A proposed method for determining the electrical resistance of coatings on existing pipe lines was published in Corrosion for July, 1951 (page 245). It was presented for study by NACE Technical Practice Committee 17—Standardization for Procedures for Measuring Pipe Coating Conductance. The published method determines pipe coating resistance from average values of current and pipe-to-soil potential changes resulting from draining test currents from a buried line.
A number of engineers consider that a preferable method utilizes the so-called "attenuation" relations. These formulas have a rigorous mathematical development and when properly applied give results entirely consistent with actual conditions encountered in the field. The attenuation formulas have been found to give results differing by only a few percent from values obtained from averaging current-voltage relationships. By neglecting the effect of attenuation the averaging method shows a poor coating to have a somewhat higher resistance than its true value.
It is recommended that the NACE adopt the attenuation method described below as an acceptable alternative procedure for determining pipe coating resistance. The attenuation measurements can be made with the standard apparatus described in the previous report. This description will therefore be limited to an outline of the proposed alternative method itself.
