCP) distribute water to industrial, agricultural and residential areas. Thousands of miles of PCCP network throughout major cities of the United States. These durable concrete pipes combine the compressive strength and corrosion inhibiting properties of concrete with the tensile strength of prestressing wire. The alkalinity of concrete generally provides sufficient resistance to corrosion for the prestressed pipe. But in high chloride environments, the passivating abilities of concrete may be compromised, increasing the risk of steel rebar corrosion and rupturing of the pipes. PCCP can suffer accelerated corrosion where the cement mortar cover is damaged, the pipe is in contact with chloride contaminated or low pH soils or is influenced by stray DC currents. These occurrences can result in sudden catastrophic failure of the pipe [1]. One means of reducing the corrosion rate is by applying a negative voltage to the prestressed wire through cathodic protection. The voltage that is most commonly used in the field is - 0.85 volts. Constant voltage throughout the pipeline is necessary, but with thousands of miles of piping, it is difficult to uniformly protect them. Higher voltages close to the rectifier are used to compensate for the voltage drop resulting from pipeline resistance. Most of the prestressed wires utilized in these pipes are high strength steel and when cathodically overprotected may become vulnerable to a phenomenon known as hydrogen embrittlement (HE) or hydrogen induced cracking (HIC) [2].
