Forgotten Cathodic Protection Systems: Whose Responsibility are They?
By Jim Eggenberger, V&A Consulting Engineers, Inc., Oakland, CA
When cathodic protection systems for buried pipelines, storage tanks and other civil infrastructure are not properly operated and maintained, the risk of corrosion damage, or even outright failure, increases significantly. For this reason owners must take responsibility to develop and implement an effective operation and maintenance program for their cathodic protection and/or corrosion monitoring systems.
There have been many recent reports covering the enormous costs associated with corrosion in the United States. One noteworthy study and report released in 2002 by the U.S. Federal Highway Administration (FHWA) concludes that the total annual estimated direct cost of corrosion in the U.S. is $276 billion, with drinking water and wastewater systems representing $36 billion of the total. Owners of civil infrastructure assets, who have incurred considerable expense in their construction, are continually looking for ways to economically manage the integrity and proper function of those assets.
Caption 1: Typical flush test station
Caption 2: Typical above ground test station
VALUE-BASED STRATEGIES
The need for an effective operation and maintenance program for corrosion monitoring and/or cathodic protection can be seen clearly when we look at asset repair costs. For example, suppose you manage a water district and operate a buried pressure pipeline that cost $6,000,000 to construct. As part of that construction cost, $200,000 was spent on the cathodic protection system. If there is a leak on the pipeline, the cost to repair, including the hard costs to make the repairs and the soft costs of down time, inconvenience to customers, public relations, etc., is estimated at $45,000.The cost to operate, maintain and perform annual CP system testing is $20,000. Therefore, operating and maintaining the cathodic protection system is inexpensive insurance. If it prevents only one leak per year, cathodic protection could actually save $25,000 per year in total costs.
Maintenance programs also raise the awareness of these underground systems so that much damage can be avoided when contractors are working around the structures. Operations people who are aware of these systems can let others know that there is a cathodic protection or corrosion monitoring system in the area. If the system is damaged, the awareness of its presence allows immediate repair, saving the cost of future repair excavations and ensuring continued protection.
THE NEED FOR STANDARD SPECIFICATIONS
Many agencies use corrosion specifications and details that were taken from past projects. A more effective approach is to standardize corrosion control and coating specifications and details to help maintain consistency for cathodic protection and coating systems at the plant. Standard specifications also provide a minimum standard of quality for corrosion control systems at the plant. Implemented systems should be monitored as outlined in the monitoring plan.
ANNUAL MAINTENANCE PROGRAMS
Cathodic protection systems require regular monitoring and maintenance to remain effective. The following minimum requirements may be used as a guide.
Inspections - Cathodic protection system inspections should be made every 2 months for the first 6 months after the cathodic protection system is installed. Thereafter, structure-to-soil potential tests should be scheduled at least once per year. Structure-to-soil potential tests should be made immediately in addition to the normally scheduled tests if the operation of the protected structure is interrupted by any of the following occurrences:
- Additions to the protected structure are made by new construction.
- Portions of the protected structure are removed by eliminating some of the underground services.
- Construction is performed in the vicinity of the cathodic protection anodes, cables or test stations.
- New DC-Powered Transit Systems are installed in the vicinity of the structure.
Tests - Tests conducted for annual maintenance of cathodic protection and corrosion monitoring systems include structure-to-electrolyte (usually soil or water) potential at test stations and other structure contact locations, anode current output, rectifier voltage and current output and other tests as may be indicated depending on changes in the environment or structure.
Structure-to-soil potentials should be measured at all test stations and at locations where direct contact
can be made to the protected structure, such as a pipe riser. The reference electrode should be placed on
the wetted soil surface above the pipeline under test or in water as close as possible to the protected tank
or other structure.
Impressed Current Systems
Rectifiers used for impressed current cathodic protection systems are normally equipped with an ammeter and a voltmeter to facilitate monitoring of the rectifier outputs. These should be read at weekly intervals during the first 3 months of operation and monthly thereafter. Remote monitoring systems are also available. Remote monitoring systems use satellites or cellular phones for data communication and are especially useful at remote rectifier sites.
It is most important to be certain that the positive output terminal of the rectifier is connected to the anode ground bed and that the instruments indicate the flow of DC current from the rectifier to the ground bed (positive to negative). If the flow is reversed, the protected structure will be seriously damaged by corrosion.
Galvanic Anode Systems
Pipe-to-soil potentials should be measured annually to maintain the galvanic anode system and to ensure adequate corrosion protection. The tests should be performed at each test station and at locations where the pipe or structure can be contacted directly.
Anode current output should be measured at all locations where anode cables are accessible for testing. The measurement should be obtained by measuring the voltage drop across a shunt resistor in series with the circuit. Anode current measurements are useful in calculating anode life.
CONCLUSION
In our experience, utility owners benefit significantly when they install corrosion monitoring and cathodic protection for their existing and future structures. The primary benefit is a more reliable asset with fewer unplanned repairs, a lower total cost of operation, and longer useful life.
How we develop and maintain civil infrastructure assets today will impact how future generations are able to maintain and develop facilities with limited funds
V&A is pleased to announce the acquisition of DeC Consultants, a San Diego based consulting engineering firm. DeC, with it’s talented staff and presence in Southern California, will expand the depth and resources of V&A and enable the larger firm to provide our clients with the quality and responsiveness they have come to expect. Like V&A, DeC serves clients in the water, wastewater, and transit industries providing corrosion control design, monitoring, and cathodic protection system repair services. In addition, DeC/V&A will offer coating system engineering and a variety of condition assessment services for water and wastewater facilities.
New DeC San Diego Office Manager
Ms. Andi Corrao has joined V&A as manager of the DeC San Diego office. She will also serve as Southwest Regional Manager for V&A’s operations in southern California, southern Nevada and Arizona. Andi brings over 20 years of experience in engineering consulting, with a specialty in the design, construction and condition assessment of water and wastewater facilities. She will represent V&A and our entire range of services with clients throughout the southwest and will manage and oversee a variety of condition assessment projects. Andi is a registered civil engineer in California, Arizona and Nevada.
Ms. Andi Corrao
