Published on 02-Mar-2024

A Comprehensive Guide on Radiography Testing

A Comprehensive Guide on Radiography Testing

Table of Content


Introduction

The progress of an intelligent species in Earth's transient yet ever-nurturing environment depends strongly on the technological and structural foundations being reliable and retaining integrity to variable ambient stimuli.

Electro-magnetic Radiation is abundant in the universe with some possessing the ability to ionize other atoms by detaching electrons on account of greater energy per Quantum. 

Radiography has been employed as a tool for structural imaging since the discovery of X-rays by William Röntgen in 1895, finds its purpose in medical imaging and the usage of Ionizing radiation (X- Rays and Gamma Rays) for industrial imaging Known as Radiography testing.

Radiography testing is among the contemporary Non-destructive Testing (NDT) Techniques employed for the examination of engineering structures without the risk of compromising structural integrity.

These NDT Inspections involve the propagation of Ionizing Electromagnetic radiation through the structure under observation while recording the observations on a radiographic film for structural deformities and imperfections.

The versatility associated with this Method of NDT Testing finds widespread usage in all sectors of industry enabling remote yet highly specific inspections furthering the real-time capabilities of structural examination in the most hostile and inhospitable environments.

History of Radiographic Testing

Light has been a great source of mystery since before Humanity had the understanding to reproduce any through kindling, let alone harness it as a tool for providing information and understanding beyond visual illumination.  

In the prehistoric era, Early men would look at lightning and forest fires caused thereafter and attribute them to divine providence against predators.

It wasn’t until June of 1752, when one of the founding fathers of the U.S., Benjamin Franklin discovered that charged particles being transferred are responsible for the brilliant display of heat and luminosity as thunder strikes, using a kite attached with a wet string to a key on the ground on a Cloudy windy evening. 

The exchange of charged particles observed by Franklin was employed in discharge tubes to produce cathode rays attributed to a flow of electrons by an English Physicist William Crookes for experimental purposes in the late 1800s. 

The fluorescence observed in the Crookes Tube was Studied by a German Professor in Physics, Wilhelm Röntgen in the year 1895 who attributed it a form of Energized radiation and called them χῖ –Rays (Greek Alphabet Chi) or Röntgen ways.

In his later Papers, attributing to the unknown nature of the ways, referred to them as X-rays, a term still used presently. 

Röntgen observed that these rays have medical applications as propagation through matter causes partial absorption and dissipation in these ways which can be further observed on a photographic plate serving as a precursor to modern-day medical Radiography. 

The discovery of infrared radiation by William Herschel in 1800 signified that sunlight passing through a prism refracts into various components, the dispersion of light and the subsequent discovery of Ultraviolet radiation by Johann Ritter in 1801 through a similar rectangular prism relayed that visible light has components which cannot be perceived by the human vision.

In the Year of 1896, Henri Becquerel a French Physicist and Engineer observed that Uranium Salts could show Fluorescence in the dark and the radiation penetrates through matter similar fashion to X–Rays and named them “Becquerel Rays”.

Marie and Pierre Curie in 1898 discovered that the radiation observed in elements similar in nature to Uranium salts like polonium and Radium was attributed to complex decay in matter over time with the Dissipation of Ionizing radiation and consequently Coined this Phenomenon “Radioactivity”.

Nuclear Research unlocked new Avenues in all Streams of technology including medicine giving rise to the contemporary Nuclear Medicine used in hospitals today. 

Earnest Rutherford, a Physicist from New Zealand later Built upon the research done by the Curies, discovered the most penetrating component of Radioactive radiation and named them Gamma Rays.

His observations included that Gamma Rays carry the highest amount of energy per photon among the components in the radiation (Alpha and Beta waves) and have a minimal deviation in a Magnetic field. 




For modern-day NDT Inspections, Radiography testing employs a combination of both X-ray and Gamma Ray Radiography Testing for a thorough examination of materials/structures using sophisticated machinery specific to the application keeping in mind that Radiation without appropriate protection can damage human DNA and hence maintain the exposure of living beings is minimal.

What is Radiographic Testing?

Radiography Test or Radiographic Test (RT) stands as one of the most used Non-destructive Testing finding Applications in Engineering, Architecture, medicine, and security among other sectors of Industry and technology. 

This testing methodology Involves the use of Ionizing Electromagnetic radiation (X-rays or Gamma Rays) propagated through the Subject/ structure under observation While the recordings are observed on a radiographic plate for further NDT X-ray testing.

