Corrosion has become an important issue in refineries as incoming crude conditions change and plants age. By following best practices in design, chemical treatment and corrosion monitoring—refineries can mitigate corrosion risk.
Christiane Lederer, in her article, Getting the Measure of Corrosion, in Hydrocarbon Engineering, November 2017, says the risk of corrosion is great in hydroprocessing units.
The growing demand for transportation fuels and the shift toward diesel makes hydroprocessing increasingly important, even with an increasingly challenging feedstock of heavier crude slates with higher contaminant levels. The three main types of corrosion (ammonium bisulfide, naphthenic acid and H2 S corrosion) affect different areas of a hydroprocessing unit.
Two of the major hydroprocessing applications are hydrotreating and hydrocracking. Hydrotreating removes undesired feedstock components and reduces contaminants, such as sulfur and nitrogen, to avoid catalyst poisoning and mitigate downstream corrosion. Hydrocrackers break down carbon-carbon bonds from heavy feedstocks to produce higher value products such as gasoline, kerosene and diesel components. Both are high-temperature and high-pressure processes, Christine notes.
In both hydrotreaters and hydrocrackers, the feed is passed to exchangers, heated by the reactor effluent and a fired heater, and fed to the reactors at 700 – 750°F (370 – 400°C). Service of steels in high temperatures over 450°F (232°C) and under high pressure hydrogen require material selection and design standards to mitigate corrosion and cracking.
Changing crude slates and aging assets create new corrosion challenges that economically threaten refiners due to unplanned shutdowns, calling for an active approach to asset integrity monitoring and corrosion mitigation. Depending on the corrosion mechanism and application, various strategies can be used, including changing the metallurgy, chemical injection to inhibit corrosion, manual inspections and corrosion monitoring. Christine points out that corrosion monitoring is needed to determine the efficacy of all these solutions.
It’s a best practice to continuously measure wall thickness and compare relative measurements over time. Corrosion monitoring can include intrusive methods (monitoring the process fluid) and non-intrusive methods (continuously monitoring the pipe wall thickness with ultrasonic sensors).
Several corrosion monitoring tools are available with different benefits and limitations, including in-line probes and non-intrusive sensors. Ultrasonic corrosion monitoring is one of the technologies available. It provides the data required to make proper decisions on a continuous basis, and provides this information directly to plant personnel. For example, Emerson’s Permasense WT210 ultrasonic sensors can monitor corrosion on a real time basis, allowing refineries to measure the effectiveness of corrosion control methods. And Christine notes that Permasense ultrasonic sensors are low cost and easy to install.
The installation costs of Permasense ultrasonic sensors are low as they do not require intrusion into the process. Process shutdown is not required because sensors are installed without pipe penetrations. Wireless data retrieval enables cable-free installation, further reducing installation and operating costs. The sensor power modules are designed to last until the next plant turnaround (typically, nine years is achievable), so no access is required between turnarounds.
Once installed, these sensors measure the thickness of the pipe wall and send data directly to server-based analysis software via a wireless network, or to any plant monitoring system. This allows refinery engineers to analyze the effectiveness of anti-corrosion measures.
Corrosion control techniques can be effective when evaluated for efficacy and optimized in real time. This can be accomplished with ultrasonic corrosion sensors.
You can find more information like this and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the WirelessHART and IIoT Groups and other specialty areas for suggestions and answers.