ISO 16826-2025 PDF

Full title and description

ISO 16826:2025 — Non‑destructive testing — Ultrasonic testing — Testing for discontinuities perpendicular to the surface. This International Standard specifies principles and practical guidance for the tandem technique and the longitudinal‑longitudinal‑transverse (LLT) technique used to detect planar discontinuities that are perpendicular or nearly perpendicular to the inspected surface.

Abstract

The document sets out the general principles for the tandem and LLT ultrasonic techniques for detecting discontinuities perpendicular to the surface, including guidelines for application to metallic materials with thicknesses typically between 40 mm and 500 mm. It also notes that the general principles for ultrasonic testing of industrial products are given in ISO 16810, and that phased‑array implementations can be used with additional verification steps where required.

General information

• Status: Published.
• Publication date: March 2025 (Edition 2, 2025‑03).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 19.100 (Nondestructive testing).
• Edition / version: 2nd edition (2025).
• Number of pages: 15 (ISO bibliographic listing).

Scope

ISO 16826:2025 provides requirements and guidance for performing ultrasonic examinations using the tandem and LLT techniques to detect internal planar discontinuities oriented approximately perpendicular to the surface. The standard is written primarily for metallic materials with parallel or concentric surfaces and is intended for thicknesses generally in the 40 mm to 500 mm range; procedures can be adapted for other materials or different thicknesses provided appropriate written testing procedures and special measures are applied. Phased‑array implementations are permitted but may require additional verification steps.

Key topics and requirements

• Principles and setup for the tandem ultrasonic technique (paired transducer geometry and coupling considerations).
• Principles and setup for the longitudinal‑longitudinal‑transverse (LLT) wave technique for near‑perpendicular flaw detection.
• Guidance on applicability and limitations for metallic materials with thicknesses approximately 40 mm to 500 mm.
• Recommendations for written testing procedures, calibration, and verification when adapting techniques to other materials or thicknesses.
• Notes on the use of phased‑array technology with the tandem/LLT approaches and the need for additional verification steps when applied.
• Reference to related general ultrasonic testing principles and symbol/equation listings in ISO 16810 and ISO 16811 (for consistent methodology and notation).
• Legacy requirement: previous edition (2012) included guidance on minimum distance to surface for some applications (e.g., the 2012 edition specified use for planar discontinuities with distance to surface greater than 15 mm); users adapting procedures should confirm any retained numerical limits in the 2025 edition or in project‑specific procedures.

Typical use and users

This standard is intended for nondestructive testing (NDT) practitioners and engineers who perform ultrasonic examinations in sectors such as heavy fabrication, pressure‑vessel and piping inspection, power generation, oil & gas, petrochemicals, and transport (rail/aerospace when applicable). Typical users include NDT service companies, in‑house inspection teams at manufacturers and fabricators, inspection authorities, certification bodies, and testing laboratories that require a validated method for detecting embedded planar discontinuities perpendicular to a surface.

Related standards

Key related documents include ISO 16810 (general principles for ultrasonic testing) and ISO 16811 (symbols and equations used in ultrasonic testing); practitioners often use ISO 17640 and other ultrasonic technique standards for complementary methods (for example TOFD or phased‑array procedure guidance) and applicable industry sector specifications or national/adopted versions (EN/BS/DIN adoptions).

Keywords

ultrasonic testing, nondestructive testing (NDT), tandem technique, LLT, longitudinal‑longitudinal‑transverse, perpendicular discontinuities, embedded planar flaws, phased array, inspection procedure, metallic materials.

FAQ

Q: What is this standard?

A: ISO 16826:2025 is an International Standard that specifies principles and guidance for ultrasonic tandem and LLT techniques used to detect discontinuities that are perpendicular or nearly perpendicular to a surface.

Q: What does it cover?

A: It covers the principles, recommended application range (primarily metallic materials thickness ~40 mm to 500 mm), procedural considerations, and notes on phased‑array implementation and adaptation to other materials or thicknesses. It also cross‑references general ultrasonic testing principles described in ISO 16810.

Q: Who typically uses it?

A: NDT inspectors, ultrasonic testing engineers, inspection bodies, laboratories, fabricators, and companies in industries that require internal planar‑flaw detection (e.g., power generation, oil & gas, heavy fabrication, pressure equipment).

Q: Is it current or superseded?

A: Current — ISO 16826:2025 is the 2nd edition published in March 2025 and supersedes the earlier ISO 16826:2012 (the 2012 edition has been withdrawn and replaced).

Q: Is it part of a series?

A: It is part of the family of ISO ultrasonic testing standards and should be used alongside ISO 16810 (general UT principles) and ISO 16811 (symbols/equations). Users may also refer to other ultrasonic technique standards (e.g., TOFD and phased‑array guidance) and any sector‑specific documents that adopt or modify ISO requirements.

Q: What are the key keywords?

A: Tandem technique; LLT; ultrasonic testing; perpendicular discontinuities; NDT; phased array; metallic material inspection; embedded planar flaws.