Radiographic Testing Procedure Writing: Complete RT Compliance Guide

Why RT Procedures Fail Review More Than Any Other Method

Radiographic testing procedures are the most technically complex single-method procedures in the NDT portfolio. They span radiation physics (source activity, energy, geometric unsharpness), film science (speed class, density, contrast), equipment specifications (SFD, IQI), and safety (radiological control, exposure calculations). A complete RT procedure touches all of these — and gaps in any area result in rejection.

RT procedures also face scrutiny from two directions: the NDT client (checking technical compliance with ASME/API) and the Radiation Protection Supervisor or regulatory body (checking radiation safety compliance). This guide covers the NDT compliance side.

Applicable Standards

• ASME Section V Article 2: Radiographic examination — the primary reference for pressure vessel, piping, and boiler RT
• ASME Section V Article 22: Radiographic examination using computed radiography (CR) and digital detector arrays (DDA)
• API 650 Section 8: Storage tank weld RT requirements
• API 1104: Pipeline weld RT requirements
• AWS D1.1 Section 8: Structural steel weld RT
• ISO 17636-1: Film RT for metallic materials
• ISO 17636-2: Digital RT (CR/DR) for metallic materials
• EN 13445-5 Annex B: European pressure vessel RT requirements

Radiation Source Specification

Your procedure must identify the radiation source with enough detail to confirm it is appropriate for the material thickness being examined. Required elements:

• Source type: X-ray (and kV range) or isotope (Ir-192, Co-60, Se-75, Yb-169)
• Source size (focal spot or source dimensions): This directly affects the geometric unsharpness calculation
• Applicable thickness range: ASME T-233 limits each source type to specific thickness ranges. Ir-192 is limited to 10–100 mm for steel in ASME; Co-60 is for thicker sections (>50 mm)
• Energy justification: For X-ray, state the kV range and the basis for energy selection relative to material thickness

Geometric Unsharpness (Ug) Calculation

This is one of the most frequently absent elements in RT procedures. ASME Section V T-285 requires that geometric unsharpness be calculated and limited. The formula is:

ASME maximum Ug limits per T-285:

Your procedure must either provide the Ug calculation for the examination setup, or provide a nomograph reference. Stating "SFD = 700 mm" without confirming the resulting Ug is compliant is insufficient.

IQI (Image Quality Indicator) Requirements

IQI selection, placement, and required sensitivity are among the most detailed requirements in any RT procedure. ASME T-276 through T-283 cover this extensively.

IQI Type Selection

• Hole-type (plaque) IQI: Standard for most ASME weld RT applications. IQI material must match the base metal radiation absorption class (Fe for steel, Al for aluminium, etc.)
• Wire-type IQI: Required for panoramic exposures and curved surfaces where a flat plaque does not maintain contact; also standard for ISO 17636 applications

IQI Placement

Your procedure must specify IQI placement per ASME T-277:

• Source-side placement is mandatory (preferred) — IQI placed on the source side of the component adjacent to the weld
• Film-side placement is permitted only when source-side placement is impractical — must be documented in the procedure with the reason
• One IQI per film (minimum) for lengths up to 254 mm; two IQIs for longer exposures
• Position relative to weld: IQI placed within the area of interest on base metal adjacent to the weld (not on the weld crown itself, except for welds where base metal is inaccessible)

Required IQI Sensitivity

ASME Table T-276 specifies the required essential hole and designated hole (hole-type IQI) or essential wire (wire-type IQI) that must be visible on the radiograph. Your procedure must state the required sensitivity explicitly — not just "per ASME Table T-276" but the actual hole size or wire diameter required for your thickness range.

Film and Processing Requirements

• Film brand and speed class: Specify film brand and classification (AA, A, or B per SE-114; or C1–C6 per ISO 5580). Class AA / C1-C2 (fine grain) is required for high-sensitivity applications
• Film density range: ASME T-282.1 requires 2.0–4.0 film density for radiographic film. Your procedure must state the required density range and the density meter calibration requirement
• Processing method: Manual (state chemistry, temperature, time) or automatic (state processor make/model, temperature setting)
• Darkroom/processing area requirements: Safelight intensity limit, fixing and washing requirements

Viewing Conditions

A frequently omitted element. ASME T-283 requires specific viewing conditions:

• Illuminator luminance: sufficient to illuminate the densest area of the radiograph (typically ≥ 30 cd/m² × 10^density at maximum density point)
• High-intensity illuminator (hot light) required for densities above 3.0
• Ambient light: must not create reflections on the radiograph that interfere with interpretation
• Masking: radiographs must be masked to block light around the film boundary

Most Common RT Procedure Non-Compliances

1. Ug calculation absent — SFD stated but geometric unsharpness not calculated or compared to ASME maximum
2. IQI sensitivity not stated in measurable terms — "IQI per ASME Table T-276" without specifying the required wire or hole for the examined thickness
3. Source activity range not stated — Ir-192 listed as source but no activity range or applicable thickness range confirmed
4. Film density range missing — Procedure does not state the required density range (2.0–4.0)
5. Film-side IQI not justified — Film-side placement used without stating the reason and the sensitivity penalty acknowledgement
6. Viewing conditions absent — No statement of illuminator luminance or ambient light requirements
7. Processing conditions incomplete — "Develop per manufacturer recommendations" without specifying temperature and time, or automatic processor settings