Welding Operations I

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parcelcheck.co.za/banana-of-the-future-just-like-time.php By melting two pieces of metal together, an autogenous weld can be created. This welding process is employed to carry out high-quality work when a superior standard finish is required, without making use of excessive clean up by sanding or grinding. As an alternative to shield welding, Flux-cored Arc Welding was developed. This welding process is quite similar to MIG or GMAW process, except for the fact that in FCAW a special tubular wire filled with flux is used and shielding gas is not always needed, depending on the filler.

This type of welding is well-known for being extremely inexpensive and easy to learn. However, there are several limitations in its applications and the results are not often aesthetically pleasing as some of the other welding methods. The semi-automatic arc is often used in construction projects, thanks to its high welding speed and portability. Professional steel fabricators at Northern Weldarc are well-trained to construct structural steel for various projects across industries.

Structural steel can be transformed for various purposes and it can be utilized for a number of applications too. Preventive maintenance PM is a frequently overlooked part of the welding operation, but it is critical to preventing unscheduled downtime and keeping repair costs low. A well-performed PM program can also help increase productivity, extend equipment life and create a workplace philosophy that encourages shared responsibility for, and interest in, preserving the integrity of the welding equipment.

Companies should develop a regular timetable to inspect their power sources, wire feeders and MIG gun or TIG torches during scheduled downtime in production. Between welding shifts is often enough time to perform routine inspections. Checking consumables regularly for spatter build-up — and replacing these components as needed — is also an important part of a viable PM program. Shielding gases also determine arc characteristics and weld penetration on a given application. Straight CO2 provides good weld penetration, but it is prone to spatter and has a less stable arc than mixtures that include argon.

High argon mixtures a minimum of 85 percent argon for solid wire or as low as 75 percent for metal-cored wires are the best choice. These mixtures can be used in the spray transfer process to promote higher deposition rates and generate less spatter.

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For both MIG and TIG welding operations, companies should purchase their shielding gas from a reputable welding distributor and be certain that it meets the purity requirements for their application. All gas delivery systems should be free of contaminants that could enter the weld puddle and welding operators should use the correct shielding gas flow rate.

Protecting the weld puddle from drafts is also critical. Due to the initial up-front cost savings, the temptation may be great for companies to purchase less expensive filler metals. However, doing so can often lead to greater long-term costs and lower productivity levels. It is not uncommon, for example, to experience downtime associated with poor wire feeding, excessive spatter or, potentially, weld defects when using lower quality filler metals. Companies may also find themselves experiencing an excessive amount of time for non-value-added activities those that do not directly contribute to their throughput , such as applying anti-spatter and post-weld grinding or rework.

For that reason, it is important to look at the total cost of using particular filler metals, as opposed to the per-unit cost. Skipping steps in weld preparation can lead to weld defects, rework or scrapped parts. Welding operators should always take care to clean the base material before welding to prevent contaminants like dirt, oil or grease from entering the weld puddle. Similarly, monitoring part fit-up is a critical part of the pre-weld process. Welding operators should carefully assess the weld joints to ensure there are no excessive gaps, as poor part fit-up can lead to issues like burn-through or distortion on all materials, but particularly when welding on materials like aluminum or stainless steel.

Clamping or fixturing a part in the correct position is also a good practice to help protect materials like stainless steel against distortion or buckling. It is not uncommon for companies to overlook the importance of their MIG gun consumables. As with filler metals, companies should also avoid the temptation to purchase less expensive, lower quality consumables.

Like other welding process, FCAW has some advantages and limitations. No needs for skilled operators and pre-cleaning of metals, suitability for use in the outdoor or windy condition it is true about self-shielded flux cored wires , suitability for use in all positions, and ease of varying the alloying constituents are mentioned as FCAW advantages. Its limitations include: emission of considerable amount of fumes in self-shielded wires, higher price of filler material and wire in comparison with GMAW, and needs for slag removal. Also, escaping of the shielding gas from the welded area leaves holes in welded metal, resulting in porosity in products [ 17 , 18 ].

Air pollution is indoor or outdoor contamination by particulates, biological molecules, or other harmful materials that changes the natural characteristics of the Earth's atmosphere. Household combustion devices, motor vehicles, forest fires, and industrial processes are common sources of air pollution.

