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.

Radiographic Testing

RT is a volumetric examination method used for examining the entire specimen rather than just the
surface. It is the historical approach to examine completed welds for surface and subsurface
discontinuities. The change in absorption of radiation by solid metal and in areas of a discontinuity is used in this method. The radiation transmitted reacts with the film, a latent image is captured, and when the film is processed (developed) creates a permanent image (radiograph) of the weld. Some methods also use electronics to create a digital image and are referred to as “filmless.” Due to the hazard of radiation, and the licensing requirements, the cost can be higher and at the same time, the number of trained personnel is limited, than with other NDE methods. An NDT examiner interprets and evaluates the radiographs for differences in absorption and transmission results. Radiographic results display is different as compared with the normal background image of the weld or part being inspected. The radiographer also makes sure that the film is exposed by the primary source of the radiation and not backscatter radiation. The NDT examiner that performs the film interpretation, evaluation and reporting should be certified as a minimum to ASNT Level II requirements. However, all personnel performing radiography are required to attend radiation safety training and comply with the applicable regulatory requirements. There are very specific requirements with regard to the quality of the produced radiograph, including the sharpness of the image, the ability to prove adequate film density in the area of interest and sensitivity to the size and type of expected flaws. Requirements listed in Article 2 include:

a. Method to determine if backscatter is present. 

b. Permanent identification, traceable to the component. 

c. Film selection in accordance with SE-1815. 

d. Designations for a hole or wire-type image quality indicators. 

e. Suggested radiographic techniques.

f. Facilities for viewing radiographs

g. Calibration (certification of source size).

The exposure and processing of a radiograph are considered acceptable when it meets the required quality features in terms of sensitivity and density. These factors are designed to ensure that imperfections of a dimension relative to section the thickness will be revealed.

Mechanical Joints

Threaded joints are the oldest method of joining piping systems. Thread cutting should be regarded as a precision machining operation. Typical threading die. For steel pipe, the lip angle should be about, but for brass, it should be much smaller. Improper lip angle results in rough or torn threads. Since pipe threads are not perfect, joint compounds are used to provide leak tightness. The compounds selected, of course, should be compatible with the fluid carried and should be evaluated for possible detrimental effects on system components. Manufacturers’ recommendations should be followed. Where the presence of a joint compound is undesirable, dry seal pipe threads in accordance with ASME B1.20.346 may be employed. These are primarily found in hydraulic and pneumatic control lines and instruments. Flanged joints are most often used where disassembly for maintenance is desired. A great deal of information regarding the selection of flange types, flange tolerances, facings and gaskets, and bolting is found in B16.5. The limitations regarding cast iron-to-steel flanges, as well as gasket and bolting selection, should be carefully observed. The governing code will usually have further requirements. Gasket surfaces should be carefully cleaned and inspected prior to making up the joint. Damaged or pitted surfaces may leak. Appropriate gaskets and bolting must be used. The flange contact surfaces should be aligned perfectly parallel to each other. Attempting to correct any angular deviation perpendicular to the flange faces while making up the joint may result in overstressing a portion of the bolts and subsequent leakage. The proper gasket should be inserted making sure that it is centred properly on the contact surfaces. Bolts should be tightened hand-tight. If necessary for alignment elsewhere, the advantage may be taken of the bolt hole tolerances to translate or rotate in the plane of the flanges. In no case should rotation perpendicular to the flange faces be attempted? When the assembly is in its final location, bolts should be made up wrench-tight in a staggered sequence. The bolt loading should exert a compressive force of about twice that generated by the internal pressure to compensate not only for internal pressure but for any bending loads which may be imposed on the flange pair during operation. For a greater guarantee against leakage, torque wrenches may be employed to load each bolt or stud to some predetermined value. Care should be exercised to preclude loading beyond the yield point of the bolting. In other cases, special studs that have had the ground of the end to permit micrometre measurement of stud elongation may be used. Flange pairs which are to be insulated should be carefully selected since the effective length of the stud or bolt will expand to a greater degree than the flange thicknesses, and leakage will occur. Thread lubricants should be used, particularly in high-temperature service to permit easier assembly and disassembly for maintenance.