The Science of Flaw Detection.
Nondestructive testing is one of the best kept secrets around. Seems almost no one knows what it is, yet almost everyone is impacted one way or another by NDT.
All sorts of industries use this type of inspection to help insure that processes run smoothly and safely and products are manufactured with a high degree of integrity. Some of the industries that profit from NDT are the Oil and Gas Industry, Power Generation, Aviation and Aeronautics, the Auto Industry including Racing, Maritime Construction, all branches of the Military and Construction of all types.
NDT stands for Non Destructive Testing and there is no real difference between NDT, NDE (nondestructive evaluation) or NDI (nondestructive inspection), the latter two being a choice of preference among members of different industries. All refer to the same category of quality control test procedures that examines the integrity (or lack, thereof) of materials, components or systems without causing damage to them.
What Is Nondestructive Testing?
Nondestructive testing is, simply stated, exactly what its name implies – testing without destroying – to investigate the material integrity of the test object. More specifically, a nondestructive test is an examination of an object, material or system in any manner, which will not impair its future usefulness.
The purpose of the test may be to detect internal or external flaws, to measure geometric characteristics, to determine material structure or composition or to measure or detect some of the material’s properties Nondestructive testing is concerned in a practical way with the performance of the test piece – how long may the piece be used and when does it need to be checked again?
Since the 1920s, nondestructive testing has developed from a laboratory curiosity to an indispensable tool of production. No longer is visual examination the principal means of determining quality. Nondestructive tests in great variety are in worldwide use to detect variations in structure, minute changes in surface finish, the presence of cracks or other physical discontinuities, to measure the thickness of materials and coatings and to determine other characteristics of industrial products. Manufacturers use modern nondestructive tests to:
1. Ensure product integrity, and in turn, reliability
2. Avoid failures, prevent accidents and save human life
3. Make a profit for the user
4. Ensure customer satisfaction and maintain the manufacturer’s reputation
5. Aid in better product design
6. Control manufacturing processes
7. Lower manufacturing costs
8. Maintain uniform quality level
9. Ascertain operational readiness
Ensuring the Integrity and Reliability of a Product – Ensuring product reliability is necessary because of the general increase in performance expectancy of the public.
Preventing Accidents and Saving Lives – But reliability merely for convenience and profit is not enough. Reliability to protect human lives is a valuable end in itself. The railroad axle must not fail at high speed. The aircraft landing gear must not collapse on touchdown. The mine hoist cable must not snap with people in the cab. Such critical failures are rare indeed. And this is most certainly not the result of mere good luck. In large part it is the direct result of the extensive use of nondestructive testing and of the high order of nondestructive testing ability now available.
What Is The Difference Between a Level I, II and III?
ASNT NDT Level III
ASNT inaugurated its NDT Level III program in 1976 with certification offerings in five NDT methods. Over the years, ASNT has certified over 5,000 individuals from more than 50 countries as ASNT NDT Level IIIs and has expanded the certification program to include eleven NDT methods. ASNT is the single largest certifying body of Level III personnel today and the ASNT NDT Level III certificate remains the most respected and widely accepted NDT certification throughout the world. Level III personnel are ultimately responsible for the training, qualification and certification of a company’s nondestructive testing Level I and Level II technicians.
The NDT Trainee, Level I, and Level II
When a person starts the training and qualification process, they are classified as a trainee. Their goal is usually to become a fully certified Level I, Level II or Level III technician. It is important that the technician be qualified in the inspection method before the technique is used and test results evaluated.
Using SNT-TC-1A as a model, the experienced direction of a Level III provides the employer with the necessary guidelines and documentation to properly qualify and certify the NDT technician. To comply with most industry standards, the employer must establish a “Written Practice” that describes in detail how future technicians will be trained, examined and certified.
Typically a Level I technician is able to carry out calibrations and perform test procedures under the supervision of a certified Level II or Level III.
A Level II Technician can calibrate, perform tests without supervision and make test assessments when required.
What distinguishes “Qualification” and “Certification” in Nondestructive Testing?
Making Sense Out of Certification for NDT Personnel per SNT-TC-1A
The confusion within the industries that use NDT services exists over the terms “certification” and “qualification.” These words have been used and abused over the decades since the 1960’s when the American Society of Nondestructive Testing (ASNT) published its first Recommended Practice, SNT-TC-1A, Certification and Qualification of NDT Personnel. Using SNT-TC-1A as a model under the experienced direction of a Level III provides the employer with the necessary guidelines and documentation to properly qualify and certify the NDT technician. To comply with most industry standards, the employer must establish a “Written Practice” that describes in detail how future technicians will be trained, examined and certified.
The Qualification and Certification Process –
SNT-TC-1A is quite specific and clear as to what proper qualification and certification of NDT Personnel involves. Here are two straightforward definitions to clarify the terms:
Qualification is comprised of three things: the organized education, the required examinations proving an individual has proper training, and sufficient work experience in a particular inspection method.
