Why the distinction matters
The global NDT industry depends on skilled personnel who can carry out inspections with precision and integrity. These professionals are expected to demonstrate their competence through rigorous training, examination, and ongoing performance review.
Most standards, specifications, and design codes that require NDT also require personnel performing it to hold certification under an internationally recognised scheme. This helps ensure that the individuals involved have been assessed as competent for the work they undertake.
Two of the most widely used NDT personnel qualification and certification frameworks worldwide, outside the aerospace sector, are those based on ISO 9712 and SNT-TC-1A. Although both are used extensively across the industry, they differ significantly in their requirements and in the way they are administered.
The distinction between ISO 9712 and SNT-TC-1A matters because it affects how organisations govern competence, how flexibly they can certify personnel, and how portable those certifications remain across an individual’s career.
History and development
SNT-TC-1A emerged in the US in the late 1960s as industry’s answer to a basic problem: there was no widely accepted, structured way for employers to qualify and certify NDT personnel. The first edition was published by ASNT in 1968 (some industry sources reference development work beginning in 1966), and it created the familiar Level I, Level II, and Level III framework for NDT qualification.
ISO 9712 first appeared in 1992 and superseded the European standard EN 473 when the two were harmonised in 2012. Its intention was to standardise the qualification and certification of NDT personnel and become the global ‘gold standard’. Whilst it shares much of the framework of SNT-TC-1A and the now instantly recognisable certification levels (1,2 & 3) there are significant differences between the two in their requirements and how they are administered.
At a high level, ISO 9712 is a third-party certification model, whereas SNT-TC-1A is an employer-based certification model. That single distinction drives most of the practical differences between the two systems.
For employers, candidates, and clients, the decision is not simply about compliance; it is about balancing governance, flexibility, and workforce mobility within the operating environment.
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How the two schemes operate
SNT-TC-1A, published by ASNT as a recommended practice, defines certification as written testimony of qualification. In practice, the key issue is who evaluates the evidence of training, experience, and examination (qualification) and who has the authority to issue certification.
ISO 9712 is an international standard. To achieve certification under a scheme derived from it, NDT personnel must meet defined qualification requirements. Certification is issued through an independent third-party or central certification body, with schemes such as PCN operating within that model.
Approved Training Organisations (ATOs) and Authorised Qualifying Bodies (AQBs) may support training, examination, and the review of on-the-job experience, but the final certification decision remains with the independent certification body. The 2022 edition of ISO 9712 also introduced clarifications and updated qualification requirements, including changes affecting experience and alignment with related standards.
As SNT-TC-1A is a recommended practice and not a governing standard, the employer defines the qualification and certification framework through a written practice based on these recommended guidelines, the requirements of which become mandatory within the organisation. This gives organisations greater flexibility to tailor certification to their actual processes, techniques, and product scope, which can be a significant operational advantage where inspection activities are narrow or highly specific.
For example, a company that manufactures stainless steel fasteners may only need to carry out water-washable fluorescent penetrant inspection as part of its production process.
In that case, the employer’s written practice only needs to define the qualification and certification requirements for that specific method and technique. It would only need to be revised if an additional method or technique were introduced into the scope of operations.
The document has been revised periodically across multiple editions, including 1996, 2001, 2006, 2011, 2016, 2020, and 2024, reflecting changes in technology, examination practice, terminology, and employer expectations.
The flexibility of SNT-TC-1A, however, depends heavily on the competence and oversight of the employer’s Responsible Level III. Whether internal or external, that individual plays a critical role in approving the written practice, maintaining technical control of qualification requirements, and influencing the employer’s decision to issue certification. Note that a Level III individual is usually certified by a third-party organisation such as an ASNT NDT Level III whom has been certified by an examination administered directly by ASNT. In some circumstances an SNT-TC-1A ‘appointed’ Level III maybe certified by the former and accepted by the employer, however this is becoming a much-reduced practice based on guidelines from more recent editions of the recommended practice.
Career portability is another major point of divergence. ISO 9712 certifications remain with the individual, subject to renewal and recertification requirements, whereas SNT-TC-1A certifications are tied to the employer’s written practice and typically lapse when the individual changes employer requiring the individual to be re-examined under the new employer’s written practice. For organisations building long-term internal capability, SNT-TC-1A can be efficient; for individuals and clients seeking portable, independently governed credentials, ISO 9712 offers a stronger proposition.
In executive terms, ISO 9712 offers stronger independence, consistency, and transferability, while SNT-TC-1A offers greater employer control and operational tailoring. The right choice depends on whether the priority is external assurance and portability, or internal flexibility aligned to a specific business model.
© Image is provided by and copyright of Argyll Ruane Ltd.
Industry context and scheme requirements
In practice, the certification scheme required is often determined by the industry sector involved and by the standards, specifications, and design codes that apply within it.
- UK and European nuclear sectors: NDT personnel are typically required to hold ISO 9712 certification at the appropriate level, alongside any additional employer-specific competence assessments and internal controls.
- ASME code applications: Historically, the ASME Boiler and Pressure Vessel Codes have required personnel to be qualified and certified in accordance with SNT-TC-1A. However, more recent editions have allowed wider acceptance of other recognised international certification schemes, usually subject to agreement between the contracting parties.
As a result, it is increasingly common for NDT personnel to hold certification under more than one scheme, depending on employer requirements and the sectors in which they operate.
Employer responsibility
Regardless of whether personnel are certified under ISO 9712 or SNT-TC-1A, the employer’s responsibility for selecting and authorising competent personnel remains critical. ISO 9712:2022, Section 5.5.2, sets out a range of employer responsibilities, including verifying that personnel hold valid certification relevant to their duties and issuing the written authorisation required for them to operate within the organisation. In other words, even where the employer does not define the certification framework, overall responsibility for NDT personnel within the organisation still rests with the employer.
Conclusion and future direction
There is no single approach to NDT personnel qualification and certification that suits every industry or operating environment. Different schemes serve different purposes, and the most appropriate choice depends on regulatory requirements, client expectations, and operational needs.
Many sectors favour the more tightly controlled central certification model offered by ISO 9712. By contrast, SNT-TC-1A is sometimes criticised not because of the recommended practice itself, but because of variations in how rigorously employers implement their written practices. Even so, it remains a valuable framework where employer-specific flexibility is essential.
Both schemes are likely to remain in use for the foreseeable future. That said, recent developments suggest a growing preference for independently governed, third-party certification. A notable example is ASNT 9712, introduced in the United States as a standalone third-party programme designed to align with ISO 9712 and replace the ASNT Central Certification Program (ACCP), while historically operating in a market long dominated by SNT-TC-1A.
Author: Nathan Bate
