Intermediate Weld Discontinuities PDF

® WSS Study Guide WD2.1 Intermediate Weld Discontinuities Table of Contents Weld Discontinuities and Causes Glossary of Terms and Definitions Lesson 1 Objectives 10 1. Weld Terminology and Classes 10 2. Process or Procedure-Related Discontinuities 11 2.1 Dimensional Errors 11 2.2 Weld...

® WSS Study Guide WD2.1 Intermediate Weld Discontinuities Table of Contents Weld Discontinuities and Causes Glossary of Terms and Definitions Lesson 1 Objectives 10 1. Weld Terminology and Classes 10 2. Process or Procedure-Related Discontinuities 11 2.1 Dimensional Errors 11 2.2 Weld Profiles 13 2.3 Overlap 19 2.4 Convexity 21 2.5 Excessive Weld Reinforcement 2.6. Underfill 23 24 2.7 Insufficient Throat 24 2.8. Insufficient Leg Size 25 2.9. Undercut 26 2.10 Concavity 29 2.11 Out-of-Line Weld Beads 34 2.12 Incomplete Fusion 3% 2.13 Incomplete Joint Penetration 37 Lesson 2 Objectives 2.14 Distortion 2.15 Surface Irregularities 3. 4. Page 2 40 2.16 Slag Inclusions 43 45 Metallurgical Discontinuities 49 3.1 Porosity 49 3.2 Cracking s5 Design-Related Discontinuities Guides and Exam Exercise Copyright © 2015 CWB Group Industry Services 40 60 62 WSS Study Guide WD2.1 pP ¡ cwbgroup Intermediate Weld Discontinuities Glossary of Terms and Definitions Acceptable weld A weld meeting the applicable requirements. Arc strike A discontinuity resulting from an arc, consisting of any localized remelted metal, heat-affected metal, or change in the surface profile of any metal object. Backgouging The removal of weld metal and base metal from the weld root side of a welded joint to facilitate complete fusion and complete joint penetration upon subsequent welding from that side. Backing A material or device placed against the back side of the joint adjacent to the Jjoint root, or at both sides of a joint in electroslag and electrogas welding, to support and shield molten weld metal. The material may be partially fused or remain unfused during welding and may be either metal or nonmetal. Backing ring Backing ïn the form of a ring, generally used ïn the welding of pipe. Base metal The metal or alloy being welded, brazed, soldered, or cut. Bevel An angular edge shape. Bevel angle The angle between the bevel of a joint member and a plane perpendicular to the surface of the member. Butt joint A Joint type in whiïch the butting ends of one or more workpieces are aligned ïn approximately the same plane. Page 3 Copyright © 2015 CWB Group Industry 5ervices 4 WSS Study Guide WD2.1 . cwbgroup Intermediate Weld Discontinuities Glossary of Terms and Definitions Code A document often considered synonymous with standard or specification; however, more often it will be found to further incorporate rules of good practice by which the results required by a standard or specification may be obtained. In the United States, “code” is used as an equivalent to “standard” in Canada. Complete joint penetration (CJP) A groove weld condition in which weld metal extends through the Joint thickness. Concave fillet weld A fillet weld having a concave face. Concave root surface The configuration of a groove weld exhibiting underfill at the root surface. Concavity The maximum distance from the face of a concave fillet weld perpendicular to a line joining the weld toes. Crack A fracture-type discontinuity characterized by a sharp tip and a high ratio of length and width to opening displacement. Crater crack A crack initiated and localized within a crater. Cyclically-loaded A condition where forces acting on an object continually change significantly in magnitude and/or direction. Page 4 Copyright ® 2015 CWB Group Industrv Services WSS quá Guide WD2.1 Intermediate Weld Discontinuities Glossary of Terms and Definitions Defect A discontinuity or discontinuities that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. The term designates rejectability. Depth of fusion The distance that a weld fusion extends into the base metal or previous pass from the surface melted during welding. Discontinuitv An interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect. Ductility The physical property of a material where it is capable of sustaining large permanent changes in shape without breaking. Effective throat The minimum distance from the root of a weld to its face, less any reinforcement. Fatigue The progressive and localized