What is NDT?
Non-destructive testing, or NDT, is the inspection of an object without physically damaging or altering its appearance. Non-destructive tests are typically performed to ensure the functionality, proper installation and maintenance, and makeup of an object. Conversely, NDT is also performed to find issues. NDT evaluates both the external and internal composition of objects under test. It can identify the makeup of an object, identify objects invisible to the naked eye, and indicate noise. Non-destructive techniques identify structural faults through non-invasive testing methods by harnessing the power of ultrasonic, infrared and laser technology. Conducting NDT saves money and time, reducing production costs by preserving the subject under test and allowing engineers to experiment with several testing parameters before returning to research and troubleshooting.
What is the ASNT?
Engineers look to the American Society for Nondestructive Testing (ASNT) for NDT personnel qualification and certification practices. When selecting an engineer to perform NDT on your product, machine or facility, refer to the following standards to verify their ASNT compliance:
- Guidelines for developing your own in-house NDT certification program; includes recommended skill levels for all tiers of NDT qualification, including training/experience hours and examination eligibility.
- ANSI/ASNT CP-189
- Establishes the minimum standards for qualifying/certifying NDT personnel. An American National Standard which differs from the “recommended practices” of SNT-TC-1A by detailing hard requirements rather than educated suggestions.
- ANSI/ASNT CP-105
- Outlines training for Level I and Level II personnel as well as topical outlines of Level III qualifications. Details minimum training courses for each.
- ANSI/ASNT CP-106
- An adoption of ISO 9712:2005 which describes certification requirements for engineers to conduct the following: Electromagnetic Testing (ET), Magnetic Particle Testing (MT), Liquid Penetrant Testing (PT), Radiographic Testing (RT), Ultrasonic Testing (UT) and Visual Testing (VT)
- ANSI/ASNT ILI-PQ-2010
- Focuses on the requirements for certifying in-line inspection (ILI) personnel who will be evaluating pipes and pipelines.
Why is NDT Important?
- Accident Prevention. Ensures products, equipment and facilities are safe for the public. Employers with the foresight to rent infrared cameras and conduct building envelope testing, for example, could avoid the corrosion of structural members in an old building, which could be ripe with potential lawsuits in case of a collapse or dangerous mold contamination.
- Reliability. Non-destructive testing assesses the reliability of a device or system, empowering project managers to make informed decisions on repairs, remodels and replacements. A flow meter will indicate to facility managers whether a new piping system is a financially sound investment or whether the current system is dependable, perhaps saving thousands of dollars.
- Meeting Standards. NDT fulfills requirements for numerous organizations, including the following and more:
- American Society of Testing and Materials (ASTM)
- American Society of Mechanical Engineers (ASME)
- American Petroleum Institute (API)
- American Welding Society (AWS)
- Aerospace Industries Association (AIA)
- International Organization for Standardization (ISO)
NDT Methods & Techniques
Vibration Analysis (VA)
Vibration analysis is a non-destructive method of testing manufacturing equipment and the rotating balance of machine’s rotors. The acceleration, velocity and displacement of the vibration distinguish device models. Vibration testing is commonly conducted in construction sites, R&D labs and manufacturing facilities, and generally requires calibration before renting.
Acoustic Emission Testing (AE)
Materials under stress generate acoustic emissions. Sound level meters and other acoustic emission test instruments act as receivers, recording the intensity and arrival time of emissions and then tracing anomalous emissions to their sources. Earthquakes, melting parts and phase transformations in metals are all possible causes for a fault which, without the help of a sound level meter, might never be remedied.
Ultrasonic Testing (UT)
A flaw detector gives engineers something a destructive test never will: insight into the material composition of a product or system. Ultrasonic testing sends short bursts of high-frequency ultrasonic waves to identify material flaws, allowing technicians to visualize material inconsistencies and attain dimensional measurements via detailed images. Mining, toy plastics and lead paint are a few of the applications for flaw detectors, flow meters and thickness gauges, which all harness the power of ultrasonic waves.
Visual Testing (VT)
Visual inspection is self-explanatory. The most common method of NDT, visual testing of an object is enhanced by borescopes and videoscopes, which can display cracks, corrosion, physical damage and misalignment of parts in striking clarity.
Thermal/Infrared Testing (IR)
Thermal testing, also known as infrared thermography, measures the surface temperatures of an object from the infrared radiation the object produces. Engineers and technicians rent thermal cameras to discover corrosion, disbands, delamination and a variety of other defects.
Electromagnetic Testing (ET)
The most common form of electromagnetic testing performed for NDT purposes is eddy current testing. A technique often applied to material sorting and surface crack detection, eddy current testing finds flaws in conductive materials through electromagnetic induction. RF survey meters and gauss meters exemplify the type of NDT instruments utilized to complete ET tests.
Laser Test Methods (LM)
Laser testing is comprised of several laser-based measurement techniques, including holographic testing, laser profilometry and laser shearography. A common laser test method is laser shaft alignment, in which a laser beam measures a device’s rotating center. This helps engineers connect two or more rotating shafts in a collinear fashion (in the same straight line). Laser micrometers are another laser testing product which determine an object’s dimensions via laser dimensional analysis.
Leak Testing (LT)
Engineers and technicians conduct leak testing to identify otherwise imperceptible gas leaks. Leak testing is conducted on both pressurized and non-pressurized systems to detect gases like oxygen, helium and other halogens. Leak detectors detect leaks and gather data about the environment under test.
Material Identification Testing
Material identification testing refers to the analysis of material composition to detect faults, corrosion, pollutants and other anomalous elements in items. Internal material analysis devices like XRF analyzers assess the chemical breakdown of a material’s elemental composition by sending X-rays through the product in question. External devices like surface roughness testers scan an object to gather parameters on its external composition.
What is ASNT Certification & Qualification?
To perform NDT testing, technicians and engineers need to follow the general requirements established by EN ISO 9712 and other quality standards. Inspectors themselves must certified as well, acquiring central third-party certification in compliance with EN ISO 9712 by a certification body accredited by ISO IEC 17024.
- Level 1: Technicians First level NDT inspectors are qualified to perform certain calibrations and tests under close supervision, following specific instructions for testing and what criteria contribute to rejection.
- Level 2: Engineers Level 2 personnel set up and calibrate test equipment and conduct NDT themselves, testing according to industry-specific codes and standards. Engineers with Level 2 certification are then entrusted to report on results, documenting the evaluation process and confirming passes and rejections.
- Level 3: Specialized Engineers Engineers with Level 3 certification direct laboratories, establishing measurement techniques and certifying personnel. Level 3 NDT personnel specialize in the non-destructive testing process, possessing intimate knowledge of both the science behind the testing and the rigors associated with conforming to ANST-associated standards and philosophy.