Cwb Level 2 Theory Quiz #1

Stress cracking is most likely to occur when welding thick material because of the increased cooling effect. When thick material is welded, it takes longer for the heat to dissipate, causing the weld to cool at a slower rate. This slower cooling can lead to the formation of residual stresses in the material, which can result in stress cracking.

The correct answer is "Exothermic." Exothermic reactions release heat and energy. In thermit welding, a mixture of aluminum powder and metal oxide is ignited, producing a highly exothermic reaction that generates intense heat and molten metal. This heat is used to weld or join metal parts together.

An inverter is used to convert direct current (D.C.) to high-frequency alternating current (A.C.). It is a device that converts the fixed voltage and polarity of D.C. power into an oscillating voltage and alternating current. This is achieved through the use of electronic switches that rapidly switch the polarity of the D.C. input, creating an A.C. output. Inverters are commonly used in various applications such as power electronics, renewable energy systems, and electric vehicles.

Fusible plugs are safety devices that are designed to melt at a specific temperature in order to release pressure or prevent an explosion. The given correct answer states that fusible plugs can melt as low as 165°F. This means that when the temperature reaches or exceeds 165°F, the plug will melt, allowing the pressure to be released and preventing any potential damage or danger.

In Canada, most welding machines are connected to a high voltage supply of 575 volts. This higher voltage is required to provide the necessary power for welding operations, as welding typically requires a significant amount of energy to heat and melt metals. The higher voltage allows for a more efficient and effective welding process, ensuring that the machine has enough power to generate the heat needed for welding.

Limestone is used as a fluxing agent in the production of pig iron because it reacts with impurities, such as silica and alumina, to form a slag. The slag is lighter and floats on top of the molten iron, allowing it to be easily separated. Limestone also helps in maintaining the proper chemical balance and temperature during the iron production process.

Steels become cast iron when the carbon content exceeds 1.7%. This means that when the percentage of carbon in the steel reaches or exceeds 1.7%, it undergoes a transformation and becomes cast iron.

The U-groove preparation cannot be used in a T-joint. This is because the U-groove is typically used for butt joints, where two pieces of metal are joined in a straight line. In a T-joint, one piece of metal is joined perpendicularly to another, so the U-groove preparation is not suitable for this type of joint.

An auxiliary view is a type of view used to show the exact shape of a part that may be difficult to determine from the standard orthographic views. It is created by projecting the part onto a plane that is perpendicular to the line of sight and intersects the part at an angle. This allows for a more detailed and accurate representation of the part's shape, especially when there are complex features or irregular surfaces that cannot be fully shown in the standard views.

Ohm's law states that the resistance (R) in a circuit is equal to the voltage (V) divided by the current (I). This means that the resistance is directly proportional to the voltage and inversely proportional to the current. In other words, as the voltage increases, the resistance also increases, and as the current increases, the resistance decreases. Therefore, the correct answer is R = V/I.

The average cable size for 150 feet of combined length of electrode and ground cables using 200 amps at 60% duty cycle would be 2. This means that the cables should have a size of 2, which indicates a larger diameter to handle the higher amperage and prevent overheating.

Structural steel plates and shapes are designated by the organizations C.S.A. (Canadian Standards Association) and A.S.T.M. (American Society for Testing and Materials). These organizations establish standards and specifications for the manufacturing and use of structural steel, ensuring its quality, safety, and performance. C.S.A. is a Canadian organization that develops standards for various industries, including construction, while A.S.T.M. is an American organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services. Together, C.S.A. and A.S.T.M. provide a comprehensive framework for the designation and use of structural steel plates and shapes.

A thicker plate groove weld would have higher restraint compared to the other options. Restraint refers to the degree to which the weld is prevented from expanding or contracting during the welding process, which can lead to residual stresses and distortion. A thicker plate groove weld would have more material surrounding the weld joint, providing greater resistance to movement and therefore higher restraint. Thinner plate groove weld, thinner plate fillet weld, and thicker plate fillet weld would have lower levels of restraint in comparison.

Martensite is formed when a material is rapidly cooled, preventing the formation of carbides and allowing carbon gas to become trapped in the ferrite structure. This results in a very hard and brittle microstructure. Therefore, the given explanation correctly states that Martensite is formed with a fast cooling rate during quenching.

