Weld discontinuities part 3 cracking joints

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. Cwi test flashcards flashcard machine create, study. A defect results in rejection of the part or product. Because of the wide range of applications and the many types of materials welded, cracking is an extremely complex subject.

Weld discontinuities part 3 cracking alcotec wire corporation. 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. Common causes are lack of shielding gas, excessive arc length, or dirty base material. Destructive tests on welds in metallic materials hot cracking tests for weldments arc welding processes part 1. Weld discontinuities part 3 cracking cracks in the base material. 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. Of the three, cracks are by far the most detrimental. 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. Those discontinuities in form of cracks might be an initial start of cracking in the spotwelded joints regarding fatigue loads. 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.

The purpose of this field manual for structural welding is to summarize basic definitions, concepts and procedures for welded joints. Effect of weld discontinuities on fatigue of aluminum butt. The consequences of cracks formed on the oil and gas pipelines weld joints. Common causes of discontinuities related to shape, size and contour. 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.

Covers how they are applied in different specifications, including consideration of residual stresses, size effect, material, welding process and environment. Dec, 2019 this study examined the lowcycle fatigue behavior of loadcarrying cruciformwelded joints containing incomplete penetration. Weld discontinuities part 3 cracking cracks in a weldment are probably the most dreaded of all the weld discontinuities. Module 10 weld discontinuities and causes flashcards quizlet. There are three factors which combine to cause cracking. The weld quality, finishing and alignment requirements specified in this section. The successful welding procedure will incorporate in its. The generation or introduction of the discontinuities in a welded structure can result when the delicate balance of welding variables is upset. Mar 22, 20 those discontinuities in form of cracks might be an initial start of cracking in the spotwelded joints regarding fatigue loads. Discontinuities like lack of fusion, laminar tearing, and most forms of cracks are one of them. Welds may contain porosity, slag inclusions or cracks. What weld discontinuity results when the welder travels too slowly, causing excess weld metal to flow out.

Corrosion of weld joints can be avoided by the careful selection of materials to be welded, the filler metal, welding techniques and finishing. Preheat or postweld heat treat weld joints that may develop a hard haz when corrosive conditions are met. Explain the mode of transfer of metal from the electrode to the weldment in each case. A sound weld means that theres uniformity with a very little variation tolerance everywhere you see, either on weld surface or in subsurface. Recommended practice for radiographic examination of fusion welded joints part 3. This is used to assure a higher iron dilution from the steel during welding and prevents cracking. Such bead shapes can have an effect on cracking, especially on cracking that occurs over time. During testing, cracking behavior was observed on the side surface of the specimen. Defects hydrogen cracks in steels identification twi. Hot spot stress approach to keep pace with the increasing use of fea is discussed. Detecting discontinuities through weld inspection matching the inspection method to the welding process by sharon m.

Another no so common cause can be arc blow, where magnetic fields cause an erratic arc. 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. They are formed by welding two or more workpieces metal or plastic according to a particular geometry. The piece can be magnetized by direct or indirect magnetization. Of more importance is the determination of the effect of weld discontinuities. Rules for classification and construction ii materials and. 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. Types of welding discontinuity and what is discontinuity. Sample questions for aws certified welding engineer. 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. This condition occurs in the haz or base material parallel to the fusion boundary in joints that are restrained.

Jul 16, 2012 you can waste a lot of time and weld metal depositing an excessively high bead profile. Weld joint cracking in subsea oil and gas systems pt ii twi. 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. Therein lies the whole problem corrosion and weld discontinuities followed by cracking and corrosion fatigue along the heataffected zone of the welded joint. 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. Defects and discontinuities tim turner elizabethtown technical college 2.

There are five types of joints referred to by the american welding society. Module 10 weld discontinuities and causes flashcards. Will the discontinuity influence the weldment in its intended service and thus be termed a defect. Methods to obtain weld discontinuities in spotwelded joints.

Understanding the difference will let you know if you need to scrap a part, repair it or simply add more weld. Pdf the consequences of cracks formed on the oil and gas. Engineering should be contacted to determine whether partial penetration of full penetration joints are appropriate for a particular situation. The manual addresses general considerations for welding, welder certification and inspection procedures. Fatigue design rules for welded structures january 2000. 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. 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.

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. The differences between discontinuities and defects. Overlap the protrusion of weld metal beyond the weld toe or weld. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Any existing defects or notches aggravate crack formation. It includes overlap, undercut, spatter, crater, excessive, convexity, surface porosity, slag inclusion, surface cracks, lack of fusion, necklace cracking and incompletely filled groove. The weld discontinuity that results from the initiation of the welding arc outside the weld joint is referred to as. 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. Any weld would be a defect if the welder or the quality control department rejects it and blacklists the product. This paper outlines the basis of current fatigue design rules for welded structures. Overlap the protrusion of weld metal beyond the weld toe or weld root.

To fully understand weld discontinuities, we must first examine some welding. The designer is therefore required to decide whether to use a tbutt weld, a fillet weld or a combination of the two. Fusion welded circumferential joints in steel pipes of up to 50 mm wall thickness. 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.

