Weld discontinuities part 3 cracking joints

Cold cracking can develop hours or days after the weld has been made, which is. Technically, a welding discontinuity is the lack of a mechanical, physical or metallurgical harmony in the weld. The weld quality, finishing and alignment requirements specified in this section. 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. Types of welding discontinuity and what is discontinuity. Dec, 2019 this study examined the lowcycle fatigue behavior of loadcarrying cruciformwelded joints containing incomplete penetration. Overlap the protrusion of weld metal beyond the weld toe or weld. Each section has notes on causes, and where appropriate, on rp. Five types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains. Welding defects can be said to be the irregularities formed in a given weld metal as a result of incorrect welding patterns, wrong welding process, or due to poor welding skills from the welders part. Fillet welds may be combined with full or partial penetration butt welds a combination weld. The likelihood of discontinuities occurring depends on a number of factors. 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. 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.

Of more importance is the determination of the effect of weld discontinuities. Detecting discontinuities through weld inspection matching. Table 2 discontinuities commonly encountered with welding processes incomplete incomplete joint weldingprocess porosity slag fusion penetration undercut overlap cracks. Will the discontinuity influence the weldment in its intended service and thus be termed a defect. The consequences of cracks formed on the oil and gas pipelines weld joints. Causes and prevention of corrosion on welded joints. There are five types of joints referred to by the american welding society. At this particular point, the crack runs between the alloy 625 weld metal, at the notch, and the interface. Inspection and repair is the tool for the control of the growth of cracks. 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. Prep, adjustments, beads and joints part 3 includes instructional photos, checklists, and stepbystep instructions. Start studying module 10 weld discontinuities and causes.

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. To fully understand weld discontinuities, we must first examine some welding. Several types of discontinuities may occur in welds or heat affected zones. Cold cracks the abcs of arc welding education center. Explain the mode of transfer of metal from the electrode to the weldment in each case. Backing piece left in place failure to remove backing. Understanding the difference will let you know if you need to scrap a part, repair it or simply add more weld. Factors affecting inservice cracking of weld zone in. Topics covered are basic welding techniques, various forms of sheetmetal work, frame repair and reinforcement, filling body holes and rust repair, tube steel, and more.

Fatigue design rules for welded structures january 2000. Jul 16, 2012 you can waste a lot of time and weld metal depositing an excessively high bead profile. Dye penetrant inspection dp, also called liquid penetrate inspection lpi or penetrant testing pt, is a widely applied and lowcost inspection method used to check surfacebreaking defects in all nonporous materials metals, plastics, or ceramics. Mgonja the consequences of cracks formed on the oil and gas pipelines weld joints, international journal of engineering trends and technology ijett, v544,223232 december 2017. Fusion welded circumferential joints in steel pipes of up to 50 mm wall thickness. 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. Welding discontinuities and defects hobart institute of. This discontinuity can be caused by incorrect welding techniques or insufficient current settings. Hot spot stress approach to keep pace with the increasing use of fea is discussed. Weld discontinuities part 1 porosity incomplete fusion incomplete penetration x this site uses cookies and other tracking technologies to provide you with our services, enhance the performance and functionality of our services, analyze the use of our products and services, and assist with our advertising and marketing efforts.

There are three factors which combine to cause cracking. The purpose of this field manual for structural welding is to summarize basic definitions, concepts and procedures for welded joints. Some joints call for considerable welder skill to obtain an. Aug 04, 2010 this feature is not available right now. Weld discontinuities part 2 unacceptable weld profiles. 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. Incomplete fusion a weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads. The test results revealed that the fatigue strength and. Visual inspection is limited to detection of surface discontinuities.

Any existing defects or notches aggravate crack formation. Covers how they are applied in different specifications, including consideration of residual stresses, size effect, material, welding process and environment. Henry june 14, 2005 discontinuities, or flaws, can often occur in the welds used to manufacture welded tubular products. System design, specifications, operation, and inspection. Aluminum butt joints 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. Defects in weld joints could result in the rejection of parts and assemblies. If the part has no cracks or other discontinuities, magnetic particles will not be attracted, and youll know your weld is without surface cracks. 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. A welding joint is a point or edge where two or more pieces of metal or plastic are joined together. Such bead shapes can have an effect on cracking, especially on cracking that occurs over time. The first step toward understanding weld discontinuities is to examine some welding terminology. Initiate arc inside the weld joint possible causes cold welding procedures travel speed too slow travel speed too fast improper joint detail possible cures increase current.