A shunt generator is a type of DC generator that is self-excited, meaning it generates its own magnetic field without the need for an external source of excitation. In a shunt generator, the field winding is connected in parallel with the armature winding, hence the name "shunt." This configuration allows for a portion of the armature current to flow through the field winding, creating the necessary magnetic field for the generator to produce electricity. Therefore, a shunt generator is self-excited and does not require an external excitation source.

High frequency units are commonly used to overcome arc rectification in G.T.A.W. (Gas Tungsten Arc Welding) of aluminum. Arc rectification occurs when the arc tends to move in one direction, causing uneven heating and potential defects in the weld. High frequency units help to disrupt the rectification process by rapidly changing the polarity of the arc, allowing for a more stable and balanced welding process. This helps to ensure a more even distribution of heat and a higher quality weld.

Oxygen transfer to the weld metal is important because it affects the toughness of the weld. Oxygen can react with certain elements in the weld metal, causing the formation of brittle compounds that can reduce the toughness of the weld joint. This can make the weld more susceptible to cracking or failure under stress. Therefore, controlling the oxygen content during welding is crucial to ensure the desired toughness and integrity of the weld.

Radiography is the most commonly used non-destructive method for detecting subsurface volumetric discontinuities in welds. Radiography uses X-rays or gamma rays to create an image of the internal structure of the weld. It is effective in detecting voids, inclusions, cracks, and other defects that may not be visible to the naked eye. This method allows for a comprehensive evaluation of the weld's integrity and can be used to ensure the quality and safety of the welded joints.

The voltage range for short circuit transfer is 16-22. Short circuit transfer is a type of welding transfer mode where the wire electrode continuously touches the weld puddle, causing a short circuit. In this transfer mode, the voltage should be low to prevent excessive heat and spatter. The range of 16-22 volts is considered ideal for short circuit transfer as it provides good control over the welding process and produces a smooth and stable arc. Higher voltages may result in a globular transfer mode, while lower voltages may cause the electrode to stick to the workpiece.

Carbon dioxide is the most common gas used with gas shielded flux cored welding. This is because carbon dioxide provides good penetration and produces a stable arc, which is essential for achieving high-quality welds. Additionally, carbon dioxide is readily available and more cost-effective compared to other gases such as argon or helium. Therefore, it is the preferred choice for many welding applications.

The correct answer is C.S.A. The CSA (Canadian Standards Association) tests their electrodes in stress relieved conditions.

In the A.I.S.I. numbering system of steel classification, the second digit represents the subclass. This means that the second digit in the classification code provides information about the specific subgroup or variation of steel within a particular grade. The subclass digit helps to further categorize and differentiate different types of steel based on their specific properties, composition, or manufacturing processes.

To evaluate a fillet weld size, three dimensions are required. These dimensions include the leg length, throat thickness, and the angle of the fillet weld. The leg length refers to the distance from the root to the toe of the weld, while the throat thickness is the shortest distance between the face and the root of the weld. The angle of the fillet weld is the angle formed between the two surfaces being joined. These three dimensions are crucial in determining the strength and quality of the fillet weld.

The minimum impact properties for an E-705-6 filler material are 20 ft-lbs at -20°F or 27J at -29°C. This means that the filler material must be able to withstand a minimum impact force of 20 ft-lbs at a temperature of -20°F or 27J at a temperature of -29°C. This requirement ensures that the filler material has sufficient toughness and resistance to fracture under low temperature conditions.

The contraction effect in the weld metal refers to the shrinkage that occurs during the cooling process after welding. This shrinkage can cause stress and distortion in the weld. The transverse contraction effect is considered to be more serious because it occurs perpendicular to the direction of the weld. This means that it can result in greater distortion and potential cracking compared to longitudinal or circumferential contraction effects. Linear contraction refers to the overall shrinkage of the weld, but it does not specify the direction and is not as significant as the transverse contraction effect.

A capped steel is similar to rimmed steel because both types of steel have a high oxygen content. In the production process, a capped steel is partially deoxidized, resulting in the formation of a cap of iron oxide on the surface. Similarly, rimmed steel also has a high oxygen content but is fully deoxidized, forming a rim of iron oxide on the surface. Both types of steel are characterized by their ability to be easily shaped and formed, making them suitable for certain applications in the manufacturing industry.

A typical current range for a 5/32 in. (4mm) E-7018 electrode is 150-220 amps. This range is suitable for welding applications using this specific electrode size and type. Using a current within this range ensures proper penetration and fusion of the weld joint, resulting in a strong and durable weld.

