But, it sounds like your product can go back through the system, or, your system is portable. Welding defects since the welded joints are finding applications in crucial elements where the failure leads to a catastrophe, the inspection procedures and approval standards are so important than the past. Solidification cracks can appear in several locations, and orientations, but most commonly are. All defects are discontinuities, but not all discontinuities are defects. To fully understand weld discontinuities, we must first examine some welding. Detecting discontinuities through weld inspection matching the inspection method to the welding process by sharon m. The first step toward understanding weld discontinuities is to examine some welding terminology. Because of the wide range of applications and the many types of materials welded, cracking is an extremely complex subject. Preventing hydrogen induced cracking welding answers.
Our last post factors influencing hydrogen induced cracking went over the factors that contribute to hydrogeninduced cracking. Manual for repair and retrofit of fatigue cracks in steel. Weld discontinuities part 1 porosity incomplete fusion. The first step toward understanding weld discontinuities is to examine. Weld cracking several types of discontinuities may occur in welds or heat affected zones. In part 2 we discussed the importance of tube fitment when fabricating headers. Fatigue strength of steel members with welded details. The objective is to be able to identify and define various types of discontinuities and defects in addition to identifying and determining the common causes of those. Excessive melt through and back side weld reinforcement.
Of the three, cracks are by far the most detrimental. Intermediate weld discontinuities methods steel cwb group. Much like other weld defects porosity or undercutting, for example weld. Welds may contain porosity, slag inclusions or cracks. Weld inspector responsibilities related to discontinuities and defects. Crack in the weld transverse to the direction of weld run. Ppt defects and discontinuities powerpoint presentation. In low alloy steels, the cracks can be transverse to the weld, perpendicular to the. With root pass welding, quickly move the arc from the. May 08, 2019 in some cases, a discontinuity can greatly affect the performance of the weld. A free powerpoint ppt presentation displayed as a flash slide show on id.
Another acceptable partial penetration joint is shown below. The abcs of nondestructive weld examination reprinted courtesy of welding journal magazine an understanding of the benefits and drawbacks of each form of nondestructive examination can help you choose the best method for your application. So as it moved down the line we would air arc out the bad spots and used wire to weld it back in. Cracks in a weldment are probably the most dreaded of all the weld discontinuities. Partial penetration joint on the left without discontinuities is an acceptable condition where appropriate. It is of great interest to figure out, if, in comparison to specimens without weld discontinuities, the crack initiating point changes and if the fatigue resistance might be reduced by the discontinuities. Please note that a discontinuity can be termed as a defect only when, if it exceeds the specified code limit, hence we can say that every defect present in a weld metal is a discontinuity but every discontinuity present in the weld metal may not necessarily be a. The term back hand welding in oxyacetylene welding refers to.
As a welding inspector, in order for you to successfully conduct your profession, it is important to understand weld discontinuities. Analyzing the failure of welded steel components in construction. A steel component that consists as part of a structure will have an independent structural function. Aug 04, 2010 this feature is not available right now. Visual inspection started too late in the sequence of welding operations cannot detect. Aluminum conference american welding society education online. A defect can be considered a rejectable discontinuity. The cwb education intermediate weld discontinuities aluminum course provides instructional material presented by our knowledgeable cwb education instructors that. Defects and discontinuities tim turner elizabethtown technical college 2. The crack begins at a void in the welding crater, caused by the solidi.
Module 10 weld discontinuities and causes flashcards. When heated to welding temperatures, alloys such as stainless steel and inconel are prone to the formation of oxides if not shielded from oxygen present in the. In some cases, a discontinuity can greatly affect the performance of the weld. Thoroughly understanding the various defects, their causes, severity, and remedies can help ensure highquality and superior performance. Suck back 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 increase travel speed increase current possible causes. There are many codes depending on what type of product you are welding on. This pocket handbook provides a convenient source for the most common base metal and weld metal discontinuities found by. Jun 12, 2003 for this reason, its important for an inspector examining the weld to be able to spot a variety of weld discontinuities, including. The everyday pocket handbook for visual inspection and. How to solve 10 common tig welding problems guide millerwelds. This article presents an overview of welding defects and discusses design strategies to help prevent them. So, in a hybrid welding process with a backfeeding mode of filler wire, the.
At any rate, the saw will do the job cleaner and faster than any of the others for any rework that is required. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Below is a representation of a convex fillet weld without discontinuities. Sample questions for aws certified welding engineer. Failures related to welding failure analysis and prevention. Typical fatigue crack across a repaired flange butt weld in a welded igirder test. Those discontinuities in form of cracks might be an initial start of cracking in the spotwelded joints regarding fatigue loads. Cracks not only reduce the strength of the weld through the reduction in the cross section thickness but also. Most forms of weld cracking result from the shrinkage strains that occur as the weld metal cools. For instance, a 4043 aluminum filler rod from one manufacturer may have different properties than a 4043 rod from another manufacturer. Pdf the consequences of cracks formed on the oil and gas.
