Approaches to Corrosion
A panel of Southwest Research Institute (SwRI) scientists and engineers recently talked with Technology Today about their respective research into corrosion’s effects, its detection and prevention.
A book on corrosion monitoring that Dr. Lietai Yang recently edited cites a 1998 U.S. Federal Highway Administration study indicating that annual direct costs attributable to corrosion amounted to $276 billion, or 3.1 percent of the nation’s gross domestic product. How accurate is that number, a decade later?
Yang: There was a report in 1950 that put the number at 2.1 percent of GDP. Another report in 1970 had the percentage at 3.5, and in 1974 there was a report in which the number was 4.5 percent of gross domestic product (GDP). Therefore, the number should be around 3 percent, so I don’t think it has changed. There are also reports from other countries, including the United Kingdom, Japan, Kuwait and Australia. The one in Japan mentions 1.2 percent of GDP. The numbers from other countries range from 1 to 5 percent, so the average is about 3 percent.
Light: An additional factor is that there’s a lot more aging; meaning things are not being replaced like they used to be. Because of cost and reduced government funding, I think the likelihood of having problems with corrosion is increasing. A lot of industries and governments are having to extend the life of a lot of things, and the major factor that’s causing damage is corrosion in most cases.
Shukla: An example is the nuclear reactors that we built in the United States. Some of them were built 40 years ago. As these reactors age, the cost of maintenance and keeping up with the corrosion issue increases.
Cragnolino: When there is a concentrated effort to increase knowledge about controlling corrosion, with appropriate research and proper prevention decisions, there is a reduction in corrosion for that period. Even though they are aging, the American nuclear power plants are far more efficient in terms of availability than they were in the ‘70s and ‘80s.
Mintz: It’s not only the efficiency of the plants, but also the techniques to monitor corrosion. Now the operators use new probes and a whole array of new technologies. That technology detects corrosion much better, before it gets to be a problem.
Dunn: The U.S. Government Accountability Office prepared a report in 2007 that put the cost of corrosion in Army vehicles and Navy ships at $4.5 billion a year. One of the difficulties encountered in determining the cost of corrosion, particularly in the Department of Defense, is that it’s difficult to go back and calculate the actual cost when there is insufficient documentation. Often when a part fails, it gets replaced and documented as a maintenance cost that is not necessarily associated with corrosion.
Of the $276 billion mentioned before, $138 billion was the direct cost due to corrosion, broken down into the following different industries: Infrastructure, $22.6 billion; production and manufacturing, $17.6 billion; transportation, $29.7 billion; utilities, $47.9 billion; and government, $20.1 billion. What do these numbers say about the strategies for dealing with corrosion among different sectors?
Dunn: I think the utilities have done a better job of accounting for the costs of corrosion. The infrastructure cost is an estimate that’s getting more attention now, but as Glenn mentioned, there are aging structures in our society such as airplanes and also bridges. The real cost of rehabilitating those bridges is not well known or well characterized. I believe that the cost of those things will go up, along with the costs of building materials and labor costs. The full extent of the problem is yet to be known.
Can you give examples of corrosion-related disasters?
Light: A pipeline explosion on August 19, 2000 in New Mexico killed 12 people and served as a wakeup call to the pipeline industry. There have also been some environmentally bad, but not fatal, catastrophes such as a pipeline leak in Alaska that went unreported for days or weeks, later determined to be caused by corrosion.
Mintz: The nuclear industry had clear warning back in March 2002 with a plant in Ohio when one of their nozzles in a reactor head failed. There were indications of corrosion but operators were unaware of it. Part of the pressure vessel head had actually corroded away. There was a pineapple-size hole in the reactor head, with only about a quarter-inch of stainless steel cladding remaining between the inner reactor vessel and the containment. They later found that there was cracking in that cladding, so that was a major wakeup to the nuclear industry. The power plant was out of operation for two years, and at $1-2 million a day, that hurts.
Cragnolino: The most infamous case involving infrastructure was a bridge over the Ohio River that collapsed on December 15, 1967 and caused 46 deaths. Corrosion-related cracking was the main cause. Some people think the more recent case of the bridge in Minneapolis in August 2007 is also related to a corrosion failure, combined with mechanical vibrations and perhaps design defects.
Yang: The cost of the Minneapolis Bridge failure is huge. At least 13 people were killed, and many more were injured. In addition to the cost of building a new replacement bridge, people there would not have a bridge for at least one year.
Dunn: You also can’t forget about airline-related issues, like the tragic Aloha Airlines flight where a section of the plane was lost from a corrosion-related failure. One flight attendant was killed in that incident. Fortunately, the plane was able to safely land, quite miraculously I think.
What specific approaches, or specific technologies, for corrosion detection and control are unique to your work?
