What is Ultrasonic testing ? How it Works?

 

Ultrasonic testing (UT) comprises a range of Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood, and composites, albeit with less resolution. non-destructive testing (NDT) techniques that send ultrasonic waves through an object or material. Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood, and composites, albeit with less resolution. Ultrasonic Testing (UT) uses High-frequency sound waves to conduct examinations and make measurements.

Ultrasonic testing can be performed using two basic methods – pulse-echo and through-transmission. A typical UT inspection system consists of several functional units, such as the pulser/receiver, transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high-frequency ultrasonic energy. Most UT inspection applications use short pulse waves with frequencies ranging from 0.1-15 MHz, although frequencies up to 50 MHz can be used. 

With pulse-echo testing, the same transducer emits and receives the sound wave energy. This method uses echo signals at an interface, such as the back of the object or an imperfection, to reflect the waves back to the probe. Through-transmission testing uses an emitter to send the ultrasound waves from one surface and a separate receiver to receive the sound energy that has reached the opposite side of the object. Oil and gas courses in Kerala cover a more detailed part of their syllabus.

Today’s most advanced ultrasonic testing instruments have a slight resemblance to those that came before. The principles are the same but calibration stabilization, measurement precision, imaging, and data sharing have advanced leaps and bounds. NDT Institute in Kerala provides the best training for students who are interested in this field.

Some of the advantages of ultrasonic inspection that are often cited include:

• It is sensitive to both surface and subsurface discontinuities.
• High penetration power, allowing for flaw detection deep within a part
• Only single-sided access is needed when the pulse-echo technique is used.
• High sensitivity, allowing for the detection of very small flaws
• Able to estimate size, shape, orientation, and nature of defects
• Able to estimate alloy structures of components with differing acoustic properties

As with all NDT methods, the ultrasonic inspection also has its limitations, which include:

• The surface must be accessible to transmit ultrasound
• Objects that are rough, irregularly shaped, very small or thin, or not homogeneous are difficult to inspect
• UT may have reduced sensitivity for volumetric flaws, particularly metal inclusions, than radiographic testing
• It normally requires a coupling medium to promote the transfer of sound energy into the test specimen.

How does it Work?

In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant (such as oil) or by water, as in immersion testing. This couplant is required to efficiently transmit the sound energy from the transducer into the part, however, This couplant is not required when performing tests with non-contact techniques such as electromagnetic acoustic transducer (EMAT) or by laser excitation.

Attributes of a Welding Inspector

To perform duties in the most effective manner, the welding inspector should be in good physical condition. Since the primary job involves visual inspection, it is obvious that the welding inspector should have good vision, whether natural or corrected. For instance, if colour or contrast is important to the inspection process being employed (liquid penetrant, magnetic particle, or colour-coded parts) then an individual should be tested for the ability to detect those colours. The AWS Certified Welding Inspector (CWI) program requires a minimum visual acuity and the ability to perceive certain colours, as determined through actual testing. Since welds could be located anywhere on a very large structure, the inspector must be capable of going to the weld at any location in order to make an evaluation. The inspector must comply with safety regulations when performing these duties. The ability of the welding inspector to get to work may be reduced if the inspection is not performed immediately after welding. For example, such aids for the welder as Ladders and scaffolding may be removed, making access impossible or dangerous. Within safety guidelines, the welding inspector should not be prevented from performing a proper inspection because of a physical condition. 

While there may be no specific level of education and training required for welding inspectors, the job may involve interpretation of results. Therefore, an individual must have at least some level of technical knowledge to perform well as an inspector. So as to perform welding inspection, the individuals must make judgments based on visual observations of physical characteristics of welds and weldments and their comparison with drawings or standards. If an individual is unable to understand some written requirements, it will be difficult to make a judgment as to a weld’s acceptability in accordance with that standard. There is more to evaluation than just reading the specifications. Once read, the inspector must interpret its meaning. Even then, some requirement of code or specification may appear very clear and straightforward when initially read; however, comparison of this written requirement with an existing physical condition may still prove to be extremely difficult. Technical ability is also a must to effectively express ideas or inspection findings. In addition, once an inspection has been performed, the inspector must be capable of describing the methods used and subsequent results with sufficient accuracy to adequately communicate to others familiar with the work being performed.

Another quality which the welding inspector should develop is an ability to understand and apply the various documents describing weld requirements. These include, in part: drawings, codes, and specifications. In fact, these documents literally constitute the rules under which the welding inspector must perform. They also state the requirements by which the welding inspector will judge the weld quality. Obviously, such documents must be reviewed prior to the start of any work, because the welding inspector should be aware of the job requirements before any production.