The S.C.R. (silicon controlled rectifier) is turned on by sending a current pulse through the gate of the S.C.R. This current pulse triggers the S.C.R. and allows current to flow through it. Discharging a capacitor in parallel with the S.C.R., closing a switch in series with the S.C.R., or opening a shunt in parallel with the S.C.R. are not methods for turning on the S.C.R.

The letter designation M in the electrode classification E-12018-M indicates that it is specifically designed to meet military specifications. This means that the electrode has been tested and approved to meet the quality and performance standards required for military applications. The M designation ensures that the electrode is reliable and suitable for use in military projects, where precision and durability are essential.

The plates for pressure vessels are usually formed with the rolling direction around the circumference because this provides the highest strength and resistance to pressure. Rolling the plates in this direction ensures that the grains of the material are aligned parallel to the circumferential axis, which enhances the structural integrity of the vessel. This orientation also helps in distributing the stress evenly, making the vessel more capable of withstanding high pressures.

Undercut in welding is a groove defect where the base metal along the edge of the weld is not properly fused and may be eroded away. One probable cause of undercut is incorrect electrode inclination, which refers to the angle at which the welding electrode or torch is held relative to the workpiece. If the electrode angle is incorrect, it can lead to insufficient fusion and undercut along the weld edges.

In welding metallurgy, the primary considerations include heat input (which affects weld strength and distortion), base metal composition (which influences weldability and mechanical properties), and shielding gas selection (which impacts weld quality and properties). Welding position, while important for practical welding operations, is not a primary consideration in metallurgical aspects but rather determines the physical orientation of the weld joint during welding.

Waveform shaping refers to the process of manipulating the shape of the electrical waveform in order to improve arc stability in G.T.A.W. with A.C. By minimizing the time taken to pass through zero, the plasma is less likely to collapse completely, allowing the arc to be re-established. This technique helps in maintaining a stable and continuous arc during the welding process.

Peening is a method used to control distortion in materials. It involves striking the surface of a material with a hammer or other tool to induce compressive stresses, which helps to counteract the tensile stresses that cause distortion. The effective depth of peening refers to the depth of the compressive stresses induced by the peening process. In this case, the correct answer is 1/8", which means that the peening process will induce compressive stresses to a depth of 1/8" in the material.

Inadequate ductility in a weld refers to the lack of ability of the weld metal and joint to deform without breaking or cracking. This defect can occur due to various factors such as improper welding techniques, incorrect selection of welding materials, or inadequate preheating or post-weld heat treatment. It is categorized under defective properties (weld metal and joint) because it directly relates to the quality and characteristics of the weld itself.

The open-circuit voltage of most welding machines is 80. Open-circuit voltage refers to the voltage measured across the output terminals of a welding machine when no load is connected. It represents the maximum voltage that the machine can deliver without any load. In this case, the correct answer indicates that the open-circuit voltage of most welding machines is 80 volts.

The correct answer is "The lowest of all." Ductility refers to the ability of a material to deform under tensile stress without breaking. When measuring ductility through the thickness of a plate, it is typically lower compared to other directions. This is because the grains in the material tend to align in the rolling direction during the manufacturing process, resulting in reduced ductility perpendicular to the rolling direction. Therefore, the ductility measured through the thickness of the plate is usually the lowest among all directions.

The statement suggests that as the thickness increases, the cooling rate decreases. However, this is not true. In reality, the cooling rate actually increases as the thickness increases. This is because a thicker material takes longer to cool down compared to a thinner material. Therefore, the correct answer is False.

The effective throat refers to the minimum distance from the root of the weld to its face, less any reinforcement. It represents the actual area of the weld that is contributing to the strength and stability of the joint. Theoretical throat refers to the maximum possible distance, while leg size refers to the length of the weld. Therefore, the effective throat is the correct answer as it accurately represents the minimum distance without any additional reinforcement.

In a 0.8% carbon steel, below 723°C (1333°F), the steel structure has two phases. This is because at this temperature range, the steel undergoes a phase transformation known as the eutectoid reaction. The two phases present in the steel structure are ferrite and pearlite. Ferrite is a relatively soft and ductile phase, while pearlite is a harder and stronger phase. The presence of these two phases contributes to the overall mechanical properties of the steel.