Shukla: Recently, we were approached by a company to take a look at test methods for coating evaluation. They are asking us to develop test methods that are really not available in books. For that project, we would evaluate coating performance at high temperatures ranging from 120 to 160 degrees Celsius. The coating will be subjected to elevated temperatures when a pipeline is carrying hot fluid. So based upon our work for the Nuclear Regulatory Commission-funded repository program and our understanding of the thermodynamics of test solutions, we are proposing new test methods for evaluating the performance of coatings used to mitigate corrosion of the external surface of pipelines employed both offshore in seawater, and onshore above or below the ground.
Dunn: We do some standardized testing, of course, but we do quite a bit of evaluation development and specialized evaluation in many of the capabilities that we have, especially in the area of high-temperature, high-pressure conditions. We have experience and unique capabilities for evaluation in environments with very toxic gases, and with corrosive media that also are physically hazardous.
Eberle: Certainly the radioactive tracer technology is unique as well. It’s been done by other institutes around the world but in very specialized situations. Having the appropriate licensing and the ability at SwRI to handle radioactive materials gives us a big advantage in being able to do this. A typical refinery wouldn’t have the licensing to be able to do that.
Chiang: Beginning two years ago, NACE International, formerly the National Association of Corrosion Engineers, formed a specific technology group to work with the technology of coupled multi-electrode array sensors for real-time corrosion monitoring and corrosion studies. The Institute developed a unique system using this technology. More and more companies and industries are starting to use this system.
Mintz: The range of special capabilities in corrosion is what makes Southwest Research Institute stand apart. I’m working on a proposal where a potential client is asking us to research corrosion at really high temperatures. We’ve got automotive laboratories that we can combine with our capabilities and generate projects that can’t be done in a small, startup corrosion lab. Many labs may have the corrosion expertise, but not the high-temperature automotive expertise.
Just how important is it to work in an interdisciplinary environment?
Shukla: Somebody long ago told me that a problem does not know which discipline it belongs to. A problem is a problem, and a multidisciplinary approach is needed to solve corrosion-related problems as well. We can put together expertise from different disciplines to solve various kinds of corrosion problems.
Dunn: It is very important. We had a client come to us a couple of years ago with a very significant corrosion problem. They were an original equipment manufacturer for an automotive manufacturer. I made a few phone calls to people in the automotive divisions and we met, put a proposal together to address the client’s needs, and sent it to the client. We successfully conducted the project.
Shukla: We conduct independent studies to evaluate long-term corrosion performance of nuclear waste containers. Some of us know corrosion, but in the background we have geochemists and hydrologists working on identifying the chemical and thermal environmental conditions that could arise in the potential nuclear repository site. The chemical and thermal environmental conditions, coupled with knowledge gained on various corrosion processes for the waste package material, help us estimate waste package lifetime. That multidisciplinary approach to solving problems is uniquely available here at the Institute.
Dunn: Pipeline companies have corrosion-related issues, of course, but in addition to that, other issues arise when they know a pipeline has been in operation for some period of time and it has some corrosion. They’ve done some nondestructive evaluation, they’ve used pigs to inspect the pipeline, and now the question is, under what conditions can they safely operate this pipeline? Some of the work we do combines inspection data with stress analysis and uncertainty analyses to determine what the maximum safe operating pressures would be for those pipelines.
How much of your work is related to the prevention of corrosion?
Light: In my area of business, which is primarily for the pipeline industry, probably about 80 percent is related to the detection of corrosion. We inspect for it, and detect it and monitor it.
Mintz: In my area, in the Center for Nuclear Waste Regulatory Analyses, where we are basically doing life prediction, most of our work is in predicting when corrosion will occur, and understanding that.
Chiang: In the high-temperature corrosion area, all of the materials have to use coatings to extend their life. So coating development is a big part of that, too.
Shukla: I personally believe that corrosion detection and corrosion prediction are two sides of the same coin. Often the same electrochemical parameters are used to predict and detect corrosion. Therefore, if you can predict when the corrosion will occur, that also helps knowing, on the other side, when and where to look to detect corrosion.
Dunn: In the Materials Performance and Characterization Section, about 70 percent of our work is either corrosion detection or corrosion prevention. That includes corrosion-related failure analyses.
How about addressing corrosion mitigation or corrosion reversal, or failure analysis?
Light: We’ve been working on the fringe of technologies to mitigate corrosion. For example, a lot of pipelines use what’s called an overwrap. If operators find corrosion, as Darrell said, the question they typically ask is, how much longer can I use the pipe or can I use it at all? One solution is a fiberglass overwrap that will give the pipe strength in that one area where corrosion is detected. We are there to inspect how well that overwrap works.
Mintz: Most in-situ techniques would be considered detection, not mitigation. But now we’re going to these online sensors, the same technologies that were being used to detect before, but which now would be categorized as a mitigation strategy.
Yang: At SwRI, we are working on a wide range of monitoring methods, including electrochemical methods, a radiotracer method, and nondestructive evaluation methods, which are used more and more for corrosion monitoring.
