SNT-TC-1A vs CP-189 — Which ASNT Standard Do You Need?

In more detail

SNT-TC-1A is ASNT's recommended practice: "should" language, the employer's Level III sets hours and examinations, and the Level III may be employer-certified. CP-189 is an ANSI standard: "shall" language, fixed minimum training and experience hours, re-examination at recertification, and a Level III who must hold an ASNT NDT Level III certificate. Both require an employer written practice.

The choice rarely rests with the employer. Referencing codes and customer specifications name the document: the API inspection codes, API 1104 and AWS D1.1 send the auditor to an employer written practice modelled on SNT-TC-1A; ASME Section V accepts either; nuclear in-service inspection under ASME Section XI names CP-189; aerospace names NAS 410 instead of either; Canadian code work requires CGSB certification. What CP-189 changes in practice is the Level III's own credential, the removal of the training-hour reductions SNT-TC-1A permits, mandatory re-examination at recertification and after an interruption of service, and record content that an auditor can trace from certificate back to question paper. Employers serving both markets write one practice on CP-189's clauses, state that it also meets SNT-TC-1A, and document which SNT-TC-1A flexibilities they have chosen not to use. The practical examination and the specific examinations remain the employer's to write under either document.

What 'shall' changes when the auditor arrives

The practical consequence of the should/shall split shows up on the audit checklist, not in the documents themselves. An auditor working to SNT-TC-1A audits you against your own written practice. The question asked of every clause is whether the practice is reasonable against the recommended practice and whether you followed it. A documented, justified departure — reduced training hours for a degreed candidate, a Level III certified by employer examination, a recertification renewed on performance evidence — is not a finding. To write one, the auditor has to show either that your practice is inadequate or that your records do not match it.

An auditor working to CP-189 audits you against the standard first and your practice second. Every "shall" is a checklist line, and a written practice that omits or softens one is itself the nonconformance. The justification you attached to the deviation carries no weight, because the standard does not provide for deviations. That is why the same records can pass one audit and fail the next when the referencing document changes mid-contract: nothing about the technicians changed, only the document the auditor held.

There is a second-order effect that catches employers on SNT-TC-1A. Once you write "shall" into your own practice, the auditor holds you to it as firmly as CP-189 would, because the written practice is the document the referencing code invokes — ASME Section V, the API inspection codes and AWS D1.1 all send the auditor to the employer's practice, not to ASNT. A practice drafted by copying SNT-TC-1A and replacing every "should" with "shall" removes the flexibility that was the reason for choosing SNT-TC-1A in the first place. Written practice development is largely the work of deciding which clauses to make binding and which to leave to the Level III's judgement.

The Level III prerequisite that decides most CP-189 adoptions

The single requirement that most often settles the choice is the qualification of the person who signs the certificates. Under SNT-TC-1A, an employer may certify its own NDT Level III by employer-administered Basic and Method examinations, or may accept an ASNT NDT Level III certificate in place of those examinations. Both routes are legitimate, and the resulting Level III certificate is an employer certificate either way. Under CP-189, a current ASNT NDT Level III certificate in the applicable method is a prerequisite for employer certification as Level III. The employer still certifies — it adds whatever specific or practical examination its practice calls for and signs the record — but it cannot certify a Level III who has not passed ASNT's Basic and Method examinations.

ASNT sets the eligibility for its Level III examinations as a combination of education and experience comparable to Level II, charges an examination fee, and renews the certificate on a five-year cycle by re-examination or by documented professional activity. For an employer, this means a CP-189 program depends on a credential the employer does not control. If the Level III lets the ASNT certificate lapse, the employer's Level III certification and every certificate signed under it from that date are exposed. The written practice should therefore record the ASNT certificate number and expiry alongside the employer certification, and the certification register should carry both dates.

The same rule applies to an outside agency Level III. Both documents allow the employer to designate a Level III from a consulting firm to perform the Level III functions; under CP-189 that person must also hold the ASNT certificate in the method. This is the situation in which a small inspection company most often reaches for ASNT Level III consulting: it holds one or two ASNT Level IIIs internally and designates a consultant for the remaining methods, with the designation and the consultant's certificate numbers written into the practice. Personnel aiming for the ASNT credential themselves can start with the Level III certification requirements guide.

