Welding Essay Example
- Category:Engineering and Construction
- Document type:Assignment
The nondestructive examinations (NDE) are the tests for welds that do not destroy the portions of the completed welds. There are numerous NDEs that range from simple visual inspections to other more rigorous tests like it will be discussed in this paper.
Visual tests is the first and the simplest NDE. It is also the most important method, and it is widely used to inspect weld acceptability. It is also used in some cases to identify the bad welds that do not meet the expectations before other more sophisticated could be applied. The reason that the visual test is famous and widely is that it is easy, quick, and relatively cheap. Among other visual testing equipment include fillet weld gauges, rulers, squares, reference weld samples, and magnifying glasses among others. The visual tests provide among other information about the weld’s basic conformity to the specifications. This could be the information that includes the crown height, crown profile, weld size, surface color, dimensions, and root side penetration among others (Davies, 1993). This is relative to the specifications given or the sample. The visual tests may also show important discontinues in the weld.
Penetrant test is another important NDE method. This is a sensitive method that is used to identify and locate minute discontinuities that open to the surface of the weld. A penetrating liquid or dye is applied on the surface of the weld, and it enters the discontinuity, and the excess liquid is then removed from the surface of the weld. Then a developer is applied on the surface of the weld and allowed to dry. Through capillary action, the dye in the discontinuity will rise to be surface making the discontinuity easily identifiable. This method is used specially in nonmagnetic materials where the magnetic particle test cannot be applied. They are basically used to test for the surface defects. This test requires that the surface of the weld to be sprayed generously with the penetrant and then it is allowed to soak for a given time.
Magnetic test is another NDE. This is used to detect cracks, seams, segregations, inclusions, porosity, or lack of fusion in the materials. It can also detect surface defects that cannot be seen with the naked eye. When the magnetic fields are established in a ferromagnetic material, the tiny poles are set up at any defect. These poles have a stronger attraction for magnetic particles than the surrounding material has. When this test is being carried, the ferromagnetic is magnetized through the use of an electric current, and the magnetic particles or powder is applied on the magnetized area. When the magnetic field is interrupted by any defect, the magnetic particles will form around the defect (Davies, 1993). The pattern that is formed is the approximate size of the defect. Small, portable, and permanent magnets are used for light materials while the transformers, generators, or rectified are needed for heavy materials. This method can either be used wet or dry. The wet method is where the magnetic particles are suspended in a fluid and is more sensitive than the dry method. The dry method uses finely divided dry particles that are dusted onto the surface of the magnetic material with the weld that is to be tested.
Ultrasonic tests is another NDE method that is used to test weld. It is used to detect the presence of internal cracks, segregations, inclusions, porosity, lack of fusions, and similar discontinuities in the welds. It is also used in conjunction with other methods to determine the depth of the defects from the surface of the metal. In this method, a very high-frequency sound waves are transmitted through the weld that is being tested. The sound waves will then return to the sender, and display on the graph or on the monitor can be analyzed for inspection (Timings, 2006). The difference in the medium that indicates the presence of a defect is shown in the graph and shows the defect. This method is portable and nonhazardous. It is used for the numerous advantages that include great penetration power, high sensitivity, and allowing the inspection to be made from one surface. This method requires specific skills to carry it out. However, it is very effective and reliable.
Radiographic test is another NDE test for the welds. It is used to reveal the presence and the nature of discontinuities in the interior of the welds. It uses short wavelength radiations like the x-rays and gamma rays to penetrate the materials to be inspected that could be opaque to the ordinary light. The picture of the weld are then displayed on a graph that is known as the radiograph revealing how the weld looks from the interior. This method is highly sophisticated, hazardous, and expensive, and it also needs specialized skills to use it (Timings, 2006). As a result of these technical challenges, it is not widely used to inspect the welds. However, when it is used, it provided good revelations of the interior of the welds.
