RFEC/TC Inspection of PCCP with no Shorting Straps at the San Francisco Public Utilities Commission

In December 2004, the Pressure Pipe Inspection Company (PPIC) conducted a nondestructive evaluation of the Prestressed Concrete Cylinder Pipe (PCCP) portion of the Bay Division Pipeline No. 4 for the San Francisco Public Utilities Commission (SFPUC) using its patented Remote Field Eddy Current/Transformer Coupling (RFEC/TC) Technology. The RFEC/TC inspection was conducted over an overall distance of approximately 8.2 miles (13.12 km) and spanned a total of 2,167 inspected pipes. Several sections of the pipeline had a large number of reported wire breaks. After consulting Simpson Gumpertz & Heger Inc. (SGH) regarding the probability of pipe failure, SFPUC proceeded to conduct a simple verification of four pipe sections before making any decisions regarding repairs or replacement. The field verification exercise grew in magnitude as a series of successively more invasive tests failed to verify PPIC's results. Two new test procedures; X-Ray and turn-to-turn resistance measurements were attempted with mixed results. After these tests were complete, SFPUC, on the advice of SGH proceeded to put the pipeline back into service with no repairs. The details surrounding the unusual and unexpected results of the SFPUC verification using accepted practices and two new technologies are of interest to owners and operators of PCCP pipelines as well as their consulting engineers since they threaten to undermine confidence in the RFEC/TC in general.