Materials Performance

MAR 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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39 MATERIALS PERFORMANCE: VOL. 57, NO. 3 MARCH 2018 turns to break in continuous torsion (greater ductility) had a lower sus- ceptibility to HE. This supported the continuous torsion requirement in AWWA C301. Susceptibility of Prestressing Wire to HE. The quality of the wire, as expressed by t he nu mber of turns to break in continuous torsion before exposure, substantially af- fects its susceptibility to HE and subsequent fracture (Figure 5). The ductilit y as expressed by continuous torsion appears to be significantly affected by an increase i n wire temperat ure duri ng t he drawing process. 11 Table 1 shows the effect of temperature on continuous torsion. The wire was severely dam- aged at 375°F (190°C). AWWA C301 was revised in 1992 to require that the surface temperature of the wire should not exceed 360°F (182°C) during the drawing process. Table 2 shows the effect of ex- tremely excessive cathodic current of 3.00 A/ft 2 (32.4 A/m 2 ) on pre- stressing wire immersed in a satu- rated Ca(OH) 2 solution for 6 months. The polarization potentials ranged from –1,060 mV CSE to –1,280 mV CSE · Continuous torsion and reduction of area substantially decreased dur- ing the 6 months of exposure, which demonstrated the drastic effect that excessive CP can have on the ductil- ity of the prestressing wire. CP of Severely Corroded Wire at pH 2. Table 3 shows the effect of CP on tensile strength, reduction of area, and hydrogen content of pre- stressing wire maintained at 60% of it s s p e c i f ie d m i n i mu m t e n si le strength in a 0.01 M HCl solution for 2 weeks without CP, simulating an acidic condition possible around severely corroded wire, followed by 2 months at –1,000 mV. Four speci- mens at –1,000 mV did not fail after 24 months of exposure. Figure 6 shows the cross section of a wire specimen exposed to 2 weeks of corrosion plus 2 months at –1,000 mV. Pits caused by t he 2 weeks of corrosion were evident Cathodic Protection Criteria for Prestressed Concrete Pipe—An Update FIGURE 7 Baseline and polarization potentials of PCCP line under CP at 12 µA/ft 2 and 100 µA/ft 2 . FIGURE 8 Simplified diagram to illustrate the CP design concept of a pipeline to meet the minimum and maximum CP criteria. and could be sites for possible frac- tures to occur while under exces- sive levels of CP. C P of L ong it ud i n a l ly Spl it Wire at pH 2. No failures occurred after 20 months of exposure, indi- cating that even severely notched prest ressi ng w i re located i n a n acidic environment prior to expo- sure is not extremely sensitive to HE. Recover y of Ductility. Table 4 shows the effect of CP on the diffu- sion of hydrogen from the wire and recovery of ductility as expressed as reduction of area. The loss of ductility, or embrittlement, is re- versible. A pipeline that is subjected to excessive CP may be returned to service by turning off or reducing the CP level to allow hydrogen to diffuse from the steel. Field Phase The objective of the field phase was to determine the approximate c urrent densit y requirements of PCCP wit h and wit hout supple-

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