Nondestructive Testing in Welding

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In the welding industry, workers do more than fuse metal together. Technicians also conduct quality control operations to ensure that an item is properly constructed and bonded. That’s where nondestructive testing (NDT) comes in.

Nondestructive Testing Explained

Nondestructive testing aids certified welders in quality control management, but how? NDT involves using a series of techniques to analyze and/or verify the qualities of an item. Such methods may be highly scientific in nature, and must not weaken the item or hinder its usefulness.

Nondestructive testing methods are used extensively for research and troubleshooting in several fields, such as engineering sciences, medicine and automotive. In many cases, there is a specific application for the results of any given test well-beyond standard quality control measures. For instance, results of NDT may be required for a patent application for a company’s new product or for forensic use in a personal injury case. NDT is beneficial because it could save a company time and money in terms of having to replace an entire product line or even pay a plaintiff in a lawsuit.

Nondestructive Testing Methods for Welding

There are numerous tests that a technician with nondestructive welding inspection training can conduct to verify the structural soundness and reliability of a given material. Each may be done alone or in combination with one another, depending on what the technician is looking for. Several methods exist, including leak testing (LT), magnetic particle testing (MT), radiographic testing (RT) and ultrasonic testing (UT).

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- Leak Testing – LT testing reveals metal surface damage such as hairline or fatigue cracks and leaks on items. A variety of methods are used in this examination, all with the goal of covering an item with a substance and seeing if that substance penetrates the object. Welders may use liquids, gases or even soap bubbles to accomplish this, which will not harm the item. To check whether a defect is present, the technician takes images of the object to reveal whether the substance has spread to the inside. If there is no structural issue, the substance will simply lay on top of the item’s surface.
- Magnetic Particle Testing – MT is concerned with surface breaks of magnetic metals like iron, cobalt and nickel. Determining the integrity of an item’s surface requires dusting it with iron particles. If an imperfection is present, these iron particles will be attracted to the area, providing a visible indication of the problem. From here, welders may determine the cause and solution to the issue.
- Radiographic Testing – RT testing checks for flaws and cracks in welds. The test involves exposing a metal object, especially piping, storage containers or pressure vessels to either gamma ray or x-ray radiation (i.e. via a high-capacity x-ray machine), which penetrates the inside of the item. Defects are evidenced by graphs displayed on film showing varied radiation absorption.
- Ultrasonic Testing – UT is a valuable stress test. The examination sends high frequency sound waves from a transducer through a metal item in order to determine its integrity. If changes in the sound waves occur as they pass through the object, it may reveal flaws such as fractures or bubbles inside of the item. Alternatively, UT can measure object thickness.

Not all items are perfectly constructed, and that doesn’t necessarily make it the fault of the welder. Metal materials frequently have inherent defects that we simply cannot see, whether they are just so small on an item’s surface or completely invisible inside of it. That’s why welders conduct nondestructive testing. After all, it would be horrible to have issues with such important things as automobiles because of a defect. Everything we use, for whatever reason, must be both safe and reliable.

Does this sound like something you’re concerned about or interested in? Check out TWS’ Associate’s Degree in Welding program to learn and experience more.

Sources:
http://www.wisegeek.com/what-is-nondestructive-testing.htm
http://en.wikipedia.org/wiki/Nondestructive_testing
http://www.engineeringtoolbox.com/ndt-non-destructive-testing-d_314.html