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Weld inspection is an important field of x-ray inspection. For example, in the production of cylinders, defects such as porosity, inclusion, crack, non-fusion, and non-penetration in the weld of cylinder do not only affect the quality of the cylinder produced, it also poses a huge security risk.
X-ray non-destructive testing equipment can be very convenient for cylinder testing and real-time imaging, detecting many defects at a glance. The on-line x-ray testing equipment for steel cylinders can be connected with the production line of the manufacturer. The fully automatic loading and unloading manipulator is adopted to reduce the labor cost and realize the integrated operation of production, testing, and judging, thus greatly improving the production efficiency.
With high resolution, high definition image quality, automatic defect identification, automatic judgment function, the whole system can realize unmanned operation and 100% on-line detection of the cylinder.
All welds are for specific purposes. They need to meet the required standards and specifications. That’s why they are assessed to confirm their quality. This process is known as x ray weld inspection. There are several methods to inspect welds, but digital x-ray systems give the best and most reliable results.
Every welding job needs to be inspected for its quality and strength. Stress, fatigue, and pressure can weaken welds overtime. So, it is important to check if a welding project can withstand the pressure of usage for several years without giving in. Also, welds need to be smooth and tidy for aesthetics and visual appeal. During x ray inspection, many features of a weld will be evaluated. Some aspects of inspection focus on weld sizes, while others are for weld discontinuities/imperfections. In other words, welds are assessed against the stipulated codes and standards required by the intended application of the welds. Methods used for welding inspection are:
Flaws and defects of a weld are the discontinuities that do not meet the requirements of the intended application of the weld. These flaws fall into the following three categories:
· General welding discontinuities
· Discontinuities in TIG welds
· Discontinuities in gas metal arc welds
the main purpose of an X-ray inspection is to detect flaws or discontinuities in welds and correct them. Weld inspection is the quality assurance aspect of welding. Without a proper inspection, there could be welding failure and other problems in the future. The size of the weld will also be inspected. To summarize it all, we need x-ray inspection for welds to check whether the welds meet all the required specifications, codes, and standards.
Also, safety relevant welds must be compliant to international standards. Flaws in them could lead to injuries, loss of lives, or destruction of properties. So, they have to be tested. A good example is the tanks and pipes used in the oil and gas industry. Pipes are buried under the ground for oil. If they don’t meet the required standards, they could get rusty and start leaking. Do you know how much revenue will be lost if an oil pipe leaks? It would be a colossal loss. That’s why there should be a thorough pipe weld inspection.
The Advantage of Digital X-ray Systems for Weld Inspection are:
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As everyone knows, welding is the most common method to fuse metal parts permanently. This old age practice is followed in more than half of the products manufactured across the world. You can’t miss this welding process, as they are in everything starting from buildings, bridges, highways to automobiles, ships, and aeroplanes.
Not all the welded joints are as durable as they should be. Few welds have defects and discontinuities that can lead to failure during the manufacturing step. As welding is employed in many products and structures, it’s mandatory to ensure their quality. Every welded product should meet its respective standards and codes in terms of quality, reliability, and strength. The manufacturers should consider these welding discontinuities seriously, else the time, energy, and energy they put in making weld may go completely useless.
Is there any way for the welding professionals to ensure that the automobiles and skyscrapers they manufacture are 100% safe for the public use? This is where quality assurance methods such as destructive and nondestructive testing help to inspect and assess the welded structures for discontinuities without destroying their original properties. Radiography is the more common method of nondestructive testing.
The occurrence of flaws or interruptions in the mechanical, physical, or metallurgical properties of a weld is called discontinuities. The extent or the count of the discontinuities for a given product is dependent on the standards of the product. For example, a greater number of defects can be permissible for a welded gate while compared to an aeroplane. It is because the aeroplane is comparatively subjected to more critical use. More number of lives could be lost if the welding pattern in an aeroplane fails.
