The moisture turns into a gas when heated and becomes trapped in the weld during the welding process. The development of the most important welding defects is explained in the following paragraphs. Pdf the impact of the internal welding defects on the joint strength. Pdf the paper looks at the impact of the internal welding defects on. Slag inclusion formation during solidification of steel. Defects imperfections in welds slag inclusions twi. As slag is the residue of the flux coating in mma welding, it is principally a deoxidation product from the reaction between the flux, air and surface oxide. Welding defects free download as powerpoint presentation. Slag inclusion causes and remedies hong ky welding machine. Micrograph of a slag inclusion in an sg iron casting. Slagis the waste material created when youre welding, and bits of this solid material can become incorporated accidentally into your weld, as in figure. Slag inclusions a little bit of slag goes a long way.
The question is to determine if they are significant considering the application. Slag inclusions incomplete fusion concave root surface suckback arc strikes underfill overlap possible causes long arc length 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. Slag inclusion is one of the welding defects that are usually easily visible in the weld. The molten slag shield in liquid form, so reduce the oxidation of metals. What is welding defects types, causes and remedies. So we will talk about the causing reason of welding slag inclusion and stomata defects here, and then we will give preventive measures for you. Consequently, the risk of slag inclusions is significantly greater with basic fluxes due to the inherent convex weld bead profile and the difficulty in removing the slag from the weld toes especially in multipass welds. Solid inclusion includes slag, metal oxides, tungsten, wagon track, etc. A casting defect is an undesired irregularity in a metal casting process. Slag inclusions and gas defects under the surface of a grey iron casting. The value of visual inspection depends largely on the experience and welding knowledge of the inspector.
All base and filler metals need to be cleaned, whether the contaminant is mill scale, oxide on aluminum or dirt and grease on filler metals. Use grinding when welding difficult butt joints otherwise wire brushing or light chipping may be sufficient to remove the slag. Strong reaction of slag accompanied by liberation of gases. One of the first things you should have learned about welding is to clean materials prior to welding. Welding defects can be welding processprocedurerelated, or related to the chemical composition or metallurgy of the alloys being welded. Too many and too thin beads, usually because the electrode is. This implies that the weld joint is expected to have equal or greater strength than the base metal. Weld defects and how to avoid them welders universe. Weld metal porosity is a cavitytype of welding defect formed by gas entrapment during solidification as a result of contamination by certain gases, such as hydrogen, oxygen, or nitrogen.
A perfect weld every time is a lofty goal, but there are simple steps you can take and preparations you can make that will keep you from ending up with the kind of welds that need to be repaired or completely redone. This photo figure 6a shows what happens when you dont clean the mill scale off hotrolled mild steel. Among the commonly known welding defects, incomplete penetration and fusion, porosity and slag inclusions are the most common to affect welding strength. Weld imperfections and preventive measures kobe welding. Welding defects asme design code generally does not describe the strength of weld joints, such as a full penetration butt weld, separate to the strength of base metal in the pressure component.
Defects such as porosity, undercut, notches, and slag inclusions are not encountered. Slag and flux inclusions are linear defects but because they do not have sharp edges compared with cracks, they may be permitted by specific standards and codes. Turbulence and oxidizing atmosphere leads to linear shaped inclusions in the surface area. Kemppi welding technology course weld defects, their. Lack of fusion is defined stringer type inclusions as unfused area between slag line weld metal and base matedifferent shapes and directions. Sharp notches in joint boundaries or between weld passes promote slag entrapment.
The gtaw process produces superior quality welds that are free from most defects. Defects of welding defects are those which can be theoretically eliminated, such as cracks, lack of fusion, slag inclusions, porosity and undercuts only when we understand the nature of these defects and why they occur, can we eliminate them 4. Imagine the many places that discontinuities and defects could be generated in this process. Lack familiarity with welding misinterpret design intent applied stresses fabrication sequence weld process capabilities typically show up in firstpart manufacture or after service failure. Incomplete penetration ip or lack of penetration lop occurs when the weld metal fails to penetrate the joint. Welding cracks can be present at the surface, inside of the weld material or at the heat affected zones. Welding defects 2442 visual inspection asme procedure 4363 visual inspection labs 6466 visual inspection examination report sheet 67 this project was supported, in part. Slag inclusions are nonmetallic particles trapped in the weld metal or at the weld interface. Weld defects and how to avoid them welding jobs, equipment. Mma, fca and submerged arc, but they can also occur in mig welding. A welding defect is any flaw that compromises the usefulness of a weldment. Slag inclusion is a type of welding defect that is easily visible in the weld. Today we will learn about welding defects, its types, causes, testing, and remedies.