Training and experience hours: where a practice can flex and where it cannot

Both documents set minimum training hours per method and level in a table — Table 6.3.1A in SNT-TC-1A — and both express experience as hours in the method plus total hours in NDT. The tables sit close to each other because they draw on the same body of knowledge, ANSI/ASNT CP-105, which supplies the topical outlines the training has to cover. The difference is in the notes. SNT-TC-1A's table lets the employer reduce training hours for candidates with relevant post-secondary education and lets the practice credit experience gained in more than one method at the same time. CP-189 states its hours as minimums that the practice cannot cut.

For ultrasonic testing, SNT-TC-1A Table 6.3.1A calls for 40 hours of training at Level I and a further 40 hours at Level II. The remaining methods and the experience columns should be read from the edition your practice cites rather than from memory, because the figures have moved between editions and a practice quoting a superseded table is a finding in itself. Where a customer specification says "SNT-TC-1A with no reduction in training hours", it is closing the gap to CP-189 on this one point without adopting the whole standard — a common compromise in refining and pipeline specifications.

Training delivery is treated differently as well. CP-189 defines the NDT Instructor as a qualification in its own right, with its own education, experience and examination requirements, and expects training to be delivered under the Level III's control against a documented course outline. SNT-TC-1A recommends organized training under the Level III but leaves instructor qualification to the practice. An employer moving to CP-189 therefore has to look at who has been teaching its internal courses, not only at the hours on the certificates. Training delivered against a CP-105 outline, with the instructor's qualification and the outline on file, satisfies either document.

Who administers, proctors and grades the examinations

The administration and grading of Level I and Level II examinations sits with the employer's NDT Level III under both documents, either personally or through a designated representative working from the Level III's answer keys. What changes under CP-189 is who that Level III must be — the ASNT-examined person described above — and how completely the examination event must be evidenced: the question papers used, the answer keys, the individual scores for the general, specific and practical parts, the composite, and the identity of the grader. SNT-TC-1A describes the same content as what the record should show.

Both documents grade on a composite: a minimum of 80 percent averaged across the general, specific and practical examinations, with no individual examination below 70 percent. The practical is where audits find the weakest evidence, because it is the one examination the employer must write itself under either document. It has to be a documented procedure with defined checkpoints on a specimen containing discontinuities the candidate is expected to find, graded against those checkpoints — not a note that the candidate "demonstrated competence". A candidate who fails may re-sit after the waiting period or additional training the practice defines, and the re-sit paper should not be the paper already seen.

Specific examinations are the second weak point. They must be written against the employer's own procedures, equipment and the codes the employer works to; a general-knowledge paper relabelled "specific" is a finding under either document. Where the employer's Level III writes the general examinations, the question bank has to be large enough that a re-sitting candidate does not see the same paper, and retired questions need retirement dates. An audit against CP-189 will trace one certificate back through all of this; an audit against SNT-TC-1A will do the same wherever your practice says "shall".

Expiry triggers: interruption of service, lapsed credentials and vision

The headline recertification difference is covered above — CP-189 recertifies Level I and II by examination, SNT-TC-1A allows renewal on evidence of continued satisfactory performance at the Level III's discretion. The less-discussed difference is what ends a certification before its expiry date. Both terminate it on leaving the employer. Both provide for interrupted service, a period in which the individual has not practised the method, but SNT-TC-1A asks the written practice to define that period and the re-examination that follows, while CP-189 fixes the period in the standard itself and requires re-examination to restore the certification.

For the Level III, CP-189 ties employer recertification to the currency of the ASNT certificate, so the five-year employer clock and the five-year ASNT clock run side by side and the practice has to track both. Under SNT-TC-1A, Level III recertification may be by re-examination or by the employer's evaluation of continued performance; an ASNT certificate, if held, is evidence rather than a condition. A technician who returns from a long absence, a Level III whose ASNT renewal is late and a certificate that simply reached its date are three different events with three different remedies, and the practice should name each.

