ASNT NDT III LT key terms

An unintended passage or opening through which a fluid escapes or enters a system, component, or enclosure. It can be a discrete hole, a porous region, or a permeable seal path.

A nondestructive method of detecting, locating, or measuring the escape or entry of fluids through discontinuities in a test object, using pressure differentials and a detection technique matched to the tracer or fluid involved.

The quantity of fluid passing through a leak per unit time, commonly expressed in units such as atm-cc/s, mbar-L/s, or Pa-m3/s. It depends on leak geometry, pressure differential, and fluid properties.

A calibrated reference leak that produces a known, stable leak rate of a specified gas under stated conditions. It is used to verify instrument sensitivity and to confirm test system performance before and after testing.

A leak artifact whose leak rate has been measured against a traceable standard and documented with a certificate. It serves as the reference for calibrating leak detectors and validating test sensitivity.

A gas introduced into or around a test object specifically to reveal leaks because it is easily detected at low concentration. Helium is common due to its small molecule, low background, and high detector sensitivity.

A leak testing technique that uses helium as a tracer and a mass spectrometer tuned to helium's mass to detect its presence. It can be applied in vacuum, sniffer, or accumulation modes with high sensitivity.

An instrument that ionizes gas and separates ions by mass-to-charge ratio to measure tracer gas concentration, typically helium. It converts detected partial pressure into an indicated leak rate after calibration with a standard leak.

The difference in pressure across a potential leak path that drives fluid flow. Leak testing requires a sufficient differential so that escaping or entering fluid produces a detectable signal.

A leak testing approach in which the test object or its surroundings are evacuated so that the pressure differential draws tracer or fluid through leaks toward a detector. It is used for high-sensitivity testing of sealed components.

A leak test in which a pressurized object is isolated and its internal pressure is monitored over time. A measurable pressure drop indicates leakage, provided temperature and volume changes are controlled or compensated.

A simple leak detection technique in which a pressurized object is immersed in liquid or coated with a film, and escaping gas forms visible bubbles at leak sites. It locates leaks but gives limited quantitative leak rate data.

A technique in which tracer gas escaping from a test object is collected in an enclosure over a period, then measured. Accumulation increases sensitivity and allows testing of large or complex parts.

A leak location method in which a probe draws ambient air near the test object into a detector, such as a helium mass spectrometer, to find and roughly quantify leaks. It is used where the object cannot be evacuated.

A technique using halogen-containing tracer gas and a detector sensitive to halogens, historically used for refrigeration and similar systems. It is less sensitive than helium methods and has environmental and safety considerations.

A method that detects high-frequency acoustic emissions produced by turbulent fluid escaping through a leak. It is useful for locating leaks in pressurized gas systems and can be used in noisy environments with directional sensors.

A leak location method in which a dyed liquid is applied to one side of a boundary and its appearance on the opposite side reveals a through-leak. It is suited to locating leaks in accessible surfaces and welds.

The detector reading caused by tracer gas or interfering species already present in the test environment, independent of the leak being sought. It limits sensitivity and must be measured, minimized, or subtracted during testing.

The smallest leak rate an instrument or test setup can reliably distinguish from background noise under specified conditions. It depends on detector sensitivity, background, response time, and test configuration.

The ability of a leak test method or instrument to detect small leak rates or tracer concentrations. It is expressed as the smallest detectable signal above background and is verified using a standard leak.

The time required for a leak detector or test system to reach a specified fraction of its final reading after a leak signal is applied. It affects test duration and the ability to locate leaks quickly.

A documented set of instructions specifying the test method, equipment, calibration, test conditions, acceptance criteria, and records for a leak test. It must be qualified and controlled to ensure repeatable, reliable results.

The process of demonstrating that a leak testing procedure consistently produces valid results for its intended application. It may involve reference standards, repeat tests, and documented evidence that sensitivity and reliability are adequate.

The defined limits or conditions that determine whether a test object passes or fails a leak test. They are stated in the procedure and may be based on maximum allowable leak rate or absence of detectable leakage.

The documented chain linking a measurement or calibration to recognized national or international standards. It supports confidence that leak rates and detector calibrations are accurate and comparable over time.

A documented employer procedure describing how personnel are trained, examined, qualified, and certified under SNT-TC-1A. It defines responsibilities, qualification requirements, and recordkeeping for the certification program.

An ASNT recommended practice providing guidelines for qualifying and certifying NDT personnel. Employers adopt it through a written practice and tailor requirements to their specific needs and applications.

An ASNT standard that establishes mandatory requirements for qualifying and certifying NDT personnel. It is more prescriptive than SNT-TC-1A and is used where a formal consensus standard is required.

The documented confirmation by an employer that an individual has met the required training, experience, and examination criteria for a specified NDT method and level. It is issued under the employer's written practice or applicable standard.

The highest NDT personnel qualification level, responsible for method expertise, procedure development, interpretation of standards, and certification program administration. A Level III may also train and examine other personnel.

A material property describing substances that are not strongly attracted by a magnetic field, such as austenitic stainless steel, aluminum, and copper alloys. This affects which NDT methods, such as magnetic particle testing, can be applied.

The reduction in energy or signal strength as it travels through a material or medium. In NDT it influences ultrasonic testing and acoustic leak detection by limiting how far or how clearly a signal can be detected.

The comparison of an instrument's indication against a known reference to establish its accuracy and adjust it if needed. In leak testing, calibration with a standard leak confirms that indicated leak rates are meaningful.

Standard expressions for leak flow, such as atm-cc/s of air, mbar-L/s, or Pa-m3/s. Consistent units are essential when comparing acceptance criteria, standard leaks, and detector readings.

A signal interpreted as a leak that is not caused by an actual leak, such as from residual tracer, outgassing, virtual leaks, or instrument noise. Recognizing and eliminating false indications is essential to valid leak testing.

An apparent leak signal caused by trapped gas slowly escaping from a void, crevice, or porous surface rather than through a true through-leak. It can mimic a real leak and must be distinguished during testing.