The Image thus recorded on the plate is inspected using image darkness as a guide for object thickness and as a composition indicator along with variations in the image indicating deformities and discontinuities in the structure. 

Basic Principles of Radiographic Testing

As discussed in the previous sections, X-rays were discovered by Wilhelm Röntgen in 1895, 116 years ago. 

These electromagnetic waves have short wavelengths with a measure of less than a hundred nanometres (nm). 

Gamma rays were discovered in 1900, by a chemist named Paul Villard.

The isolation of Radium by Marie and Pierre Curie made this discovery possible. Gamma waves, like X-rays, have a short wavelength, the shortest wavelength in the electromagnetic spectrum.

X-rays and Gamma rays are not visible to the human eye and do not have a charge or mass.

Electrically and magnetically charged fields do not affect the travel of these waves, and they move un-wavered in a straight line.

X-rays and Gamma rays also have short wavelengths.

The penetrative power of a wave is inversely proportional to the wavelength. Hence, the shorter the wavelength, the greater the penetrative power.

This ability aids in analyzing the entire internal structure of a specimen.

In Radiography testing, a specimen is held or placed in the path of the wave and flanked by the source of the X-ray or Gamma rays and the film used to capture the resulting image.

The intensity and clarity of the image formed depend on the quantity of radiation that successfully penetrates and passes through the specimen under study.

A lighter resulting image is formed if there is less exposure of the film to the radiation, whereas a darker image is formed when there is more exposure of the film.

The types of radiographic sources available are:

  • Conventional Sources
  • Micro-focus X-ray equipment
  • Nano-focus X-ray equipment
  • Linac
  • Betatron
  • Synchrotron
  • Isotropic Sources like Iridium 192, Cobalt 60, Thulium 170, Ytterbium 169, Caesium 137, and Selenium 75.

The types of radiographic detectors available are:

  • Radiographic films with grain sizes ranging from D4 to D7

Radiographic Film Cross-Section (Image credits: RSET)

  • Radiographic Image intensifiers
  • Vidicons that are X-ray sensitive in nature.
  • Fluorescent screens and charged coupled devices.
  • Imaging plates
  • Digital flat panels like Amorphous Selenium Panels and Amorphous Silicon panels.
  • Linear diode arrays

A vital part of Radiographic Imaging is the contrast of the subject, film contrast, and image definition. These factors are affected by multiple factors, such as:

  • Energy is used in the process.
  • Intensity of waves
  • Scattered radiation is caused by the interaction of beams with the specimen under study.
  • Focal spot size
  • Characteristics of the detector used.

When Radiography waves like X-rays and Gamma rays pass an object, they interact with its internal structures and are scattered.

Therefore, on impinging X-rays or Gamma rays through a specimen, and using a detecting surface on a detector, the operator may obtain an image of the specimen, with its internal structures and deformities. 

This image is two-dimensional in nature and can be inferred by an experienced operator who can observe the changes in contrast and composition of the image and gauge if the specimen has defects or deformities.

Due to the two-dimensional nature of a film image, it might be difficult to obtain data on defects that alter the thickness of the object.

The obtained image is also highly dependent on the orientations of the flaws concerning the radiation beam applied to the specimen.

Radiography quality can be measured using devices called Image Quality Indicators (IQIs).

This device measures the level of penetration of waves into a specimen and is also called a penetrometer.

This device does not aid in detecting flaws and is instead used to measure the accuracy and sensitivity of the process. 

Image Quality Indicators are of two types namely Hole type Image Quality Indicators and Wire Image Quality Indicators.

Care should be taken by operators while using penetrative waves of any nature as they alter the chemical nature of the things the waves propagate through.

This can be life-threatening to the operator and careful use of protective gear like lead boundary walls, lead suits, and shoes should be compulsory.

Care should be taken by operators while using penetrative waves of any nature as they alter the chemical nature of the things the waves propagate through.

This can be life-threatening to the operator and careful use of protective gear like lead boundary walls, lead suits, and shoes should be compulsory.

Advantages of Radiographic Testing

 Unlike many other Non-destructive Testing, radiographic testing techniques overcome the general limitations and inability to test internal structures of materials and complex geometries.

