ISO 6366:2025
(Main)Non-destructive testing — Leak testing — Radioactive tracer methods for pressured vessels and underground pipelines
Non-destructive testing — Leak testing — Radioactive tracer methods for pressured vessels and underground pipelines
This document specifies radioactive tracer methods for the detection of a leak in pressured vessels and underground pipelines. This document applies to leak testing in pressured vessels and underground pipelines using a radioactive tracer.
Essais non destructifs — Contrôle par détection de fuites — Méthodes de traceurs radioactifs pour les réservoirs sous pression et les canalisations souterraines
General Information
Standards Content (Sample)
International
Standard
ISO 6366
First edition
Non-destructive testing — Leak
2025-09
testing — Radioactive tracer
methods for pressured vessels and
underground pipelines
Essais non destructifs — Contrôle par détection de fuites —
Méthodes de traceurs radioactifs pour les réservoirs sous pression
et les canalisations souterraines
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Protection against ionizing radiation . 1
5 Leak testing using external detection methods . 2
5.1 General .2
5.2 Techniques .2
5.2.1 General .2
5.2.2 Pulse-velocity technique .2
5.2.3 Response curve technique .3
5.2.4 Displacement technique .4
5.3 Standard equipment requirements .5
6 Leak testing using internal detection methods . 6
6.1 General .6
6.2 PIG technique .6
Annex A (informative) Selection of radioactive tracer . 8
Annex B (informative) Calculation of leak rate in pressured vessels . 9
Annex C (informative) Calculation of activity of radioactive tracer required in heat exchangers.11
Annex D (informative) Case studies for leak testing .13
Bibliography .16
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee SC
6, Leak testing.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
A leak can be detected by various methods, some of which can be used on-line while others can be applied
off-line. In some cases, the same method can be used in both off-line and/or on-line situations but with
different sensitivities.
Radioactive tracers help in early detection of leaks, thus reducing shutdown time, ensuring safe operation
and protecting the environment from pollution. Radioactive tracer methods are mostly used for on-line leak
testing. This document only applies radioactive tracer methods.
According to the methods and targets, radioactive tracers for leak testing are grouped in two categories.
a) Leak testing in plant processing units, such as pressure vessels, heat exchangers, valves, flares, boilers,
pipelines.
b) Leak testing in underground pipelines.
v
International Standard ISO 6366:2025(en)
Non-destructive testing — Leak testing — Radioactive tracer
methods for pressured vessels and underground pipelines
1 Scope
This document specifies radioactive tracer methods for the detection of a leak in pressured vessels and
underground pipelines.
This document applies to leak testing in pressured vessels and underground pipelines using a radioactive tracer.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 20484, Non-destructive testing — Leak testing — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20484 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
pipeline inspection gauge
PIG
self-contained device, that moves through the interior of a pipeline for purposes of inspecting, dimensioning,
or cleaning
3.2
pressured vessel
container designed to hold gases or liquids at a pressure substantially higher than ambient pressure
Note 1 to entry: Common pressured vessels in industries are heat exchangers, valves, boilers, tanks and pipelines.
4 Protection against ionizing radiation
WARNING — Exposure of any part of the human body to ionizing radiation can be injurious to health.
Wherever radioactive sources are in use, it is the responsibility of the user of this document to
identify the appropriate legal and safety requirements and regulations.
[1]
Further information can be found in the IAEA General Safety Requirements and national regulations.
5 Leak testing using external detection methods
5.1 General
Radioactive tracers are widely used in the oil, gas and petrochemical industries for detecting leakage. They
are also used in civil engineering operations. Leak testing using radioactive tracers are probably one of
the most widespread applications of radioactive tracers in industrial troubleshooting. Radioactive tracers
help in early detection of leaks, thus reducing shutdown time, ensuring safe operation and protecting the
environment from pollution.
Radioactive tracers can be used either online (during normal operation) or offline (during shutdown).
A selection of radioactive tracers is listed in Annex A.
[2]
NOTE Background information on this technique can be found in TCS 38 .
5.2 Techniques
5.2.1 General
There are three basic external detection techniques for leak testing in pressured vessels using radioactive
tracers:
— pulse-velocity technique;
— response curve technique;
— displacement technique.
There are further techniques using external detection methods for testing underground pipelines. These
[2]
techniques are not developed in this document. Some of these techniques are described in TCS 38 .
5.2.2 Pulse-velocity technique
The pulse-velocity technique is mostly applied for testing valves. The principle and test setup are shown
in Figure 1, where a suspicious valve (3) is tested for leaks. A sharp pulse of radioactive tracer is injected
into the process upstream of the valve and a potential leak is measured by placing radiation detectors at
appropriate locations.
Key
1 main fluid flow in pressured vessel
2 pulse injection of radioactive tracer
3 relief valve
4 leak flow (if any)
5 data acquisition system
D1 first radiation detector
D2 second radiation detector
P1 signal recorded by D1
P2 signal recorded by D2
t time lapse between P1 and P2
Figure 1 — Principle and test setup of pulse velocity technique
The function of the valve can be detected using just the first detector (Figure 1). The additional second
detector is needed to measure the leak flow rate. The distance between the two detectors should be long
enough, meaning the time lapse t between two pulses should be much more than the counting time.
A case study for the pulse velocity technique is shown in D.1.
5.2.3 Response curve technique
The response curve technique is frequently used for leak testing in heat exchangers. A sharp pulse of
a suitable radioactive tracer is injected into the inlet of the high-pressure side of the heat exchanger.
Any leakage within the system will be from the high-pressure to the low-pressure side. The appropriate
deployment of radiation detectors will confirm the presence of a leak. Detailed analysis of the response
curve will enable to quantify the leak rate and its approximate location.
Figure 2 shows a typical experimental setup for the leak testing of a shell and tube heat exchanger using
three radiation detectors. A minimum of two detectors are required, D1 at the tube (high-pressure side)
inlet where the radioactive tracer is injected and D2 at the shell (low-pressure) side outlet to identify any
leakage coming as bypass. The dotted peak in the D2 response curve appears only when the injected tracer
returns to the shell side of the heat exchanger. The response curve of D2 may be used as well to quantify the
leak rate. See Annex B for an example of a leak rate estimation.
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