Industrial Radiography and x-ray testing overview
Over the years, x-ray technology and nondestructive testing methods have advanced, in order to accommodate the growing needs of the industry. With different types of radiographic techniques and x-ray inspection, users are able to access full part data for different applications. Commonly, users outsource nondestructive testing projects for more accurate part results.
What is Industrial Radiography and X-ray testing?
Industrial radiography is a form of nondestructive testing of products, utilizing different techniques, on the foundation of x-ray technology. X-ray and radiography are similar in the sense that “x-ray” is a technique used to develop a “radiograph.” However, commonly these terms are mistakenly used interchangeably.
Furthermore, industrial radiography is concerned with industrial applications only, whereas x-ray could cover a broad range, including medical applications. Industrial radiography uses ionizing electromagnetic radiation in order to observe, evaluate and analyze the subject being tested. Industrial radiography is primarily concerned with the inspection of parts and structures nondestructively, by utilization radiation.
Types of Industrial Radiography
There are multiple different types of industrial radiography procedures. A brief overview of these procedures are explained below:
X-ray – This form of industrial radiography is produced by an x-ray generator. X-ray technology relies on electricity to be powered and utilized. When an electron is accelerated and comes in contact with other atomic particles, it forcibly decelerates, producing an x-ray. There are two different atomic processes:
Bremsstahlung radiation – When an electron accelerates because of an electric field of another charged particle, radiation is exerted, called Bremsstahlung radiation
K-sell/characteristic emission – when outer-shell electrons fill a void within inner shell of atom, radiation is exerted, characteristic to element.
Gamma-radiation (Gamma-rays) – This form of industrial radiography is produced from radioactive material (commonly mad-made) within the inspection system. The most common gamma-ray sources for industrial applications tend to be Iridium-192 and Cobalt 60. Gamma-rays do not need to rely on electricity to function, as they never turn off. They must be properly shielded when they are not in use. Gamma-rays have higher exposure of radiation, with the ability to inspect dense objects such as large pipelines.
Neutron Radiography (NR) – Although very rarely utilized, neutron radiography can be used for industrial applications. Neutrons have the ability to pass through very high density material, however, they have trouble inspecting low dense materials such as plastic. Since the amount of radiation is measurable (released from the opposite side of test subject), variying radiation can assist in identifying thickness of part.
Industrial Radiography techniques
According to the American Society of Non-destructive Testing (ASNT), there are three distinct techniques in regards to industrial radiography:
Film radiography – Use of a conventional x-ray film, held in an envelope which allows x-rays to pass through. The resulting images are processed using special chemicals. This process is referred to as the “wet-process”.
Computed radiography – A mix of film radiography and digital radiography. Instead of a conventional x-ray film, a reusable photo-stimulated phosphor (PSP) plate is held in an envelope. To process the captured images, the envelope is transferred to a laser reader which develops a digital image.
Digital radiography – The radiation that crosses the subject being tested is captured digitally and can be translated into a computer immediately.
Non-destructive x-ray testing inspection and industrial radiography
Industrial Radiography & x-ray testing has become invaluable for the testing, qualifications and verification of part components in the manufacturing cycle. Industrial radiography & industrial x-ray testing have revolutionized NDT methods of inspection by assisting in the following areas:
- Ensures safety and reliability of part
- Identify, locate and measure defects
- Density variations can be analyzed for structural evaluation
- Options of different approached for industrial radiography
- Quick, cost effective and accurate
- Ability to use part after testing and analysis
- Qualify and approve part components
Equipment required for radiography
There are many different tools that are required dependent on the approach of the industrial radiography and x-ray radiography process. Some common tools for conducting industrial radiography and x-ray testing include:
X-ray or Gamma-ray source – whether it is an x-ray generator or gamma ray source via radioactive materials, a source is the most necessary aspect of industrial radiography. Depending on the project requirements, an industrial radiography or x-ray testing approach can be utilized. If the part is relatively large, requires high amount of radiation exposure in order to penetrate through the material, gamma-ray sources would be more applicable. With smaller part components ranging from plastics to metals, x-ray sources would be applied with techniques such as computed tomography (CT).
Recording medium – on the opposite side of the test subject needs to be a recording medium in order to capture the radiation and develop results for further analysis. Whether a film sheet is required or a digital detector panel, the images retrieved can be used to detect defects and failures. Although fil radiography is not obsolete for industrial applications, it is steadily being replaced by computed tomography (CT) and digital radiography (DR).
Processing Equipment – If the technique of analyzing part is film radiography, processing equipment such as chemicals are necessary to develop the image. For digital radiography or computed tomography, processing equipment such as computers and specialized software is necessary to develop, restructure and analyze the resulting image.
