Cathodic Protection

The Strange Case of the Intermittent Condition

Being a cathodic protection corrosionist is a lot like being a detective. It is necessary to examine all the evidence when solving a mystery. Sometimes it is necessary to establish a stakeout. That’s what was done to find the source of intermittent shorts in this incident. Careful use of instrumentation, data analysis, and observation solved the problem.

Wireless Remote Monitoring of Cathodic Protection Systems

Wireless monitoring technologies provide the ability to acquire impressed current cathodic protection (ICCP) system performance data from remote locations using modem-equipped personal computers. The technology can monitor the remote ICCP system’s amperage, “instant-on” and “instant-off” potentials in a central location, and provide personnel with immediate warnings of system problems. Case studies are presented for one Air Force and three Army installations, each with a different approach for the monitoring.

MMO-Coated Titanium Anodes for Cathodic Protection—Part 2

Mixed metal oxide (MMO) anodes find extensive use in impressed current cathodic protection installations. Part 1 of this article covered the electrochemistry, manufacture, and operation of these anodes. Part 2 presents three case histories showing application of MMO anodes.

Real-Time Monitoring Affects Cathodic Protection

The need for real-time data is affecting the ability to provide cathodic protection (CP) to pipelines. The connection of electronic equipment required for remote pressure monitoring, metering information, valve operators, and other functions creates a direct short from the CP on the pipeline to the electric power company alternating current grounding system. In essence, the CP system now must protect not only the pipeline, but also a sizeable bare copper grounding grid. This problem creates pipe-to-soil potentials that may not meet the desired criterion. This article covers the use of decoupling devices to remedy this problem.

Cathodic Protection of Pipe Encapsulated in Polyethylene Film

Case histories are presented where polyethylene encasement and cathodic protection have been used together to effectively control external corrosion of ductile iron pipelines in corrosive soils. The four case histories evaluated include impressed current and galvanic anode protection.

Interference Problems and Nonuniform Potentials in Cathodic Protection of a Complex Installation

After being in operation for some time, cathodic protection (CP) systems at compressor stations, refineries, and other industrial plants can experience problems. For example, the CP potential distribution can change for various reasons, because of isolating flange failures, alterations in pipeline systems, grounding systems, or reinforced concrete foundations. Some areas become underprotected and others overprotected. The extent of CP current required may exceed the capacity of rectifiers, and may also increase interference on foreign pipelines. This article describes the results of corrective measures for these problems.

Designing Cathodic Protection for Power Plant Applications

Designing cathodic protection (CP) systems for buried piping in power plants and other similar industrial facilities offers several unique challenges. This article discusses these challenges and provides case histories to illustrate the impact they have on CP system design and operation.

Hot Oil Aboveground Storage Tank Bottom Corrosion Failure and Cathodic Protection Upgrade—Part 2

Several types of anode installations for tank bottoms are possible, but the methods selected do not always produce the desired results. This two-part article discusses a case history in which existing cathodic protection (CP) was ineffective and testing methods did not identify system deficiencies. This led to the premature failure of the tank bottom. Part 1 covered the findings of an investigation conducted to identify the cause of the corrosion. Part 2 describes the remedial approach taken to enhance CP for effective corrosion control.

Hot Oil Aboveground Storage Tank Bottom Corrosion Failure and Cathodic Protection Upgrade—Part 1

There are several types of anode installations that distribute protective current to a tank bottom. In some cases, however, the methods selected do not always produce the desired results. This two-part article discusses a case history in which existing cathodic protection (CP) was ineffective and the methods used to verify the performance of CP did not identify system deficiencies. This led to the premature failure of a tank bottom. Part 1 covers the findings of an investigation conducted to identify the cause of the corrosion. Part 2 discusses the remedial approach taken to enhance the CP for effective corrosion control.

Special Cathodic Protection Requirements for Specific Pipeline Applications

Most pipeline cathodic protection (CP) applications involve either galvanic anode or impressed current CP (ICCP) systems installed in earth for protection of external surfaces. Of the galvanic anode installations in neutral soils, magnesium is the most commonly used anode material. Rectifiers are the most common source of direct current power for impressed current systems.

Close-Interval Potential Surveys

The principle of a close-interval potential survey (CIPS or CIS) is to record the pipe-to-soil (P/S) potential profile of a pipeline over its entire length by measuring potentials at intervals that do not significantly exceed the depth of the pipe (often ~1 m).

Corrosion Surveys

Two of the most fundamental and informative field measurements are soil resistivity surveys and pipe-to-soil potential surveys.

Polymeric Materials

Polymers are complex molecules formed by chains of duplicated groups of atoms (monomers); these groups are typically linked by covalent bonds along a “backbone” of carbon or silicon atoms. Important polymeric materials related to corrosion include plastics and synthetic rubbers (elastomers).

Stray Current Effects

Before preparing a cathodic protection (CP) design, the possible presence of stray currents must be considered. Stray currents are defined as those which follow a path other than the one intended. Where stray currents discharge from a structure into the electrolyte environment in order to return to the source, corrosion will occur.

Effects of Coating on Corrosion and Cathodic Protection

The four basic elements of a corrosion cell are an anode, a cathode, and the metallic and electrolytic pathways between them. Corrosion control can be achieved by eliminating (or reducing) any of these elements. One such method is to modify the electrolytic pathway by introducing a barrier between the threatened metal surface and the corrosive medium (i.e., by applying some kind of coating).