A Look at Some Common Weld Techniques
In general, there are several different methods used to create a weld, and the weld techniques used depend on the type of weld being created. The most common welding technique used for all kinds of welds, and the one we’ll discuss here, is the arc welding technique. By using a welding gun with an arch-shaped tip (the tungsten inert gas), an arc is created between the welded metals. This can be performed with the traditional arch-type or new, high-speed plasma arc welding machines. There are other varieties of weld techniques as well, including; the double-sided, direct-feed, and wet-cut. All of these methods have their benefits and limitations.
Weld inspection techniques are designed to detect problems before they become weld failure. This is accomplished by visually inspecting the welded parts to identify any defects in welds or lack thereof. In addition to visual inspection, visual weld inspection techniques include but are not limited to, bending, twisting, popping, and cracking. All of these methods can pose serious threats to the weld and may require further weld improvement techniques to prevent future weld failure.
Weld failure indicators can be visual or mechanical. weld failure indicators can be both external and internal. Common external weld failure indicators are external corrosion, warping, bulging, bending, or flaking. Typically, when these weld failures occur, they are most commonly found in uninfected areas such as flashings, joints, weld centres, in which the weld is shallow or close to an air or coolant feed. This is why welded areas must be inspected before work begins.
Internal weld inspection techniques involve various physical examinations of welded areas of the weld puddle. Two of the most common methods are the mechanical torsion test and magnetic flux-cored arc welding (FTC-MAW). The majority of weld inspection techniques use longitudinal, or flatter, beam and horizontal line flux-cored scans. While these tests can detect weld stresses and weaknesses visually, they are unable to determine whether these stresses and weaknesses are induced by external forces, or if they result from weld puddle deformation. Additionally, they do not reveal the weld puddle depths or areas of weld stress within the welded area.
Weld failure indicators using mechanical testing methods are designed to detect weld stresses, while those using magnetic testing techniques are designed to identify weld weakness. welded areas in your welded structure can be observed with both types of testing. Magnetic flux-cored arc welding (FTC-MAW) utilizes a rod in the filler metal that is heated, typically by a tungsten electrode, to induce localized heating throughout the weld puddle. The rod is then followed by a magnetic pulse and a weld puddle is generated. Because the intensity of the magnetic field fluctuates, the weld failure indicators continue to shift until the weld is weak enough to move away from the magnetic focus.
Another variation on the above method uses a hand taper probe that extends from the weld joint at the weld tip to its deepest part in the weld puddle. There is a small handhold in the weld holding mechanism that allows the user to continuously measure the weld depth and weld puddle area. The probe can be manually turned while still in the weld holding area to continuously measure the weld failure indicators. If the weld failure indicators continue to shift, this is a sign that additional tests may be needed.
A final variation of the above test is the electro-hydraulically weld failure indicators. This type of test can be performed without the use of any consumables. The tester holds electrodes in a bucket with a mixture of water and fuel. An electric current is used to generate alternating current in the filler metal as it cools, which heats the weld puddle. As the weld temperature nears the melting point, the current produces an arc that heats the filler metal as it cools.
After the filler metal has cooled to the proper melting point, the current is abruptly stopped. The welding rod now cools and fuses with the weld puddle. If the weld fails, this is the indicator that a further arc should be welded before the rod cools. The most important thing to remember when testing welds is that the weld must be allowed to cool without interruption. Otherwise, you are setting yourself up for a poor weld that will ultimately fail.