Quality of Industrial Radiography
The quality of the x-ray testing method or industrial radiography approach is dependent on many different factors:
Size/ thickness of material – if the size and thickness of the material is too large for radiation to penetrate through, it will not be able to detect any flaws or defects, or even capture the structural complexity of a part. If the part is too small or consists of low density material and the radiation exposure is too high, the resulting image may produce scatter.
Material – The more dense the material is, the more radiation it tends to absorb. When there are defects within a material such as cracks or voids, more radiation passes through them, which the detector captures and processes in the final resulting image. Since the cracks or voids do not absorb any radiation, they will appear with a higher density on the resulting image – darker on the greyscale value. The areas with high dense material will absorb radiation, therefore, it will appear lighter on the greyscale, when analyzing the resulting image. The radiation source has to be set up so that it is not too high or low for a particular material being scanned. High radiation exposure for low dense materials will develop a scattered image. Low radiation exposure for relatively high dense materials will not provide the details a project may require in a resulting image.
Orientation – Depending on the area that needs to be inspected for industrial applications, the orientation of the part in accordance with the x-ray or gamma source plays a big role. The orientation of the part in regards to the x-ray source is determined on the basis of the purpose of the test (to identify failures/defect/wall thickness etc.)
Contrast/sharpness/graininess – A minimum contrast is required in order to retrieve high quality images to analyze failures, such as porosity. Image contrast is the density variations between an area and the background density on the radiograph – if the contrast is clear, it will aid in realizing failures more accurately. Similarly, sharpness of the imaging results can help look into detail of the part deviations from initial design and certain defects. The graininess of an image can also determine whether the results are of quality. Aspects like the orientation, and radiation exposure may need to be adjusted in order to access better quality images.
Applications of Industrial Radiography and X-ray testing
Industrial radiography and x-ray testing is one of the most common non-destructive testing methods within the industrial sector. From having the ability to inspect, quantify and qualify failures and defects to being able to access internal and external geometry, industrial radiography has become an indispensable tool for the industry. Applications vary depending on the type of material, size of part and inspection requirements, although industrial radiography and x-ray inspection are commonly used for testing welds, pipe, pipeline, concrete, machined parts, and metal components, solid and flat materials. This method of inspection is also regularly utilized by the following industries:
- Aerospace – ex. Castings
- Medical Devices – ex. Stints
- Automotive – ex. Piston head
- Military & Defense – ex. Ballistics
- Manufacturing – ex. Pre-production qualification of part
- Packaging – ex. Structural integrity/leak or failure analysis or package
Industrial Radiography – Safety
Since industrial radiography and x-ray testing expose high doses of radiation, certain standards and requirements are put into place in regard to the safe use and application of such a technology. Individuals who are looking to use radiography equipment for industrial applications must have a permit, license and training. In order to use industrial radiography or x-ray testing equipment, one must ensure all areas are free of people, who could possibly be adversely affected by the radiation exposure. Commonly, such tests and inspections are conducted after hours, to remove any risk of radiation exposure. Furthermore, different pieces of safety equipment must be utilized to ensure safety:
- Radiation survey meter: measures speed at which radiation is picked up
- Alarming dosimeter: alarms when radiographer is exposed to too much radiation
- Gas charged dosimeter: total radiation received, which can also be reset
- Thermoluminescent dosimeter (TLD): measures radiographers total exposure over time
Although industrial radiography and x-ray testing are the most common method of Non-destructive testing method, many other methods can be utilized to analyze a part:
- Magnetic particle testing
- Liquid penetrant testing
- Ultrasonic testing
- Electromagnetic testing
- Visual testing
- Acoustic emission testing
- Guided wave testing
- Laser testing methods
- Leak testing
- Magnetic flux leakage
- Thermal/infrared testing
- Vibration analysis
Industrial Radiography & X-ray testing certification
Governed by the Nuclear Regulatory Commission (NRC), certain standards have been put into place in order to operate radiographic testing equipment. Certain safety courses have to be taken, with a completion of a number of on the job training hours and a complete written exam. A form of certification authorized by ASNT classifies three different levels of certification to be qualified for the operation of such equipment:
Level 1 – Individuals certified with level 1 are restricted to perform only certain calibrations or tests under supervisions by a higher level individual. They are able to report results, and are expected to follow instructions regarding procedure.
Level 2 – Individuals certified with level 2 are open to set up and calibrate inspection equipment, perform inspection according to standards and codes. These individuals are able to provide instruction to level 1 technicians, as well as report, interpret and evaluate results. Have knowledge of standards and codes.
Level 3 – Individuals certified with level 3 are specialized, experienced and qualified engineers or technicians. These technicians are able to direct NDT labs, and have extensive knowledge about testing, service and manufacturing processes as well as codes and standards.
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