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S P E C I A L F E AT U R E Managing Corrosion of Pipelines that Transport Crude Oils A cleaning pig appears clean in the receiving barrel with only a small amount of sand on the rubber. Photo courtesy of Jenny Been, TransCanada Pipelines. transport crude oils. 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. (See their biographies in the sidebar, "Meet the Panelists," pp. 32-33.) MP: The oil industry is facing concerns by the general public that heavy crude oils, particularly diluted bitumen (dilbit), are corrosive and can lead to leaks and oil spills from transmission pipelines. What are the main challenges the industry faces when managing corrosion of pipelines that transport crude oils? Moghissi: Internal corrosion is one of many possible threats to a crude oil transmission pipeline that must be managed. It should be noted that crude oil by itself is not corrosive at pipeline conditions, but water can drop out of the crude oil and allow corrosion to occur where it accumulates. Water carried by heavy crude oils, including dilbit, does not signifcantly differ in corrosivity from water carried by other crudes. Corrosion in crude oil pipelines is addressed by conventional corrosion control practices (1) FNACE denotes a NACE International Fellow. 30 MATERIALS PERFORMANCE May 2013 and is generally effective. However, pipelines travel over long distances, and what is considered unlikely at one location can become signifcant when summed over a pipeline infrastructure. Place: Crude oils, including dilbit, are not corrosive in pipelines. The main technical challenge is that trace water and sediments—not the crude oil—cause corrosion. The presence of crude oil, including the dilbits we have tested, actually decreases the corrosiveness of the standard brine used in standard testing. Although we know that we have a minimally corrosive system, we think it may be possible to reduce corrosion even further—and this possibility is what drives our research and development efforts. It is challenging to accurately measure very small or very rare things, and the corrosion that occurs in transmission pipelines is typically isolated and progresses rather slowly; this makes it diffcult to identify and assess the likelihood of internal corrosion, and also to evaluate the benefcial effects of mitigation activities. Mosher: One of the main challenges facing the industry with respect to managing corrosion of crude oil transmission pipelines is the diffculty in predicting internal corrosion. Most internal corrosion in crude oil transmission pipelines is caused by the settling of solid particles that can carry water to the pipe surface. Transmission tariffs are set to limit basic sediment and water (BS&W;) to <1% (often 0.5%). The solid particles tend to be encapsulated by a layer of water that may concentrate water on the pipe wall surface. This creates the potential for corrosion to occur if the fow conditions of the pipeline system allow for these solids to settle out. The water (an electrolyte) is a necessary component of the corrosion cell. Without it, corrosion will not occur at appreciable rates within the transmission pipeline. This type of corrosion is typically referred to as underdeposit corrosion and will often manifest as localized pitting. Moreover, pitting corrosion can proceed rapidly or lay dormant for extended periods of time, making this type of corrosion particularly diffcult to predict. Richter: The main challenge is to manage the water that is transported along with the crude oil and is responsible for the cor- rosion that occurs if it is in contact with the pipeline wall. Crude oils are not corrosive at temperatures encountered in pipelines. It is not until crude oils are heated in refneries that they can become corrosive. The industry severely limits the amount of water allowed into transmission lines to <0.5% by weight. While this small amount of water (which is heavier than the oil) can easily be kept off the pipeline wall and entrained in the crude oil, it is a challenge for the industry if production (and fow rates) decreases, making it more challenging to keep the water entrained and off the pipeline walls. However, heavier crude oils entrain the water more easily than lighter crude oils, which is benefcial for corrosion protection. Papavinasam: The main challenge the industry currently faces is to establish public confidence that the risk due to internal corrosion of oil transmission pipelines is low and that the risk can continue to be managed at the lower level using established engineering practices. Under normal oil transmission pipeline operating conditions, corrosion occurs by an electrochemical mechanism. Crude oil (including dilbit), being a nonconducting electrolyte, does not support corrosion. However, if the crude oil contains water, then corrosion may take place in those locations where water drops out of crude oil and comes in contact with the metallic surface. The bulk crude oil may indirectly affect the corrosion by infuencing the locations where water may accumulate and by infuencing the corrosivity of water in those locations. The pipeline operators keep the risk of internal corrosion in oil transmission pipelines at a lower level by limiting the amount of water to <1% BS&W; (typically to <0.5%). However, based on some non-scientifc reports and extrapolation of corrosive conditions of refneries (operating above 200 °C) to the conditions of oil transmission pipelines (operating typically below 70 °C), some members of the public are concerned that crude oils are corrosive. MP: What are the characteristics of crude oils and the transportation process that could lead to transmission pipeline corrosion? Are some crude oil grades more corrosive than others? NACE International, Vol. 52, No. 5