Nondestructive Examination Methods Flashcards

An inspector performing Liquid Penetrant Testing (PT) on a non-porous component correctly completes the pre-cleaning, penetrant application, and dwell time steps. What is the immediate next step required to ensure an accurate inspection?

Answer: Remove the excess penetrant from the surface.

After the penetrant has been allowed to dwell and seep into any surface-breaking discontinuities, the excess penetrant on the surface must be removed. This step is critical because any remaining excess can mask relevant indications or create false ones, obscuring the results. Applying the developer is the subsequent step, which works by drawing the trapped penetrant back out to the surface to form a visible indication.

Which of the following Nondestructive Examination (NDE) methods is most effective for detecting fine, surface-breaking cracks in a carbon steel weldment?

Answer: Magnetic Particle Testing (MT)

Magnetic Particle Testing (MT) is highly sensitive to surface and slightly subsurface discontinuities in ferromagnetic materials like carbon steel. It works by creating a magnetic field in the part; a surface-breaking crack will cause a flux leakage field that attracts the applied magnetic particles, making very fine cracks visible. While VT is always the first step, it may not reveal very fine cracks. RT and UT are primarily used for detecting subsurface flaws.

During an Ultrasonic Test (UT) of a thick plate, a technician uses a transducer to send high-frequency sound waves into the material. The fundamental principle that allows for the detection of an internal flaw, such as porosity or a crack, is that the sound waves will:

Answer: be reflected by the boundary of the flaw.

Ultrasonic Testing operates on the principle of sound wave propagation and reflection. High-frequency sound waves travel through a material and, upon encountering a boundary or discontinuity (like a crack, void, or inclusion), are reflected back to the transducer. The instrument measures the time it takes for these echoes to return, which allows the technician to determine the location, size, and shape of the internal flaw.

A key limitation of Liquid Penetrant Testing (PT) is its inability to:

Answer: detect subsurface or internal discontinuities.

The fundamental principle of Liquid Penetrant Testing relies on the penetrant liquid seeping into discontinuities via capillary action. This can only occur if the discontinuity is open to the surface. Therefore, PT is incapable of detecting flaws that are entirely internal or subsurface.

In Radiographic Testing (RT) of a weld, an Image Quality Indicator (IQI), or penetrameter, is placed on the part during the exposure. What is the primary purpose of the IQI?

Answer: To verify that the radiographic technique was sensitive enough to detect relevant discontinuities.

The Image Quality Indicator (IQI) is a device with known features (like wires of specific diameters or holes of a specific size) made of a material similar to the part being inspected. Its image on the radiograph provides a verifiable measure of the radiographic quality and sensitivity. It demonstrates that the technique and procedure used were capable of detecting a discontinuity of a certain minimum size, but it does not measure the size of actual flaws found in the weld.

An inspector using Magnetic Particle Testing (MT) identifies an accumulation of magnetic particles caused by an abrupt change in the part's geometry, such as a keyway or a sharp fillet radius. This type of indication should be classified as:

Answer: A non-relevant indication.

Indications in MT are classified to determine their source. A non-relevant indication is a true accumulation of magnetic particles caused by a magnetic flux leakage field, but the source is an intentional design feature of the part (like a change in section thickness or a keyway) rather than an actual flaw. A relevant indication is from a flaw, and a false indication is not caused by a flux leakage field at all (e.g., from lint or scale).