SNT-TC-1A explained: the written practice, the levels and the hours

SNT-TC-1A is the most widely used framework for qualifying and certifying nondestructive testing (NDT) personnel outside aerospace. It is published by the American Society for Nondestructive Testing (ASNT) as a recommended practice, and that one phrase explains most of what confuses people about it. SNT-TC-1A does not certify anyone and does not, on its own, require anything. It gives an employer the recommended ingredients — levels, hours, exams, vision checks, recertification — and the employer writes its own rulebook from them.

The written practice is the employer's rulebook

The one thing SNT-TC-1A insists on is a written practice: the employer's own document for controlling how its NDT people are trained, examined and certified. It is reviewed and approved by the employer's NDT Level III and kept on file (2024 edition, section 5). The foreword asks the employer to swap the recommendation's “should” for “shall” when writing it — once the written practice says something, that is the requirement an auditor holds you to.

The employer can adapt the recommendations to its own work. What it cannot do is drop the basic provisions: training, experience, examination and recertification stay. Where the written practice departs from a detailed recommendation, the technical reasons should go in an annex to it (1.4). That is why two companies can both “follow SNT-TC-1A” and certify differently, and why the first question in any audit is “show me your written practice”. Our written practice guide covers writing one.

Levels I, II and III

SNT-TC-1A writes its levels in Roman numerals. The employer may subdivide them, and a person in training is a trainee, who works beside a certified individual and does not independently perform, interpret, evaluate or report NDT (4.2). In outline (4.3):

• Level I performs specific standardizations, tests and accept-or-reject evaluations according to written instructions, and records the results, under the instruction and supervision of a Level II or III.
• Level II sets up and standardizes equipment, interprets and evaluates results against the applicable codes and specifications, organizes and reports results, and guides trainees and Level I personnel on the job. The 2025 addendum adds guidance of limited-certified personnel to that list.
• Level III develops, qualifies and approves procedures and techniques, interprets codes and specifications, chooses the methods and techniques to be used, and is capable of training and examining Level I, II and III personnel in the methods in which they are certified.

The 2025 addendum formalises a role most programs already had: the Responsible Level III, the Level III the employer designates with overall responsibility for its qualification and certification program. Those duties can be delegated — to other Level IIIs, including outside consultants — provided the delegation is documented.

There is also a limited certification: a Level II certification to a narrower scope, such as film interpretation or ultrasonic thickness measurement, for people who do not meet the full training and experience. The 2024 edition gives recommended hours for several limited certifications, including digital and computed radiography and CT interpretation for the first time, and limited certifications are approved by the Level III and documented in the certification record (6.3.1.2–6.3.1.3).

Training and experience

Table 6.3.1A of the 2024 edition sets out recommended training hours, hours of experience in the method, and total hours in NDT, by method and level. A few of the common methods, in our own layout:

The notes under that table matter as much as the numbers:

• A candidate can go straight to Level II if their training and experience add up to the Level I and Level II figures combined.
• Experience can be gathered across several methods at once, but the minimum for each method still has to be met.
• Training hours can be adjusted in the written practice for a candidate's education. Radiography candidates also need the radiation safety training their regulator requires, separately from the NDT training.
• New in 2024 (6.4): for expanded programs at colleges and training schools, extra lab hours beyond the training minimum can count toward experience, if the Level III approves it and the written practice documents it — up to a quarter of the experience, with at least three quarters gained in the field.

For Level III, the recommended route depends on education: a bachelor's degree in engineering or science plus one more year of Level II-comparable experience in the method, or two years of engineering or science study plus two years, or four years of such experience without the study (6.3.2).

Training should be organized and approved by the responsible Level III, and may be classroom, personalized, virtual instructor-led, computer-based or web-based — the last two tracking hours and content with student exams (7.1). ANSI/ASNT CP-105 provides the recommended topical outlines (7.3).

The exams

Levels I and II sit three exams in each method: a closed-book General exam on the method's principles, a Specific exam on the employer's own specifications, equipment, procedures and techniques, and a Practical, where the candidate works on at least one flawed specimen against a checklist of at least ten checkpoints. Level III sits a Basic exam (once, not per method, as long as they hold a current Level III), then a Method exam, a Specific exam and, in most cases, a Practical (section 8).

• Passing: at least 70% on each written exam, at least 80% on the practical, and a composite — a simple average — of at least 80% (8.1.4–8.1.5).
• Question counts: Table 8.3.3 gives recommended minimums by method and level. For the common methods it is 40 General questions and 20 Specific at each of Levels I and II.
• Who examines: a Level III is responsible, and may delegate the administration and grading to a trained, documented representative. The Level II practical is administered by a qualified Level III, and nobody may be examined by themselves or by a subordinate (8.1.2, 8.1.8).
• Retakes: wait at least 30 days, or receive additional training the Level III decides on, before reexamination (8.7).
• Central certificates: a valid ACCP, ASNT NDT or ASNT 9712 certificate may be accepted in place of certain exams if the Level III decides ASNT's exams meet the written practice, and the acceptance is documented.

The certification exams guide works through running them.

Vision

Near-vision acuity is checked every year: the candidate reads at least Jaeger No. 2 (or equivalent type) at not less than 12 inches, in at least one eye, natural or corrected. The 2024 edition adds that pharmacological agents — eye drops — that would improve acuity may not be used. Color-contrast differentiation, for the colors or shades of gray used in the method, is checked at initial certification and every five years. Vision exams expire on the last day of the month in which they fall due (8.2).

Certification, recertification and leaving

• Who certifies: the employer, always — even when an outside agency provides Level III services (9.1, 9.3).
• When it starts: the date the Certifying Authority signs the certification record (9.5.2), a point the 2024 edition settled after an interpretation inquiry.
• How long: a recommended maximum of five years from that date, expiring on the last day of the month (9.5.3, 12.2).
• Recertification: by evidence of continuing satisfactory technical performance, or by whichever parts of the exams the Level III decides are needed (12.1).
• Interrupted service: the written practice sets the rules for how long a gap triggers reexamination (section 11).
• Leaving: the certification is revoked when employment ends. A former employee can be reinstated without new exams within six months if the records were kept and the certification did not expire in the meantime; a new employer can recertify by examination within six months if the person was working at that level (sections 13–14).

The certification record should hold the person's name, level, method and any limitations, education and experience, a training statement, the current vision results, the exams or evidence of them, the composite grade, the verifying Level III's signature, the certification and expiry dates, and the Certifying Authority's signature (9.4). Section 9.6 adds recommendations for certificates and wallet cards, including naming the SNT-TC-1A edition the written practice follows.

When a code makes it mandatory

ASME Section V (2025 edition) accepts a written practice built on SNT-TC-1A (2024) for work that references its Article 1, but on tighter terms: the recommendations become requirements, some of the central-certificate substitutions do not apply to the specific and practical exams, the performance evaluation becomes mandatory before recertification, and a Level III writes a code-compliant procedure before their first certification with each employer (T-120). If you work to ASME, your written practice has to say all of that. See the ASME Section V and XI guide.

Frequently asked questions