NDT personnel certification: ISO 9712 vs SNT-TC-1A

In non-destructive testing (NDT), the reliability of a report does not rest on instrument calibration or procedure accuracy alone. It also rests on the system that authorized the signature at the bottom of that report. Two inspectors can radiograph the same weld: one certified as ISO 9712 Level II, the other certified under the employer's SNT-TC-1A written practice. Those two certificates are not interchangeable. This article compares the two models that shape NDT personnel certification worldwide — independent third-party certification (ISO 9712) and employer-controlled written practice (SNT-TC-1A) — from a field perspective, across levels, vision, experience, training and examination requirements, validity and recertification, and what the market in Türkiye (Turkey) actually expects.

1. Why two different certification philosophies exist

NDT results cannot be separated from the competence of the person performing the test. A misinterpretation means a missed crack. The industry therefore answered two basic questions in two different ways: who attests to competence, and who carries the responsibility?

Europe, and the ISO world more broadly, chose competence attested by an impartial certification body independent of the employer (ISO 9712). The North American ASNT tradition chose competence certified under the employer's own written practice, with the employer carrying the responsibility (SNT-TC-1A). Both philosophies aim at the same result — trustworthy testing — through different governance models. Ask for "certified personnel" on a project without understanding that difference and you usually end up with a specification mismatch.

2. Level I, II and III: the shared backbone

Both systems divide personnel into three levels, and the functional definitions overlap closely:

Level I: Performs calibration and testing according to written instructions and records the results. Does not make independent accept/reject decisions; normally works under Level II or III supervision.
Level II: Sets up, adjusts and performs the test according to procedures; evaluates and reports results against the applicable acceptance criteria. This is the level that typically signs reports in the field — but selecting the method and the acceptance criteria stays with Level III.
Level III: Writes procedures and techniques, selects methods, interprets acceptance criteria, runs personnel training and examination, and carries technical responsibility.

The definitions look alike. How the levels are earned is where the two systems diverge, and that is the real difference.

3. ISO 9712: independent third-party certification

ISO 9712 requires the certification body to be independent of the employer and accredited under ISO/IEC 17024. The certificate belongs to the person, not to the company, and remains valid when the person changes employer.

The backbone of the system:

An independent body verifies the candidate's training and experience.
The examination (general, specific, practical) takes place at an authorized examination center under impartial invigilation.
A body independent of the instructor who delivered the training makes the certification decision.
The method and the industrial sector (welding, castings, forgings, tubes and pipes, and so on) are stated explicitly on the certificate.

Because it delivers employer-independent impartiality, this model is requested as "objective proof of competence" in Europe, the Middle East and international projects generally. Many countries, Türkiye included, have adopted it as a national standard.

4. SNT-TC-1A: the employer's written practice

SNT-TC-1A, published by ASNT, is not a standard — it is a recommended practice. The critical point: SNT-TC-1A does not certify anyone directly. It provides a framework for the employer to build its own Written Practice. The employer issues the certificate, and the employer carries the responsibility.

The practical consequences:

The certificate is tied to the employer. As a rule it lapses when the person moves on, and the new employer re-evaluates the individual under its own written practice.
Training hours, experience durations and examination formats in SNT-TC-1A are recommended values. The employer adopts them in its Written Practice, or adapts them with justification.
The employer's responsible Level III makes the final certification decision and assigns the level.
The system depends on the employer's integrity and on the quality of the Written Practice. That is why audits start by reviewing the Written Practice.

Alongside this employer-based model, ASNT also publishes and operates certification structures that carry standard status. ANSI/ASNT CP-189 is an American National Standard that sets binding minimum requirements, unlike the advisory SNT-TC-1A. It still rests on employer certification in much the same way, but compliance is mandatory and the employer must have an ASNT NDT Level III. On the central, employer-independent side, ASNT is retiring the ACCP program it once operated: it stopped accepting new ACCP applications on 15 May 2023 and ACCP renewals on 30 August 2023. The ASNT 9712 program, launched in March 2023 and based on ISO 9712:2021, replaces it, and ACCP closes fully by September 2028. The central program now running on the ASNT side is therefore not ACCP but the ISO 9712-based ASNT 9712. In field jargon, however, "SNT-TC-1A certificate" still means the classic employer-based model. (Examination question banks are neither CP-189 nor SNT-TC-1A itself; they are separate ASNT publications.)