Future trends in welding

When attempting to forecast future trends in welding technology, it is convenient to differentiate between traditional materials and advanced materials. The properties and functions of traditional materials are well known; therefore, improved performance can be best achieved by reducing the cost increasing the quality of the joining process and through automation and enhanced quality control procedures. The quality of the material depends on the industry considered. Welding structural aluminium is not new in the aerospace industry, yet, it is an advanced application in automotive production. The change to a spaceframe automobile design will remove the structural redundancy afforded by current designs; thus, new joining processes will be required to overcome the limited quality of resistance welding. Brazing as well as laser, or conventional arc welding processes are to handle the fabrication requirements of new automobile structural components. The cost of many advanced materials is so high, and their properties so specialized, that they will only be used where they are essential. Consequently, products will contain more joints, a greater number of which will join dissimilar materials. Few traditional joining processes are practical in this situation; new part designs and joining processes will be required. Adhesives can always be used, but joint properties often place severe limitations on part design or function. Brazing is considered, especially to join ceramics and metal-matrix composites. Low-temperature metallic bonding using transient liquid- phase technology will probably be extended to many more alloy systems. In the brazing process, a component of the brazing material or solder diffuses into the base material resulting in isothermal solidification of the filler material. For every new material developed, joining processes must be restudied or developed to use the material effectively. Use of new materials will be limited by the capability to exploit the joining processes, rather than by the ability to design or produce such materials. The present direction of improvement of welded structures is a decrease in their weight and energy requirement in fabrication, and improvement of consistency and endurance. High strength low-alloy (HSLA) steels are the Centre of application that widening the advances in this direction. The fabrication of structures from HSLA steels without preheating is one of the main problems in arc welding. The results of researches into the problem of hydrogen welded joints have been generalized. The main tendencies of the optimization of properties of HSLA steels are i) the decrease in the content of alloying elements, ii) an increase in the number of combinations of microalloying elements, iii) a decrease in the content of carbon, hydrogen, nitrogen, oxygen, residual elements, sulphur and phosphorus, iv) an improvement of the homogeneity and the level of mechanical properties and improvement of the formability, weldability and toughness of welded joints.

Attributes of a Welding Inspector

There are many types of welding inspectors, depending upon technical requirements for the particular fabrication process or processes. These include destructive testing specialists, nondestructive examination specialists, code inspectors, military inspectors, and owner’s representative inspectors. All of these may consider themselves welding inspectors simply because they do inspect welds. The fact that welding inspectors work in many different industries performing so many quality-related tasks makes it difficult to clearly and concisely describe what a welding inspector is and how that job function is specifically performed. One fundamental complication is that an individual may perform many functions or only a single function. For example, it is common to perform numerous aspects of welding quality control (e.g., welding procedure qualification, welder qualification, in-process and final visual examination, destructive testing, and final nondestructive examination). However, it is also common for an individual involved in welding inspection to perform only one of those tasks (e.g., a non-destructive examination specialist).To Perform duties effectively, the welding inspector must be in good physical condition. Since the primary job involves visual inspection, it is obvious that the welding inspector should have good vision, whether natural or corrected. For instance, if colour or contrast is important to the inspection process being employed (liquid penetrant, magnetic particle, or colour coded parts) then an individual should be tested for the ability to detect those colours. The AWS Certified Welding Inspector (CWI) program requires a minimum 20/40 visual acuity and the ability to perceive certain colours as determined through actual testing. Physical conditioning also involves the size of some welded structures. Since welds could be located anywhere on a very large structure, the inspector must be capable of going to the weld at any location to make an evaluation. The inspector must comply with safety regulations when performing these duties. The ability of the welding inspector to get to the work may be reduced if the inspection is not performed immediately after welding. For example, such aids for the welder as ladders and scaffolding may be removed, making access impossible or dangerous. Within safety guidelines, the welding inspector should not be prevented from performing a proper inspection because of a physical condition. Technical ability is also necessary for the welding inspector to express ideas or inspection findings effectively. Also, once an inspection has been performed, the inspector must be capable of describing the methods used and subsequent results with sufficient accuracy to adequately communicate to others familiar with the work being performed.

