1996-02-08_HYDROLOGY - M1977378 (2)

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M - 72Bp/Y (24) in the case of the Friday Lowden bulkhead the required depth is greater than 127 ft for the 165 PCF overburden rock density and the 2" psi maxiaw hydraulic pressure, as follows: M . 72(290)/165 • 127 ft Corrosion Resistant Design The critical portion of any bulkhead with respect to corrosion is the piping that penetrates through the concrete* pipe penetrations are necessary to pass mine drainage through the bulkhead during construction. In additioe, some weans is necessary to permit release of impounded rater if required at some time in the future• it is also wise to be able to monitor water Pressure behind the bulkhead in order to determine the elevation of any unanticipated - The corrosion rates and the resulting probable life of piping of various stainless steels and pipe diameters were evaluated. Phis analysis used the approximate acid mine water concentrations and temperatures. Specific types of C=ro considered were aerated sulfuric acid; cupric, cop ovs and ferrte sulfate; cadmium sulfite; ferrous sulfate; and zinc sulfate. the maximum or - crosion rate estimated for Carpenter M:b-3 stainless steel pipe by the slawacturer was less than 0.005 is./yr for the aax " solution concentration, the maximum pressure and,the highest temperature. to addition, It was assumed that the solution conMtrations were held constant. TWO diameter pipes were analyzed. SAN. and 1- is-The design problem is to estimate when the strength of the corroded stainless steel piping will drop belay` the maximum hydraulic pressure (P). , The Carpenter nCbb-3 stainless steel has a yield strength of SS We which is reduced to 33 ksi for design. The minimum wall thicknesses required for the 290 psi hgrdraulic pressure at the Friday Laden site are; 063 In. for the i_in• diameter nomminal 6-is. diameter pipe and 0.009 in. for the norm pipe. These values were calculated as follows: -