How to Write an ASNT SNT-TC-1A Compliant NDT Procedure

What is ASNT SNT-TC-1A and Why Does Your Procedure Need to Comply?

ASNT SNT-TC-1A is the recommended practice published by the American Society for Nondestructive Testing that establishes the guidelines for qualification and certification of NDT personnel. It is not a mandatory standard by itself — but it is called up by most major codes including ASME, API, AWS, and the majority of client specifications in the oil & gas, petrochemical, aerospace, and power generation industries.

When a client spec or code calls up SNT-TC-1A, your Written Practice (the company-level document) and your individual NDT procedures must align with its requirements. Procedures that fail this check will not be accepted during third-party review, pre-job qualification, or regulatory audits.

The Five Core Pillars of an SNT-TC-1A Compliant NDT Program

1. Written Practice

Every company performing NDT under SNT-TC-1A must maintain a Written Practice that governs how personnel are qualified, trained, examined, and certified. This is the foundational document — individual procedures reference it, not the other way around.

Your Written Practice must address:

• NDT methods and techniques used by the company
• Education, training, and experience requirements for each Level (I, II, III) per method
• Training course content and hours per method and level
• Examination content (General, Specific, Practical) and minimum passing scores (typically 70% each)
• Certification periods and recertification requirements
• Eye examination requirements (Jaeger J1 near vision, colour differentiation where required)
• Responsibilities of each certification level

2. Personnel Qualification Requirements

SNT-TC-1A 2020 specifies minimum training hours and work experience for each level. These are minimums — your Written Practice may exceed them but cannot fall below. Key requirements:

Note: Hours vary by method. RT Level II requires 640 hours cumulative work experience; MT and PT are lower. Always reference the current SNT-TC-1A edition for your specific method.

3. Written Procedure Elements

Individual NDT procedures must contain specific elements to support qualification of personnel and demonstrate the technique is controlled. At a minimum, each procedure must state:

• Scope: What the procedure covers (material, weld geometry, component type)
• Applicable codes and standards (e.g., ASME Section V, API 650, SNT-TC-1A edition)
• Personnel qualification: Minimum certification level required (typically NDT Level II minimum)
• Equipment: Make/model/type of instruments, probes, couplants, films, chemicals
• Equipment calibration: Frequency, reference standards, acceptance criteria
• Examination technique: Step-by-step examination instructions
• Acceptance criteria: ASME, API, or client-specified accept/reject criteria with specific reference
• Reporting: Format, minimum content of examination records
• Record retention: Duration and responsibility

4. Equipment and Calibration Requirements

Your procedure must clearly specify the calibration block or reference standard, the calibration frequency (e.g., at the start and end of each shift, or whenever the examiner changes), and the response if calibration cannot be re-established. For UT, this typically means specifying:

• Reference block specification (ASME basic calibration block, IIW block, or client-specific)
• Technique for establishing DAC or TCG curves
• Scan sensitivity and reference level
• Recalibration trigger (time interval and sensitivity drift limit, typically ±2 dB for UT)

5. Acceptance Criteria and Reporting

One of the most frequently cited non-compliances is vague or missing acceptance criteria. Your procedure must state the specific code clause — not just "per ASME" but "per ASME Section VIII Division 1, UW-51" or equivalent. Acceptance criteria must be stated in measurable terms, not as a reference to a document that is not attached or specified.

Most Common SNT-TC-1A Procedure Non-Compliances Found During Review

1. Written Practice not referenced or not in existence — The procedure references "company written practice" but no such document is attached or the company has no written practice
2. Personnel qualification level not stated — Procedure fails to state minimum certification level (Level I supervised by Level II, Level II minimum, etc.)
3. No edition year for SNT-TC-1A — Procedure references "ASNT SNT-TC-1A" without specifying which edition (2016, 2020, etc.)
4. Acceptance criteria vague — "Rejectable indications shall not be present" without defining what constitutes rejectable per which code clause
5. Calibration frequency missing — No stated interval for instrument calibration checks during the examination
6. Eye examination requirement missing — No mention of near-vision acuity requirement for personnel

How to Fix These Non-Compliances

For each gap identified above:

• Written Practice: Establish a company Written Practice following SNT-TC-1A Annex A format. Reference it in all NDT procedures by document number and revision.
• Personnel level: Add a "Personnel Qualification" or "Qualification Requirements" section stating minimum level: "Personnel performing examinations under this procedure shall hold a minimum NDT Level II certification in [method] per the Company Written Practice [doc. no.]."
• Edition year: Always specify: "ASNT SNT-TC-1A, 2020 Edition"
• Acceptance criteria: State the complete clause: "Acceptance criteria shall be in accordance with ASME Section V, Article 4, Paragraph T-481."
• Calibration frequency: State explicitly: "Instrument calibration shall be verified at the start of each examination, every 4 hours during continuous examination, and at the conclusion of each examination."
• Eye examination: Add to personnel section: "Personnel shall have demonstrated near-vision acuity to read J-1 letters on a Jaeger test chart at a minimum distance of 12 inches."

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Summary: SNT-TC-1A Compliance Checklist

• Company Written Practice exists and is referenced in the procedure
• SNT-TC-1A edition year is specified
• Minimum personnel qualification level is stated
• Near-vision acuity requirement is included
• Equipment make/model/type is specified
• Reference calibration standard is identified
• Calibration frequency is explicitly stated
• Acceptance criteria reference specific code clause with paragraph number
• Reporting format and required content are described
• Record retention duration and responsible party are stated