structural damage that occurs when a material is subjected to cyclic loading. Fillet weld Aweld of approximately triangular cross section joining two surfaces approximately at right angles to each other in a lap joint, T-Joint, or corner Jjoint. Fillet weld size For equal leg fillet welds, the leg lengths of the largest isosceles right triangle that can be inscribed within the fillet weld cross section. For unequal leg fillet welds, the leg lengths of the largest right triangle that can be inscribed within the fillet weld cross section. Flaw An undesirable discontinuity. Groove angle The included angle between the groove faces of a groove weld. Page 5 Copyright © 2015 CWB 6roup Industr WSS Study Guide WD2.1 G Intermediate Weld Discontinuities Glossary of Terms and Definitions Groove face Any surface in a weld groove prior to welding. Groove weld size The Joint penetration of a groove weld. Hardness A measure of how resistant solid matter is to various kinds of shape change when a force is applied. Incomplete fusion (IF) A weld discontinuity in which fusion does not occur between the weld metal and the fusion faces or the adjoining weld beads. Incomplete joint penetration A Joint root condition in a groove weld in which weld metal does not extend through the joint thickness. Joint penetration The distance the weld metal extends from the weld face into the joint, exclusive of weld reinforcement. Joint root The portion of a joint to be welded where the members approach closest to each other. In cross section, the Joint root may be either a point, a line, or an area. Lamination A type of discontinuity with separation or weakness generally aligned parallel to the worked surface of a metal. Layer A stratum of weld metal consisting of one or more weld beads. Melt-through Visible root reinforcement in a joint welded from one side. Nondestructive Testing (NDT) Any of several examination methods where a component or assembly is evaluated without damaging or otherwise lessening Its intended service life. ® Copyright @© 2015 CWB Group Industry Set | | WSS Study Guide WD2.1 Intermediate Weld Discontinuities Glossary of Terms and Definitions Overlap The protrusion of weld metal beyond the weld toe or weld root. Partial joint penetration weld A groove weld in which incomplete joint penetration exists. Porosity Cavity-type discontinuities formed by gas entrapment during solidification or in a thermal spray deposit. Prod method A direct contact method of magnetic particle inspection using a prod that can locate surface and subsurface indications parallel to the alignment of the poles of the prod. Radiography (RT) A nondestructive testing method ïn which radiant energy is used in the form of eïither X-rays or Gamma rays for the volumetric examination of 0paque objects. Root edge A root face of zero width. Root face The portion of the groove face within the joint root. Root opening A separation at the joint root between the workpieces. Root surface The exposed surface of a weld opposite the side from which welding was done. Slag A nonmetallic product resulting from the mutual dissolution of flux and nonmetallic impurities in some welding or brazing processes. Slag inclusion A discontinuity consisting of slag entrapped in weld metal or at the weld interface. = L 5 2015 CWB Group Industry Service5 ® 0h WSS Study Guide WD2.1 Intermediate Weld Discontinuities Glossary of Terms and Definitions Specification A document that usually sets forth in some detail the requirements and/or acceptance criteria demanded by a buyer for a certain product. lt may be, or become, the basis of a contractual agreement between the buyer and the supplier. See also Code and Standard. Standard A document by which a product may be judged. In terms of welding, a standard generally summarizes the requirements for processes, procedures, consumables, materials, inspection, acceptance criteria, etc. See also Code and Specification. Statically-loaded A condition where forces acting on an object do not change significantly. Strain A measure of the change in dimensions of a body relative to a reference length. Stress The internal force induced in a material to counterbalance an externally applied force. Mathematically, it is the applied force divided by crosssectional area, and is represented by the Greek letter sigma, Ơ. Tension The type