In the day-to-day running of industries, asset inspection is of paramount importance for checking the current state of structures, in order to discover any non-conformities and failures before they can cause catastrophic accidents, production stoppages and similar inconveniences.
When inspecting assets in the field, it is essential to carefully analyze the entire structure in order to identify existing pathologies. A detailed and methodical analysis makes it possible to identify non-conformities and risks, identify possible possibilities and causes, and predict possible solutions.
Why carry out a visual inspection?
No parque industrial nacional, diversas estruturas têm suportado ativos de processo e a sua integridade estrutural garantirá que o processo produtivo ocorra sem interrupções e mitigará riscos de eventos indesejáveis com os colaboradores envolvidos. Olhando para o processo mineral, por exemplo, falhas estruturais em equipamentos como transportadores de correia, casas de transferência, prédios de processo, máquinas de pátio, viradores de vagão e carregadores de navios são de vital importância para que o processo produtivo aconteça. Sendo assim, eventuais falhas estruturais nesses equipamentos podem ser catastróficas.
In many situations in industry, due to various factors, the integrity of structural assets is not given due importance. Because of the immediate impact on production, failures in electrical and mechanical systems deserve immediate attention. However, the consequences of a catastrophic failure in a structure are unpredictable and can lead to expensive and prolonged maintenance and undesirable fatal accidents.
A Kot considera a inspeção estrutural como parte indispensável da jornada de promoção da integridade do ativo dos seus clientes. A inspeção estrutural é o segundo passo da Metodologia CARE – Controle de Ativo para a Revitalização Estrutural. Tal metodologia foi elaborada em busca de oferecer uma solução de Engenharia direcionada à promoção do cuidado com os ativos de seus clientes. Conforme explícito no próprio nome, o foco é cuidar dos ativos promovendo um controle estruturado destes e mitigar os riscos associados à utilização dos equipamentos e estruturas.
In addition to the good training and preparation of those carrying out the test, the success of the visual structural inspection will depend on a number of important factors: the tools, equipment and instruments that will be used, the characteristics of the object under analysis and the available lighting.
Sendo assim, a inspeção visual é o método de menor custo que pode ser utilizado na jornada de integridade estrutural do ativo. O método não é e nem deve ser o único a ser utilizado nessa jornada, mas o seu uso permitirá apontar a necessidade de utilização de outras formas de avaliação, como na Figura 1. Ele pode ser seguido de:
- Non-destructive testing (NDT), such as ultrasound, liquid penetrant, magnetic particles and x-ray;
- Verificação pelo método dos elementos finitos;
- Active instrumentation using extensometry and accelerometry;
- Risk Assessment.
Figure 1: Liquid penetrant test - SOURCE: Kot Collection.
In addition, tools such as drones, scaffolding, platforms, industrial mountaineering devices, borescopes and more can be used to support the visual inspection.
The main causes of damage to structures
Para iniciar a inspeção estrutural de forma adequada é recomendável que se conheça as causas de danos nas estruturas. As estruturas metálicas dos ativos industriais, de forma geral, sofrem ação do clima, do meio e do seu uso. A partir deste conhecimento, é possível estabelecer quais são as técnicas de inspeção aplicáveis.
Research on this subject is extensive. For example, according to the technical study by OEHME (1989) considered by the EUROCODE standard commission, the causes of damage to metal structures of buildings and conveyors can be grouped as shown in Graph 1.
Graph 1: Percentage distribution of causes of damage to structures
of buildings and conveyors - SOURCE: OEHME, 1989.
In the national park, small to large metal and concrete structures, such as piers, tunnels, OAEs (Special Works of Art, such as viaducts, bridges, pontoons and footbridges), buildings, etc. suffer from the weather and corrosive atmosphere. Factors such as high rainfall and the deposition of chlorides and particulates favor the appearance of pathologies and failures.
Temperature variations, heavy rainfall, pollution and a highly aggressive environment cause pathologies related to forms of structural deterioration. According to HENRIQUES (2001), the causes of pathologies in civil construction assets (in general) can be seen in Graph 2.
Graph 2: Causes of pathologies in civil construction assets (in general) - SOURCE: HENRIQUES, 2001.
