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    Long-Term Strain-Corrosion Behavior in RPM Sewer Pipes

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    The mechanical properties of reinforced plastic mortar (RPM) pipe material are typically measured prior to production in order to establish design properties, and during production to ensure quality of the pipe material. Seldom does the opportunity become available to measure the mechanical properties of service-aged (conditioned) components. In this paper, the short-term properties of the service-aged pipes are compared with the original production specifications. The long-term, strain-corrosion cracking properties have also been measured during the past 10 years on these service-aged pipes. Some laboratory specimens still have not failed after 10 years under test.

    Reinforced plastic mortar (RPM) pipes were excavated from the ground after about 15 years of sewer service, and material coupons from these pipes were subjected to various mechanical tests. Axial-direction tensile tests, hoop-direction stiffness, and acid strain-corrosion testing were performed. The acid strain corrosion tests were monitored as a function of time until failure. The resulting lifetimes were related to the initial surface strains and showed a decreasing logarithmic relationship for both concentrations of the sulfuric acid solutions. Some pipe samples have been under test for 10 years, and prior to this testing were buried in the ground, and used as sewer pipes for 15 years.

    The failed laboratory specimens were compared by fractographic examination with those from in-service failures. Laboratory specimens that failed in shorter times appeared to be overload in nature and exhibited little, if any, time-dependent fracture surface features. In-service failures indicate that the crack had been present for a significant time. Comparisons are also made between the observed fractographic appearance of the fibers and the laboratory failure time for both pH values.


    reinforced plastic mortar, fiberglass, sewer pipes, strain Corrosion, pipe stiffness, axial tensile, fractography

    Author Information:

    Hopkins, SW
    Exponent Failure Analysis Associates, Inc., Menlo Park, CA

    Duffner, DH
    Exponent Failure Analysis Associates, Inc., Menlo Park, CA

    Johnston, PR
    Exponent Failure Analysis Associates, Inc., Menlo Park, CA

    McGarry, FJ
    Professor of Materials Engineering, Massachusetts Institute of Technology, Cambridge, MA

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP38411S