of force that tends to pull an object, or a surface of an object, in opposite directions. Toughness The ability of a material to resist the growth of a crack. Uliimate tensile strength The maximum stress that a material can withstand while being stretched or pulled before necking. Page 8 Copyright © 2015 CWB Group Industry Services WSS Study Guide WD2.1 Intermediate Weld Discontinuities Glossary of Terms and Definitions Undercut A groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. Weld bead Aweld resulting from a weld pass. Weld face The exposed surface of the weld on the side from which the welding was done. Weld joint mismatch Misalignment of the joïint members. Weld reinforcement Weld metal in excess of the quantity required to fill a groove weld. Weld root The points, shown ïn cross section, at which the weld metal intersects the base metal and extends furthest into the weld joint. Welding procedure The detailed methods and practices involved in the production of a weldment. Weldment An assembly joined by welding. Yield strength The stress at which a material begins to permanently deform. Page 9 | Copyright |9 2015 CWB Group Industry Services WSS Study Guide WD2.1 Intermediate Weld Discontinuities Lesson 1 Objectives AfTter completing this lesson you should be able to: $..+vo$s2s.$e$s© -¬ Categorize weld discontinuities and defects Describe the categories of weld discontinuities Explain the types of unacceptable weld profiles and their causes Describe the use of welding gauges Define incomplete fusion and incomplete joint penetration and identify their causes 1. Weld Terminology and Classes Discontinuities are interruptions in the desirable weld. A discontinuity that represents a danger to aweld or structure is a defect. Fitness for service evaluation that seeks a balance between quality, of a welding procedure. physical structure of a fitness for service of is a concept of weld reliability and economy lf a discontinulitv is assessed and determined to be a defect, it must be removed and corrected. The term defect should be used with caution, as the importance of discontinuities, both in type and quantity, is relative to the type of weldment and ïts required service conditions. The same discontinuity may be determined to be a defect in a weldment for one application and not for another application. Relevant codes and standards should be referred to in order to determine acceptance criteria for discontinuities when a discontinuity has been clearly located, identified, sized and its orientation determined. Weld discontinuities are divided into three general classes: $ Process or procedure-related $ Metallurgical $ Design-related These classes of discontinuities can be subdivided under many headings, but since ït is impossible to state rules whereby an inspector can identify all the factors likely to cause discontinuities in welds, this study guide will describe only some of them briefly. 15 CWB Group Industry Services WSS Study|Guide WD2.1 Intermediate Weld Discontinuities Inspectors will be better qualified to judge the chances of obtaining welds that are satisfactory for a particular service ïf they have a thorough knowledge of the limitations of a given welding process and an understanding of those conditions that are likely to cause the formation of discontinuities. 2. Process or Procedure-Related Discontinuities The production of satisfactory weldments depends upon, among other things, the maintenance of specified dimensions, whether it be the size and shape of welds or finished dimensions of an assembly. Requirements of this nature will be found ïn the drawings and specifications. Typically, an engineer would be consulted to determine ïf the dimensions are acceptable or unacceptable. If it is determined to be unacceptable, the discontinuity is considered a defect and must be corrected. The more common types of dimensional errors are discussed. 2.1 Dimensional Errors Dimensional errors are the direct result of poor workmanship in operations leading up to the point at which the assembly is to be welded. Errors of this nature indicate a lack of quality control and should be reported by the welding inspector so that corrective action may be initiated. Examples of dimensional errors include incorrect bevel angles, incorrect J-groove radii, incorrect root face, incorrect fit-up, incorrect root opening and irregularities in the joint preparation surfaces as shown in Figure 1. 