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Major industrial sources of particulate matter include the metals, mineral products, petroleum, and chemical industries. Air pollution is considered as a threat to human health as well as to the Earth's ecosystems. Based on WHO report, around 7 million people worldwide died due to the air pollution in [ 20 ]. Welding, as an important operation in most industries, can considerably cause air pollution.

In all types of welding processes, fume and gases are formed as air pollutants. Due to high temperature during the welding process, different substances in the arc are vaporized. Then, the vapor condenses and oxidizes in contact with the air, leading to the formation of fumes. The fume particles are so small and they can reach the narrowest airways of respiratory system respiratory bronchioles. Some parameters like the welding type and consumables filler metal and surface coatings determine the kind and amount of generated particles and gases.

The composition of welding fumes and their generation rate is a function of different parameters. The generation of fumes depends on:. The most common gases emitted during welding are ozone, nitrous gases and carbon monoxide. Phosphine and phosgene are the other gases that may be produced during welding. Gases are generated due to the high temperature and ultraviolet UV radiation from the arc. Like fumes, some factors can affect the emission of gases during welding processes.

For instance, ozone formation during welding depends on process type, used material, and shielding gases. Welding gases can also be generated when surface coatings or contaminants contact with hot surfaces or UV radiation. Along with harming human health, air pollution may lead to various environmental impacts.

Air pollution can adversely cause critical impacts on the atmosphere and natural environment in many ways. Welding, as an industrial process, causes serious impacts on the environment depending on its operation mode and the technological equipment. Environmental pollution in welding process is the result of some parameters, such as high percentage of heat that is released into the environment and materials including large amount of gases and fumes. Some factors needed to carry out the welding operation include: energy, mineral or organic substances protective gases, cooling water, oils, grease and protective substances etc.

These consumables can be harmful for the environment. Furthermore, produced waste during the welding processes results in undesirable impact on the work or natural environment. To protect the welding region and prevent oxidation, inert gases like carbon dioxide and argon are used because of their availability and low cost. They are used as shielding gases and have undesirable impacts on the environment. To protect the environment and keep the resource for future, energy conservation and reducing greenhouse gas emissions should be considered.

In this respect, the average consumption rate, usage rate and the purity of products and consumables are important factors [ 22 , 23 ]. The generation of fumes and gases is directly related to the welding process. In some conditions, the level of fume generated during MIG welding with solid wire may be much lower in comparison with the fumes produced by MMA. The composition of fumes is directly associated with the composition of used wire. MMA welding causes adverse health effects because of forming the hexavalent chromium Cr VI in the process. During TIG welding, very little fume are generated.

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This technique uses a permanent non-consumable tungsten electrode. Most measurements are made using personal monitoring systems with a pump at a proper flow rate connected to a cassette containing a membrane filter for a suitable period of time. Metals to be joined must possess some degree of mutual solubility in solid state. There is a wide range, from low to high, for protection factors. The ultraviolet emissions resulting from welding arc can potentially cause skin tumors in animals and in overexposed individuals, however, there is no definitive evidence for this effect in welders [ 53 ].

Welding fumes may be composed of oxides of chromium, nickel and copper, with very low specific limit values. The individual elements and also their synergetic effect must be considered when assessing fume toxicity. The amount of mentioned gases during TIG welding is dependent on current, arc length and the flow and type of shielding gas.

Welding Basics for Beginners

High electrical currents cause the significant levels of ozone, nitric oxide and nitrogen dioxide. During MIG welding, significant levels of ozone and nitrogen oxides are produced because of intense current levels. There is a little information concerning emissions during plasma arc welding PAW.

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GENERAL. The purpose of this course is to introduce the basic requirements involved in metal-arc welding operations. The scope of this subcourse consists of . Welding is a fabrication or sculptural process that joins materials, usually metals or expensive for methods like laser beam welding and electron beam welding. Because of their high cost, they are only used in high production operations.

