Magnetic Particle Testing

Magnetic Particle (MT) testing is an inspection method used to identify cracks or other discontinuities open to the surface of ferrous materials.  MT can also be used to find discontinuities at subsurface level to a depth of 1/8”, depending on material properties and equipment capabilities.  There are visible and fluorescent methods as well as wet and dry methods.  MT test methods can incorporate large inspection bays with fixed equipment or portable magnetic yokes.  The yokes are most often seen in the petrochem industry for testing welds. MT is pretty basic and any Inspector should be able to competently perform inspections and evaluations.

Liquid Penetrant Testing

Liquid Penetrant (PT) or Dye Penetrant Testing is a method used to identify cracks or other discontinuities open to the surface of ferrous and non-ferrous materials.

PT test methods can incorporate large inspection bays with fixed equipment or portable penetrant kits in spray cans.  Like MT, the portable spray cans are mostly used in the petrochem industry for weld inspections. PT is again like MT in that this method is pretty basic and any Inspector should be able to competently perform inspections and evaluations.

Ultrasonic Testing

Ultrasonic Thickness Testing (UT) utilizes test machines with high sound frequencies (ulra-sound) to identify material thickness or discontinuities within a material thickness.  UT thickness is mostly used in the petrochem industry for the testing of wall thickness in piping and pressure vessels.  Material thickness may decrease over time due to process corrosion, erosion, or a combination of the two.

UT thickness testing and evaluation of data becomes more difficult and requires some training.  Many courses are offered through industry and colleges that teach UT.  A 40 hour class is typically the basic unit of education to allow one to be a UT Level I.  A Level I may perform thickness tests but is usually not authorized to make evaluations of problematic findings.  Additional training allows one to become a Level II, and supposedly able to evaluate findings. 

Ultrasonic shear wave, time of flight diffraction, guided wave testing and other, more advanced methods are utilized to inspect welds and greater lengths or volumes of material thickness.

While UT thickness requires some training to properly conduct and evaluate inspections, shear wave and other UT methods require much more training and practical application experience.  The owner of equipment should be advised that not all UT Level II or even Level II technicians can adequately perform these more technical inspections.  The Inspector should be familiar with the capabilities, limitations, and proper applications of UT testing.

Radiographic Testing

Radiographic Inspection (RT) is usually referred to as X-ray.  RT utilizes x-rays or gamma rays to volumetrically inspect materials.   In the petrochem industry, RT is used almost exclusively to test welds.  A weld x-ray is just the same as an x-ray of your broken arm.

RT inspections are performed by a two-man crew.

RT requires extensive training and safety. Federal and State laws regulate the use of a radioactive source, requiring a knowledgeable individual to be responsible for the use, storage and care of the radioactive source.

Film Reading

The inspector should be familiar with the capabilities, limitations, and proper applications of RT and should also be able to read and interpret film.  Film interpretation requires extensive training and application to be able to make competent decisions. As with most things, the more experience one has, the better film interpreter he or she may be.

Eddy Current Testing

Eddy Current (ET) Testing is used in the petrochem industry primarily for the inspection of heat exchanger and boiler tubes.  Both ferrous and non-ferrous tubes may be inspected utilizing the principle of eddy current.  This technology usually employs a two-man crew to operate the equipment.  The Inspector should be familiar with the capabilities, limitations, and proper applications of eddy current.

Other Methods

There are many other inspection and NDT methods used for any imaginable inspection within the petrochem industry.  We have just listed the 5 basic methods.  We will look at other inspection methods in the near future.

Coming soon….

In depth looks at each inspection method.  From the basics to the physics governing the method to the real life application of each method.