Mitigating Operations Risk and Increasing Asset Reliability with Corrosion Digital Twins : Corrosion Monitoring Solutions with the OLI Cloud APIs in the OLI Platform V11

Ezequiel Vicent

Director of Consulting

Digital Twins

As most industries experience a dramatic shift towards digital transformation, companies are rapidly starting to understand its value and the importance of committing to this journey. Adoption of digital transformation varies broadly both by industry type and company size. However, at the core of these efforts is the desire to break down barriers of communication between the various silos across the business. The goal, then, is to enable collaboration across siloed departments and groups, improve efficiency and increase profitability while unlocking step function improvements in productivity with advanced process automation.

Digital Transformation Increases Profitability

These digital transformation efforts can be varied, and the roadmaps can be very different from company to company. For example, a Major integrated Oil & Gas company’s digital transformation journey involved simply the breaking down of silos through enhanced communication via dashboards. The company wanted to increase collaboration and information availability to multiple stakeholders so that decisions could be made as a group, to the benefit of the entire enterprise, and sought to make the information available to the different levels through tailored dashboards. Process groups are able to access KPIs in real time from the historian, without having to hunt through large sets of data. The Operations team is able to take the KPIs and act to maintain operations at optimum levels by monitoring these values. The business team is able to look at the process plan, the current operating conditions and project profitability models, feedstock purchases, etc., to maximize asset profitability with more comprehensive insights.

Another major midstream company was continuously monitoring their gas pipelines, but still suffered with rotating equipment reliability and compressor stations downtime. The digital transformation project for this company involved interconnecting all the data available into a model that represented the physical asset, in the cloud, via a digital twin. This reliability digital twin evaluated multiple factors including unit vibration and predicted time to failure for the unit. Armed with this knowledge, the company could plan preventive maintenance for the compressor stations most at risk and greatly reduce compressor station downtime. This allowed the company to increase profits by over 40 MMUSD in two years by preventing unplanned shutdowns, and increased profits from meeting and exceeding contractual obligations.

The Challenges of Corrosion Control

As we discussed in previous posts, the global cost of corrosion is immense. NACE international released a study in 2016 which estimates this cost to be $2.5 trillion USD (yes, trillion!), which is equivalent to roughly 3.4 percent of the global Gross Domestic Product (GDP). The study concluded that implementing corrosion prevention best practices could result in global savings estimated to be between 15% to 35% of the cost of the damage, or up to $875 billion USD.

However, implementing best corrosion control best practices is not an easy task. In fact, this can be extremely time-consuming and antiquated with methods involving corrosion coupons and other similar “after-the-fact” methods. These methods require planned inspections and measurements of these coupons’ thickness “rate of change” to track the cumulative corrosion rate of the section being monitored. In some cases, these methods are measured during a planned turnaround, spanning 4-to-5-year periods (and some industries, like refining, pushing 7 years between planned turnarounds!). Often, these areas fail before the next inspection is performed.

New technologies have arisen, that can quickly monitor metal thickness and are non-intrusive to the process. X-ray radiography of metals allows the inspection of pipe sections, and just like an x-ray of a human body, can give information to the material integrity (thickness, stresses, fractures, etc.) on the section monitored. Other methods include the use of ultrasonic sensors that can detect thickness and record it over time, or technology that can detect hydrogen flux within the metal.

However, all these technologies suffer from the same problem: The user must use experience, rules of thumb, previous failures, etc. to know where to place these sensors. There are known areas where these sensors could go, for example, in refining we can look at crude unit atmospheric tower overhead lines going to the overhead condensers, the outlet of the condensers and the lines leaving the accumulator. In HF Alkylation, we should place these at the outlet of the settler, but less is known or understood about lines from the Isostripper leaving the overhead accumulator. The issue is, then, what happens to the asset’s material integrity when operations fluctuate, feedstock changes and contaminants enter the system. The usual areas will be monitored, but it is unknown to the plant what other areas are at risk.

OLI’s Corrosion Monitoring Tools

OLI has been helping clients all over the world understand corrosion risks in their plants for several decades. From Metals and Mining to Oil and Gas, Power Generation and Water Treatment, OLI’s tools provide a soft-sensor based, non-intrusive, predictive approach to understanding corrosive environments in plants.

Let us take a look, as an example, at a HF Alkylation fractionation train used in Oil and Gas Refining. Once the alkylate (saturated with HF Acid and residual water) leaves the Settler, it carries with it entrained acid. This entrained acid is not dissolved and carried as a second phase to the Main Fractionator. As it travels through a preheater, the acid phase starts to dissolve into the alkylate, to the point where, once it leaves the preheater, there is no free acid phase entering the fractionator. However, this is not always the case, with some units having a free acid phase leaving the preheater. As the temperature increases and the acid dissolves into the alkylate, the residual water amount increases in the acid phase. The highest concentration of water in HF acid will occur right before all the water-acid solution is absorbed, or at the first water-acid solution to condense (as calculated by OLI’s novel HF Alkylation thermodynamic model). At those conditions, the corrosivity of the water-acid solution may increase by up to an order of magnitude1. This is the reason why so many of these lines fail. Refiners operate the preheater at temperatures where the fluid is hot, but it still has a free acid phase.

