Non-destructive testing (NDT) or inspection methods are processes used widely in different industries for the collection of data or information on certain structures. As the name suggests, NDT techniques are used to evaluate an asset or structure without damaging or modifying it permanently. Through the application of NDT, an inspector can study the properties and integrity of a material, and determine if it has any flaws or defects.
One of the most popular NDT methods is visual inspection. Also called visual testing, this NDT method is considered the most basic and oldest of its kind. After all, what was originally required to visually inspect assets was the naked eye or the sense of sight, as well as one’s hearing, smell and touch. Since there were no special inspection devices, tools or equipment available back then, visual testing was used extensively to examine objects, sites and structures.
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What Is Visual Testing?
What is visual inspection? As indicated by its name, visual testing entails the inspector physically checking every component of an asset.
For example, in the mining industry, safety officers and professional miners conduct regular visual inspections to identify the presence of safety risks, hazards and non-compliant conditions in a worksite.
These visual inspections include checking lifting operations components. Through visual testing, the inspector can determine the structural integrity of equipment like bulldozers and underground excavators by carefully studying component parts.
Visual testing, just like other NDT methods, takes into account welding quality, and the presence of any surface defects, corrosion, degradation, blockages and foreign materials in the asset being inspected. In doing so, the inspector can recommend that the correct control measures be implemented to ensure the site is safe for workers and the activities they are tasked to perform.
Although special equipment may not always be needed for this type of inspection, it does necessitate specialised training in order for the inspector to know what to look for as they visually evaluate an asset.
Applications of Visual Testing
Visual testing can generally be used to inspect a component’s surface quality, evaluate the alignment of mating surfaces, and look for leaks.
Aside from being used extensively in the mining industry, visual testing is also widely used in contemporary manufacturing.
A visual inspector can identify dangerous flaws or impurities that can impact on how a manufactured item is utilised in the future using. It is vital to test items before they are sold or utilised, and there are many other industries where materials are tested before they are allowed for use in public.
For instance, material engineers require the assistance of inspectors in gathering data about the quality of their welding jobs, and the survivability and integrity of the material.
Besides studying industrial components, inspectors also examine things that the general public frequently uses, such stairways and guardrails. Inspectors can ensure that safe parts reach the market by looking at these components, ensuring that both customers and consumers benefit from structurally sound, high-quality products.
Other sectors that require routine visual inspections as part of their maintenance processes (and even root cause analysis) include aerospace, chemical refineries, food and beverage, oil and gas, power and utilities, maritime operations, pharmaceuticals, and research and troubleshooting.
Importance of Visual Inspection
Visual inspection, even at its most basic form, remains a popular NDT technique for the following reasons:
- Prompt detection of flaws or structural issues: Visual inspections are used frequently to detect the first indications of welding flaws. This enables the structure or appliance owner to remedy the problem quickly and cost effectively.
- Quick and precise inspection: Visual inspection takes very little time because it involves examining only the surface of an asset, tool or material component. However, the fact that visual testing is confined to surface checks does not imply that the service is of inferior quality. The entire procedure is quite precise, guaranteeing that no welding problems are overlooked. Should the inspector conclude that visual testing needs to be supplemented with another test, they may recommend the same, so the object under study gets subjected to a more thorough examination.
- Cost effectiveness: Visual inspections typically do not require the use of high-tech, expensive equipment because only the surface of the material or asset is being studied. By doing this, it is possible to save expenses while still getting quality service.
Finding problems and fixing them before they worsen is the main objective of all NDT methods, including visual testing.
If an inspector conducting a visual inspection overlooks a problem with a component, such as corrosion on the walls of the boiler, there may be disastrous consequences. For this reason, only licenced inspectors who follow very tight guidelines required by law undertake visual inspections of crucial assets like boilers and pressure vessels.
Today, visual inspections can take various forms.
In mining, for example, drones fitted with cameras are used for hazardous site inspections that would otherwise involve compromising the safety of several inspectors physically checking an area.
Visual Inspection: Advantages and Disadvantages
Just like other NDT techniques, visual inspection has its advantages and disadvantages.
Advantages of Visual Inspection
Below are the advantages of visual testing:
- It is the most affordable or lowest-cost non-destructive testing method. The reason, of course, is that an inspector can conduct a visual inspection with little to no equipment. It also allows for the early detection and elimination of possible flaws or discontinuities prior to starting or finishing a weld. In cases where major discontinuities or possible points for these are detected, the inspector can recommend other non-destructive tests to be conducted. Therefore, if your operation has limited funds, you should implement visual inspections as a primary or first step in checking the integrity of the components or materials you are using or manufacturing.
- It is a portable testing method. Since this NDT technique requires very few to no tools or equipment, it is considered an easy and convenient testing method.
