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Department of Materials and Ceramic Engineering Faculty of Engineering- Imam Khomeini International University. VISUAL TESTING. Presenter: K. Hosseini. Hosseini-k@eied.com. 1. Introduction
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Department of Materials and Ceramic Engineering Faculty of Engineering- Imam Khomeini International University VISUAL TESTING Presenter: K. Hosseini Hosseini-k@eied.com hosseini-k@eied.com
1 Introduction Visual examination is used to determine the quality levels or conditions of welds, base material processing discontinuities, bolting, and other components. A good weld should be generally uniform in height. hosseini-k@eied.com
1 Improper welding techniques can create an excessively uneven weld with high and low areas. Improper current, incorrect arc length, and incorrect welding speed may create these uneven areas. hosseini-k@eied.com
1 The high-low profile thus created is undesirable because it makes other weld defects more difficult to interpret during a visual inspection as well as making nondestructive examinations more difficult to interpret. hosseini-k@eied.com
1 Pipe, fittings, valves, and other parts come in a variety of metals, alloys, diameters, and wall thickness. Materials, components, processes, and procedures are varied. It is important to learn and understand these procedures in order to assure that all material and work meet the specified requirements. hosseini-k@eied.com
1 Various criteria are used to judge the acceptability of welds. The accept/reject criteria will determine the acceptable sizes of specific discontinuities.. hosseini-k@eied.com
1 Procedures for welding examination of ASME code stamped systems are strict, and yet we have tolerances to work with. Some discontinuities may be acceptable if they do not exceed allowable tolerances. The welding specialist must be able to recognize and disposition base metal and welding defects as required by the project scope. hosseini-k@eied.com
1 When welding is performed on materials such as beveled pipe or plate, the first pass should penetrate to the underside of the joint. A flat or slightly convexbead should appear on the underside of the plate or on the inside of the pipe joint. hosseini-k@eied.com
1 When the bead does not penetrate the required depth, the weld is considered incomplete. The bevel and the root gap should always be in accordance with the applicable welding procedure. In addition to inadequate fit-up, there are other possible causes of insufficient penetration or excess reinforcement.. hosseini-k@eied.com
1 The welding technique can cause poor penetration if the welder moves too fast and excess reinforcement if he moves to slowly. Using the wrong size electrode or filler metal and incorrect amperages can also cause unacceptable root contours. Using too large of an electrode prevents penetration into the root area and incomplete penetration results. hosseini-k@eied.com
1 Excess Reinforcement The top of the weld, or cap as it is sometimes called, is the area where excessive reinforcement may occur. Excess reinforcement can be harmful to piping because it may create an excessive load at the toe of the weld. This may induce flexing of the pipe and premature failure. hosseini-k@eied.com
1 For this reason the reinforcement should blend smoothly from the base metal to a slight crown. hosseini-k@eied.com
1 Excessive Reinforcement hosseini-k@eied.com
1 Excessive Reinforcement hosseini-k@eied.com
1 Underfill Underfill is a depression on the face of the weld which is below the height of the base material. The welder failed to fill the weld joint completely. hosseini-k@eied.com
1 Underfill Underfill is a depression on the face of the weld which is below the height of the base material. The welder failed to fill the weld joint completely. hosseini-k@eied.com
1 Underfill This is another example of underfill.. hosseini-k@eied.com
1 Inadequate or Incomplete Penetration Inadequate or incomplete penetration is the joint penetration being less than intended or a condition created when the penetration and fusion of the filler material within the joint cavity fails to reach the specified depth within the base material cross section. hosseini-k@eied.com
1 Incomplete penetration can result from insufficient root gap during fit-up or when weld shrinkage causes the root opening to close. Another common cause can be that an excessive root face or land is provided during joint preparation that precludes penetration to the back side of the joint. For joints welded from both sides, inadequate back-gouging prior to welding the second side can result in lack of penetration. hosseini-k@eied.com
1 Excessive Penetration Unacceptable root contours can result from either too much or too little penetration. Excessive penetration appears as a bead that is too high on the underside of the plate or on the inside of the pipe. When this occurs, the welder is moving or manipulating the weld rod too slowly or the current is too high. hosseini-k@eied.com
1 Drop Through Drop through is an undesirable protrusion or surface irregularity at the weld root. When the molten weld puddle does not solidify quick enough, it will sag. Generally, this condition is caused by too wide of a root gap, excessive heat, improper welding technique, or a combination of these. hosseini-k@eied.com
Lighting must be at an appropriate level and of the correct type lux (lx) the SI unit for measuring the illumination (illuminance) of a surface. One lux is defined as an illumination of one lumen per square meter or 0.0001 phot. In considering the various light units, it's useful to think about light originating at a point and shining upon a surface. The intensity of the light source is measured in candlas; the total light flux in transit is measured in lumens (1 lumen = 1 candela·steradian); and the amount of light received per unit of surface area is measured in lux (1 lux = 1 lumen/square meter). One lux is equal to approximately 0.09290 foot candle hosseini-k@eied.com
Rigid Flexible fiber optic hosseini-k@eied.com
Borescopes are devices that permit inspection of internal surfaces in piping, engines, air frames etc. They contain systems of lenses, mirrors, prisms and lighting which illuminates the test area and transmits images to the inspector. They may be either rigid or flexible. The flexible type uses optical fibres, the smallest have outside diameters of just a few millimetres and can be steered into position around tight bends. hosseini-k@eied.com
Television cameras combined with borescopes, video recorders and image processing equipment permit the remote collection and storage of visual images. This permits inspection in difficult and hazardous sites, e.g. nuclear installations and underwater pipelines. Image enhancement by computer is also possible. hosseini-k@eied.com
Surface replication using strippable films also permits the remote inspection of surfaces. Etching for metallographic examination and to reveal cracks, inclusions and localised variations in composition and hardness . hosseini-k@eied.com
Surface replication using strippable films also permits the remote inspection of surfaces. Etching for metallographic examination and to reveal cracks, inclusions and localised variations in composition and hardness . hosseini-k@eied.com
Ultimately, visual testing is dependant upon the eyesight of the inspector. Regular eyesight tests for both visual acuity and colour differentiation are essential. The time for continuous viewing must be restricted with frequent rests to reduce fatigue. hosseini-k@eied.com
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