Wld 204 non destructive testing i visual testing pcc. I used this to train qaqc engineers in asia, what defects are and the possible effects they can have on the finished products. Aug 14, 2014 the entrapment of unwanted solid particles impairs weld metal strength. Remedies increase the travel speed or electrode angle. Defects are common phenomenon in any manufacturing process. If backwelding is not possible, must remove and reweld. Slag inclusions are nonmetallic solid material entrapped in weld metal or between weld and base metal. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. The acceptance and rejection criteria of discontinuities are the roles of the standard codes such as api, asme, astm, aws, etc. In aluminum joints obtained by fusion welding, the defects such as porosity, slag inclusion, solidification cracks etc. Slag is caused by inadequate cleaning other inclusions include tungsten and copper inclusions from the tig and mag welding process m. Ramesh singh, in applied welding engineering second edition, 2016. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated.
The rounding radius of the defect depends on the welding method, the type of metal, and the stability of the welding parameters. The various types of external defects with their causes and remedies are listed below. Sharper internal defects narrow gaps, sharp slag inclusions may. Slag inclusion formation during solidification of steel alloys and in cast iron sofia adolfi 2007 department of materials science, royal institute of technology s100 44 stockholm, sweden abstract this thesis explores the formation of segregation and inclusions during solidification of. Visual inspection costs less than any other nondestructive inspection method. Such weld imperfections are developed by the inclusion of solid substances like slag, flux, foreign metal or oxide. Slag is a vitreous material that occurs as a byproduct of stick welding, fluxcored arc welding and submerged arc welding. A weld slag inclusion is a common discontinuity with the abovementioned welding processes. Weld defects and how to avoid them needless to say, such grisly possibilities keep inspectors on their toes and engineers lying awake deep into the night wondering if their designs correctly anticipated everything that might go wrong. Slag inclusions in the top part of a grey iron casting, in some cases still there, in others already removed by shot blasting.
Typically, the applicable codes or standards specify the maximum allowable limits of these types of defects in a weld based on the application. A weld defect is defined as an imperfection or group of imperfections which is outside the limits. Is can occur when the flux, which is the solid shielding material used when welding, melts in the weld or on the surface of the weld. Welding defects 109 a distinction of arising defects by their origin is shown in figure 9. Welders of all skill levels should strive to improve their welding techniques and eliminate common weld flaws. Radiograph of a butt weld showing two slag lines in the weld root slag. Which process having continuous addition of slag not required. Which weld cleaning operation from the list below, may harm the surface of the weld and mask surface defects. Visual inspection can detect and aid in eliminating discontinuities that might become defects in the completed weldment. Cluster porosity appear just like regular porosity in the radiograph but the indications will be grouped close together. There are a number of quality issues to consider in mma welding. With proper technique, slag inclusions rise to the surface of the molten.
The welds are free from slag inclusions, and if properly maintained free from any inclusions, including tungsten inclusions, they are also free of the spatter process. Feb 28, 2017 in this video you will learn about different types of welding defects such as porosity, slag inclusion, weld spatter, lack of fusion and penetration and weld. A weld defect is any physical characteristic in the. Welding technique has an important role to play in preventing slag inclusions. Slag inclusions result from faulty welding technique, improper access to the joint, or both.
Kemppi welding technology course weld defects, their causes. So we will talk about the causing reason of welding slag inclusion and stomata defects here, and then we will give preventive. Typically, the applicable codes or standards specify the maximum allowable limits of these types of. The entrapment of unwanted solid particles impairs weld metal strength.
Most welds contain defects porosity, cracks, slag inclusions, etc. As youre welding, youre likely to encounter slag inclusions foreign materials trapped in the weld metal at continuous or randomly spaced intervals. Slag inclusions are usually associated with the flux processes, i. In this weld the clean weld is formed, so no cleaning required for after welding. As further examples of some of the reasons discontinuities and defects in metals the processing of iron ore to make still is shown in the following slides. The most common is slag, a nonmetallic solid material trapped in the weld or between the weld and the base metal. Welding defects are generated in a welding job due to the faulty or poor technique used by the inexperienced or unskilled welder or due to fundamental difficulties in the welding operation. When steel pipe manufacturer such as prime steel pipe producing welded steel pipe, it is unavoidable that some welding slag inclusion and stomata defects may appear if workers dont control very well during operation. An ideal weld or good weld should be such that adequate fusion exists between the filler metal and edge preparation together with good penetration. Solid inclusions that impair weld characteristics welpedia. Slag inclusions causes slag runs ahead of the weld insuf. Porosity trapped slag lack of fusion lack of penetration or excess penetration undercut hot cracking hydrogen induced haz cracking lamellar tearing welding defects essentially a discontinuity or flaw is called a defect if it exceeds the acceptance limits established by engineering based on fitness for.
Slag inclusion is the small particles of flux that become trapped in the weld metal which prevent. Secondary processing discontinuities welding porosity. It is impossible to form a defect free welding joint but it can be reduce to some extent by taking some precautions. Weld slag inclusions can be caused by improper welding technique, improper flux or improperly handled flux. Slag inclusions are usually associated with the flux processes, ie mma, fca and submerged arc, but they can also occur in mig welding. This is due to some process limitation and some human behavior. Stressconcentration coefficients of internal welding defects.
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