7.2 Written Procedures & Technique Sheets

Why a Written Procedure Exists

The primary purpose of a written NDT procedure is to provide a repeatable, technically controlled way to perform an examination so that any qualified technician gets equivalent, defensible results. It is the document a Level III signs to say: this method, run this way, on this range of hardware, satisfies the invoked code. On the Basic exam, questions phrase this as "repeatable and technically controlled" or "reconstructable" — both point to control and traceability, not to a single technician's habit.

Required Elements of a Written Procedure

Codes such as ASME BPVC Section V Article 1, and employer written practices built on SNT-TC-1A or ANSI/ASNT CP-189, list the elements a procedure must contain. A complete procedure typically addresses:

1. Scope — the range of materials, thicknesses, geometries, joints, and temperatures it covers, plus the applicable code and edition.
2. Personnel qualification — the certification level required to perform and to evaluate.
3. Equipment — instrument type, make/model, and any required accessories.
4. Consumables/materials — penetrant family, particle type and color, film system, or couplant.
5. Surface preparation — cleaning and condition required before examination.
6. Technique details — frequencies, beam angles, magnetization method and current, exposure and source-to-film distance, lighting.
7. Calibration / standardization — reference standards and how the setup is verified.
8. Examination process — step sequence, scan coverage, and required overlap.
9. Recording and reporting requirements.
10. Acceptance criteria — by reference to the governing code or specification.
11. Essential and nonessential variables — listed explicitly.

Procedure vs Technique Sheet

A recurring exam pairing distinguishes the two documents. The written procedure is the framework: general requirements and the essential-variable list. The technique sheet is the instance: it applies that procedure to a specific part, weld, or job with the actual parameters used. A technique sheet can add job detail but can never override the procedure or the code above it.

Essential vs Nonessential Variables

An essential variable is a parameter whose change, beyond a stated range, could change the examination result or sensitivity — so a change requires the procedure to be revised, requalified, or reapproved before continued production use. A nonessential variable may change without requalification, but the documentation is still updated. Knowing which is which is a Level III judgment the exam checks directly.

Qualification and Approval by the Level III

The Level III writes or reviews, qualifies, and approves procedures. Qualification can require a demonstration on specimens with known conditions when the code demands it; the Level III's approval signature is what makes the procedure usable. If an essential variable changes beyond the approved range mid-job — say the surface condition or beam angle shifts outside scope — the correct action is to stop, evaluate the change, then revise/requalify/reapprove the procedure before resuming. Continuing production on an out-of-range procedure invalidates the results.

Scope Discipline

A procedure is valid only inside its qualified scope. If the job falls outside the covered thickness, material, or joint, the Level III extends or writes a new procedure and re-qualifies — you cannot stretch a procedure onto hardware it never covered.

Worked Example: Qualifying a Penetrant Procedure

Suppose a Level III drafts a fluorescent post-emulsifiable penetrant procedure for machined aluminum fittings. Qualification means more than writing it down: the procedure lists the penetrant family, emulsifier dwell, developer form, and the required lighting (a stated minimum ultraviolet irradiance and low ambient white light), then it is demonstrated on specimens containing known cracks to confirm the setup actually finds them. Only after that demonstration does the Level III sign the approval. If the shop later switches from post-emulsifiable to water-washable penetrant, that is an essential-variable change — a different sensitivity class — so the procedure must be requalified and reapproved before use on production fittings. Swapping to a same-class penetrant from a qualified vendor list is nonessential and needs only a documentation update.

Why the Technique Sheet Cannot Climb the Ladder

Candidates sometimes assume a detailed technique sheet can "fill gaps" left by the procedure. It cannot. The technique sheet lives below the procedure, which lives below the code. A technique sheet may record that a specific weld was scanned at a given gain and angle, but it may not authorize a gain, angle, or acceptance limit the procedure or code does not permit. If the job genuinely needs a parameter outside the procedure, the fix is upstream — revise and reapprove the procedure, not quietly widen the technique sheet.

Common Mistakes

• Continuing production after an essential variable drifts out of range instead of stopping to reapprove.
• Treating a technique sheet as a mini-procedure that can override the framework above it.
• Omitting the essential/nonessential variable list, leaving no basis to judge which changes trigger requalification.
• Using a procedure outside its qualified scope of thickness, material, or geometry.