Previously, refiners had no way to identify, monitor or even sample this fluid to check for corrosivity. Therefore, some plants were not even able to set Integrity Operating Windows (IOWs) to ensure the reliability of the system to prevent unplanned shutdowns. In the past, experience told us that we should put a measuring tool here. OLI’s predictive model confirms this and is able to continuously monitor the fluid, as well as provide insight to the plant on how to operate the system to avoid the formation of a corrosive phase.

However, once the alkylate and acid enters the tower, there will be acid and hydrocarbons leaving the overhead. If this mixture becomes trapped in a dead leg, there is a large temperature swing, etc., there may be a phase change and a highly corrosive acid phase may form as well in this line, leading to localized corrosion that eventually causes leaks, or worse, catastrophic damage. OLI’s monitoring tool allows the non-intrusive, predictive monitoring of all the lines in the system, allowing operators to continuously monitor them through a high-fidelity process model.

OLI has given refiners the ability to set IOWs using a predictive model, providing deep understanding of how changes in operations affect the reliability of the system. Now, the refinery has the ability to understand how feed changes, reactor temperatures, settler levels and flux, acid boots levels, and other parameters affect the reliability of the fractionation train. The refiner can confidently increase production armed with the knowledge of how these changes will affect the unit’s fractionation train, avoiding unplanned shutdowns and increasing asset onstream factors.

OLI’s V11 Enables Continuous Corrosion Monitoring and Democratizes Electrolyte Thermodynamics

Up to this point, OLI’s predictive, soft-sensor, tailored monitoring tools were required to be installed in PCs and training for engineers to run the models. Once the engineers were promoted to new positions within the company, OLI would provide training to the new unit engineers to maintain the knowledge base and continue to provide value to the units. Though this task becomes time consuming and must be completed every 18 to 24 months (the rotation cycle for some unit engineers), OLI has been successful in helping customers achieve a transition of knowledge.

However, at OLI we realize that electrolyte thermodynamics is a knowledge-set that sometimes requires Master or PhD degrees to fully understand and extract value from. For this matter, OLI has sought to democratize this science by making it available to all engineers, both in process design, support, operations, and R&D. We have achieved this via the development and deployment of OLI’s Cloud APIs.

The OLI Cloud APIs in the OLI Platform V11 release will enable the connection between OLI’s powerful electrolyte thermodynamic engine and field instrumentation (through data historians). In addition to this connection, the automation of calculations and the dashboarding of model outputs allows for the process support and operations engineers to quickly act upon this valuable information. This removes the engineer from having to sit down and run the models, extract knowledge, and communicate it through various business layers. Here is the real significance of Corrosion Digital Twins powered by the OLI Cloud APIs in V11 – it enables the rapid dissemination of corrosion information to all the business units and allows process and operations teams to incorporate this information in the decision-making activities that are used to run the plant and help it achieve its profitability goals.

OLI’s cloud APIs and OLI’s Corrosion Digital Twin have, effectively, transformed corrosion parameters into a process variable. Enabling the continuous monitoring of corrosion allows the business to make decisions based on profitability and asset integrity at the same time. Plants no longer must suffer from unplanned shutdowns due to leaks or metal failure due to operational changes to increase throughput, improve product quality, etc.

Corrosion Digital Twins Increases Plant Health, Safety and Profitability

Unplanned shutdowns are costly and carry inherent risk to human life, the environment, and ultimately, the health of the business. At a 150 kbpd refinery, the cost of an unplanned shutdown to the crude unit could be as high as 24 MMUSD per event. These costs are similar if the issues happen in the FCC or Coker Main Fractionators – and this does not include the risk of bringing one of these units down quickly and safely.

“At a 150 kbpd refinery, the cost of an unplanned shutdown to the crude unit could be as high as 24 MMUSD per event.”

The same is true for other industries where unit redundancy is not common practice. For example, a specialty chemicals plant that developed polymer films for solar panels suffered a catastrophic loss of heat transfer in their solvent recovery unit due to scaling. This could have brought the entire plant down for several days until a replacement bundle arrived (which was 16 weeks out!). Fortunately, the plant was able to recover some heat transfer after a chemical cleaning and avoided the shutdown while running at lower rates. The cost of the shutdown would’ve have come to 5 MMUSD/day.

Reducing the risk of an unplanned shutdown is of paramount importance to any business. OLI has developed the tools to monitor and mitigate the occurrence of these events via OLI’s corrosion monitoring tools. These tools give businesses the ability to operationalize corrosion monitoring and make it a process variable. OLI’s APIs and Corrosion Digital Twin make corrosion control a variable that becomes part of the business plan, allowing plants to run efficiently and safely, removing the risks of leaks, metal failure and, ultimately, costly unplanned shutdowns.

What tools comprise OLI’s Corrosion Digital Twin?

The OLI Corrosion digital twin consists of OLI’s thermodynamic framework and modeling capabilities available through OLI’s Cloud APIs. These will be available in the OLI Platform V11 beginning in late April 2021.
OLI has worked with clients in the past to generate models and train engineers to run them to extract the same information, providing valuable insights to plants and business who are just starting in this journey.
Contact OLI for more information or to schedule a meeting with an OLI expert to see how we can assist you.


1. NACE Technical Committee Report 5A171, “Materials for Receiving, Handling and Storing Hydrofluoric Acid”, (Houston, TX, NACE International, 2001).