- It requires very little part preparation. The component being examined usually doesn’t need to undergo many part preparations during visual testing. This adds to the speed and convenience with which visual tests are implemented.
Disadvantages of Visual Inspection
Even when visual testing presents some great benefits, it also has its limitations and disadvantages.
- It requires rigorous training. Contrary to the belief that it’s easy to train others to become visual inspectors, technicians need to undergo rigorous inspector training to be able to do it with precision. Visual testing also requires good eyesight or one corrected to 20/40.
- It is limited to the detection of surface defects. Since visual testing is surface -oriented, an inspector may overlook internal problems or significant flaws. Even though an inspector is an expert, human error could cause them to miss crucial details. They could also unintentionally misread defects or make mistakes in their report, which could result in a flaw being handled incorrectly during maintenance.
- It requires extensive knowledge and experience. The accuracy of the evaluation depends greatly on the expertise of the inspector, as well as their knowledge of the industry and project requirements.
Visual Inspection Procedure
The visual inspection procedure essentially five steps:
Step #1: This step entails compiling detailed operating instructions, guidelines and procedures as well as a list of the products, machinery, and other items that require inspection.
Step #2: The product is cleaned and prepared for visual examination.
Step #3: The object is then checked thoroughly for potential defects, flaws and inconsistencies.
Step #4: The defects identified in the asset, component or material are assessed for compliance with set standards.
Step #5: The final step involves reviewing the results of the visual inspection and deciding whether to accept or reject the product.
All steps in the NDT visual inspection procedure, especially steps #3 and #4, are of great importance to ensure the accuracy and effectiveness of the evaluation.
Visual Inspection Acceptance Criteria
For visual inspection acceptance criteria, the main reference is UIG-97, Page – 345 of the ASME BPVC Section VIII Div 1, 2017 Edition.
(a) The surface shall be free of any visible laminations, spalling, or cracks. Cracks in tubes shall not be repaired and shall be considered cause for rejection.
(b) For tubes, the depth of scratch shall not exceed 1/32 in. (0.8 mm). For all other material, the scratch depth shall not exceed 1/8 in. (3 mm).
For an acceptable limit of thickness reduction, you may refer to UW-35 (sub-para b, page – 144) which states that:
The reduction in thickness shall not exceed 1mm (1/32 in.) or 10% of material nominal thickness whichever is less, provided that the material of the adjoining surfaces below the design thickness at any point.
For the allowable limit of weld reinforcement (excess weld metal), Refer to UW-35 (sub-para d, Page – 144).
What Equipment Is Required for Visual Testing?
While visual testing typically relies on the human senses, especially good eyesight, there are visual inspection equipment in use today.
Visual inspection tools are designed to collect visual data that is accurate and reliable. Some devices enable the visual inspection of remote, unreachable or hard-to-access, or hazardous sites.
These include digital cameras, borescopes, videoscopes, video and digital microscopes, and closed-circuit surveillance television. Remote visual inspection (RVI) tools like drones and robots allow inspectors to collect visual data without the need to be physically present in the site being evaluated.
Visual NDT Inspection Report
Visual inspection report forms are typically used by quality assurance inspectors to document their pass or fail decisions regarding components or products they have visually inspected based on set defect criteria. The report usually includes reference images or captured photo evidence that show or indicate the visual defects found during examination.
Details like the product ID and location, reference images for the inspector’s pass or fail decisions, and identified surface flaws based on defect criteria are also included. The visual inspection report is then submitted with the digital signature of the inspector.
Visual Inspection Standards
The International Organization for Standardization (ISO) sets visual inspection standards and provides references regarding very specific guidelines for different industries or activities.
Below are some examples:
- ISO 17637:2003 Non-destructive testing of welds – Visual testing of fusion-welded joints (covers the visual testing of fusion welds in metallic materials)
- ISO 19828:2017 Welding for aerospace applications — Visual inspection of welds (specifies the requirements for visual inspection of welds in metallic materials and requirements for qualification and certification of personnel for visual weld inspection)
- ISO 3058:1998 Non-destructive testing — Aids to visual inspection — Selection of low-power magnifiers (specifies the characteristics of certain types of low-power magnifiers and gives recommendations for their selection for the inspection of surfaces)
Visual inspection standards are important guidelines companies adhere to, not only to ensure the functional integrity and quality of the materials, components or assets they use or make but also (more importantly) to safeguard the safety of workers and users.
Visual Inspection Services by AME
Since 2006, Asset Management Engineers has been performing visual inspections as well as other Perth NDT services, including ultrasonic, magnetic particle, liquid penetrant and eddy current testing.
Our NDT inspection services are appropriate for all project stages and are designed to provide inspection and testing support for your manufacturing and maintenance activities.
Please get in touch today to know more about the many services we offer.