Due to the similarity of TIG and PAW welding techniques, they may probably emit air pollutants with the same magnitude. Forming more nitrogen oxides in the latter process will keep the emitted ozone levels down [ 25 , 26 ]. A study by Schoonover et al. In fact, not using a consumable electrode during TIG welding results in lower exposures. Fuglsang et al. Various welding processes generate particles in different size distributions. Processes with low mass emission rates TIG and RSW generate exclusively particles smaller than 50 nm; however, the number concentration of particles in these techniques is similar to the others.

A study by Keane M. The advantages of this method include usability in any position, high metal deposition rate, and simple learning and use. Totally, the highest amounts of fume are produced by the self-shielded cored wire electrodes. These electrodes are used without a shielding gas. Using solid wire electrodes results in emission of ozone and nitrogen oxides as in MAG welding [ 25 , 29 ]. Airborne particles with diameter smaller than nm are known as nanoparticles or ultrafine particles. According to researches, nanoparticles are more harmful to human health than larger particles.

They can deeply penetrate inside the respiratory system and then enter the blood stream. The main character of nanoparticles is the high surface area, and their toxicity depends on the shape and penetration potential inside the respiratory system. Some studies have indicated that the highest values of nanoparticles are related to MAG and TIG processes when applying the highest current intensities.

Therefore, the higher amounts of nanoparticles are emitted by processes in which the higher energy intensities are used. As it was stated, the emission of nanoparticles during welding operations increases with the increase of welding parameters like current intensity. Welding with short-circuit mode results in lower value of nanoparticles, because its low current intensity and tension causes an electric arc with lower temperature and thus emitting lower amounts of elements.

Also, the high quantity of nanoparticles is generated by the stainless steel welding, which can be related to the presence of helium in the gas mixture of welding. Helium, due to high ionization energy, results in electric arc with high temperature that generates higher values of nanoparticles. Furthermore, the study of different base materials indicated that the higher quantity of nanosized particles is obtained for stainless steel compared to carbon steel. According to data from different investigations, the lowest level of ultrafine particles deposited in alveolar region of lungs was related to FSW, followed by TIG and MAG.

Totally, all welding processes can result in deposition of a significant concentration of nanosized particles in lungs of exposed welders [ 30 - 32 ]. Fume and gases emitted during welding pose a threat to human health while welding. The exposures may be varied depending on where the welding is done on the ship, in confined space, workshop, or in the open air. The welding process and metal welded affect the contents of welding fumes. On the other hand, physical and chemical properties of the fumes and individual worker factors are effective on deposition of inhaled particles.

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In this respect, particle size and density, shape and penetrability, surface area, electrostatic charge, and hygroscopicity are the important physical properties. Also, the acidity or alkalinity of the inhaled particles are the chemical properties that may influence the response of respiratory tract. Welding gases can be classified into two groups; some gases are used as a shielding gas and the others are generated by the process. Shielding gases are usually inert, therefore, they are not defined as hazardous to health but they may be asphyxiants. Gases generated by welding processes are different based on welding type and may cause various health effects if over-exposure occurs.

Welding emissions depending on some factors like their concentration, their properties, and exposure duration can lead to health effects on different parts of human body. Hazards on Respiratory System - The inhalation exposures may lead to acute or chronic respiratory diseases in all welding processes. In the occupational lung diseases, the various reactions produced in respiratory tract depend on some parameters such as the nature of the inhaled matter, size, shape and concentration of particles, duration of exposure, and the individual workers susceptibility. Chronic bronchitis, interstitial lung disease, asthma, pneumoconiosis, lung cancer, and lung functions abnormalities are some hazardous effects on respiratory systems.

The pulmonary disorders are various based on the differences in welding metals and their concentrations. Ozone, at low concentrations, irritates the pulmonary system and can cause shortness of breath, wheezing, and tightness in the chest. More severe exposures to ozone can lead to pulmonary edema. Exposure to nitrogen dioxide may cause lung function disorders like decrements in the peak expiratory [ 33 , 34 ].

Kim JY in a study showed the PM2. Hazards on Kidney- Substantial exposure to metals and solvents may be nephrocarcinogenic. Chromium can deteriorate renal function because of accumulation in the epithelial cells of the proximal renal tubules and induce tubular necrosis and interstitial changes in animals and humans. Tubular dysfunctions have been identified in subjects occupationally exposed to Cr VI [ 33 , 36 ].

