ISO 20769-2:2018

Overview

ISO 20769-2:2018 - Non-destructive testing - Radiographic inspection of corrosion and deposits in pipes by X- and gamma rays - Part 2: Double wall radiographic inspection specifies proven film and digital radiography techniques to obtain repeatable, economical inspections of cylindrical metallic components. It targets in-service detection of service‑induced wall loss (corrosion pitting, generalized corrosion, erosion) in pipes, tubes, penstocks, boiler drums and similar cylindrical bodies using X‑ and gamma‑ray radiography. Techniques covered include double wall single image (DWSI) and double wall double image (DWDI) for film, computed radiography (CR) and digital detector arrays (DDA).

Key topics and technical requirements

• Scope and applicability: Inspection of metallic pipes for material loss; welds inspected only when affected by corrosion/erosion (not standard weld defect testing).
• Double wall techniques: Detailed procedures for DWSI and DWDI, including geometry, source/detector placement and combination with tangential methods (see ISO 20769‑1).
• Radiation protection and personnel: Requirements for ionizing radiation safety and personnel qualification to ensure compliant field practice.
• Image quality control: Use and placement of Image Quality Indicators (IQI) (single-wire and duplex wire IQIs), minimum image quality values and normalized signal‑to‑noise for digital images.
• Equipment and sources: Guidance on choice of X/gamma sources, film systems, screens, CR plates and DDA selection and calibration.
• Noise and scatter reduction: Filters, collimation, shielding and backscatter interception techniques.
• Geometry and coverage: Source-to-detector distances, axial and circumferential coverage, alignment and overlap strategies for complete inspections.
• Image analysis and measurement: Methods to derive penetrated thickness from image grey levels, measurement validation, spatial resolution determination.
• Digital workflow: Scan/readout, DDA calibration, bad pixel handling, image processing, storage and viewing conditions.
• Reporting: Required test report content summarizing methods, findings and traceability.

Applications and users

This standard is essential for:

• NDT engineers and radiographers performing in‑service inspections of piping in oil & gas, petrochemical, power generation, water utilities and boiler/heat‑transfer systems.
• Inspection service providers specifying radiographic procedures for corrosion/erosion assessment.
• Asset owners and maintenance planners needing quantitative wall‑loss assessment on insulated or uninsulated pipes.
• Regulators and quality managers who require standardized, repeatable radiographic practice.

Practical outcomes include reliable detection of internal/external wall loss, guidance on selecting film vs digital methods (CR/DDA), and procedures to produce legally defensible inspection records.

Related standards

• ISO 20769-1 (Tangential radiographic inspection)
• ISO 11699‑1 / ISO 11699‑2 (Industrial radiographic film)
• ISO 17636‑2 (Weld radiographic testing with digital detectors)
• ISO 19232 series (Image quality of radiographs)
• EN 14784‑1 (Computed radiography systems)

Keywords: ISO 20769-2:2018, non-destructive testing, radiographic inspection, double wall, DWSI, DWDI, digital detector arrays, computed radiography, corrosion inspection, pipe inspection, X-rays, gamma rays.