2015 CWÊ Group Industry Services ® WSS Study Guide WD2.1 ^^. Intermediate Weld Discontinuities Incorrect Bevel Angles Incorrect Root Face Incorrect Fit.Up Incorrect Root Opening Irregularities in Joint Preparation Surfaces e1] Dimensional errors during preparogtion and fit-up An inigative of the cwbgroup. Si WSS Study Guide WD2.1 ® Analgdttve 0! i6 cwbgroup Intermediate Weld Discontinuities Insufficient root opening may cause inadequate joint penetration, incomplete fusion and slag entrapment. Km root opening Excessive root opening may cause melt-through, porositv, slag entrapment and additional distortion. KÊm --- root opening Misalignment of parts can cause insufficient effective throat and a stress concentration at the root of the weld. = Misalignment đi: 13. opyright © 2( Stress concentration An Inidalive of the WSS Study Guide WD2.1 cwbgroup „ . Intermediate Weld Discontinuities An excessive bevel angle can have two consequences; a large angle means a larger joint must be filled with weld metal and excessive distortion. ~¬ Required edge preparation _~ Actual edge preparation Bi .~¬ Additional weld metal required due to incorrect edge preparation Kê Excessive bevel or groove angle Asillustrated in Table 1, codes and specifications provide workmanship tolerances for bevel angle, root face thickness and root openings and should be followed accordingly. For example, working to CSA Standard = W59 or AWS D1.1, a groove angle specified on a drawing as 60° is required to be between 55°-70°. Alternate groove angles would only be accepted ïf a modification to the original drawing or a new detail drawing was approved by the engineer. Root Not Gouged Root Face of Joint #2 mm (1/16 in) Root Gouged Not Limited Root Opening of Joint -Without Steel Backing #+2mm(+1/18in) -With Steel Backing =¬ +6 mm (+1/4 in) (-1/8 in) NotApplicable -2mm.(-1/16in) ¬ — +2 mm (+1/16 in) -3mm - Groove Angle of Joint mm + 10 degrees - 5 degrees Workmanship tolerances (extract ƒrom CSA W59) + 10 degrees -5 degrees WSS Study Guide WD2.1 L sms ch An Iniianve gƒ the G Intermediate Weld Discontinuities Table 2 summarizes the dimensional errors and the resulting weld discontinuities or defects that may result. Dimensional Discontinuity Primary Resulting Discontinuity Insufficient root opening xe. Excessive root opening s in ung - Excessive melt through and . back side weld reinforcement - Concave root surface (in pipe welds) - Excessive distortion Misalignment (high/low) eo 2 - Insufficient groove weld size - Stress concentrations ặ Vievoi! royi Góp pyêpaïgjjon LAN ôi IBSUIEIEIBEHEIPÐGF EaCS: - Excessive melt through and back side weld reinforcement : Exeoegivo tooplacg 1 tr - Incomplete joint penetration - lrregular back bead profile Ñ - Incomplete joint penetration - Incomplete sidewall fusion TẾT - Incomplete joint penetration - Incomplete sidewall fusion 1 Gv 9g - Excessive distortion Excessive bevel angle : - Reduced mechanical Properties due to Increased local heating of weld joint (more filler metal required) Incorrect J-groove radii Zemg( IEWap5: > Incomplete sidewall fusion - Slag entrapment TAbL2| Resulting weld discontinuities from incorrect joint preparation and fit-up Page 15 Copyright © 2 5roup Industrỷ Services li WSS Study Guide WD2.1 Intermediate Weld Discontinuities - 2.1.1 Surface Irregularities Irregularities in the finished surface to be welded may also lead to various weld discontinuities. The method of preparation usually determines the types of weld discontinuity that may be experienced. " Sheared Surfaces ¬ Depending on the condition of the shear blades and the lubricants used, ~ various undesirable foreign materials may be entrapped leading to porosity, slag entrapment and incomplete fusion. - Flame Cut Surfaces ~ When oxygen is used in oxyfuel cutting, there is the potential for notches and irregularities to occur. Quite often, slag may adhere to these notches and surfaces. lf ït is not removed prior to welding, discontinuities such as . porosity, incomplete fusion, slag entrapment and chemical composition defects may 0Cccur. Codes, standards and specifications often limit surface irregularities and should be followed accordingly. ~^ r.6 Page 16 Cop\ 9 2015 CWB Group Ind; | Irregularities in the joint