Patent ID: 7189319
Filing Date: 2007-03-13
Classification: C23F,E21B,G01N

Abstract:
1. A method of determining an amount of cathodic protection current to be applied to an underground metallic structure in contact with an underground earth formation, the structure having an extended underground length extending through a corrosive zone of the formation, with one end of the length being substantially near the earth's surface and another end of the length being below the corrosive zone, said method comprising the steps of: mechanically connecting a first axial current meter (ACM) to the structure at a first underground depth substantially just above the corrosive zone for measuring a first axial current flowing through the structure at the first depth; mechanically connecting a second axial current meter to the structure at a second underground depth substantially just below the corrosive zone for measuring a second axial current flowing through the structure at the second depth; connecting a master axial current meter (MACM) to the structure substantially near the earth's surface; operating the MACM over a selected limited time period to periodically obtain a series of first measurements of the first axial current from the first ACM and a series of second measurements of the second axial current from the second ACM, each second measurement being obtained at substantially the same time as a corresponding first measurement; and determining from the first and second measurements, an amount of cathodic protection current to be applied to the structure to avoid corrosion of the structure in the corrosive zone.