Welders exposed to heavy metals like cadmium and nickel have also experienced kidney damage [ 7 ]. Pesch et al. So, it can be considered an evidence for a gender-specific susceptibility of the kidneys [ 37 ]. Hazards on Skin - Erythema, pterygium, non-melanocytic skin cancer, and malignant melanoma are the adverse health effects of welding on the skin among which erythema is a common one. The intense UV as well as visible and infrared radiations are produced by welding arc machines.

Exposure to UV can lead to short- and long-term injuries to the skin [ 33 , 38 - 40 ]. Some metals like beryllium, chromium and cobalt can cause direct effects irritation and allergic impacts on the skin. Also, they may be absorbed through the skin and cause other health effects such as lung damage. When the particles are small and there are cuts or other damages to the skin, the absorption through the skin is raised [ 7 , 36 ].

Chromium VI may cause irritating and ulcerating effects when contacting with skin. An allergic response including eczema and dermatitis may be induced in sensitized individuals exposed to Cr VI [ 34 ]. Hazards on the visual systems - Most welding processes emit intense ultraviolet as well as visible and infrared radiations. Adverse effects on the eyes may be induced by these optical radiations. In addition, Tenkak reported that, welding may cause photokeratitis and some types of cataract. Erhabor et al. Exposure to UV radiation can lead to short- and long-term injures to the eyes. Acute overexposure to UV radiation can result in the photokeratitis and photoconjunctivitis that are the inflammation of the cornea and the conjunctiva, respectively.

Hazards on Reproductive System - In the past, some studies have indicated the increased risk for infertility and reduced fertility rate in mild steel welders. There are some evidences that reduced fecundity can be related to exposure to hexavalent chromium and nickel. According to new investigations, damages to male reproduction system have been reported less than before, probably because of decreasing the exposure levels in the developed countries.

A study by Bonde showed that mild steel welding, but not stainless one, resulted in significant effects on the fertility during years [ 45 ]. Mortensen [ 46 ] observed a greater risk for poor sperm quality among welders compared to controls, especially welders who worked with stainless steel.

Therefore, welding in general, and specifically with stainless steel, may cause the reduced sperm quality. According to Sheiner, impaired semen parameters can be associated with the exposures to lead and mercury [ 47 ]. Hazards on the nervous system - Memory loss, jerking, ataxia and neurofibrillary degeneration have been attributed to exposure to aluminum.

A review of literatures by Iregren suggests that occupational exposure to manganese results in the central nervous system damage that is generally irreversible [ 48 ]. Although there are multiple toxic agents in welding, more literatures have dealt with manganese as an important agent of toxicity.

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Welders are also exposed to high concentrations of carbon monoxide and nitrogen dioxide. Carbon monoxide can cause the neurological impairments of memory, attention, and visual evoked potentials. Both central and peripheral nervous system damages may be induced by exposure to welding fumes [ 49 ]. Some neurobehavioral impairments associated with exposure to lead and manganese have been indicated by Wang [ 50 ].

A study by Bowler showed there is a relation between welding and a decline in brain functions and motor abilities. In this survey, various questionnaire and tests like neuropsychological tests were used [ 49 ]. Carcinogenic effects - There are some concerns regarding the presence of carcinogens in the welding fumes and gases.

Sufficient evidences for carcinogenicity of nickel, cadmium, and chromium VI have been reported through experimental and epidemiological studies. Ozone has been introduced as a suspect lung carcinogen in experimental animals, but there are very few documents about its long term effects on welders. The ultraviolet emissions resulting from welding arc can potentially cause skin tumors in animals and in overexposed individuals, however, there is no definitive evidence for this effect in welders [ 53 ]. Other health problems - Welding on surfaces covered with asbestos insulation may lead to risk of asbestosis, lung cancer, mesothelioma, and other asbestos-related diseases in exposed welders.

The intense heat and sparks of welding can cause burns. Eye injuries are possible because of contact with hot slag, metal chips, and hot electrodes. Lifting or moving heavy objects, awkward postures, and repetitive motions result in strains, sprains and musculoskeletal disorders. High prevalence of musculoskeletal complaints back injuries, shoulder pain, tendonitis, carpal tunnel syndrome, and white finger is seen in welders [ 54 ].

