Corrosion risk is great, and incidents can be severe – potentially endangering lives, therefore there is increased need for corrosion control in refineries. Even slight changes to the process can affect corrosivity greatly. Changing crude diets, flow rates, yields or inhibition levels can impact negatively on asset integrity. Monitoring periodically through techniques such as manual inspection do not provide the granularity, accuracy and repeatability found in continuous monitoring. This makes it impossible to correlate corrosion events to asset integrity, and the real result is refiners operating reactively and not proactively.
There are lots of potential methods for measuring corrosion such as inline corrosivity monitoring or periodic manual inspection. In addition, refineries can install fixed corrosion sensors to areas to continuously monitor wall thickness, and therefore corrosion, such as Rosemount™ Wireless Permasense corrosion monitoring solutions.
Traditional Ultrasound Monitoring
Traditionally, wall thickness monitoring has been performed using manual ultrasound. Manual ultrasound is infrequent and has poor repeatability. A lot of it comes down to the technician rather than the equipment, and it allows movement of the transducer to give a good reading, which usually means the same part of the pipe is not being measured.
In addition, manual ultrasound methods have the following disadvantages:
- High temperatures: Temperatures above ~100˚C (212˚F) can permanently damage the NDT (Non Destructive Testing) equipment. There are also safety risks to the NDT technician at higher temperature locations.
- Physical access: The NDT technician needs to have access to the equipment at the measurement location of interest, which requires scaffolding (possibly permanently installed) and stripping of insulation to expose the metal work to make the manual measurements, bringing significant cost.
Wireless Sensors for Continuous Corrosion Monitoring
Utilising permanently mounted ultrasonic sensors measuring wall thickness and employing wireless data retrieval are fast becoming best practice in refineries. The sensors are simple and cost-effective to deploy at scale and provide a quality and frequency of data that is otherwise unavailable. The data informs a wide range of operational decisions due to its sensitivity to small changes in wall thickness, robustness to extreme plant conditions, and extended battery life enabling reliable operation over the entire cycle between turnarounds. Data is transferred using WirelessHART® communications to the end users’ desk, allowing frequent, reliable, and safe wall thickness monitoring.
The range of commercially available sensors offer continuous operation at pipe temperatures up to 600˚C (1100˚F). A variety of mounting techniques offers quick and easy deployment of large sensor systems, enabling scalable digital transformation quickly.
Corrosion Monitoring System
The sensors mounted in the plant are only one part of the system, which relies on industrial WirelessHART technology to retrieve the data. Devices require new batteries up to every nine years, meaning that between scheduled shutdowns, data is retrieved without manual intervention to the plant. WirelessHART as a technology is perfect for this application, with many plants already having wireless networks running, corrosion sensors can be added easily, boosting the robustness of the mesh whilst adding valuable insight into the health of the assets.
Data retrieved is fed into Plantweb™ Insight, an industrial analytics solution, which offers instant visibility to key assets, enabling better and faster decisions to digitally transform operations. Plantweb Insight delivers known solutions for known problems in an easy to interpret manner. With pre-packaged analytics focusing on the health monitoring of plant assets, the corrosion software applications give end users the ability to monitor both the risk and impact of corrosion in their plant. A range of analytics supports abnormal situation identification to mitigate safety related incidents, as well as managing routine maintenance and turnaround scope and schedule.
There are benefits to this software interface over other technologies which allow wall thickness reading directly from the device. Onboard sensor processing typically results in lower quality readings as measurements do not consider the historical trend of the data. Patented Adaptive Cross Correlation (AXC) processing reduces noise typically seen in ultrasonic wall thickness measurements, by using a proprietary machine learning algorithm. This unique ability is one key differentiator between Rosemount Wireless Permasense devices and others, which typically use rudimentary signal processing techniques that are prone to error and inaccuracies.
Best quality and reliable measurements are key when it comes to predictive maintenance. Built-in tools allow end users to see accurately the point of retirement of the asset or piping, allowing early replacement scheduling, and consideration of metallurgy for future corrosion resistance. Wall thickness data can be combined to correlate periods of increased corrosion with process data, considering that crude TAN, flowrates, inhibition strategy often affect corrosion rates in fixed assets.
Online non-intrusive corrosion monitoring is fast becoming refining industry best practice with the availability of data-to-desk monitoring systems that provide previously unachievable quality and frequency of online wall thickness measurements. Permanently installed Rosemount Wireless Permasense sensors deliver wall thickness measurements directly to the desk for analysis by engineers and inspectors and have demonstrated the ability to know the current condition of the equipment at any point in time with no additional maintenance or costs since the system was installed. The quality and frequency of the measurements enables variations in corrosion rates to be detected, measured, and acted upon while the plant is operating.
Emerson’s customers can maximise their operations, both in productivity and profitability, whilst balancing the impact of corrosion on their fixed assets, by utilising online corrosion monitoring. Combining reliable and continuous corrosion data with any process data is now easier than ever, when using the new Plantweb Insight software platform. With over 300 installations worldwide and over 25,000 deployed, Rosemount Wireless Permasense non-intrusive monitoring solutions are industry leading.