A machine component may be turned to finished form and sizethen inspected for conformance to the appli. Crater cracks are formed by improper termination of the welding arc. Metallurgically, all fusion welds are dissimilar metal welds because. Weld discontinuities weld discontinuities are interruptions ofthe typical structure ofa weldment such as a lack ofcontinuity in its physical, metallurgical or mechanical characteristics discontinuities may be found in the weld metal, the heat affected zone and the base metal. The factors affecting weldability, welding process, base metal, filler metal and surface condition. Shielding gas inert or semiinert gas that is used to protect the weld puddle and arc from reacting negatively with the atmosphere. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Clean base metal check for proper gas coverage possible causes travel speed too slow cold welding procedures possible cures increase travel speed increase current possible causes improper electrode angle possible cures use correct welding technique possible causes insufficient weld metal possible cures reduce travel speed possible causes. Defects and discontinuities maritimeexpert website. Understand the origin and nature of common discontinuities. Module 9 weld and base metal discontinuities welding business. Weld discontinuities part 2 unacceptable weld profiles.
Ensure previous beads are free of overlap bead rollover and slag prior. In aluminum joints obtained by fusion welding, the defects such as porosity, slag inclusion. It may be caused by not raising the temperature of the base metal or previously applied weld metal to the melting point or failure to remove the slag or mill scale. Aws visual inspection workshop introduction 1 visual inspection of welding introduction rationale inspection is traditionally considered a postprocessing activity. Groove procedure qualification requirements 16 xiv. Since the line between discontinuities and defects varies from one industry to another, only a generalized explanation can give a good guide to isolating defects from discontinuities. A groove melted into the base metal and left unfilled by weld metal. Prequalified base metalfiller metal combinations for matching strength 17 xv. Laminations are flat, elongated discontinuities found in the center of wrought products such as plate. Discontinuities, which do not meet the requirements of the codes or specifications used to invoke and control an inspection, are referred to as defects. Visual inspection costs less than any other nondestructive inspection method. Back gouging the removal of weld and base metal from the other side.
Discontinuities that exceed established acceptance standards are. Overlap the protrusion of weld metal beyond the weld toe or weld root. The process uses shielding from an externally supplied gas to protect the molten weld pool. Weld defects and how to avoid them welders universe. Backing piece left in place failure to remove backing. Interpass cold lap is when the filler metal and previously deposited weld metal do not fuse sufficiently. Where weld metal does not form a cohesive bond with the base metal. Participants will learn the basic science and practical application of the most commonly utilized welding processes along with other essential topics, including welding terminology, weld design, welding safety, electrical theory, the weldability of metals, and welding quality control. A groove that is gouged in the base metal adjacent to the weld toe or weld root and is left unfilled by the weld metal main causes. Lincoln la75 and la85 electrodes, and mil880m flux at 28 volts and 340 to 350 amperes.
The value of visual inspection depends largely on the experience and welding knowledge of the inspector. Undercut this discontinuity is defined as a groove melted into the base metal adjacent to the weld toe, or weld root, and left unfilled by weld metal. Porosity occurs when gas becomes trapped in the weld pool, forming permanent bubbles as the metal cools from a liquid state. Weld zone has a cast solidified structure, while the base metal has a wrought structure the chemical composition of deposited weld metal is overmismatch or undermismatch to that of the base metal based on the required joint strength. A situation where the weld metal does not fuse or completely bond with the base metal or previously deposited weld metal. The likelihood of discontinuities occurring depends on a number of factors. A discontinuity or discontinuities that, by nature or accumulated effect for example, total crack length or amount of porosity, renders a. Incomplete fusion a weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads. Learn weld and base metal discontinuities with free interactive flashcards. Ramesh singh, in applied welding engineering second edition, 2016. Choose from 7 different sets of weld and base metal discontinuities flashcards on quizlet.
This condition can occur on a fillet weld or a butt joint. Discontinuities are interruptions in the typical structure of a material. Incomplete fusionincomplete union of the base metal with the filler metal incomplete penetrationa weld that does not continue through the full thickness of the joint. Submergedarc welding the second process evaluated was submerged arc welding with 332in. Detecting discontinuities through weld inspection matching. Below are six common welding discontinuities, along with their possible causes. The results also indicated that nominal electrode wire composition did not appear to play a.
Types of welding discontinuity and what is discontinuity. Porosity occurs, when the solidifying weld metal has gases trapped in it. Hook cracksseparations within the base metal that are parallel to the surface and turn toward the. Visual inspection is limited to detection of surface discontinuities. Common causes of discontinuities related to internal inconsistencies and weld metal irregularities. A weld discontinuity in which fusion did not occur between weld metal and fusion faces or.
Similar to machinability, it defines the capacity of a metal to be welded into a suitable design and the resulting weld joint to perform satisfactorily in the intended service. Base metal discontinuities lamellar tearing laminations and. Henry june 14, 2005 discontinuities, or flaws, can often occur in the welds used to manufacture welded tubular products. Defects and discontinuities tim turner elizabethtown technical college 2. The inspector should be familiar with design and weld requirements.
