ISO 18173:2026

• Abstract:

  This document defines general technical terms used in many non-destructive testing disciplines.

• Status: Published
• Publication Date: 08-Jun-2026
• ICS: 01.040.19 - Testing (Vocabularies)
• ICS: 19.100 - Non-destructive testing
• Technical Committee: ISO/TC 135 - Non-destructive testing
• Drafting Committee: ISO/TC 135 - Non-destructive testing
• Current Stage: 6060 - International Standard published
• Start Date: 09-Jun-2026
• Due Date: 02-Feb-2026
• Completion Date: 09-Jun-2026

• Revises: ISO/TS 18173:2005 - Non-destructive testing — General terms and definitions
• Effective Date: 06-Jun-2022

ISO 18173:2026 is an ISO International Standard for non-destructive testing (NDT). It defines general technical terms used across many NDT disciplines, so readers can use the same language for inspection, interpretation, evaluation, and reporting.

What does ISO 18173:2026 specify?

ISO 18173:2026 specifies general technical terms and definitions for NDT. It is organized into three clauses: Scope, Normative references, and Terms and definitions.

The scope is broad on purpose. The document covers vocabulary used in many NDT disciplines, rather than a single test method, so it helps align wording across different methods, standards, codes, and specifications.

What are the key requirements of ISO 18173:2026?

ISO 18173:2026 is a terminology standard, so its main content is the controlled meaning of NDT terms. In practice, that matters because the same words are used when writing procedures, judging indications, setting acceptance thresholds, and documenting results.

Core evaluation language

• Acceptance criteria and acceptance level define the basis for deciding whether a test object is acceptable. In practice, these terms matter when a buyer, inspector, or quality manager needs a clear pass/fail basis.
• Evaluation, relevant indication, non-relevant indication, and false indication separate signals that need action from signals that do not. This helps avoid rejecting a part for a signal that is not tied to a meaningful discontinuity.
• Indication is the signal or representation produced by an NDT method. In practice, it is the starting point for deciding whether further interpretation or evaluation is needed.

Defects, flaws, and discontinuities

• Discontinuity, imperfection, flaw, and defect are distinguished from one another. The document treats a flaw as an imperfection or unintentional discontinuity that can be detected by NDT, while a defect is a flaw or group of flaws that fails the specified acceptance criteria.
• This distinction matters because not every indication becomes a rejectable defect. The terminology supports a controlled decision path from detection to acceptance.

Methods, procedures, and techniques

• NDT method means a discipline applying a physical principle, and NDT technique means a specific way of using that method. For users, this helps separate the general method from the exact way it is applied.
• NDT procedure is the written description of the essential parameters and precautions to be followed. In practice, this is the document people use to run the work consistently and in line with standards, codes, or specifications.

Equipment response and traceability

• Calibration, standardization, and reference block describe how instruments are checked or adjusted against known references. This matters because repeatable response is needed before results can be trusted.
• The standard also defines recording as a stored presentation of test results and instrument settings. That supports traceability in quality systems and reporting.

Performance of the test

• Detection sensitivity, detection threshold, resolution, signal-to-noise ratio, and sizing describe how well an NDT method can find and characterize flaws. In practice, these terms are used when judging whether a method can detect small discontinuities and how much detail it can reliably separate.
• Noise is the unwanted signal that can interfere with the test or its results. Recognizing noise matters because it can mask real indications or create uncertainty.

What terms does ISO 18173:2026 define?

• NDT - Non-destructive testing: development and application of methods that do not impair future usefulness and serviceability.
• Acceptance criteria - The rules used to decide whether a test object is acceptable.
• Flaw - An imperfection or unintentional discontinuity that can be detected by NDT and is not necessarily rejectable.
• Indication - The signal or representation produced in the format allowed by the NDT method.
• Reference block - A known material piece used to set, check, assess, or quantify equipment response.
• Standardization - Adjustment of an NDT instrument using an appropriate reference block to obtain a known and reproducible response.
• Signal-to-noise ratio - The ratio of the signal from a discontinuity to the nearby average noise.

Who uses ISO 18173:2026?

ISO 18173:2026 is used by people who write, read, or apply NDT procedures and specifications. That includes NDT practitioners, procedure writers, inspectors, and quality personnel who need shared meanings for terms such as indication, evaluation, flaw, and acceptance criteria.

It is also useful in commerce and industry when the same terminology has to work across different NDT disciplines. The document supports standardization work, training, reporting, and discussions between users, suppliers, and testing organizations.

What changed in ISO 18173:2026 from the previous edition?

ISO 18173:2026 is the first edition and cancels and replaces the first edition of ISO/TS 18173:2005. The foreword states that the terms and definitions have been technically revised and harmonized with ISO/TS 18173:2005, EN 1330-2:1998, and ASTM E1316-13c.

What does the ISO 18173:2026 document contain?

ISO 18173:2026 contains a short front matter section, a foreword, an introduction, and Clause 3 with the terms and definitions. Clause 3 provides the vocabulary used to describe evaluation, detection, interpretation, recording, calibration, standardization, and related NDT activities.

The document is a terminology reference rather than a test method or a procedure standard. Its practical value is in giving users a common language for specifications, procedures, training materials, and inspection records.

The foreword also identifies ISO/TC 135, Non-destructive testing, as the technical committee responsible for the document.

International
Standard
ISO 18173
First edition
Non-destructive testing — General
2026-06
terms and definitions
Essais non destructifs — Termes généraux et définitions
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1

iii
Foreword
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This document was prepared by ISO/TC 135, Non-destructive testing.
This first edition cancels and replaces the first edition of ISO/TS 18173:2005, which has been technically
revised.
The main changes are as follows:
— harmonizes and updates the terms and definitions of Non-Destructive Testing (NDT) in ISO/TS 18173:
2005, EN 1330-2: 1998 and ASTM E1316-13c.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
This document defines the general technical terms that are used in many non-destructive testing disciplines.
These terms are not usually defined in the standards pertaining to individual non-destructive test
methods. Thus, the terms and definitions in this document serve to establish a common basis for further
standardization and general use in the field of non-destructive testing and thereby provide for enhanced
understanding in commerce and industry.

v
International Standard ISO 18173:2026(en)
Non-destructive testing — General terms and definitions
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