A quality weld goes beyond whether or not the objects being welded together meet visual inspection criteria. In other words, when it comes to a good weld there is more to it than meets the eye. A quality weld is one that must be able to do its job – keep the fusing of two parts or section of a piece together indefinitely without failing at some point. A quality weld must be able to stand up to other inspection and performance requirements as well. This is where nondestructive examination comes into play to ensure that the weld is sound. There are five commonly used methods to examine the soundness of welds. They are: visual, liquid penetrant, magnetic particle, ultra-sonic and radiographic (X-ray). Sometimes, a thorough examination is one that requires a combination of these processes.
- Visual Inspection (VT): Visual inspection is of course the oldest and least expensive NDT. It is quick and under some circumstances can – such as when the weld is grossly subpar – detect unsound welds. The problem with this technique is obvious – it is the least accurate way to determine whether or not a weld or any other material process is complete.
- Radiographic Inspection: Radiography (X-ray) is one of the most important techniques there are. It is far more accurate than visual inspection. The drawback to it is that radiographic equipment often produces radiation that can be harmful to body tissue in excessive amounts
- Magnetic Particle Inspection (MT): This technique locates and defines discontinuities in magnetic materials. Due to its limitations, magnetic particle testing should not be a substitute for radiography or utrasonics for subsurface evaluations
- Liquid Penetrant Inspection (PT): Liquid penetrant inspection is widely used for leak detection. It can be used with austenitic steels and nonferrous materials where magnetic particle inspection would be useless.
- Ultrasonic inspection: This method detects discontinuities by directing a high-frequency sound beam through the base plate and weld on a predictable path. It is the most accurate of the above techniques but just as with the, it requires qualified personnel to operate the tools that are used with it.
Of course, the quality of any weld is only as sound as the people produce the weld and those who are in charge of testing its soundness. These are the steps that one should follow in order to increase the changes of creating a proper weld.
- Process Selection – The process must be right for the job.
- Preparation – The joint configuration must be right and compatible with the welding process.
- Procedures – The procedures must be spelled out in detail and followed religiously during welding.
- Pretesting – Full-scale mockups or simulated specimens should be used to prove that the process and procedures give the desired standard of quality.
- Personnel: – Qualified people must be assigned to the job.
In the end, ultrasonic inspection equipment such as ultrasonic emersion tanks are needed to make the inspection of welds more accurate and concise. Of course, training and knowledge in the use of NDT equipment instruments is also needed to ensure that aircraft stay safe and in operation when needed.