Understanding why your welds crack part 3 location of cracks. This intermediate course is intended for managers, engineers, inspectors, welding supervisors, welders and other personnel responsible for the quality of welded aluminum products. So its best for you to avoid it from the very first. The generation or introduction of the discontinuities in a welded structure can result when the delicate balance of welding variables is upset. The value of visual inspection depends largely on the experience and welding knowledge of the inspector.
When hot crack occurs on the weld metal then it is termed as solidification crack and if it occurs in the haz then called as liquation crack. For the purposes of this section, cracking will be dis. The fracture surfaces displayed chevron marks pointing back to the weld between the frontal cover and side. Other issues may be welding defects that went undetected such as. Start studying module 10 weld discontinuities and causes. Consumables comprise only a small portion of the total cost of tig welding, but they are an important factor in creating quality welds. The presence of a weld discontinuity is relatively high regardless of whether a complete joint penetration groove weld was employed or if for some reason the. Any weld would be a defect if the welder or the quality control department rejects it and blacklists the product.
Sep 25, 2015 most common in weld discontinuities or weld defects or weld imperfections or weld faults, or weld irregularities in weld examples lack of fusion, porosity, slag inclusion, cracks, side wall. 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. This conference is designed to provide a basic understanding of aluminum welding and will include the following topics. Defects and discontinuities 1 defects and discontinuities tim turner elizabethtown technical college 2 defect. A phenomenological study of weld discontinuities and defects in resistance spot welding of advanced high strength trip steel. Weld discontinuities effect of fatigue transverse cma welds longitudinal cma welds 5456h116 aluminum discontinuity repair crack arrest methods stop holes interference bolts cation 09000039000 ref. Effect of weld discontinuities on fatigue of aluminum butt. Weld on ceramic weld metal support at high currents. Dec 04, 2018 weld cracking refers to a depression left at the termination of a weld where the weld pool is left unfilled.
If you have two welds with exactly the same leg size but one is flat and the. 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 best defense against weld cracking is to understand its causes and solutions. The piece can be magnetized by direct or indirect magnetization. A material or device placed against the back side of the joint adjacent to the joint root, or at both sides of a joint in electroslag and electrogas welding, to support and shield molten weld metal. Codes and standards define the quality necessary to achieve the integrity and reliability of the weldment. When we weld with fcaw, innershield or dualshield, and get a bad spot we clean it out and repair it with the same. The differences between discontinuities and defects. Fatigue cracks initiating from the weld toe and subsequent. Defects hydrogen cracks in steels identification twi. When welding different metals together, such as steel to coppernickel the consumable will have 65% nickel content. Overlap the protrusion of weld metal beyond the weld toe or weld root. Therefore, weld beads with a small depthtowidth ratio, such as formed in bridging a large gap with a wide, thin bead, will be more susceptible to solidification cracking, as shown in fig. Understanding the difference will let you know if you need to scrap a part, repair it or simply add more weld.
Undercut causes a stress concentration point stress riser that is a potential starting point for weld cracking. Above are several different representations of weld cracking. Describe two arc welding processes which involve slagmetal reactions. Suck back arc strikes underfill overlap possible causes long arc length dirty base metal. Every crack, regardless of its type or origin, weakens. Pdf a phenomenological study of weld discontinuities and. It is the welding inspectors function to identify these discontinuities through visual inspection and often to evaluate their acceptance, or rejection, through the use of the. Weld defects and discontinuities 1 weld defects and discontinuities 2 defect.
Both solidification cracking and hot cracking refer to the formation of shrinkage cracks during the solidification of weld metal, although hot cracking can also refer to liquation cracking. Common causes of discontinuities related to shape, size and contour. Aluminum welded applications and why we are seeing a continued increase of aluminum being used in industry. Do not perform autogenous welding, this will result in porous weld joints, due to the structure of the cuni alloy that contains no deoxidizers due to a deficiency in deoxidants in the alloys, porosity is a problem and they cannot be welded autogenously. There are three factors which combine to cause cracking. A flaw or flaws that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. If you recall, we mentioned you need all three factors to be present in order to have hic. Several types of discontinuities may occur in welds or heat affected. Repair of discontinuities american welding society. Bridge welding code should keep discontinuity size sufficiently small to. If the contraction is restricted, the strains will induce residual stresses that cause cracking. In this case, the centre of the weld which is the last part to solidify, is a narrow zone with negligible cracking resistance. Porosity is one of the classic discontinuity that happens in welding. The cracking mechanisms that can occur during laser welding can generally be.
If a discontinuity renders a weld incompetent or lowers its quality, it would be classified a defect. Welding defects classification, causes and remedies. As the torch moves back into the puddle, the molten metal doesnt stop and wait. Timing did the crack occur immediately after welding hot crack, did occur after the weld and base metal cooled down cold crack. Weld discontinuities part 1 porosity incomplete fusion incomplete penetration. No matter how hard you try to repair it, youll only waste your time and resources, making it not worth the fuss.