According to HENRIQUES (2001) and day-to-day experiences in the field, it can be said that most structural failures are due to mistakes during the design phase, failures during assembly and non-conformities in manufacturing and asset use issues (operating and maintenance conditions). In order to detail the most frequent structural pathologies in steel structures and their respective main causes, an interesting understanding was proposed by PRAVIA and BETINELLI (2016). This understanding can be seen in Table 3.
| Pathologies in metal structures | Main causes |
| Localized corrosion | Deficiency caused by inadequate drainage of rainwater and errors in construction details, resulting in puddles, accumulation of moisture and aggressive agents such as deposition of chlorides and particulates (ore, pollution, soot, etc.). |
| Generalized corrosion | Deficiency caused by inadequate protection against different corrosion processes. |
| Excessive deformations | Deficiency caused by overloads and/or thermal effects that were not considered premises in the original project (supply specifications, conceptual, basic and detailed drawings). |
| Global or local buckling | Deficiency caused by the use of structural models that are not correct and do not reproduce reality and/or do not comply with the standards for verifying stability and rigidity. |
Table 1: The most frequent structural pathologies and their main causes - SOURCE: PRAVIA and BETINELLI (2016).
Thus, there can be several causes of structural non-conformities. Possible design flaws can have their risks minimized by carrying out a structural asset audit. Also known as a design review or double check, the following activities are carried out:
- Support in drawing up technical specifications;
- Avaliação técnica das proponentes;
- Suggestions for basic design;
- Equipment verification using the finite element method;
- Proposing solutions and any reinforcements for non-conformities found.
How to carry out the visual inspection
The visual inspection test can be divided into two forms: direct and indirect. In the direct form, the naked eye and auxiliary optical equipment such as magnifying glasses, microscopes, borescopes and binoculars can be used. Indirect inspection requires the use of auxiliary vision tools, through the use of an artificial vision method.
Basically, visual inspection comprises the following steps:
- Evaluation of the structure in conjunction with the evaluation of technical design drawings. To this end, visual inspection of the structure aims to identify the absence of bolts in connections, corrosion points in assets, visible plastic deformation of plates and profiles, visible cracks and other detectable non-conformities. Photos and videos can be used to record the faults found;
Figure 2: Evaluation of corrosion points on bolts and connecting elements - SOURCE: Kot Collection.
- Classification of non-conformities and deviations found in terms of criticality and indication of actions;
- Elaboração de relatório técnico, destacando as verificações realizadas e indicando as não conformidades detectadas. O detalhamento do relatório deverá variar conforme a complexidade do documento ou dos requisitos do cliente. Muitas vezes, a inspeção do objeto pode ser regida por normas específicas, leis designadas ou por procedimentos próprios dos clientes;
- Finally, suggest actions to mitigate the problems detected.
Main advantages and limitations
The advantages of using the visual test methodology are its low cost, the quick way in which the test can be carried out, the simpler interpretation when compared to other test methods and the ease with which it can be carried out.
On the other hand, there are some limitations. These include the possibility of detecting discontinuities only on the surface of the structural element, limiting the detection of internal cracks. It is also necessary to ensure good visual acuity on the part of the tester and prior knowledge of the object under analysis.
For the future, it is important to pay attention to what is recommended by CHA (2018) for OAEs, but which also applies to other structural assets. In the understanding presented, visual changes in civil infrastructures, such as cracks or corrosion, are very important to warn about structural health conditions. Despite the critical role of bridges in public safety and the economy, inspection based on human vision has the limitations and disadvantages already mentioned. Therefore, engineering will increasingly look to the automation of visual inspections to solve the limitations of the common human visual approach. Researchers and companies are increasingly attracted to the development of computer vision-based methods for detecting structural damage.
A Kot pode fornecer aos seus clientes opções de ensaio visual através de intervenção humana, bem como métodos de visão computacional para promover a integridade dos ativos dos seus clientes, utilizando, por exemplo, o tratamento de imagem. Consulte nossa equipe para mais informações!
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References:
OEHME, Peter. Analyse von Schäden an Stahltragwerken aus ingenieurwissenschaftlicher Sicht und unter Beachtung juristischer Aspekte. 1989.
HENRIQUES, F. M. A. Notion of Quality in Buildings. Communication to the National Construction Congress. Lisbon, 2001.
PRAVIA, ZMC; BETINELLI, E. A. Falhas em estruturas metálicas: Conceitos e estudos de caso. Curso de Engenharia Civil da FEAR–UPF, 2016.
CHA, Young Jin et al. Autonomous structural visual inspection using region-based deep learning for detecting multiple damage types. Computer-Aided Civil and Infrastructure Engineering, v. 33, n. 9, p. 731-747, 2018.
