{"operation":"document","citation":"PI-73-004","title":"Cathodic Protection Service — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1973-01-08","effective_on":null,"summary":"PI-73-004 response to Cathodic Protection Service concerning 192.457.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-73-004.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-73-004.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-73-004","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1973/PI73004.pdf","body":"<<<PAGE 1>>>\n\nMr. E. P. Doremus, P. E.\nService Division\nCathodic Protection Service\nP. O. Box 66387\nHouston, Texas 77006\nDear Mr. Doremus:\nThank you for your letter of November 2, 1972, in which you forwarded information and\ncomments concerning the two-electrode surface potential survey method for locating areas of\nactive corrosion. Your comments were made with reference to an interpretation contained in the\nOPS Advisory Bulletin 72-8 of August 1972 in which it was stated that OPS does not feel that the\n\"leap-frogging\" survey method will provide any useful information in determining where active\ncorrosion is taking place on Dresser-coupled pipelines (insulated joints). The Bulletin went on to\nsay that there are other types of electrical equipment that will do this job.\nYour letter suggests that the \"leap-frogging\" technique is no longer in use and that, therefore, it\nmay not be appropriate to refer to it. However, the interpretation quoted in the Bulletin was in\nresponse to a specific question, and, as indicated \"leap-frogging\" is not useful for Dresser-coupled\npipelines with insulated joints. On the other hand, the \"leap-frogging\" surface potential survey\nmethod is being successfully used for locating areas of active corrosion on electrically continuous\npipelines. As your letter recognizes, the purpose of \"leap-frogging\" is to compensate for\nelectrode potential differences. While we recognize that there is equipment available today which\nmakes it unnecessary to use \"leap-frogging,\" the leap-frogging technique remains available for use\non electrically continuous pipelines.\nYour letter also states that the two-electrode surface potential survey method is the most\nsatisfactory approach for providing Dresser-coupled pipelines with adequate cathodic protection.\nTo the extent that you are referring to the use of two electrodes in continuous contact with the\nearth, we agree. The proper technique provides for a continuous voltage difference measured\nbetween one electrode placed over the pipeline and the other electrode located five feet from the\npipeline and perpendicular to the pipeline. The survey is normally conducted on both sides of the\npipeline to identify existing galvanic anodes.\nYour interest in this important aspect of pipeline safety is appreciated. If you have further\nquestions, or comments, please contact us.\nSincerely,\nJoseph C. Caldwell, Director\nDB\nC:\\WP51\\INTERPRT\\192\\457\\73-01-08\n1","truncated":false,"body_characters":2435}