Managing Corrosion Of Pipelines That Transport Crude Oils: Part 2

April 2013, Vol. 240 No. 4

With the intense controversy surrounding the proposed Keystone XL Pipeline construction, unprecedented attention is being placed on the transportation of unconventional crude oil products, in this case diluted bitumen originating in the vast tar sands of Western Canada.

Although pipelines have long been recognized as the safest and most efficient means of transporting oil and natural gas products, the fact is their use still poses an intrinsic risk due to failures and leaks. Following the March 1 report from the U.S. State Department that said Keystone XL posed minimal risk, President Obama seems likely to approve the long-sought presidential permit needed to build TransCanada’s Keystone across international borders. That, however, will not make the issue go away, especially with those who believe the pipeline and the means of producing and refining the tar sands oil, will add to climate change.

To better understand how corrosion can impact the safety and reliability of transmission pipelines, NACE International asked several of its members in the oil and gas industry to discuss the challenges faced by the industry when managing corrosion of pipelines, in particular the pipelines that transport crude oils, particularly diluted bitmen (dilbit). The first part of this report was published in the March issue of P&GJ (visit www.pgjonline).

Panelists are Jenny Been with TransCanada Pipelines; Oliver Moghissi with DNV; Michael Mosher with Alberta Innovates-Technology Futures; Sankara Papavinasam, FNACE,(1) with CanmetMATERIALS; Trevor Place with Enbridge Pipelines; and Sonja Richter with Ohio University.

NACE: How does the industry typically control corrosion that may be caused by transporting crude oils?

Richter: There are two main ways in which corrosion of crude oil pipelines is controlled, by design and by mitigation. When new pipelines are designed, the material selection and the wall thickness allowance is determined based on a prediction of the corrosion using models that take the water chemistry, type of flow, temperature, etc. into consideration.

Once the pipeline is built, corrosion is monitored with corrosion measurements, and corrosion inhibitors are used to manage the corrosion. On top of that, companies employ pipeline integrity strategies by using inspection and preventive maintenance to ensure the integrity of the pipeline.

Moghissi: Corrosion is typically controlled by minimizing water contact with the pipe wall (i.e., low BS&W, flow rates above the critical entrainment velocity, avoidance of no-flow designs such as dead-legs, and pigging), chemical treatment (i.e., corrosion inhibitors and, rarely, biocides), and cleaning (i.e., pigging) to disrupt micro-organisms attached to the pipe wall.

Place: There are a number of common internal corrosion mitigation strategies, the selection of which is dependent on the commodity being shipped, the flow conditions in the pipe, and the expected corrosion mechanism. A simplified analogy for pipe corrosion is tooth decay. Tooth decay can occur if there is a build-up of food and bacteria in the nooks and crannies of your teeth. The foremost method of preventing tooth decay is routine dental care. If you brush regularly, you probably won’t have many problems with your teeth.

Similarly, if you sweep your pipeline clean of potential corrodents, you won’t have many problems with corrosion. Such sweeping can be purely hydraulic — by the flow of the product — or facilitated by pipeline pigs. Some people continue to have tooth decay even when they brush regularly, and those people might find that a mouthwash provides incremental protection by killing cavity-causing bacteria.

Similarly, a pipeline operator can use a batch corrosion inhibitor to reduce problematic bacteria or to provide a protective film along the pipe wall (just like fluoride strengthens tooth enamel). I must credit both Tom Jack and Joe Boivin for this analogy.

Been: Internal corrosion is managed through the use of preventive measures and monitoring tools. Normal pipeline operating conditions include turbulent flow to prevent water drop-out and solids deposition. Preventive measures include the use of cleaning pigs to remove deposits.

These tools are run at a frequency that is established based on operating history and an understanding of the deposition mechanism and corrosion rates. It is continuously reassessed, based on the volume and nature of sludge observed to be present. Other integrity assessments such as ILI are also leveraged in terms of adjustments to the cleaning program.

