Published on 07-Jul-2022

Radiography testing - Types and Benefits

Radiography testing - Types and Benefits

Radiography testing - Types and Benefits

What Is Radiography?

Radiography is an imaging technique that uses X-rays, gamma rays, or other forms of ionizing and non-ionizing radiation to observe an object's internal shape. Medical radiography (therapeutic and diagnostic) and industrial radiography are two examples of radiography applications.

Industrial radiography is an NDT - non-destructive testing method that can be used to inspect the interior structure and integrity of various produced components. X-rays or gamma rays can be used in industrial radiography.

Both are electromagnetic radiation types. The wavelength is what distinguishes different types of electromagnetic energy. Because X-rays and gamma rays have the shortest wavelengths, they can penetrate, pass through, and exit diverse materials, including carbon steel and other metals. Industrial computed tomography is one of the specific ways.

What Is Radiography Testing?

RT - Radiographic Testing is a non-destructive testing (NDT) procedure that examines the interior structure of produced components using either x-rays or gamma rays to find any flaws or defects.

History of radiography testing

There are two origins in the history of radiographic testing. The first began with Wilhelm Conrad Röntgen's discovery of X-rays in 1895. The second began with Marie Curie's revelation in December 1898 that she had established the presence of a new radioactive material termed "Radium."

What is the Radiography testing principle?

The part to be evaluated is sandwiched between the radiation source and a sensitive film or detector in radiography testing NDT. Once the x-ray or gamma-ray radiation is initiated, the test part's material density and thickness will block some of the radiation. Less radiation will travel through the specimen if the material is thicker and denser. The amount of radiation (known as a radiograph) that reaches the film through the test specimen is recorded on the film (or an electronic device). Defects can simply be identified by reviewing the radiograph data. If the material is sound and free of flaws, all rays will travel through it uniformly. However, rays passing through faults will be absorbed to a minor level due to imperfections' density shift in materials.

There are two types of radioactive sources for industrial applications: X-ray and Gamma-ray. Higher energy levels, i.e., shorter wavelength, electromagnetic waves are used in these radiation sources. Due to the radioactivity involved in radiography testing NDT, the Local Rules must be rigorously followed during the procedure.

Defects in the parent metal diminish its density, allowing it to transmit radiation more effectively than sound metal. As a result, the defect-exposed area of the radiological film appears darker.

The energy of the radiation affects the penetrating power of rays. Higher-energy radiation may penetrate thicker, denser materials. Due to the high radioactivity of high-energy x-ray and gamma-rays, local restrictions must be rigorously obeyed.

Defects are found utilizing thickness variation in the radiographic examination. As a result, the wider the variation, the easier it is to discover a fault. However, when rays do not travel parallel to a crack, thickness variation is reduced, and the crack may not be visible.

As a result, doing radiographic examination by delivering rays at various angles is always recommended.

 

Fig. 1: Radiographic Testing

We hope that you are now aware of the radiography testing principle.

Radiographic Testing Procedure

The radiographic testing technique will vary slightly depending on the project requirements. The procedures for radiographic testing are outlined in the following paragraphs.

  • Step 1: Preparation of the Surface: Surface abnormalities must be removed so that the image is not masked or misinterpreted as a flaw. All butt welded joints should have a completed surface flush with the base material.
  • Step 2: Choosing the appropriate radiation source and radiographic film: The radiation source (x-ray or gamma-ray) must be chosen based on radiographic sensitivity and material thickness. High-definition radiographic films with fine grain can be used.
  • Step 3- Penetrameter Selection: Whole type or wire type penetrameter must be selected according to ASME V & ASME Sec VIII Div I, SE 142 or SE 1025 (for the whole type) and SE-747 (for wire type).
  • Step 4: The radiographic testing procedure is either single or double wall exposure. The distance between the source and the object must be determined beforehand.
  • Step 5: Defect inspection and removal: The radiograph will be examined for possible defects and fixed if any are found.
  • Step 6: Data recording: All data must be accurately recorded.

Why Is A Radiography Test Required?

Radiographic testing leaves a lasting record in the form of an X-ray image and a very sensitive image of the material's internal structure. The thickness and density of an object determine how much energy it absorbs. Exposure to the radiography film is caused by the object's energy that is not absorbed.

Is Radiographic Testing (RT) dangerous?

Most of us know that X-rays and gamma rays are harmful to humans and other living things. As a result, we do much of our radiography testing in specially constructed concrete bunkers. A safe perimeter is built around the inspection zone when radiographic testing is performed on-site. During the inspection, no one is allowed within that boundary. As a result, it frequently occurs outside of business hours. The investigated objects are not radioactive after testing and can be handled safely. The X-ray tubes and gamma-ray isotopes required for industrial radiography are stored, transported, and used safely by numerous companies.

Types of Radiography

There are several different types of RT procedures, including conventional radiography and other digital radiography examinations. Each one works a little differently and has its own set of benefits and drawbacks.

Conventional Radiography

Conventional radiography captures an image of the part to be evaluated using a sensitive film that reacts to the released radiation. This image can then be inspected for damage or faults. This method's major drawback is that movies can only be utilized once, and processing and interpretation take a long time.

Digital Radiography

Digital radiography, unlike conventional radiography, does not require a film. Instead, a digital detector is practically utilized to display radiographic images on a computer screen. This enables a significantly shorter exposure period, allowing for faster image interpretation. Furthermore, digital images are of far more excellent quality than conventional radiography images.

The technique can be used to discover material faults and foreign items in a system, inspect insulation for corrosion, and evaluate weld repairs because it can record high-quality photos.

Direct radiography, computed radiography, real-time radiography, and computed tomography are the four most prevalent digital radiography techniques utilized in oil, gas, and chemical processing industries.

