Monitoring Cathodic Protection Effectiveness and Record keeping CHAPTER 7 Monitoring Cathodic Protection Effectiveness and Record keeping

Introduction Field measurements represent a very important part of monitoring any corrosion control system. Although there are many remote monitoring systems in use today, it is still necessary to take field data to ensure that cathodic protection systems are operating properly and are providing adequate protection to the structure. It is essential that clear, accurate data be taken. The data will be used to evaluate the effectiveness of cathodic protection, interference bonds, stray current control devices, and the like. If the data are not accurate and correct, the evaluation will be faulty and those responsible for the corrosion control program will be misled into thinking that systems are working properly when they may not be.

Introduction This could lead to failures, leakage, fires, explosions, and other hazardous situations. You must know how instruments work and what errors are possible. This means having a thorough understanding of the instruments you use and a knowledge of how the data should appear. It means taking the time in the field to review your data and make certain they are correct. Remember, if the data does not look right, they probably are not. Of course, unusual data may indicate a malfunction, and it is important that you recognize these situations, too.

Reasons for Monitoring The most obvious reason to monitor cathodic protection is to make sure corrosion is under control. When a structure corrodes, leaks may occur, product may be lost, and structural damage may occur. There is also concern over public safety and environmental damage. For this reason, regulations have been enacted in many industries and countries to make sure structures containing hazardous products are adequately protected to reduce the risk to the public and the environment.

Monitoring Cathodic Protection To determine that a cathodic protection system is operating properly and protecting a structure from corrosion, the following data are recorded on a routine basis: Structure-to-electrolyte potential. Rectifier voltage and current outputs. Current output of galvanic anodes. Magnitude and direction of current through mitigation bonds. Resistance of groundbeds. Integrity of rectifiers, isolating joints, electrical bonds, and other physical features associated with the corrosion control system. Measurement of structure-to-electrolyte potentials is the only method of determining when adequate cathodic protection is achieved. After a potential survey has been conducted, however, other indirect measurements can be used to monitor a system before the next potential survey. For example, measuring current output of a rectifier does not provide any information about the protection level of a system.

Monitoring Cathodic Protection If an annual corrosion survey indicated that a well coated structure was adequately protected with 10 amps and after the survey the structure became electrically shorted to some large bare structure, would measuring 10 amps at the rectifier still represent adequate protection on the structure of interest? The answer is probably no. The only way current output can be used, as a measure of cathodic protection is if the system has remained unchanged since the potential survey was conducted. Therefore, all other measurements and tests that are done between potential surveys are based on the assumption that everything is the same as during the potential survey. Other procedures for monitoring the effectiveness of cathodic protection, which may be conducted at specified intervals or as appropriate, include: Coupon test stations Electric resistance probe test stations Structure examination by excavation or divers Close interval potential surveys

Recordkeeping Importance of Good Record Keeping Documentation is the only way to follow the history of a system. The data you turn in become part of the company cathodic protection records. Consequently, you are an important part of the record keeping operation. Technical Accurate data is essential for detection of malfunctions in C.P. systems. Trends can be analyzed over extended time and plans can be made for maintenance and repair. Legal In the event of an accident or lawsuit, good records are essential to legal defense.

Recordkeeping Data Sheets Data sheets are extremely important. Data must be entered accurately and neatly. Obviously, it isn't always possible to keep neat data sheets, particularly when working in inclement weather or in adverse or dirty conditions. It may be necessary to copy the data onto fresh sheets after returning from the field. Data sheets must be kept in such a way that someone else could go back on the same job, repeat your measurements, and obtain data in the same locations as you did. Remember that you may be assigned to do an annual inspection on an unfamiliar structure using only the data sheets of the person who was there before you.

Recordkeeping Data must be legible if it is to be of any value. Date, Time, and Weather Date, time, and weather conditions should always be noted on data sheets. Sketches Show layout of structure(s). Show location of measurements with polarity of measurement. Record name and serial numbers of all instruments used. Site Conditions Always indicate unusual site conditions. Legibility Data must be legible if it is to be of any value.

Computer Records and Spreadsheets Nearly all corrosion records today are kept on computer databases. Usually these databases show the test points, date of last test, the measurement itself, whether or not the data meet the selected criterion, and when the next test is due. Printouts are then generated at the appropriate times for technicians to take into the field for the next scheduled tests. The latest data are then entered into the database. Spreadsheets can also be generated showing test points that do not meet criteria. These can be taken into the field for trouble shooting.

Computer Records and Spreadsheets If you have been collecting data on a computer data logger, the data can be entered directly into a computer. Graphs and spreadsheets of data can be generated, or the data can be downloaded into the company computer system. Large companies, particularly those with operations spread over a large area, are now using Internet access for corrosion control data. This makes it possible for all data in a technician 's area to be available without having to have a large computer system in local offices.

Facility Maps and Work Documentation Companies that operate underground plants, such as pipelines or cables, maintain atlas maps showing the location of structures, test points, cathodic protection installations, and many other data. The same is true of many large industrial plants, refineries, college campuses, and similar facilities. You need to be familiar with what these maps show and be able to work with them in the field. Documentation of your work is essential. Those responsible for updating facility maps will depend on your information to keep the maps current or to generate new maps. Consequently, as-built drawings of corrosion control installations must be accurate. Likewise, if you are involved with repairs of structures or corrosion control components, accurate information must be turned in. Accuracy in your work documentation is just as important as accuracy in your data sheets, as discussed above under "Data Sheets."