Radiography Test for Welding

What Is Radiographic Testing in Welding?

Are you aware that welding can successfully fuse metal components permanently? This ancient practice is followed in most of the goods that are manufactured internationally. No one can miss the products developed by welding. They are omnipresent. You can see them in bridges, highways, buildings, airplanes, etc. 

As mentioned already, not all welds are strong enough. Some may have defects that will affect product quality. How can the manufacturers ensure that the products they manufacture are safe and reliable for the public? Here comes nondestructive testing to assess the target welds and certify their quality without changing their properties.

Moreover, the radiographic test is the most common, significant, and popular type of nondestructive testing. One can determine the hidden defects within the welds. The types of defects include porosity, slag, blowholes, cracks, oxide or flux inclusion, mismatch, lack of fusion, incomplete penetration, tungsten inclusion, etc. Let us understand its principle in detail:

In radiography testing, short wavelength electromagnetic radiations are used. Gamma rays (γ) and X-rays come under this short wavelength electromagnetic radiations. Do you wonder why these two radiations are used? Only they have high intensity with high penetrating ability. Hence, they can penetrate deeply into any target object of any thickness.

X-ray for weld

An X-ray tube is an evacuated glass tube. It consists of a tungsten anode as well as an electrically heated filament. It’s this filament that releases electrons. They finally hit on a tungsten anode. Since these high velocity electrons collide on the tungsten anode, it emits X-rays.

Next, these X-rays are passed through the test sample. The photographic film should be placed on a cassette behind the test sample. Finally, place a penetrameter (or) Image Quality Indicator IQI on the side of the radiation source along with the test sample.

After exposing the sample to the X-rays for a prescribed time, switch off the source light. Subsequently, take the film into the dark room for developing it. Only after the film development, the X-ray inspector can assess the processed film and determine the quality of the test sample.

Radiography using Gamma-rays

In gamma-ray testing, it’s the radioactive isotopes that emit gamma rays. Usually, the nucleus of the radioactive isotope will be unstable.

The commonly used radioactive isotopes for industrial radiography testing are:

•       Caesium-137 (Cs137): Half-life of 30 years
•       Iridium 192 (Ir192): Half-life of 72 days
•       Cobalt 60 (Co 60):  Half-life of 5.3 years

Here, the gamma radiation source of around 300 mg is placed inside a tungsten or lead-based alloy container having enough thickness. Only these containers with sufficient thickness can give the right protection. The gamma rays emitted from the source penetrate through the test sample. Similar to the X-ray radiographic testing, photographic film should be placed on a cassette behind the test sample. Finally, place a penetrameter (or) Image Quality Indicator IQI on the side of the radiation source along with the test sample. The exposure, film processing, and interpretation are the same as X-ray testing.

How Does Radiographic Testing Work?

Usually, destructive testing methods break the weld in order to assess its mechanical properties. However, radiographic testing is not so. It doesn’t break the target object. This radiographic assessment will keep the target object intact during the inspection. X-ray test is typically used in the industrial sector like how it is used in the medical field. In both these sectors, inspectors use electromagnetic rays to inspect the internal conformation of a target sample without removing it away.

Here’s how the radiographic testing is performed to inspect the welds:

Step 1: Once when the machine is on, the radioactive isotope will start emitting X-rays or gamma rays.

Step 2: These rays are passed through the target weld sample onto a photographic film.

Step 3: A radiographic image of the internal conformation of the target weld is formed on the photographic film.

Step 4: If the image shows darker areas, it depicts only the thin areas of the target weld. The inspector will interpret the presence of common welding defects such as porosity, cracking, etc. Similarly, if the image shows lighter areas, there may be high density inclusions like tungsten.

Step 5: It’s the radiographic inspectors who are skilled to assess the film images. Only, they can recognize weld defects by observing the variations and shape of light and dark areas in the final image.

What Are the General Advantages and Disadvantages of Radiographic Testing?

There are several pros and cons for radiographic testing:

Advantages of Radiographic Testing

Radiographic testing can successfully determine the cracks, porosities, voids, and inclusions within the target weld materials.

It is possible to assess the surface as well as subsurface defects.

The interpreter can measure the angles and dimensions of the test sample without any segmentation.

It is also possible to detect delicate changes in thickness, corrosion, flaws, and material density. 

Disadvantages of Radiographic Testing

Only a qualified, skilled, and a well experienced radiographic inspector can only interpret the radiographic findings.

One should pay attention while interpreting the test results. A wrong interpretation can restrict productivity and will prove to be costly.

What Are the Different Types of Radiographic Testing?

Radiographic testing is classified into two major types:

•       Conventional radiography
•       Digital radiography

Both these types have their respective advantages and disadvantages.

Conventional Radiography

As mentioned above, conventional radiography employs radiations and a sensitive film. It helps to capture the images of the target welds in the sensitive photographic film.

Advantages:

•       This conventional method shows defects or flaws in a target weld sample.
•       It also delivers a permanent record of the target weld quality via the film.

Disadvantages:

•       The sensitive photographic film can be used only once.
•       It consumes a lot of time to process and interpret the films.
•       Since both X-rays and gamma rays are invisible, these radiations can lead to serious health issues.

Digital Radiography

A digital approach in this case has got many variations, compared to the conventional one. Here, the computer screen is used in the place of a photographic film. Thus, the final image of the target weld’s internal structure will be displayed on a computer screen directly.

Advantages:

•       This imaging technology delivers high quality image, compared to the conventional radiography
•       The time of exposure and interpretation is very quick.

Where Is Radiographic Testing Used?

Radiographic testing has got multiple applications:

•       It can inspect the target welds and detect defects
•       Recognize corrosion if any, under insulation
•       Determine the presence of foreign substances in the target sample.

You don’t have to delay in making up your mind. Consult our fully certified Uni X-ray company to purchase the equipment for industrial radiography testing.