DOWNLOAD a PDF of this article as it appeared in Flow Control magazine:


The sheer cost of purchasing and running assets both off and onshore has propelled the importance of maintenance and asset life extension into the spotlight. The results of poor asset integrity management have been showcased around the world, leading to the increased concern operators have regarding asset maintenance. One of the most common and destructive threats to these assets is corrosion, and once it has set in, fighting corrosion can become expensive and very difficult to deal with.

Corrosion Inhibitor Monitoring

Corrosion has a number of detrimental effects if left untreated. It can result in assets becoming unsafe, unreliable and inefficient, and failures in these areas not only pose significant threats to operational and human safety, but also to the environment. In turn, this can have damaging consequences to a company’s reputation.

Structural failure within critical infrastructure can result in premature loss of containment. The consequences of such failures have been exposed to the world since the beginning of the search for hydrocarbons through a number of major incidents. Health and safety regulation is now tighter than ever, forcing companies to put employee and operational safety at the top of their agenda. It is now more important than ever to ensure all safety measures are robust and implemented to protect all employees and contractors at all times, on all assets, whether on or offshore.

READ ALSO: 5 Reasons Why You Should Be Managing Corrosion 

With environmental protection becoming a key driver for regulatory framework, there is an increased responsibility for companies to take the necessary precautions to avoid damaging the environment by ensuring safe operations. Even the smallest leak can quickly pollute the surrounding area with catastrophic effects. Effective corrosion management is therefore a key element in significantly reducing this risk.

Corrosion is a very expensive problem, and companies must plan for potential spending in the event of unexpected corrosive attack. Corrosion costs the energy industry over $1 billion every year, and with a pipeline costing approximately $3 million per km to replace, prolonging asset lifespan is both desirable and valuable to an operator.

Corrosion Inibitor Monitoring Technical Overview

There are a number of options available to the industry to help combat corrosion. Internal corrosion monitoring usually involves coupon testing, residual inhibitor monitoring, corrosion rate probes and intelligent pigs. These solutions can, and are, often used together to mitigate corrosion.

A common solution that has been adopted by operators within the oil and gas industry is the use of corrosion inhibitors. These inhibitors form a protective barrier on corrosion-prone surfaces and protect infrastructure from corrosive attack. However, without effective corrosion inhibitor monitoring, it is extremely difficult to determine when the optimum amount of inhibitor is being used in the system. A simple explanation of this is using the “Goldilocks Principle” — too much inhibitor is costly, adds no benefits, and can cause upset to the system, but too little can increase the risk of corrosive attack. Finding the optimum amount is therefore key,  resulting in the significant reduction in costs, as well as improved and informed decision-making with less inhibitor being discharged to the environment.

In some cases, corrosion inhibitors are currently toxic to land and marine environments, and companies who do not monitor the level of inhibitor will often continue injecting systems unnecessarily. This results in excess inhibitors being pumped straight into the environment with the potential to cause serious damage.

Therefore, the effectiveness of corrosion inhibitor is important and is determined by measuring the presence of micelles; microscopic groups of corrosion inhibitor molecules. These micelles form when the dose of corrosion inhibitor reaches the “critical micelle concentration” (CMC). The diagram below illustrates this.

Corrosion Inhibitor Levels
Photo courtesy LUX Assure

Reports over a 40-year period have demonstrated a link between the CMC of surfactant-based corrosion inhibitors and the inhibitory effect. Below the CMC, the film consists of a non-continuous surface, which can be penetrated and allow corrosion to occur. Above the CMC, the film is denser and multi-layers can form. There is a significant drop in corrosion inhibitor performance at concentrations above the CMC, with the potential to cause additional production issues, such as formation of emulsions, separation, increased costs, and environmental discharge issues. Regular monitoring and maintaining the CMC is therefore a critical element in mitigating damaging and costly corrosive attack, while optimizing the dosage of corrosion inhibitors.

The level of inhibitor can be determined through laboratory testing on or offshore, however, there can be problems when carrying out the analysis. Field conditions can differ from those in the lab with regard to the mix of treatment chemicals, pressure and temperature. Samples taken for analysis can also expire if left for too long, highlighting the importance of providing timely, accurate and actionable information. There are technologies now available to provide this information, which represent a step change in the ability to accurately detect the optimum level of corrosion inhibitor, allowing management to improve decision-making and resulting in significant cost savings.

Under-dosed Corrosion Inhibitor
Optimally Dosed Corrosion Inhibitor
Optimally dosed
Over Dosed Corrosion Inhibitor

Images courtesy LUX Assure

Article continued on next page