At this particular point, the crack runs between the alloy 625 weld metal, at the notch, and the interface. 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. Cold cracks the abcs of arc welding education center. Exhibit the proper sequencing and placement of weld beads in multipass groove welds. A welding defect is any flaw that compromises the usefulness of a weldment. In some cases, a discontinuity can greatly affect the performance of the weld. When welding different metals together, such as steel to coppernickel the consumable will have 65% nickel content. For the purposes of this section, cracking will be dis tinguished. Technically, a welding discontinuity is the lack of a mechanical, physical or metallurgical harmony in the weld. Prep, adjustments, beads and joints part 3 includes instructional photos, checklists, and stepbystep instructions. 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. 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. Effect of weld penetration on lowcycle fatigue strength of.

Welding discontinuities and defects hobart institute of. The introduction of excessive stresses to the weld joint, particularly in conjunction with a material in a cracksensitive. Weld discontinuities part 2 unacceptable weld profiles. The inspector should be familiar with design and weld requirements. Defects in welding joints can be classified into two types as internal and external. The crack begins at a void in the welding crater, caused by the solidi. 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.

Such a weld is unsightly and almost always unacceptable, mainly because of the weld reentrant angle to the base metal see figure 3. Discontinuity an interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. Methods to obtain weld discontinuities in spotwelded. Defects in weld joints could result in the rejection of parts and assemblies. The value of visual inspection depends largely on the experience and welding knowledge of the inspector. Not all weld discontinuities are weld defects, but all weld defects are discontinuities. 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. Table 2 discontinuities commonly encountered with welding processes incomplete incomplete joint weldingprocess porosity slag fusion penetration undercut overlap cracks. The slightly hardened heataffected zone of the weld is where most cracks occur. Welds may be single sided joints, welded all from one side, or double sided, welded from both sides, fig. The weld throat may be the full section thickness, a full penetration joint, or a proportion only a partial penetration joint.

Factors affecting inservice cracking of weld zone in. 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. There are a number of cracking mechanisms associated with the welding of. 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. Above are several different representations of weld cracking. Henry june 14, 2005 discontinuities, or flaws, can often occur in the welds used to manufacture welded tubular products. Some joints call for considerable welder skill to obtain an. 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.

Detecting discontinuities through weld inspection matching. The problems of inservice cracking of weld zones can be minimized by attention to the important factors summarized below. 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. Causes and prevention of corrosion on welded joints. Weld discontinuities part 1 porosity incomplete fusion. 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. Fillet welds may be combined with full or partial penetration butt welds a combination weld. Types of welding joints design and welding symbols. 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. Five types of specimens with different sizes of weld penetrations and weld leg lengths were tested under cyclic plastic strains.

Each section has notes on causes, and where appropriate, on rp. 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. 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. 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. Undercut a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. Several types of discontinuities may occur in welds or heat affected zones. Visual inspection started too late in the sequence of welding operations cannot detect.

Incomplete fusion a weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads. Visual inspection is limited to detection of surface discontinuities. As a welding inspector, in order for you to successfully conduct your profession, it is important to understand weld discontinuities. All defects are discontinuities, but not all discontinuities are defects. 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 weld s ductility may decrease with a high carbon equivalent and a high cooling speed after solidification.

This discontinuity can be caused by incorrect welding techniques or insufficient current settings. The first step toward understanding weld discontinuities is to examine some welding terminology. Weld cracking several types of discontinuities may occur in welds or heat affected zones. Incomplete joint penetrationis a discontinuity in a groove weld in which the weld metal doesnt extend through the joint thickness. Backing piece left in place failure to remove backing. Weld flaws may come in different sizes, shapes, and degrees of severity. Cold cracking can develop hours or days after the weld has been made, which is.

The everyday pocket handbook for visual inspection and. Common causes of discontinuities related to internal inconsistencies and weld metal irregularities. 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. 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. 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. Porosity cavities in the weld caused by trapped gas during solidification of the weld metal. Rules for classification and construction ii materials and welding 3 welding 2 design, fabrication and inspection of welded joints. System design, specifications, operation, and inspection.

If the part has no cracks or other discontinuities, magnetic particles will not be attracted, and youll know your weld is without surface cracks. Cracking often is caused by stress concentration near discontinuities. Weld inspector responsibilities related to discontinuities and defects. A welding joint is a point or edge where two or more pieces of metal or plastic are joined together. Weld discontinuities part 1 porosity incomplete fusion incomplete penetration. Following are descriptions of some of the basic weld discontinuities. Describe two arc welding processes which involve slagmetal reactions.

This pocket handbook provides a convenient source for the most common base metal and weld metal discontinuities found by. The consequences of cracks formed on the oil and gas. A defect can be considered a rejectable discontinuity. Inspection and repair is the tool for the control of the growth of cracks. No matter how hard you try to repair it, youll only waste your time and resources, making it not worth the fuss.

The test results revealed that the fatigue strength and. There are many codes depending on what type of product you are welding on. 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. The likelihood of discontinuities occurring depends on a number of factors.

Start studying module 10 weld discontinuities and causes. Sep 12, 2016 defects in welding joints can be classified into two types as internal and external. Below is a representation of a convex fillet weld without discontinuities. The penetrant may be applied to all nonferrous materials and ferrous materials, although for ferrous components magneticparticle inspection. 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. Whereas there are acceptable limits for slag inclusions and porosity in welds, cracks are never acceptable. Discontinuities in weldscause and effect journal article. 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.