The oil gas industry depends on its infrastructure to keep product flowing. With thousands of miles of pipeline spanning its facilities, maintaining asset integrity is of the utmost importance. Any unexpected failure in the piping can have disastrous consequences on in multiple respects, leading to loss of product, serious environmental concerns and regulatory penalties, just to name a few. Operators in the oil and gas sector must be diligent about minimizing their operational risks, which means any signs of deterioration and degradation need to be acted upon quickly to prevent these issues. However, the sheer scope of their infrastructure makes traditional inspections virtually impossible.
This is why the industry turns to technology to provide insights into the condition of their pipelines. Corrosion monitoring techniques and devices make it possible for operators and technicians to keep a close eye on their assets without a lot of effort. This enables them to spot early warning signs of failure so they can be addressed in time to prevent the worst-case scenario.
There are two main techniques for corrosion monitoring in the oil and gas sector — corrosion coupons and corrosion probes. Although they serve more or less the same purpose, they go about it in different ways. Which method is best at detecting the early signs of corrosion, depending on the circumstances? Knowing the pros and cons of each approach can be critical for keeping assets in good working condition.
What is a Corrosion Probe?
A corrosion probe is a device inserted into the pipeline at strategic locations. There are two main techniques these instruments use:
- Electrical Resistance: A sacrificial element is exposed to the process fluid, with its electrical resistance compared to a reference element sealed inside the body of the probe. The change in electrical resistance over a fixed period is directly proportional to the material’s average corrosion rate for that same period.
- Linear Polarization: Because the electrical conductivity of a fluid is correlated to how corrosive it is, these probes can monitor the reactions occurring inside the pipeline by measuring the current between two charged electrodes.
Either way, probes enable technicians to observe the rate of corrosion, comparing the results from the probe to the average corrosion rate of the pipeline material over the same fixed period. Any deviations from the corrosion rate measured by the probe indicate there is an issue that needs to be addressed.
One of the key advantages of probes is how quickly they can provide results. In the case of linear polarization probes, they can deliver real-time data that enables immediate discovery of any changes within the pipeline. On the other hand, they require specialized equipment as well as costly installation and calibration to function as intended. Another limitation is that they are only capable of monitoring corrosion in the area immediately surrounding them, which means they may not be helpful in detecting corrosion elsewhere in the system.
What is a Corrosion Coupon?
Although more of a low-tech solution compared to probes, corrosion coupons also provide an effective means of measuring corrosion rates inside pipelines. These are samples of material inserted into the process fluid and left for a specific amount of time. At the end of the cycle, they are removed and weighed. The difference in their weight between when they were inserted into the stream and after they are removed is used to measure the rate of corrosion and metal loss. Additionally, other indicators such as the buildup of any deposits are taken into consideration.
These coupons are made from the same material as the pipe or vessel being monitored, or a material that is similar in chemical composition. They are attached to coupon holders that are inserted into access fittings installed in specific locations throughout the pipeline.
Among the benefits of using corrosion coupons is that they are relatively simple and inexpensive to use, requiring no specialized equipment. However, they can be limited in what they have to offer because they don’t provide the real-time results of probes. They also may be influenced by differences in flow rate at various points in the pipeline, meaning they may not always provide an accurate assessment of the corrosion rate throughout the entire system.
Key Differences Between Corrosion Probes and Corrosion Coupons
Choosing between corrosion coupons and corrosion probes starts with understanding the capabilities and limitations of each method. This can be broken down into a few main categories:
- Data frequency: Probes are connected to monitoring equipment and software, meaning they can provide updates in real-time. Coupons, on the other hand, need to be removed and analyzed before any results can be gleaned from their condition.
- Installation complexity: With coupons, they can be inserted directly into the access fitting with relatively little effort. However, probes require a bit more in the way of setup because of their connections to monitoring equipment. This means they take longer to install.
- Cost: Thanks to their simple design, coupons are a less-expensive method of corrosion monitoring. However, the fact that they need to be removed and analyzed to provide results makes them more labor-intensive than probes that continuously provide data in real time. The relative complexity of probes makes them costlier to deploy under most circumstances. In many cases, installing them into the pipeline also may require the flow to be shut down, resulting in lost productivity.
- Maintenance requirements: The connected nature of probes means they may require more attention in terms of maintenance and calibration to ensure they provide the most accurate information. By comparison, coupons generally need little to no maintenance until they are retrieved from the pipeline.
Choosing the Right Corrosion Monitoring Solution
To choose between corrosion probes and corrosion coupons, it’s necessary first to understand the operation’s specific needs. In the most basic terms, probes should be used if there is a need for real-time monitoring to spot any fluctuations in the corrosion conditions. This may be required due to the corrosive nature of the fluid or gas, the materials used in the pipeline, environmental conditions, and other variables.
On the other hand, if there is no need for immediate updates regarding corrosion status, using coupons on their own may turn out to be the more cost-effective option. Using coupons also may be the better option in instances where the access to the pipeline is too restrictive for probe installation.
However, there’s also an argument to be made that a hybrid approach might be best. This is because corrosion probes and corrosion coupons can complement each other and provide operators with a more-complete view of their pipeline conditions. The probes can deliver instantaneous updates, while coupons allow technicians to see the condition of the metal surfaces in ways that raw data may not be able to illustrate. For example, an exposed coupon can reveal pitting and other warning signs that are much more difficult to determine via electrical resistance or linear polarization testing.
Get Expert Consultation With SMARTCORR®
As the leaders in corrosion control and monitoring, SMARTCORR® provides comprehensive asset integrity solutions. These include corrosion monitoring consulting services that help our clients choose the techniques and tools that make the most sense for their requirements. The experienced corrosion specialists here work closely with our clients to develop a strategy that deliver the most accurate and actionable results.
To learn more about what SMARTCORR® can do, reach out for a personalized consultation on corrosion monitoring solutions.