There are varied discontinuities in welds such as:
Let us discuss the six most common welding discontinuities, along with their potential causes. If these discontinuities exceed the product’s standards, they are considered as defects.
Porosity arises if the gas gets entrapped in the weld pool, creating permanent bubbles as the metal cools from a liquid state to a solid. This extensive porosity can lead to a loss of weld strength.
Inclusions arise if slag, oxides, or other nonmetallic materials get stuck between the weld and the base metal, between the weld beads, or in the weld metal. The physical integrity of the weld can get easily compromised due to the presence of inclusions.
If the weld does not enter the joint well enough to attain a complete fusion of these metals, it is considered as an inadequate joint penetration. This discontinuity can turn out to be a defect if it acts as a source of stress in the weld that can lead to weakness and failure.
Incomplete fusion can take place in two ways: lack of sidewall fusion and interpass cold lap.
Lack of sidewall fusion where the weld metal and joint face fuse improperly.
Interpass cold lap where the previously deposited weld metal and the filler metal fuse inadequately.
If the arc strikes parts other than the joint, it liquefies the metal and causes small, confined discontinuities in the surface. This step can be the initial point for cracking, weakness, and failure.
Overlap refers to the weld deposits that flow over the exterior base metal as they are bigger than the specified joint design. These overlaps can prevent metals from fusion.
If the product has more discontinuities than its code of standards permits, it is deemed as defective and unfit for usage. Is there any way to make out if a product crosses the line from having discontinuities to being defective? There is something called tolerance measurement. The limit of tolerance determines whether the product is ideal, or just fit for use in spite of its discontinuities. Other factors such as the location, type, and size of the discontinuity can determine the quality of the product.
Welding is a method used to connect two metals during the manufacturing step of industrial products. Here, nondestructive testing (NDT) is mandatory to check whether the weld fulfils international quality standards such as ISO, ASME, EN-17636, and many others. These standards are applicable for pipes as well as boilers or tanks used in the oil and gas industry. Additionally, the aerospace industry complies with the above quality standards.
There are four types of nondestructive testing (NDT) to check the quality of welding:
1. Leak Testing (LT) – LT reveals metal surface damages including cracks, leaks, hairline, or weakness on the surface of the metals. Though there are varied examination methods, they work by covering the object with a substance and checking if that substance infiltrates the object. Welders use liquids, gases, or soap bubbles to carry out this test so that they will not harm the object. To detect if there is any defect, the technician will take images of the object to check if the substance has disseminated to the internal part. If there is no issue in its physical structure, the substance will remain above the object’s surface.
2. Magnetic Particle Testing (MT) – MT highlights the breaks in the surface of magnetic metals such as nickel, cobalt, and iron. By dusting the object with iron particles, it is possible to determine the integrity of its surface. In case of any imperfection, these iron particles get attracted to the portion, giving a clear visible indication of the problem. Hence, it is easier for the welders to detect the cause and solution to this issue.
3. Radiographic Testing (RT) – RT detects the presence of flaws and cracks in the welds. By exposing the metal object like storage containers, piping, or pressure vessels to either X-rays or gamma rays, they penetrate the internal part of the test object. Defects if any can be shown in the film according to the varied absorption in radiation.
4. Ultrasonic Testing (UT) – UT is a stress test that sends higher frequency sound waves from a transducer through a metal item for detecting its integrity. If there are any changes in the sound waves while passing through the object, it may reveal flaws like bubbles or fractures inside the object. On the other hand, UT can also measure the thickness of the object.
Remember that not all the products are ideally constructed, and it’s not the fault of the welder. Metals have intrinsic defects that are mostly invisible due to their small size on the metal’s surface. Hence, welders are recommended to perform nondestructive testing. Whatever we use should for any reason be reliable and safe. It’s not acceptable to have issues or accident due to a defect.