Mosher: The industry controls internal corrosion by three main mitigation methods. In the first method, crude oil pipeline operators maintain a turbulent flow regime to prevent the settling of solid particles and water droplets to the bottom of the pipe. In the second method, cleaning pigs remove any solids and/or water from the pipe surface and force them downstream. By taking away the solids and water from the pipe surface, the corrosive environment is removed.

The third method is a chemical corrosion inhibitor package, applied following a cleaning pig run to suppress corrosion in a location where water collects. The inhibitor accomplishes this by suppressing either the cathodic or anodic reactions. In some cases, a biocide may be added to the inhibitor package when MIC is believed to be a factor.

Papavinasam: The internal corrosion of production pipelines is primarily controlled by cleaning their surface using pigs and adding corrosion inhibitors and biocides. Crude oil transmission pipelines, on the other hand, are less susceptible to internal corrosion because they predominantly transport oil (more than 99%) and, by industry standard, their BS&W is limited to <1% (typically to <0.5%) volume to volume. All other corrosive substances are removed in the oil separators upstream of the crude oil transmission pipelines. However, the oil transmission pipelines may suffer internal corrosion in locations where water might accumulate. The operators control the internal corrosion by adjusting the flow rate so that water does not drop out and accumulate; using cleaning pigs to sweep off the accumulated water and sediment particles; and treating the surface with corrosion inhibitors and biocides. NACE: Are enough technologies available to effectively identify and control transmission pipeline corrosion or is more research and development work necessary to address the issue?

Papavinasam: Several advanced and reliable technologies are available and used in the industry. But there is always room for innovation and further improvements, and there are some specific areas where additional research and development is needed. For example, computer simulation and industry experience indicate that the locations where water may accumulate in oil transmission pipelines are different for light and heavy oil; yet the boundary where the transition occurs is not well established. Further R&D is required to develop and validate reliable models to accurately predict the locations of water accumulation based on crude oil types.

Also, laboratory methodologies to determine how the crude oils may influence the corrosivity of the water phase are established (ASTM G205); however, determining these properties requires withdrawing crude oil samples from the pipeline and carrying them to the laboratory for analysis. Advancements in techniques for online measurement of these properties would not only lessen the time lag between the sample collection and analysis, but also would alleviate errors due to possible contamination of the samples.

Additionally, ILI to directly measure the size and shape of the corrosion features is fairly established, but advancements in the algorithms and techniques to easily and quickly match the corrosion features from consecutive runs are required.

Been: The currently available tools and processes are sufficient to manage the internal corrosion threat for transmission pipelines; however, improvements and optimizations could be achieved with better predictive models regarding solids deposition and sludge corrosivity. We are actively involved in joint industry projects and R&D initiatives on internal corrosion monitoring and mitigation, including participation in public forums and conferences on crude oil corrosivity.

During these events, we share our operating experiences and relevant integrity management practices. One industry effort employs a pilot-scale crude oil flow loop for the evaluation of cleaning pig designs and chemical inhibitor treatments and the assessment of corrosion monitoring equipment for under-deposit corrosion.

Moghissi: Improving our technical understanding of transmission pipeline internal corrosion would be helpful, especially with respect to predicting where extreme-value corrosion rates might occur. In addition, improving systems and processes for managing corrosion risk would have an impact. This includes methods to incorporate corrosion in risk management systems. If corrosion risks were better tied to overall risk, operators could make more effective and efficient decisions.

Mosher: Technologies used in the detection and mitigation of internal corrosion for crude oil pipelines have progressed significantly in recent years but there is still a need for improvement and advancement. As long as corrosion failures are occurring, it is imperative that better technologies be explored through R&D and field implementation. If we are to ever meet the industry target of zero incidents, detection and mitigation technologies will need to improve, either by refining the current tools or developing new and novel technologies.

Richter: There is already considerable technology and know-how that goes into controlling transmission pipeline corrosion. However, new issues can surface, such as corrosion due to bacteria, which can occur under conditions that would not be very susceptible to acid corrosion. Furthermore, increased understanding of the fundamentals of the corrosion process and the mitigative methods needed to control it are an important aspect of keeping the state-of-the-art up to date.