Vision is the expiry trigger that catches everyone. Near-vision acuity is tested annually under both documents, and the certification is invalid — not merely deficient — for any period in which the test is overdue. A dispatch control that treats an overdue eye examination with the same severity as an expired certificate is the practical answer, and the requirement is identical under either document.

What the record has to prove, link by link

An auditor reading a certification record under either document is reconstructing a chain: education and prior experience claimed; training hours with dates, outline and instructor; experience hours with dates and the supervising Level II or III; vision test date and result; examination papers, keys, grades and composite; the Level III's signature and the Level III's own qualification; and the expiry date. CP-189 makes each link a "shall" and adds the Level III's ASNT certificate to the chain. SNT-TC-1A recommends the same content. A record that presents only the certificate and the composite grade fails the chain under CP-189, and fails under SNT-TC-1A wherever the practice promised more.

The written practice itself is a controlled document. It must state the edition of the ASNT document it is based on — SNT-TC-1A was revised again in 2024 — and a contract that cites an earlier edition needs a written reconciliation, not a silent reissue. It must be approved by the Level III, revision-controlled, and reviewed at the interval it declares. Retention of records for the period the practice states, and for the life of the contract where a customer requires it, is a records obligation under either document; the finding "exam papers not retained" is a retention failure the practice should have prevented by naming the period and the custodian.

Refining, pipelines, nuclear, aerospace and Canada: who names which document

Refining and petrochemical: the API inspection codes and owner-user inspection programs send you to the employer's written practice modelled on SNT-TC-1A, and a refinery's own examination specification will typically add overrides — no training-hour reductions, a named minimum experience, Level II for interpretation, sometimes a requirement that the Level III hold the ASNT certificate. Read those overrides as the customer moving toward CP-189 on the points that matter to them. Pipeline construction under API 1104 likewise requires interpretation by Level II or III personnel certified under SNT-TC-1A or an equivalent it lists; the 49 CFR pipeline safety rules require qualified personnel and documented procedures rather than naming a document, so the operator's specification governs.

Nuclear: in-service inspection under ASME Section XI names CP-189 directly, with Section XI's own additions layered on top, including performance demonstration for ultrasonic examination under its Appendix VIII. Nuclear construction and NQA-1 supplier programs reach the same place through the utility's or prime's quality specification, because a quality program built on "shall" cannot hang from a recommended practice. If a purchase order carries a nuclear quality clause, expect CP-189 or SNT-TC-1A with nuclear overrides, and expect the auditor to check the Level III's ASNT certificate first.

Aerospace and Canada are the two markets where neither ASNT document is the answer. Aircraft and aerospace primes specify NAS 410 in North America or EN 4179 in Europe, an employer-based scheme with its own Level 3 requirements audited under Nadcap; ASNT Level III certificates are used within it as one route to Level 3, but an SNT-TC-1A or CP-189 practice does not satisfy it, so a company serving both aerospace and energy customers runs two practices. In Canada, code work requires CGSB certification issued through NRCan's NDT Certification Body, and a technician holding only an employer certificate needs the CGSB credential before working to CSA codes — see NDT training for the Canadian market for how the two schemes sit together.

A decision sequence for an employer choosing between them

Start with the contracts, not the documents. List the referencing codes and customer specifications for the revenue you have and the revenue you want over the next two years, and mark which name CP-189 outright, which name SNT-TC-1A with overrides, and which leave it to the employer. If any contract of consequence names CP-189, the decision is made: the standard becomes your floor and everything else is satisfied by it. If none does, the remaining questions are about what CP-189 would cost you in flexibility.

Second, count your Level IIIs against the methods you certify in. CP-189 requires an ASNT NDT Level III in every method you certify, held internally or by a designated outside agency. If you certify in six methods and hold ASNT certificates in two, the gap is closed by an examination programme for your Level IIIs, by a consulting designation, or by staying on SNT-TC-1A for the methods no contract forces. Third, look at the technicians whose certifications rely on SNT-TC-1A's notes — reduced training hours for a degree, experience credited across methods, a Level III renewed on performance evidence. Under CP-189 those individuals need the gap closed before their next certification date; there is no grandfathering clause to lean on.