1.Computed Radiography

In contrast to conventional radiography, computed radiography (CR) employs a phosphor imaging plate to replace film. This method is faster than film radiography, but it is slower than direct radiography. In comparison to direct radiography, CR necessitates several different stages.

A component's picture is captured indirectly on a phosphor plate and then transformed into a digital signal that can be shown on a computer monitor. The image quality is adequate, but it can be enhanced with the right equipment and procedures (e.g., adjusting contrast, brightness, etc., without compromising integrity). It's crucial to understand how tools like contrast adjustment affect the image. It's also essential to ensure that minor flaws aren't disguised following changes

2. Direct Radiography

Direct radiography (DR) is a type of digital radiography that is quite similar to computed radiography. The main distinction is in the method of photographing. A flat panel detector is used in DR to take direct pictures and display them on a computer screen. This technology is more expensive than computed radiography, despite being faster and producing higher-quality images.

3. Real-Time Radiography

Real-time radiography (RTR) is a type of digital radiography that occurs in real-time, as the name implies. Through an item, RTR emits radiation. These beams subsequently engage with a phosphor screen or a flat panel detector with microelectronic sensors. The panel's interaction with the radiation results in a digital image that can be viewed and evaluated in real-time.

More radiation reaching the screen results in brighter spots in the image. This refers to the component's thinner or less dense part. On the other hand, darker spots indicate where the component is thicker since less radiation interacts with the screen.

RTR has various advantages and the ability to make photos available more quickly and analyze them in real-time. Digital photographs, for example, do not require physical storage space, making them easier to keep, transfer, and archive than films.

This strategy, on the other hand, has several drawbacks. RTR has a lesser contrast sensitivity and worse image resolution than conventional radiography. Uneven lighting, poor sharpness, low resolution, and noise are common problems with RTR images. These variables have a significant impact on image quality.

4.Computed Tomography

CT is a technology that captures hundreds to thousands of 2D radiographic images and superimposes them to form a 3D X-ray image, depending on the size of the component.

CT can be accomplished in two methods in an industrial context. The component to be inspected remains stationary in one technique while the radiation source and X-ray detector spin around it. For large components, this method is more likely to be employed. The second method involves keeping the radiation source and X-ray detector stationary while rotating the component 360 degrees. The second procedure is more useful when the component is small or has a complex geometry.

Although this technology is expensive, contemporary, and requires a large amount of data storage, CT provides highly accurate images, is repeatable and reproducible, and minimizes human error.

Advantages of Radiographic Testing

The main benefits of radiographic testing are as follows:

  • Inspection of assembled components is straightforward.
  • Minimal surface preparation is required.
  • Flaws on and beneath the surface can be detected.
  • Internal flaws in complicated items/structures can be easily verified.
  • Detect and measure internal defects automatically.
  • The sample's dimensions and angles can be measured without sectioning.
  • In lieu of golden joints, radiographic testing is one of the best NDT procedures.
  • It can be used with numerous materials.

Disadvantages of Radiographic Testing

The following are the primary drawbacks of radiographic testing:

  • Extremely dangerous; extreme caution is required.
  • A high level of expertise and experience is necessary.
  • Expensive affair.
  • Take your time.
  • Access to the component from both sides is necessary.

Applications of radiography testing

Some of the Applications of radiography testing are in the following industries;

  • Aerospace industries
  • Automotive industries
  • Manufacturing industries
  • Marine industries
  • Military defence
  • Offshore industries
  • Petrochem industries
  • Power-gen industries
  • Transport industries
  • Waste Management

Acceptance criteria for Radiographic Testing

For process piping: The radiographic testing acceptance criteria shall be as per table 341.3.2 A of ASME B 31.3 for normal fluid service, along with the exception of piping class E.

For structural steel: The non-tubular structure acceptance criteria shall be in as per the requirement section 6.12.1 of AWS D1.1, and for tubular joints, section 6.12.3 of AWS D1.1

FAQs

How Is Radiographic Sensitivity Calculated?

The sensitivity is determined by the diameter of the smallest hole seen on the radiograph, which is computed as hole diameter divided by component thickness reported as a percentage. The sensitivity assessed with a wire IQI differs from the sensitivity evaluated with a step wedge IQI.

Why Is Radiography Test Required?

Radiographic testing creates a permanent record in the form of a radiograph, which is a very sensitive representation of the material's internal structure. The thickness and density of an object determine how much energy it absorbs. Energy not absorbed by the item causes exposure to the radiography film.

What Is The Process Of Radiography?

An x-ray beam is made to pass through the body during a radiography operation. The interior structure absorbs or scatters a portion of the x-rays, leaving the remaining x-ray pattern to be delivered to the detector and recorded for subsequent review.

What Is RT Test In Boiler?

RT - Radiographic Testing is a non-destructive examination (NDE) technique that involves viewing the internal structure of a component using x-rays or gamma rays.

Which Rays Are Used In Radiography Test?

A beam of gamma rays OR x-rays is directed at the item being evaluated in industrial radiography. The beam on the item's other side is aligned with a detector. The detector records gamma rays or X-rays that pass through the substance. Fewer x-rays or gamma rays can flow through a thicker substance.

What Is Radiographic Testing In Welding?

Radiographic Testing (RT) — this type of weld testing uses X-rays from an X-ray tube or gamma rays from a radioactive isotope to produce X-rays. Weld radiographic inspection follows the same basic principles as medical radiography.

Conclusion

In this article, we have tried to cover all the aspects of radiographic testing.  From the benefits to advantages/ disadvantages, this article on radiographic testing has it all. 

Got any queries related to radiographic testing? Drop them in the comments section and let the One Stop NDT team take care of it all



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