The force or pressure with which an electric current is forced through a circuit is known as electromotive force (EMF). EMF is the energy per unit charge supplied by a source, such as a battery, to drive the electric current. It is measured in volts.

The transition point from globular to spray transfer generally occurs at 220 amps. At this current level, the metal transfer shifts from large droplets (globular) to a fine spray of small droplets (spray transfer). This transition is important in welding as it affects the quality and appearance of the weld.

The electrode coating in welding serves several important functions, including:

Controlling the bead shape and smoothness: The coating helps to shape the weld bead and ensure a smooth finish by influencing the stability of the arc.

Controlling the hydrogen induced into the weld metal: The coating can help to control the amount of hydrogen that is introduced into the weld metal, which can prevent hydrogen-induced cracking.

Protecting the weld metal from contamination: The coating forms a protective gas shield around the weld area, preventing contamination from atmospheric gases like oxygen and nitrogen.

Aiding in the removal of gases and other impurities from the weld metal: The coating can help to remove impurities and gases from the weld metal, improving the quality and strength of the weld.  

So, all the options you mentioned are correct. The electrode coating plays a crucial role in the welding process. It’s designed to improve the quality and efficiency of the weld, and to prevent common welding issues.

Normalizing is a heat treatment process used to refine the grain size of steel and improve its properties. During normalizing, the steel is heated above its critical temperature and then allowed to cool in still air. This process helps to achieve a uniform and fine-grained microstructure, which enhances the mechanical properties of the steel, such as strength and toughness. Normalizing also reduces internal stresses and improves the machinability of the steel. Therefore, normalizing is the correct answer for the given question.

Hydrogen cracking, also known as cold cracking, is a type of weld defect that occurs when hydrogen atoms become trapped in the weld metal during the welding process. These hydrogen atoms can cause the metal to become brittle and crack under stress. The cracking can only occur after the weld has cooled down to below about 100°C, as this is the temperature at which the hydrogen atoms are most likely to diffuse and accumulate in the metal. Therefore, the correct answer is 100°C.

The WHMIS label is a standardized label used in Canada to provide information about hazardous materials. It typically includes the product identifier, WHMIS hazard symbol, and risk phrases to indicate the potential hazards of the product. However, the hazardous ingredients are not normally found on the WHMIS label. This information is usually provided in the Safety Data Sheet (SDS) for the product, which is separate from the label. The SDS provides more detailed information about the composition of the product, including hazardous ingredients.

The electrode E-7014 has a rutile and iron coating.

X-rays are not a non-ionizing radiation. Non-ionizing radiation refers to electromagnetic radiation that does not have enough energy to remove tightly bound electrons from atoms or molecules, resulting in minimal biological damage. X-rays, on the other hand, are a form of ionizing radiation that have higher energy and can cause ionization, leading to potential harm to living tissues and cells.

In a face-centered cubic (F.C.C.) structure, carbon atoms can dissolve in the lattice of a metal. The question asks about the maximum percentage of carbon that can be completely dissolved in this structure. The correct answer is 1.7%. This means that up to 1.7% of the total atoms in the F.C.C. lattice can be carbon atoms, beyond which the lattice will not be able to accommodate any more carbon atoms.

A hollow root is a structural discontinuity in the weld zone where the root of the weld is not properly filled or fused, resulting in a void or hollow space. This can weaken the weld joint and compromise its integrity. It is important to ensure that the root of the weld is properly filled to avoid any potential defects or failures in the welded structure.

Tempering is a heat treatment process that involves reheating a material, typically steel, to a temperature below its critical point. The purpose of tempering is to reduce the hardness and brittleness of the material, while increasing its toughness. The correct answer of 723°C (1333°F) indicates that tempering involves reheating the material to a temperature below 723°C, but above room temperature. This temperature range allows for the desired changes in the material's properties to occur, resulting in a more suitable and usable material for various applications.

Ferro-silicon is the usual deoxidizing material added to the melt when making semi-killed steel. Deoxidizing materials are added to steel to remove oxygen and other impurities, preventing the formation of defects such as porosity. Ferro-silicon is a commonly used deoxidizer due to its ability to effectively remove oxygen from the melt. It contains a high percentage of silicon, which reacts with the oxygen to form silicon dioxide, a stable compound that can be easily removed from the steel.

If higher deposition rates are a concern when using the Submerged Arc Welding (S.A.W.) process, the most suitable current type would be D.C.E.N. (Direct Current Electrode Negative).

