Leak Testing (LT)
Leak Testing (LT) verifies the pressure boundary integrity of vessels, piping, and tanks by detecting and quantifying fluid leakage using methods such as pressure decay, bubble emission, mass spectrometer helium tracing, or ultrasonic leak detection.
Definition
Leak Testing (LT) is the NDT method used to confirm that a closed system holds pressure or vacuum without unacceptable leakage. Techniques range from simple soap-bubble visual inspection to mass spectrometer helium leak detection capable of resolving leaks below 10⁻¹⁰ Pa·m³/s.
Technical Context
Common methods include: pressure-decay (monitor pressure drop over time), bubble emission, helium mass-spectrometer (sniffer or hood), halogen detection, and ultrasonic leak detection. The method chosen depends on required sensitivity, system geometry, and gas compatibility.
When It Is Used
- Final acceptance testing of pressure vessels and piping
- Vacuum-system qualification in semiconductor and aerospace
- In-service tank-bottom leak monitoring
Related Standards
ASME Section V Article 10, ASME B31.3 Chapter VI, ASTM E432, ISO 20485, API 510, API 653.
How it works
A pressure differential is established across a boundary and the passage of a tracer — air, a bubble-forming solution, halogen, helium — is detected on the low-pressure side. Sensitivity spans many orders of magnitude depending on the technique chosen.
What it finds
Through-wall breaches, whatever their cause. It answers the question of containment directly, where every other method answers it by inference from wall condition.
What it will not find
Anything that is not yet through-wall. A crack ninety percent through the thickness leaks nothing and passes a leak test, which is why leak testing complements rather than replaces volumetric and surface examination.
How it is actually done
Technique selection follows the sensitivity required: bubble testing for gross leakage, pressure change for closed systems, halogen or helium mass spectrometry where small rates matter. System cleanliness, temperature stability and hold time govern whether a pressure-change result means anything at all.
Governing codes and standards
ASME Section V Article 10 covers leak testing and its appendices define the individual techniques; ASME Section VIII references it for pressure boundary acceptance.
Where it goes wrong
Reading a pressure drop as a leak without correcting for temperature. A modest ambient swing moves system pressure enough to imitate a leak, or to mask one, on any test whose hold time is short relative to the thermal time constant.
Frequently asked questions
Is a hydrostatic test a leak test?
It demonstrates strength and gross tightness, but it is not a sensitive leak test. Water is a poor tracer at small leak rates and the test proves the boundary held at pressure — a different and coarser question than whether it leaks.
Where Leak Testing fits in an inspection programme
A term is only useful when it connects to a decision. Leak Testing appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
- Acoustic Emission Testing (AE) — Acoustic Emission (AE) is a passive NDT method that detects transient elastic stress waves emitted by active discontinuities such as growing cracks, plastic deformation, or leaks, using sensors mounted on the component during loading.
- Pressure Vessel — A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from ambient, typically constructed per ASME Section VIII and inspected in service per API 510.
- Storage Tank — A storage tank is a low-pressure, large-volume welded container for the storage of liquids — typically atmospheric (API 650), low pressure (API 620), or for water (AWWA D100) — inspected in service per API 653.
More method terms
Ultrasonic Testing · Radiographic Testing · Magnetic Particle Testing · Penetrant Testing · Eddy Current Testing · Visual Testing · Thermography / Infrared Testing · Microwave Testing · Phased Array Ultrasonic Testing · Time-of-Flight Diffraction
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.