Usually, exposure standards apply to long term exposure to a substance over an eight hour work per day for a normal working week, over an entire working life. According to Work Safe Australia exposure standards cannot be used as a fine dividing line between a healthy and unhealthy workplace. Adverse health effects below the exposure limits might be seen in some people because of individual susceptibilities and natural biological variation.

Each metal or gas within the welding has its own exposure standard. As Table 2 indicates, biological media, Biological Exposure Index BEI , and carcinogenicity class have been proposed for some welding emissions [ 55 , 56 ]. Managing the risks of pollutants generated by welding process is carried out in some steps inculing identifying hazards, assessing the risks arising from these hazards, eliminating or minimising the risks via proper control ways, and checking the effectiveness of controls.

Welding process leads to chemical exposures to fumes and toxic gases in enormous quantity. The hazard identification and risk assessment are necessary to work safely in a welding environment. Enough information, education, training and experience are required in this respect. In addition to the full-time welders, a large number of part-time welders who work in small shops and workers in the vicinity of the welding process may also be exposed.

There is a greater potential for exposure due to welding in confined spaces with poor ventilation such as ship hulls, metal tanks and pipe, therefore, monitoring such welders should be seriously considered. Materials and consumables used in welding determine the chemical composition of welding emissions. The specific toxicity of each element and the synergetic effect of generated constituents must be considered to evaluate the exposure status of welders.

There are some other workplace specific factors, including the ventilation condition, welder position or posture, and the volume of welding room, that influence the exposure level. The emission rate and also its concentration in the breathing zone of the welder or in the work environment are directly related to the mentioned factors. To evaluate the hazards caused by different welding emissions, collecting various information is recommended. Thus, during the health and safety program, air monitoring is used to identify and quantify welding emissions.

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To evaluate air contaminants, a sampling strategy is used for collection of exposure measurements. The choice of the best strategy is based on site-specific conditions. In a sampling strategy, some parameters like selection of workers for personal monitoring, sampling duration and required number of samples are important.

The measurement of contaminants is carried out in the breathing zone of selected worker. The collected samples must be representative of the normal work activity and exposure of welder, because the sampling results are used to prevent overexposures. Air monitoring in welding processes includes the sampling and analysis of welding fumes and welding gases [ 61 ].

Within recent years, standard practices have been developed to monitor exposures considering the occupational exposure limits for elements. Most measurements are made using personal monitoring systems with a pump at a proper flow rate connected to a cassette containing a membrane filter for a suitable period of time. To obtain the accurate result, filter cassette must be placed inside the welding helmet.

Time-weighted average concentrations of total fumes is obtained by weighing the filter before and after exposure; the concentrations of elements are determined by chemical analysis methods provided by related organizations like American Welding Society and British Standards Institution [ 51 ], NIOSH Manual of Analytical Methods NMAM for metals in air and urine and OSHA Sampling and Analytical Methods are used to monitor the welding workplaces. It is worth mentioning that the microwave digestion can be used instead of acidic ashing to prepare samples, leading to reduction in ashing time up to 90 percent, as well as cost saving and providing a healthier work environment for laboratory operators.

Golbabaei et al. As it was stated previously, there are different workplace conditions for workers who are welding in confined spaces compared to other welders. Limited access and little airflow or ventilation are the characteristics of a confined space. Hazardous concentrations of welding emissions can accumulate very quickly in such small spaces. Hazardous concentrations of welding emissions can accumulate very quickly in such small space. In some situations, continuous air monitoring may be necessary when workers are welding in a confined space with special conditions. Almost for all analyzed metals, there were significant differences between back welders and controls.

Back welding is a task that workers perform welding inside the pipe as a confined space. Based on risk assessment, back welding was a high risk task [ 16 ].

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Back welders group had maximum exposure to total fume and mentioned elements [ 52 ]. Determination of occupational exposures to gases must be based on workplace measurements, because the local ventilation and workplace design can affect the actual concentrations of toxic gases ozone, carbon monoxide, nitrogen oxides in the welders' breathing zone.