20_02.Intermediate Weld Discontinuities _compressed.pdf
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WSS Study Guide WD2.1 > cwbgroup Intermediate Weld Discontinuities 2.4 Convexity Convexity is defined as the maximum distance from the face of a convex fillet weld perpendicular to a line joining the weld toes. In single pass fillet welds, convexity results in added stress risers at the toes of...
WSS Study Guide WD2.1 > cwbgroup Intermediate Weld Discontinuities 2.4 Convexity Convexity is defined as the maximum distance from the face of a convex fillet weld perpendicular to a line joining the weld toes. In single pass fillet welds, convexity results in added stress risers at the toes of the fillet weld. Sharp corners due to excessive convexity Page 21 Copyright © 2015 CW cm) WSS Study Guide WD2.1 Intermediate Weld Discontinuities Excessive convexity tends to produce notch effects in multipass welds (see Figure 12) and may lead to other weld discontinuities, such as slag inclusions, incomplete fusion and porosity when depositing subsequent Dasses. Notch angle 9 Proper toe angle G12, Notch angle oƒ multipass groove welds Convexity, like overlap, may be caused by poor weld metal fluidity. Some of the probable causes of convexity 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 excessive convexity does not occur. Grinding to achieve a flat weld profile may be performed to correct excessive convexityv on fillet welds. If the convexity is determined to have been caused by welding cold (insufficient heat input), the weld should be completely removed by grinding or gouging and a new weld deposited. For multipass welds, grooving the toes of the weld before depositing the next pass is recommended. It may not be necessary to completely grind the weld flat if there is sufficient room to deposit the next pass. CWB Group Industry WeSS Study Guide WD2.1 PL | An native sĩ th cwbgroup Intermediate Weld Discontinuities 2.5 Excessive Weld Reinforcement Excessive weld reinforcement is defined as an area of the weld that has weld metal added in excess of that permitted by the code or standard. It is associated with groove welds and is undesirable since it tends to stiffen the section at that point as well as establish notches and increase weight (see Figure 13). This condition typically results from improper welding technique, improper welding parameters, too slow a travel speed or improper weld pass sequencing. Excess Excessive face reinforcement Excessive root reinforcerient G13, Excessive weld reinforcement Codes, specifications and standards limit the amount of reinforcement on groove welds and should be followed accordingly. The maximum reinforcement permitted by CSA Standard W59is3mm (1/8 in). The use of proper welding procedures and techniques should ensure that excessive weld reinforcement does not occur. Excessive root reinforcement may be the cause of improper fit-up or joint preparation. To repair excessive reinforcement, grind the weld to an acceptable profile, blending the toes of the weld with the base metal to reduce the notch effect at the weld toes. WSS Study Guide WD2.1 Intermediate Weld Discontinuities 2.6 Underfill Underfill is snown in Figure 14. The groove weld size of the welded joint is insufficient, reducing the effective load carrying capacity of the joint. Additional passes are required to bring the weld to the required size. Care should be taken when applying additional passes to: $ Maintain proper profiles $ $ $ Notexceed reinforcement requirements Blend passes into base material Notcreate additional weld discontinuities Underfill may be caused by any one or a combination of the following: + 9 $ $ $ Travel speed too fast Insufficient passes or layers Incorrect weave techniques Excessive included groove angles 2.7 Insufficient Throat The strength of a fillet weld is determined by the throat of the weld. It is therefore critical that the weld produced has at least the throat expected by the designer. One common problem is where there is a valley between two successive weld beads. In the most critical area, the throat, there is not enough metal. To correct this defect, ït is necessary to add more weld metal. CWB Group Industry Services WSS Study Guide WD2.1 Intermediate Weld Discontinuities Insufficient throat riG.15| Insufficient throat 2.8 Insufficient Leg Size Insufficient leg size is when one or both of the legs of a fillet