What is corrosion monitoring?
Corrosion monitoring is a process that involves assessment of crucial components, structures, industrial materials, process units, facilities, and plants for signs of corrosion.
Corrosion monitoring helps to analyse the rate, exact location, and the cause of corrosion. Regular corrosion monitoring can extend the life of your asset, ensure safety and reduce replacement costs. There are many corrosion monitoring equipment available in the market that help in analysing corrosion in pipelines, petrochemical plants, chemical, etc.
A significant benefit of implementing a corrosion monitoring program is to detect the early signs of corrosion and deploy techniques that prevent creating a corrosive environment. Moreover, with the help of corrosion monitoring, you can check how effective your current corrosion prevention method is.
Importance of corrosion monitoring
Damage caused by corrosion is a significant threat to process-intensive industries. Equipment that have been purchased long ago are more susceptible to corrosion. Over time, they lose their ability to endure harsh environmental conditions. An active corrosion monitoring program improves the safety of the equipment, maximizes its efficiency and reduces maintenance cost.
In case of existence of a damaging corrosion process, corrosion monitoring will help in detecting the early warnings. Once you are aware of a malfunction, you can take the right preventive measures to stop further damage. Also, it will make it easy to analyse the correlation changes and their effects on the system’s corrosion. With the help of corrosion monitoring, it becomes easy to investigate the causes and parameters controlling the corrosion. Moreover, it helps in evaluating the performance of a particular corrosion control method.
Corrosion Monitoring Techniques
Corrosion testing for any material depends on the type of service environment it will be subjected to. The testing takes place through a liquid or gaseous medium, under static and dynamic conditions and different temperatures and pressures.
Several techniques help monitor the effects of the occurrence of corrosion. These techniques are:
- Electrical Resistance Monitoring
The Electrical Resistance or ER technique is a commonly used method to determine the change in a metal element’s resistance as it rusts in a process environment. Corrosion minimizes the cross-sectional area of the element, thus increasing the electrical resistance. In the case of uniform corrosion, the resistance change is proportionate to corrosion increment. The total corrosion can be obtained after taking multiple readings over a period of time.
Electrical resistance probes adapt well to any corrosive environment. This technique is simple to use and allows for periodic or continuous monitoring for one or multiple probes.
- Electrochemical Methods
Corrosion is an electrochemical process, and this is why electrochemical methods can help to monitor corrosion in materials. Linear Polarisation Resistance Monitoring and Galvanic Monitoring are widely used in electrochemical techniques. Electrochemical techniques are different from ER technique because they offer rate information, unlike the ER technique that provides information on the total loss of material.
- Linear Polarisation Resistance Monitoring
The Linear Polarisation Resistance Monitoring also known as the LPR technique, works on a microscopic scale. It detects the microscopic corrosion cells that are present within the plant. The method is ideal for calculating the corrosion current flowing between anodic and cathodic half cells. To measure the current flow, a small voltage is applied to a corroding metal electrode. Since the ratio of voltage to current is inversely proportionate to the corrosion rate, it becomes easy to calculate the corrosion.
- Galvanic Monitoring
This technique forms its basis on the fact that two different metals, when immersed in an aqueous liquid, assume different electrode potentials. Externally connecting the metals will lead to current flow due to the half-cell reactions occurring simultaneously and leading to corrosion of the more negative metal. This will also reduce the availability of any species like oxygen at the positive electrode’s surface. Removing oxygen from the system will lead to suppression of the reduction process and the galvanic current falling to a low level, showing the reduced corrosion rate.
This is a ratiometric metal loss measurement device featuring a resolution better than existing ER based devices. The resolution is at least 100 times better. This method is perfect for examining oil/gas production and processing systems. It is also suitable for determining sand erosion in producing systems.
- Hydrogen Monitoring
This method involves the detection of hydrogen in plants, indicating the presence of corrosion. Plants that are exposed to wet sour gas or acid solutions have higher chances of generating hydrogen. As the hydrogen gets directly absorbed into the plant’s fabric, there are chances of occurrence of blistering, stress corrosion cracking, etc.
To check the presence of hydrogen in a plant, hydrogen monitoring probes can be inserted into the plant or connected to the outer of the plant in a saddle mode. However, it is important to ensure that this saddle mode is capable enough to detect the diffusion of hydrogen through the plant.
- Weight Loss Coupons
This method involves exposing a coupon or specimen of the material to the environment for a set period of time to check for the resulting weight loss. The specimen can be in any shape – be it of a disc, plate or rod. Though this method is a great way to detect corrosion, it requires a lot of manual work. Also, it’s essential to know that the coupons only offer data for integrated corrosion loss.