A welding defect is any flaw that compromises the usefulness of a weldment. Corrosion of weld joints can be avoided by the careful selection of materials to be welded, the filler metal, welding techniques and finishing. 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. Rules for classification and construction ii materials and welding 3 welding 2 design, fabrication and inspection of welded joints. Whereas there are acceptable limits for slag inclusions and porosity in welds, cracks are never acceptable. Effect of weld discontinuities on fatigue of aluminum butt. To remove slag from the undercut after production weld. Weld inspector responsibilities related to discontinuities and defects. 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. Defects and discontinuities tim turner elizabethtown technical college 2.

Defects in welding joints can be classified into two types as internal and external. Another no so common cause can be arc blow, where magnetic fields cause an erratic arc. When welding different metals together, such as steel to coppernickel the consumable will have 65% nickel content. Because of the wide range of applications and the many types of materials welded, cracking is an extremely complex subject. Describe two arc welding processes which involve slagmetal reactions. The welded parts will be failed due to various reason such as to improper welding procedures, composition of filler metal and base metal, selection poor work operator are some causes of weld joint failure. A defect can be considered a rejectable discontinuity. The weld throat may be the full section thickness, a full penetration joint, or a proportion only a partial penetration joint. Aug 18, 2019 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. Rules for classification and construction ii materials and. Discontinuities like lack of fusion, laminar tearing, and most forms of cracks are one of them.

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. The everyday pocket handbook for visual inspection and. The weld discontinuity that results from the initiation of the welding arc outside the weld joint is referred to as. Types of welding joints design and welding symbols. Destructive tests on welds in metallic materials hot cracking tests for weldments arc welding processes part 1. The inspector should be familiar with design and weld requirements. What weld discontinuity results when the welder travels too slowly, which causes excess weld metal to pour out of the joint and lay on the base metal surface without fusing. Hat cracks get their name from the shape of the crosssection of the weld, because the weld flares out at the face of the weld. Jul 11, 2017 a welded joint can have a low resistance to corrosion due to the varying chemical composition, residual stress and metallurgical structure of the weld zone. In case of wide differences in tensile strength between welding electrode and the base metal, there will always be chances of cracking and other welding discontinuities.

Above are several different representations of weld cracking. This one sample displays common weld discontinuities, providing the student with an excellent visual aid when learning how to identify and measure various weld surface characteristics order number seq1 weld groove sequencing plates. In some cases, a discontinuity can greatly affect the performance of the weld. Following are descriptions of some of the basic weld discontinuities. Weld flaws may come in different sizes, shapes, and degrees of severity. All defects are discontinuities, but not all discontinuities are defects. As a welding inspector, in order for you to successfully conduct your profession, it is important to understand weld discontinuities. This condition occurs in the haz or base material parallel to the fusion boundary in joints that are restrained. Of the three, cracks are by far the most detrimental. There are many codes depending on what type of product you are welding on.

Common causes of discontinuities related to shape, size and contour. Such a weld is unsightly and almost always unacceptable, mainly because of the weld reentrant angle to the base metal see figure 3. This condition can occur in fillet welds and butt joints and can produce notches at the toe of the weld that are undesirable due to their resultant stress concentration under load. Weld discontinuities part 3 cracking alcotec wire corporation. Cracking in the weld metal may not be typical, throughout the thickness of the whole sample, in part due to the undulating weld profile and other effects subsurface of the face of the polished specimen. Exhibit the proper sequencing and placement of weld beads in multipass groove welds. Methods to obtain weld discontinuities in spotwelded.

Module 10 weld discontinuities and causes flashcards quizlet. This pocket handbook provides a convenient source for the most common base metal and weld metal discontinuities found by. 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. For the purposes of this section, cracking will be dis tinguished. Visual inspection started too late in the sequence of welding operations cannot detect.

Recommended practice for radiographic examination of fusion welded joints part 3. Weld cracking several types of discontinuities may occur in welds or heat affected zones. The successful welding procedure will incorporate in its. Common causes are lack of shielding gas, excessive arc length, or dirty base material. A weld s ductility may decrease with a high carbon equivalent and a high cooling speed after solidification. Preheat or postweld heat treat weld joints that may develop a hard haz when corrosive conditions are met. 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. Weld discontinuities part 3 cracking cracks in the base material.