The methods that have been chosen for this project is the penetrant method and the ultrasonic tests. The penetrant method has been selected because it has the ability to show the surface defects like the cracks effectively. It is also relatively cheaper and easy to use. The penetrant method works as discussed above. The ultrasonic test has been selected because it is effective in showing the internal structures of the welds and reveal defects like the cracks (Timings, 2006). It is also nonhazardous to the users. The ultrasonic method will provide images of the defects and the welds to reveal their presence and their nature.
The destructive tests are the tests used for welder qualification and certification and welding procedure qualification. They are done by pulling apart the sample units. Because they end up destroying the material being tested, they are not used for materials that needed for use. The examples of destructive tests are discussed below.
Bend tests. These are used to determine the internal weld quality. The bend tests maybe be classified into; face bend, root bend, and side bend where each name is derived from the part of the sample being tested. In these tests, the weldment is sliced into test strips that are used as specimens called coupons. The weld is then bent around a die that is of a specific size that makes it create something like a horseshoe. This process will stretch the coupon to test the integrity (Davies, 1993). The outer bend of the coupon may be examined by methods like visual tests or penetrant method.
The tensile test is another method that is used to test the welds. This is used to compare the weldment to the base metal mechanical characteristics and specification requirements. The sample is sliced into coupons, and then each end is pulled in opposite directions until the coupon breaks or fails. The pulling is done by the tensile test machine. The tensile tests could be carried to determine a number of things that include the ultimate strength of the weld which denotes the point at which the weld will fail under tension, yield strength of the weld that denotes the point at which the weld yields or stretched under tension and will undergo permanent deformation, and elongation that denotes the amount of stretch that will occur in the weld under tension.
Notch-toughness test. This, like the name suggests, is used to show the ability of welds to resist cracking or crack propagation under extreme conditions like low temperature. This test is important especially when the weld is to be used in low temperatures. The sample is cut into coupons which are notched, cooled to low temperatures and they are then put under pressure until they fail. The coupons that are cut are prepared for tests like Charpy or Izod impact tests (Davies, 1993). When the tests are carried out, they are then compared to the specifications of a specification or the base material with known and the desired characteristics.
Cross section test is another destructive test that is used to examine the weld. This is used to define the internal structure and quality of the weld. The material to be tested is cut into cross sections that are then polished, etched, and examined visually or with the use of other specialized testing equipment. The specialized cross-section testing tests include the macrotest, the microtest, and microhardness test (Smith, 1995). For each of these tests, the cross section sample is prepared differently to capture the desired quality characteristics.
Nick-break tests is another destructive test that is used to determine the internal quality of a weld with respect to porosity, lack of fusion, and slag. The coupons are prepared and notches made on the side of the weld coupon in the weld area (Smith, 1995). These coupons are then laid across a support on each end, and then force is applied with a hammer in an attempt to break the weld sideways for the internal inspections. The nick that is made onto the coupon is used to make it possible for it to break when force is applied.
This report have shown the various tests that can be used to examine the welds to find and analyze cracks. There are tests that have been discussed that are important for welder qualification and certification and welding procedure qualification. These are the nondestructive tests and destructive tests. The nondestructive tests that were recommended for the company to be used in identifying the cracks in the welds are the penetrant tests and the ultrasonic tests. The penetrant tests is recommended because it will help the company find the cracks and other defects on the surface of the welds. The ultrasonic tests will be important in that they will provide the information regarding the internal defects or the internal structure of the welds. The advantages of the nondestructive tests is that they preserve the material being tested for use. This is unlike the destructive tests where the materials is destroyed. The nondestructive tests are also easy to be used and some are portable meaning that the tests can be carried to where the components are on remote test locations.
Davies, A. C., 1993. Science and Practice of Welding, Volume 1. London: Cambridge Univeristy Press.
Davies, A. C., 1993. Sience and Practice of Welding, Volume 2. London: Cambridge Univeristy Press.
Smith, B., 1995. Welding Practice. London: Butterworth-Heinemann.
Timings, R., 2006. Fabrication and Welding Engineering. London: Newnes.
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