Welding process

Choosing the right machine is just as important as a technique in welding. The type of welding you purchase should be suited to the specific functions you need it for because there is no such thing as a “one size fits all” welding machine. Weighing the pros and cons of the different welding processes and the projects you are most likely going to use your welder for, is essential to making your selection. People think that there is no single welding process suitable for all welding situations. What’s important is understanding which process is best suited to your application. The most common welding processes include:

 Metal Inert Gas (MIG),
 Tungsten Inert Gas (TIG),
 Flux-Cored Arc Welding ((FCAW),
 Manual Metal Arc Welding (MMAW) often referred to as ‘Stick’ welding;

Each of which has its own set of benefits and limitations. As such there are several factors that
must be considered to determine which welding machine will be the most appropriate for your needs. These include:

 Type of material being welded
 Thickness of material
 Required weld metallurgy
 Welding position
 Available power supply, for example, single-phase or three-phase
 Amount of available current
 Time requirements

Arc welding is a specialized type of welding that uses electricity to join two metal components and
includes sub-types such as gas metal arc welding and plasma arc welding. The reason for its growing popularity is the rising awareness regarding its inherent advantages. For example, due to high heat concentration, arc welding speeds up the welding process, saving both time and energy. This also leads to fewer distortions in the finished product. Furthermore, this type of welding does not entail any extra costs and does not swell the cost of production. Lastly, arc welding has a higher safety quotient as it produces less smoke, which is usually hazardous to human health. Thus, these advantages of this welding process will augur well for the market and its development during the forecast period.

Attributes of a welding inspector

To perform duties in the most effective manner, the welding inspector should be in good physical condition. Since the primary job involves visual inspection, it is obvious that the welding inspector should have good vision, whether natural or corrected. For instance, if colour or contrast is important to the inspection process being employed (liquid penetrant, magnetic particle, or colour coded parts) then an individual should be tested for the ability to detect those colours. The AWS Certified Welding Inspector (CWI) program requires a minimum 20/40 visual acuity and the ability to perceive certain colours, as determined through actual testing. Another aspect of physical conditioning involves the size of some welded structures. Since welds could be located anywhere on a very large structure, the inspector must be capable of going to the weld at any location in order to make an evaluation. The inspector must comply with safety regulations when performing these duties. The ability of the welding inspector to get to the work may be reduced if the inspection is not performed immediately after welding. For example, such aids for the welder. As ladders and scaffolding may be removed, making access impossible or dangerous. Within safety guidelines, the welding inspector should not be prevented from performing a proper inspection because of a physical condition. While there may be no specific level of education and training required for welding inspectors, the job may involve interpretation of results. Therefore, an individual must have at least some level of technical knowledge to perform well as an inspector. In order to perform welding inspection, the individual will continually be asked to make judgments based on visual observations of physical characteristics of welds and weldments and their comparison with drawings or standards. If an individual is unable to understand some written requirement, it will be difficult to make a judgment as to a weld’s acceptability in accordance with that standard. There is more to evaluation than just reading the specifications. Once read, the inspector must interpret its meaning. Even then, some requirement of code or specification may appear very clear and straightforward when initially read; however, comparison of this written requirement with an existing physical the condition may still prove to be extremely difficult. Technical ability is also necessary in order for the welding inspector to effectively express ideas or inspection findings. In addition, once an inspection has been performed, the inspector must be capable of describing the methods used and subsequent results with sufficient accuracy to adequately communicate to others familiar with the work being performed.

Gas in Arc welding

Gases used in arc welding processes are the shielding gases. Shielding gases used in arc welding are argon, helium, and carbon dioxide. The gases have a remarkable effect on the overall performance of the welding system. The main function of these gases is to protect the weld pool from adverse reactions with atmospheric gases. Oxygen, nitrogen and water vapour present in ambient air can cause weld contamination. Weld shielding, always involves removal of potentially reactive gases from the vicinity of the weld, preventing the detrimental effects on the molten metal of the surrounding atmosphere. Shielding gases also stabilizes the arc and enhances the metal transfer mode in arc welding processes. The shielding gas interacts with the base and filler metal and changes basic mechanical properties of the weld area, such as strength, toughness, hardness and corrosion resistance. Shielding gases moreover have important effects on the formation of the weld bead and the penetration pattern. The usage of shielding gases can lead to different penetration and weld bead profiles. However, apart from all these important effects, the gases have to be handled with care. These gases that stored in compressed gas cylinders are potentially hazardous because of the possibility of a sudden release of gas by removal or breaking off of the valve. High-pressure gas escaping from such a cylinder causes it to be like a rocket which may smash into people and properties. In storage, transport and operation of compressed gas cylinders it is imperative to observe the following rules: Whether in use or stored, the cylinders should be kept vertical and secured so as to avoid falling by means of chains and clamps. To open cylinder valves hammers and wrenches must not be used. The proper trolley should be used for moving cylinders from one point to another in the workshop. The cylinder should never be carried on shoulders because in case it falls it can not only injure the person but may also explode. Compressed gas should not be exposed to sunlight or heat as this may lead to an increase in the pressure leading to an explosion. The temperature of the gas cylinder should not be allowed to exceed 54 oC. Cylinder valve must be opened gradually with proper care otherwise it may damage the regulator diaphragm. Cylinders must have caps during storage and transport.