Certification is a written testimony by an employer affirming that an individual has met the requirements of training and experience regarding a particular inspection method as stated in the company’s Written Practice.
Qualification of the Technician
Step One – Training
Training is an organized program developed to provide inspection personnel with the knowledge and skill necessary for qualification in a specific method. In such a program the principals and techniques (referred to as the “Body of Knowledge”) of the particular test methods are taught to the degree prescribed by the employer. The necessary amount of training (typically stated in numbers of hours) and examination requirements (such as content and number of test questions) is stated in the employer’s Written Practice.
Recommended Training Hours per SNT-TC-1A
Method Level I Level II Total Hours
Magnetic Particle 20
Liquid Penetrant 12
Radiography I 40
Radiography II 40 Ultrasonic I/II 40 + 40
Eddy Current I /II 40 + 40
Step Two – Examinations
Written General and Specific examinations, a Practical examination and finally, an annual Visual examination that proves Near Vision Acuity and Color Differentiation Skills by use of Ishihara Color Plates are administered to NDT personnel.
~ The General examination covers the basic principles (Body of Knowledge) of the applicable method.
~ The Specific examination covers the procedures, equipment and techniques that the employee will be required to perform in their job assignment.
~ The Practical (hands-on) examination allows the employee to demonstrate their ability to operate the pertinent test equipment and to perform defined calibrations and tests according to relevant specifications.
Individuals are required to score 70% or higher on each of the three exams and generate a composite score (a simple average of all three exams) of at least 80% or higher.
Step Three – Experience
Method Level I Level II Total Hours
Magnetic Particle 210
Liquid Penetrant 140
Ultrasonic Testing 630
Eddy Current 630
Work activities accomplished in a particular test method under the supervision of a certified individual in that particular method is referred to as Time in Method and includes time spent observing, setting-up and executing specific test procedures, performing calibrations and carrying out other related activities. Time spent in organized training programs does not count as experience.
A Level II or Level III technician supervises the processing so that if the trainee makes an error, the test can be repeated and the supervising technician can evaluate the test object and accept or reject, and the trainee will observe the evaluation. Time spent in organized training programs does not count as experience. The length of experience required prior to certification is stated in the employer’s Written Practice.
Certification of the Technician
Certification of NDT personnel is the responsibility of the employer. Personnel are certified when they have completed the initial training, examination and experience requirements stated in the employer’s Written Practice. The length of certification and method of re-certification is also stated in the employer’s Written Practice. Documentation that states each applicant’s qualifications according to the requirements of the Written Practice are required before certification can occur. Key points to keep in mind are:
~ Certification is a document of testimony on the part of a knowledgeable person in a particular NDT method – typically the candidate’s supervisor, department manager or corporate officer depending on the size of the employer;
~ Certification in any NDT method is properly earned after a candidate has completed the process specified by the employer’s Written Practice;
~ A technician’s certification ends concurrent with his or her termination of employment.
The bottom line is that the employer adopts full responsibility for the technician’s actions and decisions once they are qualified and certified, but assumes no further responsibility for actions beyond the employment period (no such thing as a person claiming Level II status unless they are employed by the company that put them through the qualification process).
The most significant fact to understand about certification is this: if certification has been properly earned through a stepped qualification process, the technician should be capable of providing consistent and trustworthy service.
Integrity: At the Heart of the Matter
The nondestructive testing profession has suffered over the years because owners or managers have sent poorly or incompletely trained people to perform services for clients who have not always been savvy enough to recognize the difference between certified technicians and unqualified individuals.
The work of the NDT technician is much too important to be treated carelessly. The integrity with which we accomplish our profession will have an impact on the health and safety of those who work in, on or around the items we inspect. They deserve our very best. Mistakes can and have cost lives!
Technology alone will never suffice. Only technicians who are qualified and able to embrace integrity of character and the importance of their profession can produce the observation, application and analysis required by the industry they serve and the public they keep safe.
The Written Practice for Qualification and Certification of NDT Personnel
The Written Practice is the controlling document that adapts the recommendations of the ASNT Recommended Practice SNT-TC-1A to meet the specific requirements of the Company/Employer. The Written Practice should be developed or evaluated and approved by the employer’s NDT Level III. It should be maintained on file for easy access, reference and maintenance by the Level III administrator, as well as for ready review in situations such as customer and jurisdictional audits. Issues covered within this dynamic document include:
~ The control and administration of NDT personnel training, examination and certification;
~ A description of the responsibilities of each level of certification;
~ A description of the training, experience and examination requirements for each level of certification;
~ Determinations of the acceptability of materials or components in accordance with applicable codes, standards, specifications and procedures.
In summary, the following Certification Triangle may help. All three sides of the triangle must be in place before a candidate is truly certified. Assuming this, and further assuming that the central portion of the triangle is being fully adhered to by the employer, the chances are very good that the qualification program will produce certified NDT technicians who will positively define their profession into the future.