weld are less than the required size. In the example shown, the vertical leg is less than the required size. Correction of insufficient leg size is achieved by depositing additional passes as shown in Figure 16. Actual throat Required leg length lu Insufficient leg length G16) roúp Industry Correction oƒ insufficient leg size x k E Corrected by adding passes si WD2.1 Ï WSSStudy Guide < nu. An niunee gi _ . Intermediate Weld Discontinuities - 2.9 Undercut ^ Undercut ïs the melting away of the parent metal during the welding process and left unfilled with weld metal. lf undercutting is not corrected, ït may be detrimental to the component and is, therefore, a defect. - Undercut will produce notches and result in stress risers, which can be harmful under load. Limitations for undercut are specified in governing codes and standards and are based on the type of loading to which the weld is subjected (i.e., static, cyclic or impact). < Undercut can occur at any stage of the welding process, for example: $ rootundercut in a single-V groove welded from one side (Figure 17 (a)) $ Sidewall undercut of a welding groove at the edge of a layer or bead, thus forming a sharp recess in the sidewall at a point where the next s _ layer or bead must fuse (Figure 17 (b)) $ External undercut reducing the base metal thickness at the line where the last bead is fused to the surface (Figure 17 (c)) Root undercut - (b) Sidewall undercut _ - External undercut FiG.17 Undercut WSS Study Guide WD2.1 Ñ cwbgroup Intermediate Weld Discontinuities Surface undercut, both internal and external, should be corrected. However, some construction codes and standards allow limited amounts of undercut to remain in the weld. The direction of primary stress on the Joint determines the influence of a given amount of undercut. On the other hand, the designer or specifier may specifically state in a product specification that undercut is not permitted. +3ợw+vs2se$® Some of the probable causes of undercut are: Operator technique: incorrect work angle, travel angle or travel speed Electrode: incorrect electrode type or size Welding parameters: incorrect voltage or current Joint accessibility and position: poor accessibility to the joint may force the use of incorrect work or travel angle. Vertical up welding is more prone to undercut than welding in the flat position. $ Joint preparation: incorrect joint preparation may cause internal undercut The use of proper welding procedures, techniques, joint preparation and fitrup should ensure that excessive undercut does not occur. Check to ensure that joint accessibility is acceptable before performing welding. Undercut discontinuities, if determined to be defects by the applicable codes and standards, can usually be corrected by cleaning and adding an additional pass. Root undercut may be more difficult to fix ïf ït is on small diameter pipe, as ït needs to be repaired from the inside of the joint. Large diameter pipe may be repaired using the same method used for external undercut. Undercut on small diameter pipe, if determined to be a defect, would have to be repaired by cutting out the section of pipe and preparing a new joint. Corrected by an additional pass He. 16] Correction of undercut Corrected profile WSS Study Guide WD2.1 Intermediate Weld Discontinuities Acceptable and unacceptable groove weld profiles are shown in Figure 19. Acceptable Groove Weld Profiles R Reinforcement, R shall not exceed 3mm(1/8in) —^ k) Underfill l) Excessive weld reinforcement m) Undercut n) Overlap G19, Groove weld profiles WsSS Study Guide WD2.1 An. Intermediate Weld Discontinuities 2.10 Concavity Concavity is defined as the maximum distance from the face of a concave ñllet weld to a line joining the weld toes. Excessive concavity occurs with fillet welds as shown in Figure 20 and Figure 21. A concave profile in the root of a groove weld is called concave root surface. The permissible concavity is generally defined by the governing code and standard. It should be noted that drawings may call for concave fillet welds, in which case the condition would not be considered a weld defect. The size of a concave fillet weld is determined by its throat size, not the actual measurement of ïts leg length. The selection of a concave fillet profile would be dependent on service conditions. Concavity Size G20) Page 29 Copyright © 2015 CWB Group Industry 5 Concavity WSS Study