In the S.A.W. process, D.C.E.N. (also known as straight polarity) allows for higher deposition rates because it typically produces deeper penetration and faster melting of the electrode, leading to increased metal deposition per unit time. This is advantageous when productivity and efficiency in welding are key concerns.

The electrode with the highest percentage of iron powder in the coating would be E-XX024. This can be inferred from the fact that E-XX024 is listed first in the options, indicating that it is the most likely answer. However, without additional information about the composition of the coatings or any other context, it is difficult to provide a more specific explanation.

The moisture levels for cellulosic electrodes should be kept at approximately 3-7%. This range ensures that the electrode maintains its stability and performance during welding. If the moisture content is too low, the electrode may become brittle and prone to cracking. On the other hand, if the moisture content is too high, it can lead to excessive spatter and poor weld quality. Therefore, maintaining moisture levels within the 3-7% range is crucial for achieving optimal welding results with cellulosic electrodes.

When welding or cutting on a structure about 5m high, spatter refers to the small molten metal particles that are produced during the process. These particles can be propelled away from the welding or cutting area due to the intense heat and force involved. The given correct answer suggests that the spatter is not likely to travel more than 1m away from the area. This means that the majority of the spatter is expected to fall within a close proximity to the welding or cutting site, minimizing the risk of it causing damage or injury at a significant distance.

The correct answer is 2000 because this is the recommended amount of air exchange (ventilation) measured in cubic feet per hour per welder. This level of ventilation helps to ensure that there is enough fresh air circulating in the welding area to remove any harmful fumes or gases produced during the welding process. It is important to have proper ventilation in order to protect the welder's health and safety.

The C.S.A. electrode number classification is a system used to classify welding electrodes based on their characteristics. The third number in the classification indicates the position in which the electrode can be used. In this case, the third number is 1, which means that the electrode can be used in all positions, except for the vertical down position. This means that the electrode is suitable for welding in various positions, such as flat, horizontal, vertical up, and overhead, but not for welding in the vertical down position.

The correct answer is -40°C. This means that when using a F74/F4804 flux for S.A.W., the toughness of 27J is met at a minimum temperature of -40°C.

The curve of the output voltage vs. current under steady conditions is known as the static characteristic. This curve represents the relationship between the output voltage and current when the system is in a stable state. It provides information about the behavior and performance of the system under normal operating conditions. By analyzing the static characteristic, engineers can determine the linearity, stability, and efficiency of the system.

The core wire in most covered electrodes is typically made from killed steel. Killed steel is fully deoxidized, meaning that it has a uniform composition without gas pockets, making it ideal for use in welding electrodes. This ensures consistent welding properties, better structural integrity, and reduced risk of defects in the weld. The other types of steel, such as rimmed and semi-killed, contain more impurities or gas pockets, making them less suitable for this application.

Potassium is used in electrode coatings intended to operate on A.C. because it has good electrical conductivity and stability at high temperatures. It helps to improve the performance and efficiency of the electrode by facilitating the flow of alternating current. Additionally, potassium can also enhance the adhesion of the coating to the electrode surface, ensuring better durability and longevity of the electrode in A.C. applications.

Cementite is the correct answer because it refers to the phase structure of three atoms of iron and one atom of carbon. Cementite is a hard and brittle compound that forms in iron-carbon alloys, particularly in high carbon steels. It has a distinct crystal structure and is one of the constituents of pearlite, which is a microstructure found in steel.

Efficiency is the correct answer because it refers to the proportion of total energy that is converted into heat and eventually enters the plate. Efficiency is a measure of how effectively energy is being utilized and is commonly used to evaluate the performance of systems or processes.

Hydrogen embrittlement is maximized at around room temperature in steels, and most metals are relatively immune to hydrogen embrittlement at temperatures above 150°C1. Therefore, the options that fall within the range where hydrogen will have no embrittling effect on steel are:

200-250°C

250-300°C

The correct answer is 1/2 lb. per min. per 1000 amps. This means that for every 1000 amps of current, the electrode will melt at a rate of 1/2 lb. per minute. This indicates that the higher the current, the faster the electrode will melt.

In the case of iron ore smelting, carbon monoxide acts as the reducing agent. This means that it donates electrons to the iron oxide, causing the reduction of iron from its ore. Carbon monoxide has a strong affinity for oxygen, and when it comes into contact with iron oxide, it reacts to form carbon dioxide and pure iron. The reaction can be represented by the equation: Fe2O3 + 3CO -> 2Fe + 3CO2. Therefore, carbon monoxide is the correct reducing agent in the process of iron ore smelting.

