MATE1104 [NDT] Radiography Testing

Introduces the basics of Radiography Testing

General Principle of Radiography

A part is placed between the radiation source and a piece of film

The part will reduce some of the radiation

Thicker and more and dense area will stop more of the radiation

Film darkness (darkness) will vary with the amount of radiation reaching the film through the test object

[LIGHTER = LESS EXPOSURE]

[DARKER = MORE EXPOSURE]

Flaw Orientation

RT has sensitivity limitations when finding cracks.

X-rays “see” a crack as a thickness variation

The larger the variation = the easier the crack is to find

If the path of the x-rays is not parallel to a crack, the thickness variation is less and the crack may not be seen.

The orientation must be well known if RT is used to inspect the materials.

X-Ray RT

Cathode has a small filament which is equal to the amount in a light bulb

Current is passed through the filament which heats it, causing electrons to be stripped off due to heat.

The high voltage causes the electrons to be pulled toward a target materials (typically made of tungsten) thats in the anode.

The electrons have contact against the target, causing energy exchange which makes x-rays.

Gamma RT

……are made from a radioisotope

Radioisotope = unstable nuclei that does not have enough binding energy to hold the nucleus together

The rapid break down of an atomic nucleus resulting in energy and matter released = radioactive decay

Uses of RT

Flaw detection

Looking at the internals of a component

Corrosion monitoring

How to display a RT

Through:

Film [Commonly used, contains microscopic material silver bromide]

Real Time Radiography

Computed Tomography

Digital Radiography

Computed Radiography

Image Quality

To determine image quality, devices called penetrameters or Image Quality Indictors are used to inspect quality and sensitivity of the image

To do so it is based on the smallest hole or wire diameter that is created on the image.

Terminology

Unit of radiation based upon disintegration of radioactive material

Half-Life — the length of time taken for a radioactive to decay to half its original material

Radiation Dose — Unit for radiation can be the Roentgen. But REM is commonly used in terms of considering people affected by radiation. In SI it is the Sievert

1 Sv = 100 REM

Basic ways to lower radiation dose rate

Less time spent near radioactive source = less radiation received

Greater distance from source = Less radiation received

Behind a wall from source = less radiation received

RT— Pros

Technique is not limited by material type or density

Can inspect assembled components

Minimum surface preparation required

Sensitive to changes in thickness, corrosion, voids, cracks, and material density changes

Detects both surface and subsurface defects

Provides a permanent record of the inspection

RT— Cons

A lot of safety precautions when using stronger radiation

Requires a lot of technician experience and training before use

Access to both sides of sample is required

Orientation of equipment an flaw can be rucial

Determining flaw depth is impossible w/o additional angled exposures

Expensive initial equipment costs