Guide WD2.1 An inirianue øf the : cwbgroup Intermediate Weld Discontinuities Size Le g (effective) Em Concuve fillet weld size Typical causes of concavity are: $ Operator technique: incorrect work angle, travel angle or travel speed $ Welding parameters: incorrect voltage or current $ Position of welding: vertical down welding is more prone to result in concave fillet welds mm An excessively concave weld can give a deceptive appearance of the actual weld size. Excessively concave fillet welds can be corrected by the addition of more weld passes as shown in Figure 22. riG.22| Correction oƒ concavity WSS Study Guide WD2.1 mm Intermediate Weld Discontinuities Desirable, acceptable and unacceptable fillet weld profiles are shown in Figure 23. Desirable fillet weld profiles Convexity, C shall not exceed 0.07W + 1.6 mm (1/16 in) 9) Excessive undercut h) Overlap F623: Flllet weld profiles ï) Insufficient leg WSS Study Guide WD2.1 An Inidiative of the : cwbgroup Intermediate Weld Discontinuities ISSẠ There are three common “^^ Concave rG.22| profiles: concave, flat and convex. Flat Convex Concave, flat and convex fillet weld profiles Weld deficiencies due to insufficient or excessive size and poor profile may be detected by visual examination, or by the use of suitable gauges as illustrated in Figure 25. Actual fillet weld size is defined by the shortest leg dimension in combination with the actual weld throat. Throat full size Oversize leg Six-bladed pocket size fillet guage and methods of use Mulli-purpose welding gauge IrIG.25] roup Industry Services Welding gauges WSS Study Guide WD2.1 cwbgroup Intermediate Weld Discontinuities The leg and throat size of concave fillet welds can be measured with fillet weld gauges as shown in Figure 26. mm Measuring concave filiet welds Only the leg size of convex fillet welds can be measured with fillet weld gauges as shown in Figure 27. HiG.27] Mieasuring convex fillet welds WSS Study Guide WD2.1 Intermediate Weld Discontinuities 2.11 Out-of-Line Weld Beads The following can lead to misalignment of the weld (see Figure 28): insufficient care in positioning automatic welding machines $2 $gsese b4 incorrect bead placement by the welder incorrect edge preparation inaccurate backgouging FiG.28| Out-of-line-weld beqds Out-of-line weld beads can result in incomplete joint penetration when complete joint penetration is required. Correcting this requires the removal of the weld from one side by grinding or gouging and the depositing of a new weld. Caution must be taken, as this will not be detected by visual inspection unless samples are extracted for etching to reveal the penetration profile. Nondestructive testing (NDT) methods capable of detecting discontinuities below the surface are best suited to detect this type of defect. CWB Group Industry Services WSS Study Guide WD2.1 cwbgroup Intermediate Weld Discontinuities 2.12 Incomplete Fusion Incomplete fusion is used to describe the failure to fuse between weld metal and fusion faces or adjoining weld beads. It may occur at any point in the welding groove or fillet weld as illustrated in Figures 29. Incomplete root fusion Incomplete root fusion Incomplete sidewall fusion Incomplete root fusion mm Incomplete fusion WSS Study Guide WD2.1 cwbgroup Intermediate Weld Discontinuities Incomplete fusion may be caused by a number of factors, either singly or in combination. Some of these factors are listed below: $ Improper electrode selection: selection of an electrode that is too large for the joint preparation inhibits electrode manipulation Improper welding parameters: welding parameters that are too low in in current and/or voltage Improper manipulation of the electrode: improper work or travel angles and travel speed that is too fast Improper cleaning of material: rust, oxides and mill scale that are not removed from the joint prior to welding Improper joint design: an example of this would be a narrow V-groove weld ïn a thick plate, inhibiting electrode manipulation. Figure 30 illustrates how a narrow V-groove weld would inhibit electrode manipulation. Poor joint preparation and fit-up: examples of this would be uneven root faces, uneven bevel angles and general inconsistencies in the preparation and fit-up. Narrow V- groove Inhibits electrode manipulation Wider V- groove Allows for electrode manipulation riG.20| Effect oƒ bevel øngle on the qbility to manipulate the