preparation surface can trap slag | WSS Stud) Gúide WD2.1 Intermediate Weld Discontinuities Plasma and Laser Cut Surfaces When plasma cutting is used, there is a potential for notches and irregularities to occur. Dross may adhere to the cut surface, as well as an oxide film that can produce weld discontinuities, such as porosity, if it ïs not removed by grinding ñirst. When cutting high-strength quenched and tempered steel such as ballistic armour for military applications, a localized martensitic microstructure forms along the edge of the cut surface from the localized heating and fast cooling associated with the cutting process. lIt may be necessary to remove up 2 mm of material by mechanical means to remove the hard, heat-affected zone. This high-hardness hardness region promotes crack formations due to a combination of residual stresses developed from the thermal cycles generated during cutting and subsequent welding operations. Water Jet Cut Surfaces Water jet cutting is not a thermal process and there is no change in the microstructure of the material being cut along the cut surface. There is no oxide formation or slag requiring cleaning. Welding can be successfully performed on a water jet cut surface with no preparation as long as the surfaces are uniform. Machine Cut Surfaces Milling machines, lathes and saws use oil as a lubricant when making cuts. Ít is necessary to remove this lubricant before welding to avoid weld discontinuities such as porosity. 5 CWB Group Industry Services WSS Study Guide WD2.1 Intermediate Weld Discontinuities Codes and standards, along with company welding procedures, should always be referred to before any cutting and material preparation begins. Becoming familiar with code and procedure requirements ahead of time allows for educated decisions to be made regarding cutting and preparation methods. Material should always be inspected upon receipt to ensure that its condition is acceptable and that it is the proper type and grade. Mill Certificates for material ordered should always be requested to ensure that proper type and grade of material is received. Machinists that are made aware of the required tolerances will be more likely to adhere to the requirements and advise of any problems at the early stages of the —¬ s material preparation work. 2.2 Weld Profiles Weld profiles of fillet welds and possible areas where deficiencies may be lên present as illustrated in Figure 7. Convex fillet weld with =_ Leg W « xAK? Leg unequal legs kL Concave fillet weld with equal legs Convexity Convexity > - Leg Throat Leg 'Throat ¡ `ề Throat : Leg Throat Leg L ¬ - Convex fillet weld with equal legs sẽ 67] Page 18 15 CWB Group Ind Weld profiles Concave fillet weld with Leg Leg unequal legs CWBï WSS Study Guide WD2.1 Intermediate Weld Discontinuities An nhe BH cwbgroup 2.3 Overlap Dverlap is a condition where an excess of weld metal exists at the toe of a weld beyond the limits of fusion. This produces notches that can cause a stress concentration under load as shown in Figure 8. In the case of ñillet welds, ït may reduce its effective throat. Overlap can also mask Incomplete fusion. Overlap Qverlap Km Overlop Size Notch angle Proper toe angle KÊm Notch angle oƒ fillet welds WSS Study Guide WD2.1 Intermediate Weld Discontinuities Overlap is common in fillet and groove welds with various processes and produces weld metal that is not fused to the parent metal. Some of the probable causes of overlap are: $ $ $ $ Operator technique: incorrect work and travel angles, travel speed too slow, improper weave technique Electrode: incorrect electrode size for the application Welding parameters: incorrect voltage, current, contact tip-to-work distance Surface contaminants: oil, paint, rust, mill scale The use of proper welding procedures and techniques should ensure that overlap does not occur. lf ït does occur, make sure procedures and welding techniques are reviewed to eliminate further overlap. Overlap is corrected by grinding to remove the overlap and blending to achieve the desired weld profile is acceptable. Magnetic particle testing (MT) would be a good choice after the repair to ensure that all the overlap isremoved and not hidden by the grinding operations. = Poteniial initiation point for a crack .. QOverlap Corrected by grinding and blending rie.10] Correction oƒ overlap