Radiographic testing (RT) can inspect welded joints that can be accessed from two sides, with the exclusion of double-wall signal image techniques on several pipes. Though this NDT method is slow and expensive, it can detect cracks, voids, inclusions, and porosity in weld interiors. RT involves the use of gamma rays or X-rays. Gamma rays are produced by a radioactive isotope whereas, X-rays are produced by an X-ray tube.
WATER COOLED X-RAY TUBE
Step 1: A radioactive isotope produces X-rays or gamma rays.
Step 2: This radiation is passed through the welding material onto the photographic film.
Step 3: An image of the inner structure of the welding object is formed in the film.
Step 4: The darker areas of the image reflect thinner areas of the test object. They suggest discontinuities such as porosity or cracking, the common welding issues. Similarly, the lighter areas of the film show high-density inclusions, like tungsten.
Step 5: The trained radiographic interpreters evaluate the films and identify the weld discontinuities by the shape and differences of its dark and light shades.
Radiography based nondestructive testing involves the use of X-rays produced by an X-ray tube, or gamma rays by a radioactive isotope.
The working principle of radiographic inspection of welds is similar to the medical radiography. The penetrating rays are passed through a test object, such as a weld, to create an image onto a photographic film. The resulting image shows the test object’s internal structure. The quantity of energy absorbed by the test object depends on its density and thickness. The non-absorbed energy by the test object will lead to the exposure of the radiographic film. After developing the films, these areas will remain darker. But the areas of the film subjected to less energy will remain lighter. Hence, the areas of the test object where there is a difference in thickness due to discontinuities like cracks or porosity will appear as darker outlines on the film. Low-density inclusions like slag will appear as dark areas on the film while high-density inclusions like tungsten will appear as light areas. All these discontinuities are assessed by viewing shapes and differences in the density of the processed film.
Advantages of Radiographic Testing
Disadvantages of Radiographic Testing
RT must be performed only by a qualified radiographic interpreter. Even a single false interpretation may prove costly by affecting the productivity of the products.
There are two types of radiography: Conventional and Digital Radiography.
Conventional Film Radiography
Conventional radiography uses a sensitive film that reacts with the emitted rays to capture an image of the component to be tested. This image can then be checked for the presence of any damage or flaw. The limitation of this technique is that the films can be used only once. It will take a long time to process and interpret.
Digital radiography doesn’t require a film, unlike conventional radiography. Here, it uses a digital detector to show radiographic images on a computer screen immediately. The exposure time is comparatively shorter, and it is easier to interpret the images more quickly. Moreover, the digital images are of higher quality compared to the conventional radiographic images. This technology is used to identify foreign objects in a system, flaws in a material, inspect weld repairs, and corrosion under insulation.
The four commonly used digital radiography techniques in the chemical processing, as well as oil & gas industries, include direct radiography, computed radiography, real-time radiography, and computed tomography.
Computed radiography (CR) uses a phosphor imaging plate instead of a film in conventional radiography techniques. This method is quicker than conventional film radiography yet slower than direct radiography. CR involves extra steps compared to direct radiography. It indirectly captures the image of the test object on a phosphor plate and converts it into a digital signal which can be visualized on a computer monitor. The quality of the final image is fair but can be improved by adjusting the brightness, contrast, etc. using the right tools or techniques without compromising its integrity. It is mandatory to be aware of how adjustments can make varied effects on the final image. Proper care should be taken so that the minor defects should not get hidden even after making the necessary enhancements.
Direct Radiography (DR) is similar to the computed radiography. But the major key difference remains on how the image can be captured. In direct radiography, a flat panel detector is used to capture the image directly and display it on a computer screen. Though this technique is quick and produces high-quality images, it is costlier than computed radiography.
As the name suggests, Real-time radiography (RTR) is a form of digital radiography that takes place in real-time. RTR works by emitting rays through the test object. These rays then react with either a flat panel detector containing micro-electronic sensors or a special phosphor screen. The reaction between the radiation and the panel forms a digital image that can be viewed and analyzed in real-time.