The benefits of Radiographic testing are vast and constantly growing in number, some of which are:

  • Radiographic testing is not limited to test subjects of specific materials and hence can be used for a variety of materials and many applications.
  • Data losses and the need for thorough inferences and meticulous transcription of test data are eliminated. The data obtained from radiographic testing is permanent, visually represented, and can be either digitized directly or developed on a film.
  • Radiographic waves like X-rays and Gamma rays are highly penetrative in nature and can infiltrate the material, giving clear imagery of the internal structure of the material under test.
  • Fabrication errors that sometimes reflect on a material surface can often be misinterpreted by many other NDT Techniques, as the inability of the technique to interpret sub-surface and internal defects may make the defects appear as minor surface defects. Radiographic testing can detect internal defects accurately while providing a clear idea of the nature, size, and depth of the deformity. This makes the process of detecting fabrication errors simple.
  • Discontinuities in the structure of the test subject can be analyzed by radiographic testing techniques.
  • Surface preparation is skipped in radiographic testing and hence the process is time-effective.
  • The accuracy provided by radiographic testing is impeccable and the methodology can detect minute flaws.

Disadvantages of Radiographic Testing

Radiographic Testing is a highly sensitive technique and can provide ample benefits to the quality testing phase and intermediate analysis phases of a production process.

This methodology, however, like every other scientific technique comes with limitations that may or may not be avoidable or resolvable. 

Those limitations include the following:

  • Radiographic equipment is limited to the direction in which the impeding radiographic waves are applied. This makes it difficult to obtain sufficient testing reach in test subjects with complex geometries.
  • Radiography testing specimens can only be tested from two sides as the apparatus used in radiographic testing can only be used in specific orientations.
  • Specimens with defects oriented parallel to the surface of the material and angular defects are difficult or unlikely to be picked up by radiographic testing.
  • X-rays and Gamma rays are extremely penetrative rays in the electromagnetic spectrum. These rays can interact and pass through clothes, plastic, human tissue, etc. Hence extra measures need to be carried out to protect the operators and workers in the vicinity of the testing machines to ensure their safety. Lack of regard for such measures can lead to long-term damage to the humans in the proximity of the Radiographic testing machine.
  • Radiography testing equipment is designed to perform analysis using highly penetrative waves like X-rays and Gamma rays and hence the equipment and peripherals are expensive.
  • The depth of indications is hard to infer from the results of a radiographic examination.
  • The impinging radiographic waves must be oriented in accordance with the angle of the discontinuities, it will result in the test results not detecting such defects.

Industry Codes and Standards for Radiographic Testing

Industries all over the globe recognize the impact of inconsistencies and errors in NDT Testing Processes and the need to perform testing procedures uniformly and accurately.

Hence, multiple organizations have set guidelines, or standards for performing such testing, which not only creates a directory or simplification of testing procedures for certain testing scenarios but also eliminates errors in calculation or inference caused due to human error.

Some of these industry codes and standards are as follows:

