Corrosion is a serious problem around the globe, costing industries and governments billions of dollars annually in prevention and remediation while simultaneously taking critical equipment and infrastructure out of service. As a naturally occurring phenomenon, corrosion is caused by an electrochemical process that gradually destroys metals. This damages equipment and infrastructure and necessitates expensive repairs.
According to a study commissioned by the U.S. Federal Highway Administration the direct e-ffects of corrosion cost U.S. industry and government $276 billion annually. Adding indirect costs, such as lost productivity due to outages, delays, failures, and litigation, increases the overall costs to an estimated $551 billion or more annually.
A recent study by the American Society of Civil Engineers found that, by 2039, continued underinvestment in public infrastructure at current rates will cost $10 trillion in gross domestic product, or GDP. Fortunately, a new method for assessing these risks was recently designed to help organizations take a more proactive approach to corrosion management.
Details are available below via a technology brief from The National Center for Manufacturing Sciences (NCMS), a cross-industry technology development consortium.
A recent initiative from The National Center for Manufacturing Sciences (NCMS) (Ann Arbor, Michigan, USA) brought together stakeholders from the U.S. Army and industry partner Jensen Hughes to create a corrosion risk-based assessment (RBA) tool to help combat the high costs of corrosion.
According to NCMS, the RBA tool offers a dynamic survey that helps quantify the corrosion susceptibility and consequence of equipment and infrastructure. Its results can be compiled into an overall score and mapped to a risk matrix, which allows users to determine how to best handle those risks. The process enables reduced life-cycle costs and improved performance.
While the tool was developed for the Army’s assets, it is widely applicable to a broad range of high-value assets including bridges, buildings, industrial equipment, utility systems, and sustainment facilities. The tool can be adapted for use by public or private organizations.
RBA Tool for Corrosion Mitigation
The RBA tool is designed to be used during the design phase of infrastructure and equipment. Specifically, it is most e¬ffective when incorporated during the preliminary design review after some of the engineering and design work has been done, but before the design is locked in.
The tool is intended to serve as a check early in the design process to help organizations make sound decisions regarding corrosion, NCMS explains. While the tool is intended to be utilized by an individual familiar with the design of the component, no special technical background or training is required to use it.
The tool takes a logical, stepwise approach, factoring in all the considerations that may a¬ffect the corrosion-resistance properties of equipment and infrastructure.
Created in a Microsoft Excel format to make it widely accessible, the tool asks approximately 50 questions and utilizes programming logic and automation features prompting users to answer additional questions based on previous responses. It takes less than 60 minutes to complete and produces real-time results in the form of a risk matrix (Figure 1, top image).
While some of the questions are specific to the Army, most are applicable to any component of equipment or infrastructure—military, civilian, or commercial. The tool is designed to assess one component at a time, not a full system or a collection of components.
Corrosion Susceptibility
The RBA tool prompts users to answer questions pertaining to five categories that influence corrosion: environmental severity, operational hazards, design, preventive maintenance, and storage when not in use.
The environmental severity questions ask how the component is going to be used from an environmental exposure perspective. For organizations with components that must operate everywhere, the user can select a default of the most corrosive environment.
For organizations concerned about a single location, the tool can tailor the risk assessment to just that location, and the tool will help them decide if the equipment is corrosion-resistant enough for that specific environment.
The environmental questions are based on International Organization of Standards (ISO) 9223, which establishes a classification system for the corrosivity of atmospheric environments.
Once the environmental severity has been determined, the tool takes operational hazards into consideration including the accumulation of mud or dirt, gravel impingement, contact with deicing salts, and exposure to oceanic atmospheres.
The next set of questions ask about the asset’s design and focus on six types of corrosion. Uniform corrosion occurs when metal is corroded at an even rate on the exposed surface area. Pitting corrosion is an extreme, localized attack resulting in holes or pits in the meal surface. Galvanic corrosion happens when dissimilar metals electrically connected in a conductive electrolyte accelerate the corrosion of the less noble metal. Crevice corrosion is an accelerated type of corrosion occurring in crevices with a small volume of stagnant solution.