Place: There is already a great deal of relevant technology available, but I don’t think any engineer or scientist would ever say that there is enough technology. We are steadily increasing our understanding of the flow conditions that could promote the accumulation of potential corrodents, and there are new test methods being developed to determine the corrosion-related properties of crude oils.

We have excellent pipeline inspection tools that rival medical-imaging techniques, and we are developing new and improved processes to quantify pipeline reliability. However, integrity management is all about putting another zero between the decimal point and a failure incident; in true reliability terms, these probabilities are already very low, but not yet zero. I am confident that the industry at large will continue to undertake more research and development in the pursuit of perfect system reliability.

NACE: How would you rate the industry’s track record in terms of managing transmission pipeline corrosion and preventing oil leaks and spills caused by pipeline degradation? Are current practices adequate or does more need to be done?

Mosher: I believe the industry’s track record for managing pipeline corrosion has been generally improving over the past couple of decades, despite facing an aging infrastructure. The industry has taken great steps to improve its integrity management systems; and this, in combination with ever-enhancing technologies for both corrosion detection and mitigation, will ensure an increasingly safer pipeline. Although the industry’s record is quite respectable, neither industry nor the public should remain content with maintaining the status quo. Current practices cannot be deemed adequate while spills and leaks are still occurring.

It is certain more work must be done to improve the integrity of our vital transmission pipeline network. To this effect, many of the larger pipeline companies actively support R&D efforts to improve their pipeline integrity.

Place: The statistics indicate that transmission pipeline performance is very good on its own merit, and extremely good as compared to other forms of hazardous materials transportation. That being said, our industry has experienced some significant releases in recent history, so there is an ongoing need to improve and ultimately achieve our goal of zero releases on an annual basis.

With the application of new technologies and continued growth in the application of reliability engineering principles, our industry performance continues to improve. There is significant investment by our industry through our research and development partner, Pipeline Research Council International (PRCI), as well as efforts led by the American Petroleum Institute (API), Association of Oil Pipe Lines (AOPL), and Canadian Energy Pipeline Association (CEPA).

Through these efforts our industry is well-positioned for continuous improvement. The world’s pipeline infrastructure is increasing in scope and capacity in direct response to our society’s ever-increasing requirement for transportation of these important cargoes. So while current practices are excellent, our industry’s perpetual desire for better and safer results lends itself to continuous learning and, therefore, changes and improvements in all of our integrity management practices.

Papavinasam: The oil transmission pipeline operation is mature and has a good track record. The industry has been successfully and reliably transporting oil in pipelines for more than 100 years. Studies have indicated that the amount of oil spilled from oil transmission pipelines as a consequence of failure is <0.0001% of the total amount of oil being transported by the pipelines. The industry strives hard to improve the overall management system and to ensure that all tools and information available are effectively and consistently used. These efforts will further enhance the track record of the industry. The industry is undergoing tremendous change in terms of workforce. It is important to properly and systematically educate the next generation so that vast experience gained over the years is not lost and past mistakes do not reoccur. Richter: As the infrastructure ages, the importance of corrosion management is increasingly being recognized within the industry and is taken very seriously. Current practices are adequate as they make use of state-of-the-art technology; however, it is advisable to continue to develop the technology and to increase the knowledge so we don’t fall behind. This is especially true when it comes to corrosion mechanisms that are rather poorly understood, such as under-deposit corrosion and microbiologically induced corrosion.

Been: In our short term of operation, we have successfully managed transmission pipeline internal corrosion. The combination of the 0.5% BS&W limit and typically turbulent flow predisposes internal corrosion on crude oil transmission lines to be a low risk. However, the application of cleaning runs, ILI, and thoughtful design to minimize dead legs further mitigates the already low risk.

Moghissi: Although current corrosion management practices are generally good, the occurrence of leaks indicates that more can be done. It is my opinion that improving our understanding of how corrosion affects total risk, especially from unlikely events, can reduce the number of future leaks and spills.

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