What is the importance of Corrosion Inhibitor Optimisation?
The Oil and Gas industry uses corrosion inhibitors extensively for the control of corrosion to extend component lifetime as well as improving production. Research has found that the global market spend on corrosion inhibition in 2015 to be approximately USD 6 Billion.
Corrosion inhibitors are commonly deployed in main oil export pipelines, gas export pipelines, subsea tiebacks and production systems to reduce the corrosion rates by a minimum of 90%. The treatments are usually delivered by either continuous pumping into the system or batch treatment depending on conditions. The typical dose rates are between 10-50 ppm (parts per million), based on total fluids for continuous injection. In the selection process, a number of test procedures must be followed before the inhibitor can be considered. This is of critical importance, as any omission or oversight in the inhibitor design can result in significant flow assurance issues, for example, incompatibility of chemicals/ fluids, emulsion problems, foaming tendency and potentially loss of containment through premature failure. Therefore, selecting a corrosion inhibitor suitable for the operating facility is a crucial step to minimize costs, optimize chemical dosage, increase corrosion inhibition efficiency and decrease the corrosion related costs.
Corrosion Inhibitor Optimisation Strategy
AIE’s corrosion inhibitor testing procedures are dependent on application and include multiple stages which are directed to enhance the efficiency and ensure a robust chemical selection process which can be further optimized once deployed in the facility.
The laboratory tests are conducted under simulated field conditions which are deemed to best represent the corrosivity of the system and other non-performance test conditions are also commonly utilized to ensure the most effective treatment is identified. Parameters such as partial pressures of H2S and CO2 are replicated in the laboratory and synthetic brines and field crudes are used to ensure the corrosion inhibitor is tested in as near field conditions as possible. Additional considerations such as temperature, shear stress, water cuts, crude type and materials are also commonly built into the testing regime, depending on the application. Further refined tests are usually conducted to look at welds used in the system and the performance of the corrosion inhibitor on specific elements of the weld such as the parent material, HAZ and weld bead. The degree of sophistication of testing is dependent on the application, conditions and criticality of the component.
There are multiple stages involved in the selection of a corrosion inhibitor, each designed to specifically identify and select corrosion inhibitors based on its performance to ensure at the final stage the optimum chemical has been selected for the field application. The initial screening of corrosion inhibitors involves basic physical properties identification and compatibility tests to ensure there is no adverse effects of using the corrosion inhibitor in the process systems. This varies from pH, viscosity, thermal stability measurements to the foaming, emulsion or gunking properties of the corrosion inhibitors.
Following the initial screening, electrochemical performance tests are conducted to evaluate the corrosion inhibitors under simulated field conditions, commonly by Linear Polarization Resistance (LPR) in a bubble test, with the addition of different doses of corrosion inhibitor, a typical test arrangement and performance result is shown in Figure 1.
Figure 1: Typical Bubble Test Result
In the case of an oil system, the partitioning ability of the corrosion inhibitor would be evaluated in the presence of the field crude to determine how effective the inhibitor is under different water cuts. In a gas corrosion inhibitor, the effects of velocity on performance can be critical and the effects of shear stress would be evaluated using a Rotating Cylinder Electrode (RCE) arrangement.
Further advanced testing would then be conducted on the corrosion inhibitors that had passed the initial performance screening tests. There are number of advanced tests available including High Temperature High Pressure Autoclaves, High Pressure Rotating Cage Autoclaves, Jet Impingement and Flow Loop Tests, each designed to evaluate parameters required for the particular corrosion inhibitor application.
The Benefits of Corrosion Inhibitor Optimisation
The key to successful selection and deployment of corrosion inhibitors is ensuring that the chemical selected matches the demands of the system. This is achieved by laboratory testing, field trials and consistent fluid analysis once the corrosion inhibitor program is in place. Operational, production and inspection data can be analyzed to adjust the chemical dose to optimize the chemical injection performance.
Any changes in the field conditions over time should be monitored to ensure that the corrosion inhibitor dosing is adequate to protect the system; this can allow optimization in the field to either reduce or increase injection to meet the changing requirements in the field. One of the key benefits of having a robust chemical selection program is that this can be further refined once in place to optimize the dosage requirement while ensuring adequate inhibitor efficiency. A reduction in a few parts per million of chemical injection can equate to thousands of dollars a year in savings.
Within AIE, we strive to ensure the best use is made of the corrosion data collected and reviewing chemical injection programs in such a way ensures real benefits are achieved in terms of achieving optimum inhibitor performance and cost effectiveness; this is accomplished by simply understanding the requirements of the field and adjusting accordingly. As previously stated, approximately USD 6 billion is spent on corrosion inhibitors annually and therefore it makes great business sense to analyze what is currently used and determine whether chemical dosing can be adjusted to reduce costs on corrosion inhibitor programs without compromising on inhibitor performance.
At AIE, we routinely perform corrosion inhibitor optimisation independently for all major operators, commonly in conjunction with independent selection and optimization of flow assurance chemicals due to the symbiotic relationship between production chemicals. If you would like to know more on how AIE can assist in chemical optimisation please visit our contact us page and we will promptly respond to your inquiry.
If you would like to know more about our consultancy services and how our team can support your requirements, please visit our contact us page and we will promptly respond to your inquiry.
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