The availability of light tight oils (LTOs) is driving U.S. refiners to take advantage of the significantly higher margins available from processing this feedstock. But, these LTOs also pose corrosion issues.
Jake Davies, director of Permasense Technologies products at Emerson Automation Solutions, writes in his article, Continuous Corrosion Monitoring of Crude Overhead Systems, in Hydrocarbon Processing magazine, how continuous corrosion monitoring can help refineries find problems and avoid shutdowns. Jake explains the problem.
The production of LTOs relies on the use of fracking fluids, a cocktail of chemicals is used to stimulate oil to flow from the field. In many instances, these chemicals can end up in the crude oil feedstock to the refinery. In addition, the transportation of LTOs by railcar requires the addition of H2S passivator chemicals that can introduce other corrosion-related problems.
Processing of LTOs at a refinery increases the risk of corrosion across a wide area of the crude overheads system. This can result in unplanned shutdowns driven by unacceptably high corrosion activity. If unnoticed and unmitigated, increased corrosion can lead to a hydrocarbon leak and, in the worst case, result in an explosion or fire. Continuous corrosion monitoring using Permasense sensors solves the problem, and Jake says the technique is being widely used.
Oil and gas facility operators worldwide are solving this puzzle by deploying continuous wall thickness monitoring systems to track corrosion in critical locations. Not only does tighter monitoring enable cost-effective tracking of corrosion in areas of concern, it also enables a refiner to pinpoint specific feedstock or process operations causing accelerated corrosion rates.
Jake goes on to explain that crude tower overhead systems are particularly susceptible to corrosion and offers a detailed description of how Permasense corrosion sensors work, and where to place them in the overhead systems.
A typical overhead monitoring system would consist of 20-30 measurement locations, with between two and five sensors per location, for a total of 40 to 150 sensors, depending on the system configuration, metallurgy and operating conditions. Real-time corrosion data from ultrasonic sensors installed in the crude overheads system provides an effective understanding of the equipment integrity and the effectiveness of the overhead chemical treatment program.
Jake offers two examples of refiners using corrosion monitoring with great success. In the first case, corrosion monitoring is used to adjust chemical treatments. In the second case, a refiner is identifying differences in batches of crude that caused increased corrosion.
A European refiner used a network of ultrasonic sensors installed across the overhead system to adjust the treatment chemical dosage to stabilize corrosion. Once the chemical dose was optimized, the sensor data showed that the corrosion trend had been stabilized. A North American refiner was able to monitor corrosion rates in the overhead system attributable to specific batches of crude. Analysis showed a high and unusual level of organic chloride in the crude oil, probably due to the use of well-stimulant chemicals in the upstream oil production process. This refiner now routinely tests every new batch of crude feedstock for organic acids to pre-empt any corrosion problems.
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