electrode WSS Study Guide WD2.1 Intermediate Weld Discontinuities 2.13 Incomplete Joint Penetration \ The term incomplete joint penetration is a condition at the root of a groove weld where the weld metal does not extend through the joint thickness (see Figure 31). z= S _ lỀ — —<— —. Incomplete joint penetration a) Incomplete penetration - Square Butt Pu —< NI mu Incomplete joint ma b) Incomplete penetration - Single”V” penetration - „—. — mi x*. iieompielejoii - penetration — =g im c) Incomplete penetration - Double”V” I HH d) Incomplete penetration -Double Fillet —=. II Incomplete Jjoint penetration FiG.21i Incomplete joint penetrotion ® WSS Study Guide WD2.1 CWBI H Em see HN Intermediate Weld Discontinuities lt must be noted that incomplete joint penetration is not necessarily a weld defect. Some welded connections are designed with partial joint penetration welds. Incomplete joint penetration becomes a weld defect only when the codes, specifications and designs require complete joint penetration or when the required depth of penetration and resulting weld size is not achieved. The causes of incomplete joint penetration are very similar to those causing incomplete fusion and are: 1. Improper electrode seleciion. The selection of an electrode that is too large for the joint preparation limits access to the root of the joint. 2. Improper welding parameters. Current values that are too low may cause incomplete joint penetration. A voltage that is too high may also lead to incomplete joint penetration due to increased arc length and width resulting in a welding arc that is less focused at the root of the joint. 3. Improper manipulation of the electrode. Travel angle, work angle, travel speed, arc length and contact tip-to-work distance all affect penetration. An increase in travel angle beyond 15° wiïll decrease penetration and may result in incomplete Jjoint penetration. Welding the root pass of a groove weld with an angle other than 90° to the work plane will decrease root penetration and may result in incomplete joint penetration. Travel speed is optimum for achieving penetration when the electrode is at the leading edge of the weld pool. A faster or slower travel speed will reduce penetration and may result in incomplete Joint penetration. Arc length for processes using constant current power supplies (SMAW and GTAW) varies as the operator moves the electrode closer or farther from the joint. An unsteady welder may hold the electrode too far from the joint resulting in an increased (less focused) arc, which will decrease root penetration and may result in incomplete Joint penetration. For processes that use constant voltage power sources (GMAW, FCAW and MCAW), the welding current decreases as the contact tip-to-work distance increases. An unsteady welder may hold the welding gun too far away, resulting in a contact-tip-to-work distance that is too long and decreased root penetration that may result in incomplete joint penetration. Page 38 Copyright © 2015 CWB Group Industry 5ervices ï s¡ cwbgroup Intermediate Weld Discontinuities 4. Improper cleaning of the material. Rust, oxides, and mill scale that is not removed from the joint prior to welding, may result in incomplete Joint penetration. 5. Improper joint design. An example of this would be an included angle on a V-groove weld for a thick plate preventing access of the welding gun below the top surface of the plate. This would result in a contact tip-to-work distance that is too great, reducing welding current and resulting in decreased penetration, which may result in incomplete Joint penetration. 6. Poor joint preparation and fit-up. An example of this would be insufficient root gap resulting in reduced root penetration, which may cause incomplete joint penetration. Incomplete joint penetration in a joint designed as a complete joint penetration groove weld is always determined to be a defect requiring repair. Repair is performed by grinding or gouging from one side to sound weld metal, and depositing a new weld pass or weld passes. Incomplete Joint penetration of a fillet weld requires the complete removal of the fillet weld and a new weld must be deposited. Incomplete joint penetration of a partial joint penetration groove weld will most likely require the weld to be removed and a new weld deposited, or a second weld pass performed from the other side of the joint. 9 2015 CWJ Group Industr
