1.1 Class A welds must pass visual, dimensional, surface, and volumetric inspections, as well as any other inspections specified in the engineering drawing. All fracture-critical welds are, by definition, Class A joints based on the implications of failure. For example, a weld that separates into two pieces when pulled apart at its midpoint has failed an impact test required by some codes.
Class A welds are those that do not affect the structural integrity of the component being joined. They include all fillet welds, where the root radius is equal to or less than half the thickness of the metal being joined; and groove welds, where the depth of the groove is equal to or greater than half the thickness of the metal being joined. Groove welds that do not reach through the entire thickness of the metal being joined (such as short groove welds) are considered to be fillet welds. The term "weld" is used broadly herein to include all forms of jointing, including but not limited to brazing, soldering, gluing, etc.
Class B and C joints should be inspected visually before welding. Inspect for defects such as cracks, holes, or areas where metal has been removed from either side of the joint. Discoloration may indicate a defect even if it is not visible to the eye.
Visual inspection entails inspecting a weld with the naked eye and/or under magnification. Our inspectors often look for cracks, pits, surface pores, undercuts, underfill, missing joints, and other flaws in the weld. They also evaluate the amount of heat input during welding to determine if the metal was properly joined.
Inspectors use different tools to perform their examination. Some common tools are microscopes, calipers, gauges, penetrometers, and weld torches. Microscopes allow the inspector to see small details invisible to the naked eye. Welding machines used by inspectors to test for defects in welds include magnetic flux core detectors, pulse-echo sounders, and radiographic film readers. These instruments provide information about the quality of the weld that is not readily apparent to the unaided eye.
Welding produces carbon which can discolor skin and clothes. The color varies depending on the type of metal being welded. Darker colors indicate heavier metals such as steel or iron. Light colored gases and slag indicate materials such as aluminum or zinc. Skin protection from the heat of welding includes protective clothing, goggles, and a face shield. A full body suit is best because it protects against hot metal splashing up onto your skin and clothing.
Welding also emits substances into the air that are harmful if inhaled.
Fillet welds are prequalified as a joint configuration and do not require testing to design a method. However, they must be performed in accordance with welding procedure requirements.
Welding procedures typically require that certain temperatures be maintained during the process to ensure integrity of the metal being joined. For example, MIG welding requires that a metal inert gas (MIG) shield be used to prevent oxidation of the metal during welding. The shield should be maintained at least 15 mm away from the surface to be welded for this reason; otherwise, the weld may have defects caused by oxidation. Other welding processes such as TIG welding or plasma cutting also require specific temperatures be maintained during processing to ensure quality of the weld.
If these temperatures cannot be maintained during processing, then prequalification of the joint configuration does not protect against defects due to heat treatment. For example, if a MIG weld is cooled rapidly after being deposited, then the metal may be below its recrystallization temperature when removed from the torch resulting in a grainy weld. This defect can be avoided by maintaining the welding process at a high enough temperature so that the metal remains above its recrystallization temperature upon cooling.
A third-class welder is defined as an employee who utilizes any of the aforementioned types of welding gear in tacking prior to the completion of work by another employee. Sample No. 1; Sample No. 2; and Sample No. 3 Using 51 papers, each sample page is printed on one side of the sheet with 12 points per inch. The samples are printed in black ink.
Third-class welders operate all types of welding equipment such as oxyacetylene torches, plasma cutters, and electric arc welders. They usually work under the direction of a second-class welder or supervisor. Most third-class welders have training in metal fabrication, machinery repair, and electrical wiring techniques. Some employers may not consider anyone without formal training in welding to be qualified for this job. The majority of companies that use third-class welders are self-employed individuals or small businesses.
Third-class welders typically work in construction or industrial settings. Some examples include manufacturing plants, oil fields, refineries, mining operations, and bridges. The number of jobs available for third-class welders will increase significantly between now and 2028. The growth rate of these types of welding jobs is much higher than the average for other occupations. In fact, the number of third-class welders is expected to increase by more than 50 percent over the next eight years.