In the foothills of the Andes, among the sprawling vineyards of picturesque Mendoza, Argentina, stands an innocuous equipment cabinet located by the side of an infrequently used mountain pass. The cabinet's superficial surface rust belies its importance as one of the most significant technological developments in modern day corrosion prevention. The cubicle, battered from years of an abrasive cocktail of arid Patagonian winds and coarse earth, hides the cradle of a revolutionary approach to cathodic protection. The equipment within the cabinet resulted in an entirely new range of products.
Ever since 1824, when Sir Humphry Davy first proposed the idea of attaching chunks of iron below the waterline of copper-clad British warships to prevent their rusting, cathodic protection has been one of the most commonly used techniques for the prevention of corrosion. Today, essentially two types of cathodic protection are used to protect steel and other structures from corrosion.
The first employs the use of galvanic or sacrificial anodes in various shapes and alloys with a more negative electrochemical potential than the metal (typically steel) structure they are designed to protect. The sacrificial anodes corrode over time, sparing the remainder of the structure. The anodes have only a limited life. Once they are no longer capable of protection, the structure begins to corrode.
This method is unable to provide complete protection for larger structures, such as pipelines. These types of applications require an impressed current CP system that includes a rectifier, which converts an alternating current power source to direct current that is properly calibrated to provide the required protection. Since the power source is delivered to the anode and not generated by degradation of the anode, the power supply may be recalibrated to the anode to provide additional power, when needed, as long as the anode remains functional and optimal protection to the pipeline or other structure.
Pipeline operators, however, traditionally purchased manual type rectifiers that typically required frequent site visits for troubleshooting and required significant maintenance and operational support. The pilot system installed some 20 years ago in the Piedras Coloradas oil field in the Mendoza region owned by Perez Companc incorporated state-of-the-art switch-mode power control technology along with the latest in remote control monitoring capabilities. At the time, switch-mode technology was considered somewhat complex and not fully understood. However, the application of sound fundamentals resulted in a stable, efficient, reliable and resilient solution.
That pilot system protected half a dozen well casings. The rectifier and deep ground bed system were located in the center of the field approximately equidistant to each of the producing boreholes. Now after 18 years, a recent visit to the facility revealed the corrosion protection system continuing to operate silently and maintenance free. Although peak oil production from the field is now well in the past, it continues to modestly contribute to the county's infrastructure, which is a testimony to solid application of sound engineering principles combined with new technologies.
Further Evolution of Cathodic Protection Systems
Today's advanced cathodic protection systems have evolved from the early breakthrough achieved with reliable switch-mode technology. Spurred on by their early success at Piedras Coloradas (much was learned regarding lightning protection in different terrains and the affect of altitude and geographical dynamics), an AMETEK development team launched a second generation system.
The second-generation rectifier system had many subtle refinements. Newer switch-mode-specific components had been introduced to the market that enhanced the system's product reliability and efficiency. The system also benefited from application of environmental protection strategies. In addition, a remote monitoring and control system was designed that would leverage new communications technologies. Engineering personnel could spend more time analyzing data and prioritizing corrosion prevention in a proactive mode rather than reacting to corrosion threats with heavy consequences.
The vast distances pipelines cover and the often remote location with little supporting infrastructure had to be overcome. With this in mind, a strategic alliance was formed with a third-party, low-earth orbit satellite communications provider. By integrating a data transport layer as part of the system and offering it in combination with analytical software, the power conversion solution was complete.
The system incorporated digital and analog control loops, enabling accurate constant potential cathodic protection. This complemented new polymer pipeline coatings in development that were particularly susceptible to disbondment with excessive protective potentials.
What has always been paramount in CP design has been the need for accurate, automated potential control, yet many older manual systems in the field still rely on moving coil volt meter and ammeter indications. With the incorporation of digital controls, newer systems remove the possibility of parallax errors that occur when observing a needle on a meter from differing, non-perpendicular angles, thus compromising the calibration and tolerance of the indicating device. The increased accuracy helps deliver optimized energy conversion, maximizing the effectiveness of the corrosion control device.