Fourth, decide what the audit exposure is worth. CP-189 removes an entire category of argument from an audit — whether your deviation was justified — at the price of removing the deviations. For an employer whose customers already audit to their own overrides, the practical difference is small and the CP-189 compliance route is mostly documentation. For an employer relying on flexible hours to certify quickly, it is a real cost in time to certification. Neither choice is wrong; the wrong choice is a practice that claims one and runs the other.

Writing one practice that survives an audit against either

The technique is to structure the practice on CP-189's clauses and to state at the front that it complies with ANSI/ASNT CP-189 (2020) and, in doing so, meets the recommendations of SNT-TC-1A (2024). Then, clause by clause, adopt the stricter of the two: CP-189's training and experience hours with no reduction notes; the ASNT NDT Level III certificate as a prerequisite for Level III; re-examination at recertification for Level I and II; CP-189's interruption period; the full record content; a defined instructor qualification. A cross-reference table mapping each clause to its SNT-TC-1A section lets an auditor working to either document find their checklist item without translation.

What you give up is documented in the same place. The practice states explicitly that the reduction provisions of SNT-TC-1A Table 6.3.1A are not applied and that experience-based renewal is not used. Auditors read a deliberate non-use of a permitted flexibility as a strength; they read a practice that quietly mixes the two as a nonconformance against whichever document they hold. Keep the deviations section present and empty rather than absent, so that its emptiness is a statement.

Two traps remain. First, editions: name both, and where a contract cites an older SNT-TC-1A edition, add a one-page reconciliation rather than a second practice. Second, the practical examination: a combined practice does not relieve you of writing it, and it is the part no ASNT document supplies. A written practice template built to CP-189's clause order is the starting point; the method-specific specimens, checkpoints and specific examinations are the work. Atlantis drafts and audits these practices from Houston, with a Level III mobilised to the client's site or an arranged venue for the examination and certification stages and theory delivered online where the client prefers.

Frequently asked

What are the ASNT CP-189 requirements in summary?

An employer written practice meeting every "shall" in the standard; an NDT Level III holding a current ASNT NDT Level III certificate in each method certified; minimum training and experience hours that cannot be reduced; general, specific and practical examinations administered and graded under the Level III with an 80 percent composite and a 70 percent minimum per examination; annual near-vision testing; certification records with defined content; recertification at intervals not exceeding five years by re-examination; and re-examination after a defined interruption of service.

What is the difference between SNT-TC-1A and CP-189 for a small inspection company?

Mainly the Level III. A small company on SNT-TC-1A can certify its Level III by employer examination and adjust training hours for degreed candidates. On CP-189 it needs an ASNT NDT Level III in every method it certifies, on staff or designated from an outside agency, and it loses the hour reductions. The examination and record work is similar in volume; the difference is who signs and how little room there is to deviate.

Can a company move from SNT-TC-1A to CP-189 without recertifying everyone?

Usually the move is made at each individual's next certification event rather than in one step. Training and experience already documented count under CP-189 if they meet its minimums without the SNT-TC-1A reductions; individuals certified using those reductions need the gap closed before their next certification date. The Level III must hold the ASNT certificate before signing anything under the new practice, so that credential sets the timetable for the whole transition.

Which edition of SNT-TC-1A should a written practice cite?

The edition the practice is written to, stated explicitly. The current edition is 2024, following 2020 and 2016. Referencing codes and contracts often cite an earlier edition, so the practice needs a short reconciliation showing where the cited edition differs from the one adopted, rather than a separate practice per contract. The same applies to CP-189, whose current edition is 2020.

Does Atlantis NDT write and audit CP-189 written practices?

Yes. Atlantis NDT drafts, reviews and audits written practices under SNT-TC-1A, CP-189 or both, and provides ASNT NDT Level III designation for methods a company does not hold internally. Level III examiners are mobilised from Houston, Texas to the client's site or an arranged venue for the examination and certification stages, with theory delivered online where preferred. Scope and quotation on request via info@atlantisndt.com or the contact page.