Factors such as the environment, the quality of metals, proper preventive maintenance, among others are essential to determine the level of corrosion in a structure.
by Juan Manuel Álvarez*
Aging is a process that is generated over time and that therefore involves a step by step within which variables, parameters, and conditions are found so that it can be contextualized as aging.
For the purposes of assessing and monitoring aging, it must be clear what are the criteria that allow determining the progress of aging. The term "progress" is pointed out because aging as a process is developed on a day-to-day basis.
Thus, the variables, parameters and conditions must be identified to monitor the aging process and have the criteria that allow assessing or measuring in order to determine a trend that leads us to consider that materials, regardless of their type, have a life cycle.
Within this life cycle, there are different stages; stages that begin when the materials have all their properties at 100% (result of production or process), which gradually decreases in a staggered way by complying at each stage with a level of response with respect to its properties that are particularly required to comply with the mechanical work for which it was destined since its selection.
Later stages in which the materials tend to strictly comply with the demands within the normal working or standard working or service conditions, until in its last stages the reliability of the material and the mechanical responsibility it has had throughout the useful life are affected, reaching that last stage in which the reliability was affected and the deterioration it makes becomes evident impossible for the material to respond to the demands of everyday life.
The variables are mainly determined by the environment, if analyzed from the chemical (reactive) point of view. Reactive affectation is related to the corrosion process. In addition, the mechanical environment is considered as part of the overall environmental environment. The mechanical work to which the material responds both inside and on its surface (non-reactive).
The parameters are determined by the thresholds to which the properties of the material must respond, both reactive and non-reactive. That is, in terms of mechanical resistance and corrosion. It is important to remember at this point that the rate of deterioration of the material is given by the result of reactive and non-reactive affectations.
Conditions are those that are required for the particular properties of the material to fail to meet the service needs for the longest amount of time. That is, the conditions are based on external agents that lead to fatigue in non-reactive properties, or to the formation of corrosion products generated by reactive conditions.
The criteria that are reached are really the result of the evaluations or measurements that are observed or not, which allow to give an opinion regarding the remaining useful life of a structure or to dictate what preventively determines the term of the useful life of the material before a failure occurs.
Based on the previous article of this cycle of articles related to aging, the concepts of material fatigue and degree and level of corrosion are those that determine and allow to conceptualize the aging of materials.
Aging is determined by the sum of reactive and non-reactive affectations; and it will be greater when these are presented simultaneously, and even greater when they are presented outside the parameters with which these materials were considered in their selection and in their design or manufacture.
Unifying and adding all the above concepts can be determined that there are various issues that have an influence on the aging of materials and products (ferrous, non-ferrous, plastics, composites, coatings, etc.).
Some of the topics are as follows:
- Selection of materials: A poor selection of materials can generate premature aging due to not complying with the selected work or service parameters.
- Environmental monitoring: When we talk about monitoring, it is because it is necessary to know the trend to determine that the product is within the environmental parameters with which it was selected; environmental changes occur cyclically and must be monitored to assess the impact on the aging process.
- Structural stability: It is related to behaviors that are considered outside the estimate in the selection of materials or products and that may occur in the useful or service life. For example, vibrational behavior, seismic phenomena, overloads, thermal shocks, etc.
- Use of the material or product: This issue that may well affect good aging is related to poor maintenance, those that do outside the scheduled time, or with the lack of timely repair of materials or products.
- Inspections: Non-compliance with monitoring or non-destructive inspections of both materials and products affects the aging criteria that may be in a material, in such a way that premature aging may be generated, and the lack of inspection at certain times does not allow to have the criteria to determine in what state the material is to fully comply with the working conditions.
Conclusions
The above are some of the issues that allow us to affirm that materials or products have a natural aging in standard conditions, which can have a premature aging due to the effect of a poor selection of materials.
Premature aging can also occur as a result of environmental changes or structural behavior, and in the same way, poor maintenance will result in premature aging (lack of maintenance generates natural aging).
The lack of monitoring or periodic inspections will allow natural aging, but if you carry out a monitoring in time, you can detect in a timely manner the affectation of the properties of the materials that would prevent fully complying with the working conditions and thus generate the necessary maintenance to preserve these properties.
The following article will deal with the topic "material fatigue" with which concepts about non-reactive or mechanical effects in materials or products will be handled.
As always I wish you a good aging and many successes in your work.
* Juan Manuel Álvarez is a Consulting Member of the technical committees of NACE International, Member of A.S.T.M, of ACICOR (Colombian Association of Corrosion Engineers), of ASCOR (Colombian Association of Corrosion and Protection), of ACOSEND (Colombian Association of Welding and Non-Destructive Testing), of ICONTEC (Colombian Institute of Technical Standards), of the technical committees of END, Welding, Coatings, Fuels and others. He is also a university professor, lecturer and specialist in metal structures and composite materials. Advisory Services, Audits, Training and Contracts for the Control and Prevention of Corrosion. You can write to the e-mail: [email protected]
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