Material Type
Each NDT method has its own suitability for certain materials, and each material has it’s own characteristics and behaviours. So, understanding what the material is and what information you need to obtain is the first step in choosing an NDT method.
If you know the type of material your product or component is made of, this will help to narrow down the type of NDT test you need. For example, if your product is a composite material, then Ultrasonic Testing would be the most appropriate. If your product is made of metal, but you’re unsure exactly what type of metal, then Positive Material Identification would be a good place to start.
Material Shape
When choosing an NDT method, you need to think about the shape and size of your sample, as some tests do not work as well as others. For example, if you have a curved material or a thin surface, then Ultrasonic Testing would not be suitable as it requires a thick, flat surface.
You also need to consider the size of your material; pipelines and other large components will need extensive scanning or measuring to detect any faults and flaws, so multiple setups may be required to cover the entire area.
Surface Condition
NDT testing will also depend on the surface or finish of your material. Rough or coarse surfaces can impact the effectiveness of certain tests; Eddy Current Testing needs considerable contact with a material surface, and some test methods will require preparation of the area before testing. Dye Penetrant Testing is not suitable for porous materials but are better suited for smooth surfaces so that the penetrant can effectively soak into defected areas.
Defect Type
The type of defect present on your material and its severity will influence the type of NDT test method you need. Radiography is ideal for analysing internal defects, whereas Magnetic Particle Inspection is better for visible surface cracks. If you have a shallow hairline crack, then Dye Penetrant Testing may be more suitable.
Location, Accessibility and Environment
This is a crucial consideration when thinking about your NDT requirements. If the material is in a difficult to reach location, such as underwater or underground, this can present challenges for certain NDT methods. It may be difficult to take certain pieces of equipment into confined spaces or remote locations where power sources are not accessible. Other considerations such as environment, temperature, and exposure to hazardous environments means that it might be necessary to use remote controlled, drone, or automated equipment for health and safety purposes.
Standards and Regulations
The frequency of NDT testing will vary depending on industry-specific regulations. For example, piping inspections in accordance with API 570 provides guidance on the frequency of Ultrasonic Testing and Visual Inspections.
It is important to consult any necessary standards or guidelines within your industry to remain compliant with legal, quality and safety processes.
As a general guideline, critical safety components should be inspected more frequently, while standard and low-risk components will have less-frequent inspections.
Budget and Timeframe
The cost and speed of testing can vary depending on the sample size, location, number of samples needing to be tested, the equipment and resources involved.
Larger material samples may need more resources and multiple inspectors to carry out the work within a specific timeframe. If the location is not easily accessible, then this could increase the time required to carry out testing and inspections, which may lead to higher costs.