Dirty base metal inadequate gas coverage possible cures use proper arc length. Cracking is often associated with stress amplification near discontinuities in welds and base metal or near mechanical notches associated with weldment design. Undercut is defined as a groove melted into the base metal adjacent the weld toe, or weld root, and left unfilled by weld metal. Dirty base metal inadequate gas coverage possible cures use proper arc length clean base metal check for proper gas coverage possible causes travel speed too slow cold welding procedures possible cures increase travel speed increase current possible causes improper electrode angle possible cures. Fillet procedure qualification requirements 15 xiii. Transverse cracks are associated with longitudinal shrinkage stresses in weld metal that is embrittled by hydrogen. If the contraction is restricted, the strains will induce residual stresses that cause cracking. May 01, 2018 interpass cold lap is when the filler metal and previously deposited weld metal do not fuse sufficiently. Weld defects and how to avoid them needless to say, such grisly possibilities keep. Low amperage, steep electrode angles, fast travel speed, short arc gap, lack of preheat, electrode too small, unclean base metal, arc off seam. Undercut a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal.
These interruptions may occur in the base metal, weld material or heat affected zones. A response or evidence of a response disclosed through nde that requires. Start studying weld and base metal discontinuities. Weld and base metal discontinuities free download as pdf file. A sound weld means that theres uniformity with a very little variation tolerance everywhere you see, either on weld surface or in subsurface. A discontinuity consisting of any localized remelted metal, heat effected metal, or change in. The differences between discontinuities and defects. Base metal melting point, thermal conductivity and cte. Leaving slag or oxides on joint surfaces or neglecting to break up oxide layers on the base or filler metals.
The first is the melting away of the base material at the side. The discontinuous weld bead defect in highspeed gas metal arc. Cavity type discontinuities formed by gas entrapment during solidification of weld metal main causes. We will consider some of the discontinuities associated with weld profiles. Module 9 weld and base metal discontinuities welding. Fins, scabs, seams and laps are all terms that describe base metal discontinuities located in the heat affected zone of the weld and result from fabrication operations. The term undercutdescribes two specific conditions. Undercut, overlap, insufficient throat, and excessive convexity.
Lack of sidewall fusion is when the joint face and weld metal fail to fuse properly. Undercut can be present at a weld to weld junction or a weld to base metal junction toe of weld. Detecting discontinuities through weld inspection matching the inspection method to the welding process by sharon m. Undercut can be present at a weldtoweld junction or. Common causes of discontinuities related to shape, size and contour. Weld and base metal discontinuities welding fracture scribd. Is a condition where the base metal has been melted away during the welding operation and there is insufficient filler metal deposited to adequately fill the resulting depression. The process uses shielding from an externally supplied.
Also caused by shrinkage stresses in high constraint areas. Recognize the appearance of common discontinuities and the variables involved with interpretation. Jun 12, 2003 the second condition is reduction of the base metal s thickness at the line where the weld bead on the final layer of weld metal ties into the surface of the base metal. May 08, 2019 a sound weld means that theres uniformity with a very little variation tolerance everywhere you see, either on weld surface or in subsurface. Base metal properties such as chemical composition, cleanliness, laminations, stringers, surface conditions, and mechanical properties can affect weld quality. Weld and base metal discontinuities flashcards quizlet. Defect a flaw or flaws that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. Visual inspection started too late in the sequence of welding operations cannot detect improper joint. Module 9 aws cwi questions answers pdf download the below twenty 20 questions are model of 2018 version module 10. It can be generated by a seismic disturbance, metal fatigue or stresses in the heataffected zone haz. Weld metal protrusion beyond toe, face or root tungsten inclusion tungsten electrode particles entrapped in weld meltthrough condition where arc melts through weld root spatter metal particles expelled during welding that do not become part of the weld. Table 2 discontinuities commonly encountered with welding processes incomplete incomplete joint weldingprocess porosity slag fusion penetration undercut overlap cracks. Groove melted in basemetal adjacent to weld edge and left unfilled. Any weld would be a defect if the welder or the quality control department rejects it and blacklists the product.
Discontinuities, which do not meet the requirements of the codes or specifications used to invoke and control an inspection, are referred to. A sound weld is the best form of the weld, it will have the ability to withstand its designed stress, which means that the quality of fusion between the weld metal and the parent metal is top notch. Module 9 weld and base metal discontinuities free download as powerpoint presentation. C m ertification anual for welding inspectors certification certification certification certification certification fourth edition. The shrinkage stresses increase as the volume of shrinking metal increases.
The aws welding fundamentals course provides a comprehensive overview of the basic principles of welding. Slag cooled flux that forms over the top of the weld. Because of the large number of variables that can cause defects. Understanding weld discontinuities the fabricator metal. Welding fundamentals i american welding society education. Discontinuities may be found in the weld metal, the heat affected zone and the base metal. Q109 what base metal discontinuity, located at the weld toe, is caused by the. Oct 10, 2014 piping symbols,welding symbols,nde symbols. A weld discontinuity where fusion did not occur between weld metal and the joint or adjoining weld beads. If these discontinuities surpass a given products standards, they are defects. Gas metal arc welding gmaw, by definition, is an arc welding process which produces the coalescence of metals by heating them with an arc between a continuously fed filler metal electrode and the work. Incomplete fusion may result when the temperature of the base material or previously deposited weld metal is not elevated to its melting point. Transverse cracks are perpendicular to the weld and may propagate from the weld metal into the haz and base metal. However, a surface irregularity or weld discontinuity is not a rejectable.
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