  • International Organization for Standardization 10675-1:2021-Non-destructive Testing of Welds — Acceptance levels for radiographic testing — Part 1: Steel, nickel, titanium, and their alloys
  • International Organization for Standardization- 5576- Vocabulary
  • International Organization for Standardization- 11699- Equipment Detector
  • International Organization for Standardization- 5579- General Rules, of Radiographic Testing Draft Digitization
  • International Organization for Standardization- 5817- Evaluation, General Rules
  • American Society for Testing and Materials- E1316- Vocabulary 
  • American Society for Testing and Materials - E1165- Equipment Source
  • American Society for Testing and Materials -E1815-Equipment Detector
  • American Society for Testing and Materials -E2002- Image Quality Indicator, Radiographic Testing
  • American Society for Testing and Materials -E142- Image Quality Indicator, Radiographic Testing
  • American Society for Testing and Materials -E592- Image Quality Indicator, Radiographic Testing
  • American Society for Testing and Materials -E747- Image Quality Indicator, Radiographic Testing
  • American Society for Testing and Materials -E1025- Image Quality Indicator, Radiographic Testing
  • American Society for Testing and Materials -E1936- Image Quality Indicator, Radiographic Testing
  • American Society for Testing and Materials -E94- General Rules of Radiographic Testing
  • American Society for Testing and Materials -E1742- General Rules of Radiographic Testing
  • American Society for Testing and Materials -E1032- Welding Inspection
  • American Society for Testing and Materials -E390- Welding Inspection ref. Radiographs
  • American Society for Testing and Materials -E1030-Casting Inspections
  • American Society for Testing and Materials -E155- Casting ref. Radiographs
  • American Society for Testing and Materials -E431- Electronics evaluation
  • European Committee for Standardization- EN1330-3-Vocabulary, Radiographic Testing
  • European Committee for Standardization- EN12543-Equipment Source
  • European Committee for Standardization- EN12544-Equipment Source
  • European Committee for Standardization- EN12579-Equipment Source
  • European Committee for Standardization-EN 584- Equipment Detector
  • European Committee for Standardization-EN 25580- Equipment Detector
  • European Committee for Standardization-EN462- Image Quality Indicator
  • European Committee for Standardization-EN444- General Rules of Radiographic Testing
  • European Committee for Standardization-EN1435-Welding Inspection, Radiographic Testing
  • European Committee for Standardization-prEN12681-Casting Inspection, Radiographic Testing
  • European Committee for Standardization-prEN10246-10- Steel Tube Inspection
  • European Committee for Standardization-EN2581- Evaluation of Quality Levels
  • European Committee for Standardization-EN12062- General Rules of Evaluation
  • European Committee for Standardization-EN12517- Welding Evaluation, Radiographic Testing
  • Japanese Industrial Standards- K7627-Non-Destructive Testing - Industrial Radiographic Film - Part 1: Classification of Film Systems for Industrial Radiography
  • Japanese Industrial Standards- Z3110- Non-destructive Testing of Welded Joints, Methods
  • Japanese Industrial Standards- K0131- General Rules of X-ray diffractometric analysis
  • Japanese Industrial Standards- Z3104:1995- Methods of radiographic examination for welded joints in steel
  • Japanese Industrial Standards- Z4751-2-54-2012- Particular requirements for the basic safety and essential performance of X-ray equipment for radiography and radioscopy
  • Japanese Industrial Standards- JIS Z 4560:2018-Apparatus for Industrial Gamma Radiography
  • Indian Standards- IS 2595:2008-Industrial Radiographic Testing
  • Indian Standards- IS 12938:1990- Acceptance Standards for Radiographic Inspection
  • Indian Standards- IS 1182- Recommended practices for Radiographic inspection- Non-destructive Testing.

Applications of Radiographic Testing

Radiography Testing is an Advanced NDT Technique, that due to the sheer nature of its methodology and capabilities, is useful for a wide range of industries and applications.

The industries where Radiographic Testing comes under use are:

  • Offshore Petroleum Oil and Gas Extraction Industry
  • Marine applications and shipping
  • Construction and repair of ships.
  • Leisure Yachts and boats
  • Construction and Structural engineering
  • Machine building and steel construction
  • Recreational Industry
  • Wind Turbine and alternative energy generation.
  • Process industry and energy

Conclusion

Radiography has been the method of choice for most Non-destructive Testing needs, it eliminates limitations based on materials, size, and testing time.

Novel Radiographic Techniques have been designed and developed to keep up with the times and requirements.

These newer methodologies allow for accurate analysis of materials and specimens that are in operation. 

Radiographic techniques have been used in the field of medicine for ages and much development and research has been put into the field.

However, care should be taken to ensure the radiographic techniques used for industrial Evaluation of Non-destructive Testing of machines and structures should consider theoretical data that has been designed to accommodate medical applications.

Radiography Films, Imaging techniques, and Inference methods must be studied deeply to ensure that the Non-destructive Evaluation using Radiographic techniques is appropriate for the intended applications of the test specimen. 

Newer techniques provide the option of using Films, Real-Time Systems, or Digital Detectors to record data for inferences.

These NDT Techniques along with the amalgamation of robots and drones with Radiographic Testing apparatus allow for automation and the removal of the human factor from the testing process completely. 

Artificial Intelligence can be trained to perform testing operations using robots. 

These mechanisms can also be remotely controlled by an operator in certain situations, aiding in eliminating the dangers of a hazardous working environment for the workers.

Radiography Testing, among other Non-destructive Testing Inspection Methods (NDT Inspections), has kept up with the change and growth of technologies and has stood the test of time.

Newer materials can continue to be tested by radiographic techniques, and the use of mobile testing apparatus has allowed for the testing of more advanced machinery and structures Furthering Human testing capabilities far beyond previously thought possible.

References

1. AERB

2. Benjamin Franklin History Society

3. D-Kuru/Wikimedia Commons

4. Wikimedia Commons

5. NASA

6. WERMAC

7.HistoryOfScienece101

8. Review about radiopharmaceuticals

9. RSET 



Tree PNG back

Companies

Tree PNG back

Articles

Webinars

Webinars

Tree PNG back

Jobs

Application Notes

News

onestop ndt application

NDT Trends #84 is out!!
Grab your FREE copy now.