The brighter areas on the image occur due to the high radiation level that comes in contact with the screen. This corresponds to the thinner or less dense section of the test object. On the other hand, darker areas due to the less radiation level that comes in contact with the screen indicate the thicker portion of the component. Apart from making the images quickly available with prompt analysis in real-time, RTR has few advantages. The digital images don’t require any physical storage space and hence it is easier to transfer, store, and archive compared to the film radiography.
RTR has a few disadvantages. Compared to conventional radiography, it has a low contrast sensitivity with limited image resolution. The resultant images often have limited resolution, uneven illumination, lack of sharpness, as well as noise which can make a huge impact on the results.
Computed tomography (CT) is a form of digital radiography that takes hundreds to thousands of scans via 2D radiography depending on the component size and superimposes them to generate a 3D radiographic image.
In an industrial scenario, CT can be performed in two ways. In the first method, the test object to be inspected remains still whereas the radiation source and the detector rotate around the test object. This technique is followed usually for large components. In the second method, the radiation source and the detector remain stationary whereas the test object is rotated about 360 degrees. This technique is useful for smaller components or the ones that have a complex geometry.
Though this technology is expensive, timely, and requires more data storage, CT is reproducible, repeatable, and delivers highly accurate images with minimal human error.
The radiographic testing of welded components can be performed with one of two types of devices. There are two methods of radiographic testing to visualize welds and welding defects such as X-ray RT and Gamma rays RT, based on the radiation source.
The first method of radiographic testing uses X-rays produced by an X-ray tube that can accelerate electrons or through the K-shell-emission technique which helps in manipulating the electrons in their atomic shells. The K-shell emission device emits X-rays of high intensity, compared to the rays produced by the X-ray tubes.
The second method of radiographic testing uses gamma rays produced due to atomic radioactive decay. Similar to X-rays, gamma rays also come under electromagnetic radiation.
The radiographic weld testing has become mandatory in the manufacturing sector to validate the quality of assembled metal components. The inspection methods to check the welds vary according to the application and industries. However, before selecting the inspection method, it is recommended to consider the following points:
Precision and accuracy are mandatory in any inspection method. Accuracy refers to the proximity of the inspection results to the ideal value. Alternatively, precision refers to the reproducibility of the test results. Hence, it is recommended to calibrate the testing instruments regularly to a known standard.
For the assembled metal components such as joints, pipes, and bends, companies employ the combination of NDT methods and not just one. Therefore, it is possible to ensure the comprehensiveness of inspection and the consistency of test results.
Several sectors including aerospace, automotive, petroleum perform a quality check on metal structures and components before putting them into practice. Hence in addition to the X-ray testing, the manufacturers perform an ultrasonic inspection, magnetic particle inspection, and dye penetrant testing. All these methods have their strengths and weaknesses.
Every defect in a given sample requires specific inspection methods to assess the quality. For instance, it is difficult to detect planar cracks and de-laminations using X-ray testing or other radiographic methods. Hence, ultrasonic as well as acoustic-based methods are recommended to detect these types of defects.
Even the size of the surface area can determine the testing methodology to be used. Again, for instance, dye penetrant testing can rapidly inspect large surface areas at an affordable low expense.
But the weakness of this method includes exhaustive surface preparation as well as chemical handling precautions.
Before understanding the importance of an X-ray test for welded parts, you first need to know how X-ray inspection works.
All X-ray inspection devices are composed of three basic features:
X-ray imaging test works with the help of X-ray photons, which are passed through the target material kept on the operation platform. The resultant rays will be collected on the other side through a detector, which results in an image formation. Based on the differential absorption principle, the X-ray photons pass through the target object in a differential manner depending on its physical properties, such as density, atomic weight, and thickness.
Usually, heavier objects absorb more X-rays, so that they can develop into an image, whereas lighter objects are more transparent. Since different objects has unique characteristics, different amounts of X-ray photons are collected on the other end of the target object, to form a final image.
So, it is easier to view internal defects of welded parts through an X-ray image.
