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Ultrasonic flaw detectors are widely used in critical safety-related and quality-related applications involving structural welds, steel beams, forgings, pipelines and tanks, aircraft engines and frames, automobile frames, railroad rails, power turbines and other heavy machinery, ship hulls, castings, and many other.



  • Advantages of ultrasonicinspection are:
    • Internal defects can be detected and sized when a validated procedure is applied
    • Thick specimens take no more time to examine than thin ones, assuming correct instrumentation set up
    • Access to only one side of the component is needed
    • There is no radiation hazard in ultrasonic examination, and hence no disruption of work as there is with radiography
    • Volumetric and crack like defects can be detected, irrespective of their orientation



  • Disadvantages of ultrasonicinspection as a method of Non-Destructive Examination are:
    • A high degree of operator skill and integrity is needed. Hence, the need for trained and certified NDT personnel
    • In most examinations, there is no permanent record of the inspection as there is in radiography, however more recent equipment does offer this facility
    • In certain materials, like austenitic steel, the large grain size found in welds can cause attenuation and this may mask defects
    • Spurious indications, and the misreading of signals, can result in unnecessary repairs, which is why a validated procedure should be applied when carrying out any ultrasonic examination.


Training and certification

➤ It is important that NDT technician be qualified in the Ultrasonic Testing method before the technique is used and test results evaluated.

➤ The American society for non-destructive testing recommends using ASNT SNT-TC-1A, 2020 edition for training, certification and recertification.

➤SNT-TC-1A provides the employer with the necessary guidelines to properly qualify and certify the NDT technician in all methods.

➤ To comply with SNT-TC-1A; the employer must establish a written practice that describes in detail how the technician will be trained, examined, and certified.

➤ Students are advised to study Latest edition of SNT-TC-1A to determine the recommended number of hours of classroom instruction and the required number of the months of experience necessary in order to be certified as a Ultrasonic Testing technician.


Levels of qualification

In the process of being initially trained, qualified and certified, an individual should be considered a trainee. A trainee should work with a certified individual. The trainee shall not independently conduct, interpret, evaluate, or report the results of any NDT test.


➤ The three basic levels of qualification are as follows:


  • NDT LEVEL I: He/she should be qualified to properly perform specific calibrations, specific NDT, and specific evaluation for acceptance or rejection determinations and record the results under supervision of a certified NDT LEVEL II or level III individual.


  • NDT LEVEL II: He/she should be qualified to set up and calibrate equipment; interpret and evaluate results with respect to applicable codes, standards and specifications. He/she should be thoroughly familiar with the scope and limitations of the methods qualified and should supervise on the job training and guidance of trainees and NDT LEVEL I personnel. The NDT LEVEL II should be able to organize and report the results of NDT tests unsupervised.


  • NDT LEVEL III: He/she should be capable of developing, qualifying, and approving procedures, establishing and approving techniques, interpreting codes, standards, specification and procedures; and designating the particular NDT methods, techniques and procedures to be used. The NDT level III should have sufficient practical background in the applicable materials, fabrication and product technology to establish techniques and to assist in establishing acceptance criteria when none are otherwise available.


The SNT-TC-1A document recommends that NDT LEVEL I and NDT LEVEL II technicians shall be examined in the following areas:

  1. General examination
  2. Specific examination
  3. Practical examination


The SNT-TC-1A document recommends that NDT LEVEL III personnel be examined in the following areas:

  1. Basic examination
  2. Method examination
  3. Specific examination


ASNT holds Level III examination and certification services in the Basic & Method areas.

Because of the individual requirements of the many industries using NDT, the SPECIFIC EXAMINATION is still the RESPONSIBILITY OF THE EMPLOYER.


Table 6.3.1 A: Recommended Initial Training and Experience Levels

Examination Method

NDT Level


Training Hours


Min. Hours in Method or TechniqueTotal Hours Level in NDT
Penetrant TestingIAll470130
Magnetic ParticleIAll1270130
Radiographic TestingIRadiographic40210400
Ultrasonic TestingIAll40210400
Visual TestingIAll870130