Writing and maintaining an NDT written practice

If a nondestructive testing (NDT) program has one document an auditor reads first, it is the written practice. It is the employer's own rulebook for how NDT personnel are trained, examined and certified, and every certification in the building is only as good as the practice it was issued under. SNT-TC-1A and NAS410 both require one. They ask different things of it, and the difference shapes how you write it.

What the written practice is for

Under SNT-TC-1A, the written practice is where recommendations become requirements. The 2024 edition is a set of guidelines, and asks the employer to write its practice with “shall” in place of the recommendation's “should”. The employer may modify the detailed recommendations to fit its work, but not remove the basics — training, experience, examination, recertification — and the technical reasons for any modification go in an annex (1.4).

Under NAS410, the standard is already mandatory. The written practice is where its minimums are put into practice for one employer, together with anything the employer, its prime contractors or the cognizant engineering organization adds, such as extra levels or longer experience (4.1.2). It may raise the bar; it may not lower it.

A code can tighten either. ASME Section V (2025) accepts a practice based on SNT-TC-1A (2024) only on terms that make it mandatory, and adds requirements of its own (T-120(e)). If you do code work, your practice has to carry those too.

What it has to cover

Pulling the two documents together, a written practice that will survive an audit covers at least the following. Clause references are to SNT-TC-1A (2024) and NAS410 Revision 6.

Scope and responsibilities

• The methods and the techniques within each method that apply to your operations (SNT-TC-1A 5.4; NAS410 4.1.3), and the scheme and edition it follows.
• The levels you use, any subdivisions or limited certifications, and what each level may do — including who may accept or reject product (SNT-TC-1A 5.2; NAS410 5.1).
• Who runs the program: the Responsible Level III or Responsible Level 3, any Examiners and instructors, outside agencies, and who keeps the records and where (NAS410 4.1.6–4.1.7, 4.3.2). The 2025 SNT-TC-1A addendum wants delegations of the Responsible Level III's duties documented.

Qualification

• Training and experience hours for each level, method and technique, and how prior training and experience are credited.
• The training outlines, or where they are referenced from (NAS410 4.1.4; SNT-TC-1A 7.3 points to ANSI/ASNT CP-105).
• What happens when a new technique is introduced for someone already certified — the extra training, experience and exams (NAS410 4.1.3).

Examination

• Who administers exams, the number of questions, passing scores and how the composite is calculated (NAS410 4.1.5; SNT-TC-1A 8.1).
• The practical exam: specimens, the checklist, the acceptable detection rate and false calls (SNT-TC-1A 8.5).
• The vision exam: which test, who gives it, how often (NAS410 names the vision method in the practice itself).
• Retake rules and limits, and when an outside certificate may be accepted in place of an exam.

Certification and after

• Who signs certifications, and what the certification record holds.
• The certification period and how recertification is done.
• Interrupted service: how long a gap triggers reexamination (SNT-TC-1A section 11), or NAS410's suspension and revocation rules.
• Expiration, suspension, revocation and reinstatement, and the annual proficiency review for NAS410 (4.1.1).
• How long records are kept (SNT-TC-1A 9.4 leaves the duration to the practice).

Approval and revision control

SNT-TC-1A requires the practice to be reviewed and approved by the employer's NDT Level III and kept on file (5.5–5.6). NAS410 has the Responsible Level 3 approve it, and requires it to be available to customers and regulators (4.1.1). Beyond that, treat it like any controlled document:

• Give it a document number and revision letter, and show both on every certification issued under it. SNT-TC-1A's own certificate recommendations ask for the practice's number and revision and the SNT-TC-1A edition it follows (9.6.1–9.6.2).
• Keep a revision history that says what changed and why.
• Keep superseded revisions. A certification issued under revision B is judged against revision B, and an auditor may ask for it.
• Review it on a schedule, and whenever a new edition of the governing standard lands. The standard revisions guide covers that routine.

Keeping the practice and the records in step

The most common written-practice finding is not a missing clause. It is a practice that says one thing while the records show another:

• The practice sets a pass mark or question count higher than the standard, and an exam was graded to the standard's figure.
• The practice lists a technique — phased array, digital radiography — that nobody is certified in, or someone is certified in one the practice never mentions.
• Certifications cite a revision that was superseded before they were issued.
• The practice names a Level III who left the company two years ago.
• Training hours on file fall short of the practice's own table, even though they meet the standard's.

Each is a sign that the practice lives in a binder while the program lives somewhere else. The fix is to make the practice's numbers the numbers your records are checked against, not a separate document you reread once a year.

Frequently asked questions