An analysis of the degree of aging of the different materials that allows successful recovery programs to be executed.
by Juan Manuel Álvarez*
Aging is commonly considered as the passage of time through which a material loses quality characteristics, defining as quality the "Degree of aptitude of a good or service to meet the needs and desires of the consumer".
The process of corrosion must be related to the mechanism of aging, when after some time and from the beginning of the interaction with some type of fatigue that may occur as a result of the mechanical use of the part, element, component or structure in a cyclical or repetitive way, including that a structure supports its own weight; the material synergistically deteriorates.
It can deteriorate in such a way that problems arise that even come from the same manufacture, through the treatments that have been carried out at the surface or subsurface level such as thermal, immersions to apply metal coatings, machining and even surface preparations that mechanically affect its capacity by including internal stresses, or by modification of the thickness that in a timely manner affects the material, once the properties of the material begin to decline when the deterioration due to corrosion reactions and the deterioration due to the effect of the fatigue of the material converge.
The corrosion process involves interaction with the environment, where it is required that chemical or electrochemical reactions be developed that generate corrosion products, which chemically relate to some of the variables of the environment such as humidity, temperature, pH (chemistry of the environment), and others such as those generated by mechanical work that when accumulated over time produce cycles to which the material already inside it does not respond to the original elastic behavior of the same, which generates affectations that result in the aging mechanism, which accelerates the deterioration of the material that as a structure has a purpose for which it will no longer be suitable, due to a curve with a cadence that leads to the destruction of the structure by fracture mechanisms.
Analysis of the degree of aging
One way to consider the degree of aging of materials is to monitor through inspections, measurements, statistics, log analysis, corrosion mapping and performance assessment based on expected natural aging.
The above considerations must be taken into account for the elaboration of the aging program of any structure and that form the performance criterion of a structure resulting from the trend the estimation of the remaining time of useful and safe life of a structure, considered from the perspective of the capabilities of the materials that make it up.
Inspections, such as procedures, are part of predictive maintenance, which non-destructively uses different techniques that allow to know the state of the materials at the surface, subsurface and volumetric level or inside the material. The importance lies in the objective of the inspection, the ideal technique to be selected for the achievement of that objective and the frequency with which the characteristic to be inspected of the material is monitored.
As measurements can be considered the determination of the remaining thickness of the material, compliance with tolerances and clearances of elements and assemblies; in short, measurements that allow to establish the condition in which they are found as materials or assemblies, the structures that by effect of their use or mechanical work may undergo changes that lead to the understanding of their behavior over time.
The management of statistics for the purpose of considering the degree of aging in which a material or a structure is found, lies in the knowledge base regarding the repairs made, results of inspections, measurements, conditions of use and accumulated time of use. The good management of statistics generates a trend that can predict future behavior and even the failure that causes accidents.
The analysis of the log refers to the evaluation of the accumulation of events that due to the fulfillment of the maintenance programs, particularly of the corrective and recuperative maintenance, have occurred. This evaluation generates a real trend of how both the structure and the materials have behaved.
Corrosion mapping corresponds to the exhaustive inspection of a structure in which all corrosion problems are related, including defects that are potential corrosion problems and that may occur in the future, determining their location and level of corrosion present. The mapping should result in the aging behavior that the materials of the structure have suffered.
The performance assessment refers to the integral result of the information of the aforementioned items, which must be included in the aging program so that the remaining life of the materials can be estimated as a structure, in conditions of safety and work.
The comparison with the expected service life from its design and construction highlights the difference between the expected natural aging, as a result of the selection and resistance of materials for its construction, and the modification of the aging given by its use.
Coatings as materials also suffer from aging, a topic that will be discussed in another article in the next edition.
I wish you a good aging!
* 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 and lecturer. You can write to the e-mail: [email protected]
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