The correct answer is C.P. with D.C.E.P. This means that the power source used most often with G.M.A.W. is Constant Potential (C.P.) and the current type is Direct Current Electrode Positive (D.C.E.P.). G.M.A.W., or Gas Metal Arc Welding, requires a constant potential power source to maintain a stable arc and control the welding process. D.C.E.P. is used because it provides better penetration and allows for better control of the weld pool.

The G.T.A.W. hot wire process is a welding technique that uses a high-frequency alternating current (A.C.) power source. This power source is used to preheat the filler metal, which helps in achieving a better weld quality. Using an A.C. power source for filler metal preheat is common in this process because it allows for better control of the heat input and ensures uniform heating of the filler metal. Using a direct current (D.C.) power source may not provide the same level of control and uniformity in preheating the filler metal.

In G.M.A.W. (Gas Metal Arc Welding), a short circuit metal transfer method is used. This method involves the transfer of small droplets of molten metal from the electrode to the workpiece. To limit the maximum available current in this process, the slope is used. The slope refers to the rate at which the welding current increases or decreases during the welding process. By controlling the slope, the maximum available current can be limited, ensuring a controlled and efficient welding operation.

The suffix "C" in a low alloy electrode designates Nickel Steel.

Iron exists in the body-centered cubic (b.b.c.) structure at temperatures below 910°C (1670°F). This means that at temperatures below 910°C, the iron atoms arrange themselves in a specific pattern known as body-centered cubic, where each iron atom is surrounded by eight neighboring atoms. However, at temperatures above 910°C, the iron undergoes a phase transition and changes its crystal structure to face-centered cubic. Therefore, the correct answer is 910°C (1670°F).

Overlap is a dimensional weld fault that occurs when the weld metal extends beyond the intended joint area, resulting in an overlap of the welded material. This can weaken the joint and compromise its integrity. It is usually caused by incorrect welding technique or improper alignment of the parts being welded. Overlap can lead to reduced strength and increased stress concentration, making the weld susceptible to failure under load.

Power sources can be classified into two categories: rotating types and stationary types. Rotating types include generators, which convert mechanical energy into electrical energy through the rotation of a coil within a magnetic field. On the other hand, stationary types refer to power sources that do not involve any rotation, such as transformers or rectifiers. Transformers transfer electrical energy between different voltage levels, while rectifiers convert alternating current (AC) to direct current (DC). Therefore, the correct answer is rotating or stationary types, as it encompasses the two main classifications of power sources based on their operation.

Alloy steels and steels with greater than 0.3% carbon are classified as "killed". This means that during the steel-making process, the molten steel is fully deoxidized by adding a strong deoxidizing agent, such as silicon or aluminum. This ensures that all the oxygen is removed from the steel, preventing the formation of unwanted oxides. Killing the steel results in a more uniform and consistent composition, improved mechanical properties, and better surface finish.

Diffusion welding is a welding process that involves the use of heat and pressure to achieve coalescence of the contacting surfaces. In this process, the metal surfaces are heated to a high temperature, causing atoms to diffuse across the interface and bond together. The application of pressure helps to ensure a strong and durable joint. Unlike other welding processes, diffusion welding does not require the use of filler material, making it a cost-effective option for joining similar or dissimilar metals.

Inductance is used to control the rate at which the current rises in short-circuiting transfer. Inductance is a property of electrical circuits that opposes changes in current, and it can be used to limit the rate at which current increases. By introducing inductance into the circuit, the current rise can be slowed down, preventing abrupt changes and reducing the risk of damage or instability. Therefore, inductance is an important factor in controlling the current rise in short-circuiting transfer.

Structural discontinuities refer to faults or defects that occur within the structure of a weld. Oxidization, which is the process of a metal combining with oxygen to form an oxide, can lead to the formation of pores or voids in the weld. These pores weaken the weld and create structural discontinuities, making it the correct category for oxidization as a weld fault.

E-7020 electrode is generally referred to as mineral coated with iron oxide. The mineral coating in this electrode helps in providing excellent arc stability and high deposition rates. It also offers good resistance to cracking and provides a smooth and clean weld appearance. This electrode is commonly used for welding structural steels and is suitable for both vertical and overhead welding positions.