5. Vision (visual acuity) requirements

Both systems make visual acuity a mandatory prerequisite. But the near-vision threshold differs between the two, and mixing the two up is the single most common error in this comparison:

Near vision (ISO 9712): In at least one eye, ability to read Jaeger 1 or Times Roman N4.5 letters at a distance of not less than 30 cm; corrected or uncorrected is acceptable.
Near vision (SNT-TC-1A): In at least one eye, ability to read Jaeger Number 2 letters at a distance of not less than 12 in. (about 30.5 cm).
Color and gray-scale differentiation (both systems): Ability to distinguish the colors and shades of gray the method requires. This matters most in penetrant testing (PT) and magnetic particle testing (MT), where color contrast drives the evaluation.

Retest frequency is another point that gets over-generalized. Both systems verify near vision every 12 months and keep the record. Color and gray-scale differentiation, by contrast, is not annual: SNT-TC-1A requires it at initial certification and at least every 5 years thereafter, while ISO 9712 ties color vision verification to recertification (in practice once within the last five years, at the frequency the certification body defines). The record most often missing in the field is the current near-vision examination — and it is one of the first things an auditor asks for.

6. Training, experience and examination requirements

The numerical criteria of the two systems follow similar logic here. The governance does not.

Training: Both systems define minimum formal training hours for each method and level (radiography and ultrasonics, for example, require far more training than penetrant testing). Under ISO 9712 these hours are binding in the standard. Under SNT-TC-1A they are recommended values that the employer adopts in its Written Practice.

Experience: Supervised industrial experience in the specific method is mandatory. Level II experience is normally cumulative: it includes the Level I experience. For certification in more than one method, proration rules apply to the total.

Examination:

Under ISO 9712 the examination has three parts: general (principles of the method), specific (product/sector, procedures and acceptance criteria) and practical (testing and reporting on real specimens). To pass, the candidate must score at least 70% in each of the three parts separately. A high score in one part does not compensate for another, and there is no separate "overall average" threshold. (At Level III, different provisions replace the practical part.)
Under SNT-TC-1A the examination structure is similar (general, specific, practical), but the employer's Level III prepares and administers it, and the Written Practice sets the passing criteria.

The core distinction is clear: ISO 9712 examinations are impartial and held at an independent center; SNT-TC-1A examinations run in house, under the employer.

7. Validity, renewal and recertification

Two ISO 9712 concepts get confused constantly: renewal and recertification.

ISO 9712: The certificate is typically valid for 5 years. At the end of year 5 the certificate is renewed, and renewal normally requires no examination: a current vision examination and evidence of continuous work (no interruption longer than 12 months) are enough. Recertification, which does require a practical examination, comes at the end of the second validity period — that is, at year 10. At that point a practical re-examination applies for Level I/II, or a structured credit file for Level III. Because the certificate is employer-independent, it travels with the person.
SNT-TC-1A: Recertification intervals are defined in the employer's Written Practice. The current edition (2020) recommends a maximum cycle of 5 years for all three levels, normally renewed by examination or by an evaluation of competence. But because the certificate is tied to the employer, it effectively lapses when the person leaves.

In both systems, annual renewal of the near-vision examination is a separate, continuous requirement that keeps the certificate alive.