What would you see as the trend in industry; toward monitoring, or toward corrosion-resistant materials? Would the emphasis be on prevention, or would it be on monitoring and control?
Light: I think there’s two approaches to this: the scientific-engineering approach, and the operator approach. The operator approach is trying to detect it and monitor it. The science and engineering approach is trying to develop corrosion-resistant materials. They probably save money with corrosion-resistant materials, but I think corrosion is so generic and overwhelming that it always finds a way. It’s sort of like Murphy’s Law: No matter what operators do, they’re going to have corrosion.
Dunn: I think you’re going to have both, and there are a couple of trends that I believe will be important. Condition-based maintenance is one of them. Condition-based maintenance is going to be a requirement for Air Force aircraft because they have significant corrosion-related issues. It is likely to be implemented in other parts of the Department of Defense and probably in other industries. There are certainly needs for developing new materials, but there are limitations. Some of the corrosion-resistant materials, the coatings, cannot be made in a bulk form. Coatings need to be used in order to combine the strength of a base metal and the corrosion-resistance of the coating. One of the challenges for new material development is the need to have a better understanding of the material-environment interactions, and the important factors that contribute to the various corrosion processes.
Light: Also, as humanity pushes for more energy, and more of this and more of that, we’re going where no man has gone before in a lot of cases. A program on television recently showed that there was significant corrosion and growth of microbes in completely saturated sulfide environments. You’d think that nothing can live in that, but there’s all kinds of microbial stuff growing there. We’re putting oil derricks and steels and all kinds of materials in the oceans where some of that occurs.
Mintz: In the nuclear energy industry, we haven’t seen a new power plant built in the U.S. in roughly 30 years. You’re not dealing with new materials because it would be too expensive to think about replacing every pipe. So instead, it’s more practical to think about detection and inspection and monitoring techniques. The method used depends on the industry.
Dunn: However, there is significant interest in newer, high-temperature gas-cooled reactors Ñ those are going to operate in a temperature regimes that are well beyond what has been seen before. There’ll certainly be new problems that develop because we don’t have enough knowledge about the material-environment interactions under these conditions.
Chiang: Operators have materials working at higher temperatures. Because they have higher performance, operators also expect them to have a longer life. There is continuous movement toward higher performance, and higher temperature, and longer life.
Eberle: In the case of refineries, with the oil shortage, operators are drilling deeper and deeper in the oceans, and a lot of those oils have much higher total acid numbers than refiners have typically been used to handling. The Athabascan tar sands present similar challenges. A lot of refineries have already up-alloyed to be able to process these crudes, and they’re putting more money into research to be able to better understand and prevent naphthenic acid corrosion.
What are the trends for being able to expand our knowledge base in the future, and what is the likelihood that it will be accepted by industry, as opposed to going with something more tried-and-true?
Light: I think the operators and the construction companies are trying to satisfy a specification, as cheaply as possible. One of the things about inspection that led to condition-based monitoring and inspection is that inspection is done routinely, and there’s an expense associated with that. There’s a push to be more efficient; to monitor, and only to inspect at the first signs of corrosion.
Dunn: As plants and infrastructure age, the tried-and-true technologies that are used, and the limitations associated with these technologies, become apparent. Also, new degradation mechanisms are discovered that were not known when these plants were originally built.
Overall, how are newly built structures safer from corrosion-related failure today than they were a decade or two ago?
Light: I think builders have tried to address the known corrosion factors in most of these plants. But every time a new material goes into a plant it somehow surprises us with a new or unexpected corrosion mechanism. I think safety has really been improved, but operators have to be constantly vigilant to make sure they’re not missing something.
Mintz: Ten or 20 years seems like a long time, but for some corrosion processes, that’s when things are just getting started.
Dunn: We’re better today in those situations where we’ve taken the knowledge that’s been gained and applied it, but aging infrastructure remains a long-term problem. The U.S. Air Force is still flying its 40-year-old KC-135 tanker. It was designed for a lifetime of 20 years, and they’re going to fly it for another 40 years. The U.S. military is flying helicopters in Iraq that were designed for Cold War operations in Europe. There have been significant corrosion-related problems in Iraq that nobody thought would occur, because of the corrosive sands that are encountered there. The need to fly at higher altitudes with greater loads puts additional stresses on the aircraft. There are also more demanding operational tempos in the current theater of operations, and that limits the time available for inspection.
Yang: I think if there is a common thread throughout this discussion, it is that clearly the corrosion problem is insidious and must be attacked from all angles, all the time. To do this requires a combination of investment, vigilance, commitment and innovation on a scale that calls on the combined skills of many areas of expertise. Here at the Institute, we are dedicated to applying a multidisciplinary approach to many aspects of corrosion, including prevention, detection, monitoring and mitigation.
Published in the Spring 2008 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.