The system was deployed in significant numbers by the transport division of Repsol YPF in the late 1990s. In particular, 53 units were placed on their oil pipeline, which starts at the Lujan de Cuyo refinery in Mendoza and runs all the way through Montecristo (Cordoba), ending in San Lorenzo in Santa Fe province near Rosario, Argentina. The feedback was extremely encouraging, so the evolution of the advanced cathodic protection system continued.
Eventually, a revolutionary single module cathodic protection system was released, which incorporated the latest in component technology as well as digital control loop topologies. The system incorporated internet-based structures and broadened systems connectivity from just satellite to fiber optic, VHF/UHF radio, microwave and cellular modems.
Flexibility was the keyword. With the ability to remotely control as well as monitor the most remote of locations, companies saved significant operating costs.
Particularly attractive to users was the system's ability to remotely initiate an instant off test synchronized to a highly accurate GPS clock. This in itself was not new, but when integrated with switch-mode technology and state-of-the-art communications capabilities, the end result was a radically different operating experience. With a technologically advanced, automated and intelligent network, engineers were no longer required to trek to remote locations to conduct field maintenance or analysis.
In addition, users could select and refine cathodic protection remotely on an à la carte basis. For instance, users were now able to alter operation mode between constant potential, voltage or current or altering set points, all from behind a desk without deploying field resources. All outputs were automatically self-regulating, thus removing the need for engineers to carry out potentially lethal tap changing procedures, which lead to only an approximated protection potential and can significantly threaten personal safety.
Newest Protection System Technology
Driven by the economic advantages of remote control and monitoring and system automation, a multi-module system was developed that is similar to its predecessors but can not only protect multiple assets at one time, but can also control and monitor through a single communications conduit. This significantly reduces initial capital required for cathodic protection systems in applications where multiple storage tanks, pipelines and well casings are co-located. However, because of the system modularity, power modules can be paralleled for higher power outputs.
Operators now have the benefit of a "one system fits all" solution. This leads to reduction of spares holding, easier engineer training and the benefits of reduced operating costs. Web-based portal software allows multiple personnel to monitor and securely control systems at one time. Operations and engineering users can be mobile, but still connected to their cathodic protection network.
The open architecture of the software system allows users to potentially integrate the cathodic protection systems into third party software analysis asset management products. A defect progression system allows the network to report faults (however infrequent) and expedite necessary rectification through to full network serviceability. These enhancements provide additional tools to underpin 100 percent asset integrity.
Safety is also at the forefront of advanced CP rectifier design. In recent years, older CP systems have become (due to the extended life of pipelines) less relevant to the needs of the modern corrosion engineer. Several high profile cases of fatalities and injuries due to exposure to potentially lethal voltages, a safe working environment when troubleshooting or setting up of an increasingly archaic infrastructure have made owner/operators increasingly aware of the need to enhance safety through training, shielding and system interlocks.
Among the most significant recent advancements in advanced CP systems is the ability to digitally implement setup, control and monitoring parameters. The simple issue of creating a panel with push buttons rather than the older method of hands-on manual turning of potentiometers with live potentials provides for a safer work environment. Physical error-proofing safety barriers as well as reducing the need to interact with equipment on-site increases personnel safety and reduces client liability.
The Future of Cathodic Protection
A modern CP system should not only be able to protect an asset or multiple assets but should also provide a quantifiable return on investment. It should be a total systemic approach with supplemental communications conduits and analytical software that are easily accessible from mobile locations and increase resource flexibility and responsiveness to specific unplanned events. It should have the ability to turn data into information by answering typical questions like where do we need to intervene? Or, how well is the system performing? By benchmarking against these common questions and integrating geographical and meteorological data, significant overall savings can be realized as well as proactive control of corrosion rather than responding to its effects and consequences.
Several decades have passed since implementation of the first hybrid switch-mode concept at the Piedras Coloradas oil field. However, from that simple idea of applying smarter technology in response to a client's environmental and economic needs, a new approach to cathodic protection emerged.
No longer is cathodic protection a necessary evil. Instead, it can extend the life of a production, transport or storage asset well beyond previous expectations and do so at a fraction of traditional costs. This makes new geologically challenging fields, such as those recently discovered in Brazil and elsewhere in Latin America, well placed opportunities for cathodic protection.
September 2009, Pumps & Systems