Environmental cracking is caused by the simultaneous presence of tensile stress and corrosion. Hydrogen embrittlement occurs when a high concentration of atomic hydrogen in a metal structure reduces the structural integrity of high-strength alloys, resulting in failure at stress below the theoretical yield strength.
The next set of questions deal with preventive maintenance. These include cleaning and washing, corrosion inspection, coating repair, and corrosion inhibitor application.
The corrosion susceptibility decreases if users have established all four preventive maintenance procedures and increases if the user has established two or fewer, NCMS explains.
The final questions ask about storage, allowing users to select from five diff¬erent types of storage: controlled humidity storage (enclosed and controlled environment); warehouse or hangar storage (enclosed but uncontrolled environment); shed storage (covered but unenclosed and exposed to the environment); open storage (no cover and exposed to the environment); and a protective repairable container that seals against environmental exposure.
Corrosion Consequence
After collecting data on corrosion susceptibility, the survey targets information pertaining to a consequence component. The consequence score is determined by looking at the severity of impacts if a critical component erodes.
Corrosion on some components may cause immediate malfunctioning, whereas corrosion on others may have only a minor functional impact.
NCMS defines corrosion stages from stage 0 to stage 4. Stage 0 indicates no visible signs of corrosive attack—no presence of white, red, or black corrosion products, and no presence of paint film blistering.
In stage 1, general surface corrosion is present with white, red, and/or black corrosion products on the surface of the component, but no significant attack is present. Minor blistering of the coating may have also occurred.
In stage 2, heavy corrosion products are present on the surface of the component. This is the beginning of base metal loss; however, no significant loss has yet occurred. Moderate white, red, and/or black corrosion products are present on the component surface. Severe blistering of the paint may have also occurred.
In stage 3, corrosive attack has resulted in significant base metal loss. Reduction in the cross-section thickness of the component has occurred. Voluminous white, red, and/or black corrosion products are present on the component. The structural integrity of the component may or may not be compromised. Pinholes, which may or may not penetrate through the base metal, may have developed.
In stage 4, perforation of the base metal has occurred. No metal remains at the point of severest corrosive attack, and the component has lost structural integrity.
Overall Corrosion Risk Score
The assessment collects information to compute two measures: life-cycle cost and asset performance. Once all the questions have been answered, the RBA tool provides an overall risk score and is plotted on a risk matrix, which offers a visual representation of the risk calculation. The matrix plots the likelihood of an event occurring versus the severity of that event.
For the corrosion RBA, likelihood is determined by calculating the corrosion susceptibility of a critical component. Meanwhile, severity is determined by calculating the consequence of the component’s failure through corrosion.
According to NCMS, the overall risk score highlights corrosion vulnerabilities that designers may have overlooked while assisting users in examining risk mitigation options to bring that corrosion risk to acceptable levels.
The final decision for what constitutes acceptable risk falls to the user. If users determine that the risk is unacceptable, they can adopt mitigating actions. From there, they can repeat the assessment to determine if the risk has been reduced to an acceptable level.
In addition to an overall risk score, the RBA tool outputs a list of the leading drivers that resulted in the calculated risk level. The intent is to help users focus their mitigating actions on the areas more likely to improve or reduce corrosion-related risks.
Public Benefits
The new processes established by the RBA tool are designed to enable broad benefits across many sectors, NCMS explains. While the tool itself is not yet available to the general public, the questionnaire used to create the tool can be reviewed in the NCMS final report.
This RBA tool can be used by public and commercial organizations with corrosion-prone assets or infrastructure—especially in the construction, oil and gas, automotive, aerospace, and marine industries—to identify corrosion-related risks and proactive steps to mitigate those risks.
By identifying the most critical components and the associated corrosion risks, users can focus on areas that are the most susceptible to corrosion and most impactful to system performance, rather than spreading their resources thin by trying to address all potential areas of risk.
Thus, the hope of NCMS and the tool’s developers is for users to take action to mitigate those risks, which can prevent more costly repairs and replacements down the line.
Source: NCMS, www.ncms.org/about.