- CATHODIC PROTECTION SERVICES
1.1 OVERVIEW OF CATHODIC PROTECTION
Cathodic Protection (CP) is one of the most effective methods for preventing most types of corrosion on a metal surface. In some cases, CP can even stop corrosion damage from occurring. Metals, especially ferrous metals, corrode in the presence of oxygen, water, and other impurities such as sulfur. Without CP, metals act as the anode and easily lose their electrons and thus, the metal becomes oxidized and corroded. CP simply supplies the metal with electrons from an external source, making it a cathode.
Cathodic protection (CP) is the process of using DC currents to prevent or reduce the corrosion of metal surfaces by transferring the corrosion from the protected structure to another known location, where the current-discharging anode(s) can be designed for maximum life and ease of replacement.
Corrosion is a leading cause of premature failure in metallic structures. Operators can extend the service life of their facilities and equipment by installing CP systems and testing them regularly.
A wide range of civil and industrial applications have used these systems to prevent corrosion for many years. They are typically installed during original construction, major expansions or upgrades.
Cathodic protection systems (CP Systems) protect infrastructure assets such as above ground storage tanks, buried pipelines, reinforcing steel in concrete structures, heat exchangers, marine piles, sheet pile walls or other metallic structures from corrosion.
Oxidation — Loss of electrons
Reduction — Gain of electrons
Anode — Where oxidation reactions take place
Cathode — Where reduction reactions take place
1.2 METHODOLOGYS FOR SURVEY:
1.2.1 CLOSE INTERVAL POTENTIAL SURVEY(CIPS):
Descriptive Technical Memory CIPS (Close Interval Potential Survey) technique is an inspection system developed for the detailed analysis of cathodic protection systems in underground pipelines. The technique consists of the continuous measurement of pipeline potentials regarding the copper/copper sulfate reference anode. The operator carries out duct routing extending a fine caliber wire from the nearest test post. The wire is connected to a pair of reference cells through a field computer. The reference cells are located in turn lying on the ground while the operator moves along the pipeline and the field computer records potential values. The pipeline potentials are recorded with switched on current (“on” potentials) and with switched off current (“off” potentials) to eliminate “IR” errors in measurements caused by current flow between the pipeline and the reference cells. In order to obtain “off” potentials, cyclic timers are placed in all the cathodic protection sources having influence on the zone under study. Timers must work in perfect synchronization to allow “off” potentials accurate measurements.
1.2.2 DIRECT CURRENT VOLTAGE GRADIENT (DCVG)
Direct Current Voltage Gradient (DCVG) technique is a system developed for the detection and analysis of defects in underground pipeline coating. Defects are localized by examining potential gradients in the soil covering the pipelines to determine the direction of cathodic protection current flows.