PRCI PR-3-505

L51585e

Battelle Memorial Institute

Need: It has been widely recognized that the pipe-to-soil potential of pipelines under cathodic protection varies seasonally, depending primarily on the soil moisture content. In dry seasons, for instance, the pipe-to-soil potential becomes less negative so that meeting the -0.85 V (Cu/CuS04) criterion can be difficult if not impossible. The American Gas Association (AGA) through the Pipeline Research Council International, Inc. (PRCI), accordingly, initiated a research program at Battelle Columbus Division to study the effects of soil moisture content on corrosion and cathodic protection of underground pipelines. Cathodic protection is widely used for preventing corrosion in underground, buried structures. The overall objective of this research was to examine the effects of seasonal variations in soil moisture on the cathodic protection requirements to prevent corrosion of pipe steel in soils.

Result: The research consisted of four major tasks: Task 1: Characterization of the Effects of Moisture Content; consisted of a series of laboratory experiments in which the electrochemical behavior of pipe steel in soils of different moisture contents were examined. Task 2: Characterization of the Effects of Cyclic Moisture Fluctuations; was concerned with evaluating, through another series of laboratory tests, the effects of seasonal moisture fluctuations on the electrochemical behavior of cathodically-protected pipe steel. Task 3: Cathodic Protection Requirements as a Function of Moisture Content; consisted of analyzing the results of Tasks 1 and 2 and thereby assessing the cathodic protection potential and current requirements as a function of soil moisture content. Task 4: Field Tests; was concerned with verifying the laboratory results, obtained in Tasks 1, 2, and 3, in the field. This verification was done by (1) comparing and correlating the laboratory results with available field data from other PRCI funded projects and (2) performing a limited field test.

Benefit: Based upon the laboratory and field test data, it was concluded that cathodic protection requirements decrease with decreasing soil moisture content. The cathodic protection potential required to mitigate corrosion below a 1 mil per year rate, for instance, was found to be about -0.6 V, Cu/CuS04, in soils having 5 weight percent moisture content, which is 250 mV more positive than the recognized criterion of -0.85 V, Cu/CuS04.

Product Details

Published:

12/01/1988

Number of Pages:

109

File Size:

1 file , 1.8 MB