Non Destructive Testing

Ultrasonic Testing

In ultrasonic testing, very short ultrasonic pulse-waves are sent into materials to detect internal flaws or characterize materials. This method is often used to determine the thickness of an object, or to detect internal flaws in bonding/welding.

Advantages:
High penetrating power, which allows the detection of flaws deep in the part
High sensitivity, permitting the detection of extremely small flaws
Only one surface needs to be accessible
Some ability of estimating the size, orientation, shape and nature of defects.
Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.
Capable of highly portable operation.

Disadvantages:
Parts that are rough, irregular in shape, too small or too thin, are difficult to inspect
Surface must be prepared by cleaning and removing loose material

Phased Array Testing

Phased Array ultrasonics is an advanced method of ultrasonic testing that has applications in nondestructive testing. The Phased Array probe consists of many small ultrasonic elements, each of which can be pulsed individually. By varying the timing a pattern of interference is set up that results in a beam at a set angle. Basically, the beam can be steered electronically. The beam is swept back and forth searching the object being examined and the data from multiple beams is put together to make a visual image showing a slice through the object.

Advantages:
Same as conventional ultrasonics
Increased sensitivity
Visual images showing indications

Disadvantages:
Extra training is required prior to use
Equipment is more expensive

Magnetic Particle Testing

Magnetic Particle testing is a method for detection of surface and sub-surface defects in ferrous materials. By using an externally applied magnetic field or electric current through the material, and the principle that the magnetic flux will leave the part at the area of a flaw.

The presence of a surface or near surface flaw in the material causes distortion in the magnetic flux through it, which causes a leakage of the magnetic fields at the flaw. This leakage will “hold” magnetic particles in the area, revealing the flaw to the technician.

Advantages:
Easy to perform
More sensitive than plain visual inspection
Will work through paint

Disadvantages:
Equipment is bulky and unable to fit into some areas
The method only works on ferrous materials (does not work on stainless steel)
Only able to detect flaws approximately ¼” below the surface.

Dye Penetrant Testing

Dye Penetrant testing is a method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). A low surface tension fluid is applied to the component which penetrates into clean and dry surface-breaking discontinuities. After adequate penetration time has been allowed, the excess penetrant is removed, and developer is applied. The developer helps to draw the penetrant out of the flaw where a visible indication becomes apparent.

Advantages:
Works on both ferrous and non-ferrous materials
Works on all non-porous materials (metals, plastics, or ceramics)
Increased sensitivity with high visual contrast
Easy to perform

Disadvantages:
Will not work through paint
Only able to detect flaws open to the surface
Components with poor profile are difficult to inspect

Visual Testing

Visual testing is a method where an inspector visually searches a component for defects in welding and configuration. Visual testing can be done on any material and any component following a predetermined set of guidelines. A visual test is usually performed alongside other testing methods. Another form of Visual testing is Quality Control. Quality Control is a method where procedures, processes, and specifications are reviewed alongside a component to ensure proper quality is obtained.

Advantages:
Can be performed on any material or configuration
Can be performed quickly in comparison to other methods
Can be used to ensure quality

Disadvantages:
Cannot be used to find internal flaws
Is not as sensitive as other methods