The below listed seven parts are required to build a basic X-ray machine for welding:
There are three types of X-ray tubes listed below:
The maintenance tips are categorized day-wise, monthly, bi-annually, and annually. Let us go through each of them in detail:
1 Daily check items
1.1. Check whether the safety induction switch found at the back door of the X-ray machine is working properly.
Method: Close both front and back doors to see whether the contact indicator of the relay is ignited. If the contact indicator light on the relays KA2(front door) and KA3(back door) is on, the safety induction switch is effective. If the indicator light is not on, the safety induction switch is considered as unacceptable.
1.2. Check whether the X-ray machine rotation axis and four-axis movement are working properly.
Method: Once when the total power is turned on, click on the software, and shake the joystick on the comfort to see whether the motion of X-axis and Y-axis is normal. Click both up and down buttons of the X-ray tube and the image detector on the software interface to check if the two axes are moving properly.
1.3. Verify if the motion axis of the X-ray machine sensors is working appropriately.
Method: This test is done to control the movement of each axis to the position of the equivalent limit sensor. When the indicator light of the sensor is switched on, the movement will halt. Check whether the computer is booting properly.
2 Monthly check items
2.1. Inspection of the X-ray machine movement mechanism
2.2. Inspection of the emergency stop switch working condition
3 Biannual check items
3.1. X-ray machine power detection
Method: First, open the back door. Check whether 24VDC and 5VDC power supplies are working properly.
3.2. Equipment guide rail on the lubricating oil for its clean appearance
Method: First, turn off the device as well as disconnect the power supply. Open the back door, lubricate each screw rod with grease, and run it over and over to lubricate while cleaning the portions of the inner wall. In the end, open the side door and wipe it with a clean cloth.
4 Annual maintenance
4.1. Check for the signs of damage on the inner side and the outer side of the machine, if any.
4.2. Check the observation window glass to find if there is any scratch.
4.3. Check the rotation pattern of the X-ray light tube, platform movement axis, as well as the detector.
4.4. Check all the fans and clean the filter properly with cotton.
5 Check X-ray image quality
Description of the problem
Analysis of the problem
The computer has a starting problem
· Loose computer power connectors
· Presence of virus can cause a system failure
· Reinsert your computer’s power plug
· Reinstall the entire system
Automatic reboot after power-up
Presence of the virus in the computer
Perform system restoration
X/Y/Z axis motors are not running properly
· Issues with the power
supply to the drive
· Loose B joints
· Drive anomalies
· Replace the power supply
· Use fasteners
· Use replacement Drive
Jarring of the rail
during the movement
· Loose couplings
· Linear guide and roller screw without any lubrication for a longer duration due to dryness
· Check couplings and tighten them.
· Lubricate the linear guides and roller screws using grease
Inadequate power supply
Change the power supply
The following parameters should be taken into consideration while choosing the right X-ray machine.
If you are planning to buy a good camera, obviously the one with a higher pixel rate, say 24MP (megapixel), is better than the one with say 15MP, right? If this is the case for photography, choosing the best qualitative X-ray machine can be even more complicated. A lot of physics along with clever software is involved. The factors that can affect image quality in the X-ray machine may include voltage, power, spot size, the field of view, the proximity of the X-ray source to the target object, as well as the detector resolution. Consider voltage as an example; a higher voltage (say 160kV) system will have greater X-ray penetration ability, compared to the lower voltage one (say 130kV). The higher voltage can unfavorably affect the image contrast and henceforth the ‘quality’. In that case, how can you determine the quality? The best practical solution is to pick several typical sample assemblies and create the X-ray system. Determining the quality of an image can be a subjective opinion. The good news is that you can very well find the internal defects in welded parts. Perhaps, this is connected more with the inspection set up rather than the technical competence of its components.
The letter ‘D’ stands for dimensions. There are three kinds of dimensions:
Remember the more details you view, the slower the examination is. That is why complex CT scans take hours to complete.
