Inspection methods refer to a variety of techniques utilized to detect, identify and measure defects in materials. These methods are also used to assess the components or entirety of these material properties.
As the term ‘advanced’ implies, advanced inspection methods are emerging technologies and, as a result, are more complicated. Due to the complicated nature of these methods, the need for well-trained and highly experienced experts becomes necessary.
The reason for shutdown times in operations is because the material being tested or its part is destroyed or damaged during the inspection process. These shutdown times can be effectively reduced by employing advanced inspection methods, as the purpose of these methods is to inspect and test materials safely and stably, such that won’t necessitate shutting down plant operations or wreak damage to the material.
These advanced inspection methods include:
1. Digital Radiography (DR)
In this method, x-rays or gamma rays are employed to view the internal structure of the material property. It is a non-destructive method often used to inspect machinery and detect flaws. So, how does it work?
In conventional radiography, a film that reacts to radiation being emitted is used to capture the image of the component being tested. In digital radiography, a digital detector rather than a film is used to display images on a computer screen. This is usually done within a short period for faster interpretation of images.
There are some common techniques used in techniques which are Real-Time Radiography (RTR), Computed Radiography (CR), Direct Radiography (DR), and Computed Tomography (CR). These are the most common digital radiography techniques utilized in industries such as the chemical processing industry and oil & gas industry.
The Digital Radiography method is a very efficient one as it produces digital images that are of much higher quality, unlike conventional radiographic images.
Due to its ability to capture high-quality images, this method is used to inspect for corrosion under insulation, identify flaws in material properties, examine weld repairs, identify foreign entities in a system, etc. This method is very effective in exposing abnormalities, flaws, or aspects of a material that can be hard to detect with the naked eye.
2. Eddy Current Testing (ECT)
Eddy Current Testing Inspection Method is one of the various electromagnetic testing methods that make use of electromagnetic induction or measurement of electrical currents in a magnetic field around an object. It works to evaluate the material property, locate and characterize surface level and sub-surface level defects.
Here, interruptions caused by defects or flaws are identified by examining the flow of electrical (eddy) in the magnetic field that encompasses the conductive material.
The Eddy Current Testing method is very efficient as it makes use of light and portable equipment, provides immediate feedback, and has a quick preparation time as the surfaces do not require a lot of pre-cleaning. This method is also able to detect cracks as small as 0.5mm, which can be at a surface level, below the surface, and defects through several layers.
The Eddy Current Testing is a non-destructive inspection method used to detect flaws and imperfections, measure the thickness and density of a material, identify the material, and a variety of purposes.
3. Ultrasonic Testing (UT)
Generally speaking, Ultrasonic Testing Inspection uses sound waves to detect flaws or defects in a material. Ultrasonic Testing is a group of techniques that use high-frequency sound waves to examine, characterize and locate the internal structure and imperfections in the material property. We say high-frequency sound waves because the frequencies employed in ultrasonic testing exceed human hearing. They are very much higher than the limit of human hearing.
Ultrasonic Testing works by emitting sound waves into a material property and these sound waves are measured. By measuring the ultrasound, the properties and flaws of the material can be identified. It uses sound energy moving through the material specimen to evaluate the internal structure of the material and detect flaws.
The sound waves passing through the object can be displayed on a Liquid Crystal Display (LCD) or Cathode Ray Tube (CRT). They appear as data nodes on a computer test program or vertical signals on the CRT screen.
Ultrasonic Testing can be done either through Immersion Testing where the part of the specimen under examination is completely immersed in a liquid couplant such as water, oil, or any other suitable liquid; or Contact Testing where the component being examined is coupled with a glutinous material that can be either liquid or paste.
There are two methods of receiving sound waves to carry out Ultrasonic inspection and Testing; the first is Reflection, also known as Pulse-Echo, and the second method is Attenuation.
- Pulse-Echo mode: Here the transducer sends sound waves which reflect on the device. This ultrasound is received by the transducer as pulsed waves. The sound waves reflect by hitting an interface such as a foreign object within the material or by bouncing off the back wall of the material.
- Attenuation: also known as Through-Transmission mode. As the name implies, a transmitter sends sound waves through one surface of the material. After moving through the object, a receiver detects the amount of sound that has reached it. The presence of flaws and other internal conditions of the object are revealed as they reduce the amount of sound being transmitted.
The Ultrasonic Testing Inspection method is completely undestructive and is more accurate in determining the thickness of the material and depth of internal flaws, unlike other non-destructive methods. It poses little to no hazard to the object, plant operations, or personnel carrying out an inspection.
Advanced inspection methods are not limited to the ones mentioned above. They also include several methods such as Leak Testing (LT), Acoustic Emission (AE), Internal Rotating Inspection Systems (IRIS), Phased Array (PAUT), Ground Penetrating Radar (PAUT), etc.
These advanced inspection methods are cost-effective in the sense that just a part or component of the material or object is needed for testing. This allows for the survival of the material, thereby saving time, money, and resources.
These methods are quite predictable, highly accurate, and harmless to people and plant operations, which makes them very safe, thereby reducing shutdown times effectively.