8. Practice and market expectation in Türkiye

The dominant framework for personnel certification in Türkiye is ISO 9712, and independent bodies accredited by TÜRKAK, the Turkish Accreditation Agency and an EA MLA signatory, carry out the certification. In welded fabrication, pressure equipment, power, petrochemical and infrastructure projects, specifications mostly call for ISO 9712 certified personnel; the expectation is especially clear in work under the Pressure Equipment Directive (PED 2014/68/EU) and under EN 1090 for steel structures. One PED detail deserves attention: for NDT personnel working on permanent joints, approval by a recognized third-party organization (RTPO) is mandatory only for category III and IV pressure equipment (Annex I, clause 3.1.3), and that approval is separate from a plain EN ISO 9712 certificate. Categories I and II carry no such obligation.

On projects driven by international main contractors or US-based licensors — some pipeline, refinery and offshore work, for example — the contract may instead call for employer certification based on SNT-TC-1A, or for personnel qualification by reference to the ASME code. Experienced companies therefore keep their personnel competent in both systems. The field reality is simple: the specification decides the certificate type. Assume that "we hold ISO 9712, so we are covered everywhere" and a client who asked for SNT-TC-1A will reject your personnel. Before a job starts, establish which system the personnel qualification clause of the inspection plan actually invokes.

From the field

When we mobilize to a site, we open the personnel file and check three documents. First, the original certificate: the method, level and sector scope have to match the specification exactly. Second, the current near-vision examination: anything older than 12 months is a finding. Third, for SNT-TC-1A, the employer's Written Practice: the framework behind the certificate has to exist and to be signed by the responsible Level III. The mismatch we see most often is an ISO 9712 Level II inspector put on castings when the sector scope on the certificate says welding. The certificate is valid, but the work sits outside its scope. The second most common error is a certificate still inside its 5-year validity while nobody renewed the near-vision examination that year — technically, that leaves the person unqualified for the job. Close those two gaps before an audit and most of the rejection and rework risk disappears.

Related standards

ISO 9712 — Qualification and certification of NDT personnel (third-party, under ISO/IEC 17024).
ISO/IEC 17024 — General requirements for bodies operating certification of persons; certification bodies are accredited against this standard.
ASNT SNT-TC-1A — Recommended practice for the qualification and certification of NDT personnel (based on the employer's Written Practice).
ANSI/ASNT CP-189 — American National Standard setting binding minimum requirements for employer-based NDT personnel qualification and certification (the standardized, stricter counterpart of SNT-TC-1A).
ASNT 9712 — ASNT's employer-independent central certification program based on ISO 9712:2021 (the replacement for the ACCP program now being closed).
ASME BPVC Section V — NDE methods (Article 2 RT, Article 4 UT, Article 6 PT, Article 7 MT, and others); refers to the applicable code and to SNT-TC-1A for personnel qualification.
AWS D1.1 and EN 1090 — Inspection/NDT personnel for welded structures; under EN 1090, NDT personnel are qualified to EN ISO 9712.
EN ISO 9606 — Welder qualification testing; this covers welders, not NDT personnel, and is listed here for context only. (For welding coordination personnel, EN ISO 14731 applies.)
PED 2014/68/EU — For NDT personnel on permanent joints, approval by a recognized third-party organization (RTPO) is required in categories III and IV (Annex I, clause 3.1.3).

Türkiye-specific note

Türkiye has adopted ISO 9712 as a national standard, published as TS EN ISO 9712. The "TS" prefix marks that national adoption only; the technical content is the ISO text, so this article refers to it throughout as ISO 9712. Certification bodies operate under accreditation from TÜRKAK (Turkish Accreditation Agency), a signatory to the European Accreditation Multilateral Agreement (EA MLA), so certificates issued under that accreditation are recognized across the EA member states.

Take it to the field: To keep these NDT methods, standard references and field steps in your pocket — completely offline and free — take a look at the Doawise NDT Guide app.

At DoaWise we carry out NDT personnel qualification and inspection processes to international standards (ISO 9712, ASME BPVC Section V, SNT-TC-1A), and we document every step — from certificate scope and near-vision examination date to certificate validity and Written Practice audits — so the output is recordable and auditable. Matching the right certificate type to the specification is the most concrete way to avoid lost time and cost in the field.