If you would like to check any missing solder balls or shorts between them, then 2D can be fine. Nevertheless, tilting will help in getting a better view if there are any components concealing the target area of interest. Hence, 3D will be used for an extensive detailed qualitative study of the target object.
Several X-ray systems allow a grade of automated inspection, like pass/fail criteria through programming sequences of inspections. This strategy helps to operate easily with repetitive inspection, thereby allowing an “in line” process if needed. Hence you need relevant skills to set it up and perform ad-hoc inspections. Nowadays in the recent X-ray machines, it is easier to interpret the final images easily with the help of varied colours. Though modern X-ray systems are easy to use, the inspector, at times, need to understand the application of all the settings like voltage and contrast settings.
Remember that the Health & Safety Executive (HSE) must be notified in advance before using an X-ray machine. There will be obligations for creating instructions, procedures for use, and involving radiation protection supervisors with advisors. The machine suppliers should provide timely advice, and perform an annual qualitative check on the system.
It is a well-known fact that there are varied types of the X-ray tube. “Open tube” types are comparatively quick, inexpensive, and easy to replace. Perhaps, you need to spend a few pounds and a couple of hours. But the tube should be replaced every 200-300 hours or so of use. In the case of ‘Closed tube’ types, they can last for many years. But they are relatively more expensive, where you will spend thousands of pounds. Hence the selection of the best one depends on how much you will be using the system.
Select the X-ray detectors with standard or High Definition flat panels. The flow of X-rays leads to the degradation of detectors over time, say around 20% after ten years. Hence, it is recommended to replace every 8 to 12 years when the machine is in use.
Never forget to check for the common system failure modes, since the similar component parts can be assembled in varied ways. Remember to replace power supplies, cables, or connectors in time.
We have the right combination of the technical knowledge with qualified service expertise to provide proper maintenance service on our every X-ray system. If you have any query about our products or services, you can immediately contact us via online chat, phone, or email, so that our professional team will solve them at once.
Uni-Xray has a team of well-experienced engineers to provide timely services for every customer, including consulting services, custom design, equipment qualification, safety inspection service, and so on.
Uni X-ray offers an exceptional range of after-sales services, such as online video instructions and installation guides for our customers to ensure that their new or existing equipment is in safe and good operating mode, with a long life cycle. Additionally, we provide prompt safety inspection with regular maintenance service as per the personalized needs of our customers. These services are also available for X-ray machines delivered by other suppliers.
Once when you share the application details to our team, we will recommend the best X-ray inspection solution for you. At times, a customized solution will be the best, where we’ll work with you to suggest the right X-ray machine that will meet all your requirements. Hence, you can contact our sales and support team to discuss our services at any time as per your convenience.
Hope you have found this detailed blog post more informative that helps you to understand all the focus areas in detail before investing in industrial X-ray inspection equipment.
Does your equipment emit excessive radiation? What methods do you use to ensure radiation safety?
Safety Radiation: Chinese and international standards are both <1uSn / h. Radiation from our equipment is much smaller than this standard. We have an environmental exemption certificate.
Our radiation control methods are:
What is the warranty period for your equipment? After the warranty period, how do you guarantee?
The equipment warranties period is one year. During the warranty period, repairs and possible parts and component changes are free.
What does your warranty cover?
The warranty covers defects in machines. It does not cover damages issues caused by damage due to handling, shipment, storage, accident, impact, abuse, or misuse.
We have bought your equipment. How can we get started? What kind of training do you offer?
We offer three training methods:
What is the image quality of your device? How do you ensure high-quality images?
The customer provides samples and takes pictures for a report. Images taken are subject to customer approval.
The operating software is in Chinese and English (switchable) with a human-computer interaction screen, easy to use.
What is the delivery time for your equipment?
For overseas customers, do you recommend shipping by sea or air?
This can be done according to the needs of customers. Shipping costs are cheap and long, while air freights are expensive but take a shorter time.
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