NDT in Process equipment industries

Radiographic Testing

Radiography is used in a very wide range of aplications including medicine, engineering, forensics, security, etc. In NDT, radiography is one of the most important and widely used methods. Radiographic testing (RT) offers a number of advantages over other NDT methods, however, one of its major disadvantages is the health risk associated with the radiation.
In general, RT is method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials. The intensity of the radiation that penetrates and passes through the material is either captured by a radiation sensitive film (Film Radiography) or by a planer array of radiation sensitive sensors (Real-time Radiography). Film radiography is the oldest approach, yet it is still the most widely used in NDT.

Basic Principles

In radiographic testing, the part to be inspected is placed between the radiation source and a piece of radiation sensitive film. The radiation source can either be an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137). The part will stop some of the radiation where thicker and more dense areas will stop more of the radiation. The radiation that passes through the part will expose the film and forms a shadowgraph of the part. The film darkness (density) will vary with the amount of radiation reaching the film through the test object where darker areas indicate more exposure (higher radiation intensity) and liter areas indicate less exposure (higher radiation intensity).
This variation in the image darkness can be used to determine thickness or composition of material and would also reveal the presence of any flaws or discontinuities inside the material.

Advantages and Disadvantages

The primary advantages and disadvantages in comparison to other NDT methods are:

Advantages

 Both surface and internal discontinuities can be detected.
 Significant variations in composition can be detected.
 It has a very few material limitations.
 Can be used for inspecting hidden areas (direct access to surface is not required)
 Very minimal or no part preparation is required.
 Permanent test record is obtained.
 Good portability especially for gamma-ray sources.

Disadvantages

 Hazardous to operators and other nearby personnel.
 High degree of skill and experience is required for exposure and interpretation.
 The equipment is relatively expensive (especially for x-ray sources).
 The process is generally slow.
 Highly directional (sensitive to flaw orientation).
 Depth of discontinuity is not indicated.
 It requires a two-sided access to the component.