Weld cracking lincoln electric global sites select your. Defects in weld joints could result in the rejection of parts and assemblies. Discontinuity an interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. The successful welding procedure will incorporate in its.
A crack on a water pipe would be a defect since the water will leak while an unacceptable profile could pass as a discontinuity as long as the pipe doesnt leak. 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. Weld discontinuities select your country or region. Figure 2b shows the way an aluminum tig bead should look. Cracking cracking, especially, in stainless steels. Weld discontinuities part 2 unacceptable weld profiles the profile of a completed weld may have considerable affect on the performance of that weld in service. Im not sure why you were taught that lowhydrogen was the only way to repair discontinuities. Welding inspection and quality control upon completion of this module you will be able to. Magnetic particle inspection mpi is a nondestructive testing ndt process for detecting surface and shallow subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. Residual stress in a weld can be larger than expected if it contains weld discontinuities such as incomplete fusion, incomplete joint penetration, overlap, undercut, slag inclusions, and porosity. Visual inspection is limited to detection of surface discontinuities. This is used to assure a higher iron dilution from the steel during welding and prevents cracking. When tig welding, you want to choose torch consumables that offer both consistency and durability. Fatigue crack growth from weld at end of partial length cover plate beams, indicated that the fatigue strength of the welded beam was the upper bound that could.
A crack may be defined as a local discontinuity produced by a fracture which can arise from the stresses generated on cooling or acting on the structure. Effect of weld discontinuities on fatigue of aluminum butt joints. There shall be no any open discontinuity in the weld or heat. Detecting discontinuities through weld inspection matching. Discontinuities like lack of fusion, laminar tearing, and most forms of cracks are one of them. Acceptance criteria represent the minimum weld quality and are depending upon the test of welded specimens containing a few discontinuities, usually, a safety factor is added to give the. Identify the different inspection methods used in non destructive testing. N ot all weld discontinuities are weld defects, but all weld defects are discontinuities. A weld s ductility may decrease with a high carbon equivalent and a high cooling speed after solidification. The inspector should be familiar with design and weld requirements. Most common in weld discontinuities or weld defects or weld imperfections or weld faults, or weld irregularities in weld examples lack of fusion, porosity, slag inclusion, cracks, side wall. Explain the mode of transfer of metal from the electrode to the weldment in each case. Jul 11, 2006 welding discontinuities can affect product performance and longevity. A fix for an incomplete penetration joint would be to back gouge and weld from the other side.
Effect of weld discontinuities on fatigue of aluminum butt joints a 40% to 75% reduction in fatigue life was observed in weld repaired specimens that did not have their weld reinforcement properly ground or peened by g. Incomplete fusion a weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads. You can use a back stepping technique or use the crater fill option on some of the newer power sources. We will now go over how to prevent hic from happening. Use correct welding technique possible causes insufficient weld metal possible cures reduce travel speed. How to choose the right tig torch welding consumable. It happens when there are just so many gas molecules trapped inside during welding. Module 10 weld discontinuities and causes flashcards quizlet. Weld discontinuities can prevent a weld from meeting the minimum quality requirements. It is the most serious type of imperfection found in a weld and should be removed. Figure 3 shows a bead with a grainy appearance, which is typically caused by filler metal problems. Dec 06, 2017 any irregularity discontinuity or flaw in the weld metal, which exceeds the applicable code limit, is termed as a weld defect.
It is important to remove the entire weld by grinding it back and. Learn how to weld pipe, structural steel, mig, tig, stick, flux core and more. Intermediate weld discontinuities methods aluminum cwb. Underbead cracks are cold cracks that form in the haz when three conditions are met. Following are descriptions of some of the basic weld discontinuities. The material may be partially fused or remain unfused during welding and may be either metal or nonmetal.
Henry june 14, 2005 discontinuities, or flaws, can often occur in the welds used to manufacture welded tubular products. This intermediate course is intended for managers, engineers, inspectors, welding supervisors, welders and other personnel responsible for the quality of welded steel products. Weld discontinuities part 3 cracking cracks in a weldment are probably the most dreaded of all the weld discontinuities. Crater cracks causes the welding ended far too abruptly. Understanding why your welds crack part 3 welding answers. Saw will go back over itself and the repair area just fine. Welding discontinuities defects imperfection youtube. Common causes of discontinuities related to internal inconsistencies and weld metal irregularities. 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. It is caused by the diffusion of hydrogen to the highly stressed, hardened part of the weldment. The cwb education intermediate weld discontinuities steel course provides instructional material presented by our knowledgeable cwb education instructors that covers. This phenomenon of fatigue crack growth from a small discontinuity to failure, and the fatigue strength reduction. The likelihood of discontinuities occurring depends on a number of factors.
Fortunately, as with any part of the welding process, the best defense against. Undercut a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. Weld discontinuities part 3 cracking cracks in the base material. Welding discontinuities and defects hobart institute of. This month, we will discuss techniques involved with back purging exhaust tubes. Understanding why your welds crack part 3 location of cracks comment 1 share.