A sound weld means that theres uniformity with a very little variation tolerance everywhere you see, either on weld surface or in subsurface. Overlap the protrusion of weld metal beyond the weld toe or weld root. Discontinuities in weldscause and effect journal article. During testing, cracking behavior was observed on the side surface of the specimen. If a welder is qualified by testing in 3 8 inch thick tubular structural steel in the 6gr position cjp using a e701 8 electrode, is the welder qualified to weld a pjp on 1 inch thick structural steel plate in the vertical down position. 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. Hence to prevent cracking and other welding discontinuities we should always choose and electrode having minimum tensile strength equivalent to the parent metal being welded.

Weld discontinuities part 1 porosity incomplete fusion. Detecting discontinuities through weld inspection matching the inspection method to the welding process by sharon m. 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. Not all weld discontinuities are weld defects, but all weld defects are discontinuities. The generation or introduction of the discontinuities in a welded structure can result when the delicate balance of welding variables is upset. Weld joint cracking in subsea oil and gas systems pt ii twi. Weld discontinuities part 3 cracking cracks in a weldment are probably the most dreaded of all the weld discontinuities.

The piece can be magnetized by direct or indirect magnetization. Welds may contain porosity, slag inclusions or cracks. Welds may be single sided joints, welded all from one side, or double sided, welded from both sides, fig. It includes overlap, undercut, spatter, crater, excessive, convexity, surface porosity, slag inclusion, surface cracks, lack of fusion, necklace cracking and incompletely filled groove. The crack begins at a void in the welding crater, caused by the solidi. 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. What weld discontinuity results when the welder travels too slowly, causing excess weld metal to flow out. There are a number of cracking mechanisms associated with the welding of. The designer is therefore required to decide whether to use a tbutt weld, a fillet weld or a combination of the two. The problems of inservice cracking of weld zones can be minimized by attention to the important factors summarized below. The introduction of excessive stresses to the weld joint, particularly in conjunction with a material in a cracksensitive.

Therein lies the whole problem corrosion and weld discontinuities followed by cracking and corrosion fatigue along the heataffected zone of the welded joint. They are formed by welding two or more workpieces metal or plastic according to a particular geometry. Common causes of discontinuities related to internal inconsistencies and weld metal irregularities. The penetrant may be applied to all nonferrous materials and ferrous materials, although for ferrous components magneticparticle inspection. Cwi test flashcards flashcard machine create, study. 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. Sep 12, 2016 defects in welding joints can be classified into two types as internal and external. Methods to obtain weld discontinuities in spotwelded joints made of advanced highstrength steels article in welding in the world, le soudage dans le monde 551112. Those discontinuities in form of cracks might be an initial start of cracking in the spotwelded joints regarding fatigue loads. Discontinuity an interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. Defects hydrogen cracks in steels identification twi. A defect results in rejection of the part or product. The consequences of cracks formed on the oil and gas. This is used to assure a higher iron dilution from the steel during welding and prevents cracking.

The value of visual inspection depends largely on the experience and welding knowledge of the inspector. Engineering should be contacted to determine whether partial penetration of full penetration joints are appropriate for a particular situation. The slightly hardened heataffected zone of the weld is where most cracks occur. Cracking often is caused by stress concentration near discontinuities. Dec 06, 2017 any irregularity discontinuity or flaw in the weld metal, which exceeds the applicable code limit, is termed as a weld defect or welding defect. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Porosity cavities in the weld caused by trapped gas during solidification of the weld metal. Effect of weld penetration on lowcycle fatigue strength of. Incomplete joint penetrationis a discontinuity in a groove weld in which the weld metal doesnt extend through the joint thickness.

The manual addresses general considerations for welding, welder certification and inspection procedures. 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. Therefore, depending upon the application, failure of weld joints may occur in different ways and hence a different approaches are needed for designing the weld joints as per application and service requirements. Any weld would be a defect if the welder or the quality control department rejects it and blacklists the product. No matter how hard you try to repair it, youll only waste your time and resources, making it not worth the fuss. Undercut a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. Below is a representation of a convex fillet weld without discontinuities. This paper outlines the basis of current fatigue design rules for welded structures.