1、$1 2 The Everyday Pocket Handbook for Visual inspection and Weld Discontinuities- Causes and Remedies Compiled as a useful tool for on-the-job welding personnel by the AWS Product Development Committee (Edited by Ted V. Weber, Principal Consultant, Weber a dis- continuity is not necessarily a defect
2、.” A defect refers to “A condition, or conditions, that render a part unable to meet applicable minimum accep- tance standards or specifications.” All defects are discontinuities, but not all discontinuities are defects. A defect can be considered a rejectable discontinuity. This pocket handbook pro
3、vides a convenient source for the most common base metal and weld metal discontinuities found by effective VT. The handbook is arranged by discontinuity type, including appli- cable VT detection methods, and likely causes and remedies in addition to suggested repair methods. 6 Cracks A crack is defi
4、ned as “A fracture type discontinuity characterized by a sharp tip and a high ratio of length and width to opening displacement.” Cracks are usually considered the most severe discontinuity because of their tendency to propagate under stress. Cracks are usually further described by their location ge
5、ometry, time of occurrence, or common usage terms; see figure below for AWS crack terminology. iEGEND: 1 CRATER CRACK 8 THROAT CRACK 2 FACECRACK 9 TOE CRACK 3 HEAT-AFFECTED 10 TRANSVERSE CRACK ZONE CRACK 11 UNDERBEAD CRACK 4 LAMELLAR TEAR 12 WELD INTERFACE CRACK 5 LONGITUDINAL CRACK 13 WELD METAL CR
6、ACK 7 ROOT SURF ACE CRACK 6 ROOTCRACK m Types of cracks often include the following prefixes: base metal, cold, crater, delayed, face, heat-affected zone, hot, hydrogen, intergranular, lamellar tear, longitudinal, quench, root, service induced, stress corrosion, throat, toe, transgranular, transvers
7、e, underbead, weld metal, and others. Crack detection can be achieved visually if the crack is present on the surface and is of sufficient size to be visi- ble to the eye. Smooth, clean surfaces, oblique angle lighting, and a lox power magnifier are extremely helpful during visual inspection for sur
8、face cracking. If the surface cracking cannot be found visually, the next step is the use of the Penetrant Test method (a). Magnetic Particle Testing (MT) can also be used, but is limited to testing magnetic base materials. Ultrasonic Testing (UT), Eddy Current Testing (ET), and Radiographic Testing
9、 (RT) are required for the detection of subsurface cracking. Refer to the AWS Welding Inspection Technology materials for more details regarding IT, MT, UT, ET, and RT. Cracking can be caused by a multitude of conditions, but the more common causes are: embrittlement of the base or weld metal caused
10、 by too-rapid cooling and the formation of brittle martensite, weld shrinkage stresses, insufficient root bead size, poor joint design, nonmatching filler metals, and corrosive environment. See follow- ing chart for specific causes and recommended remedies. Repairs to cracks include the following ge
11、neral requirements: 1. Locate crack extent and orientation. 2. Grind to remove completely; confirm with NDT. Do not weld over (on top ofl cracks. 3. Weld using proper procedure, including preheat if required, use small diameter electrodes and stringer bead progression. 4. NDT finished weld and base
12、metal. Note: The above procedures may not result in a suitable repair of stress corrosion cracking, which may require 8 replacement of the affected part or parts. Causes: Weld Metal Cracking Highly rigid joint Excessive dilution Remedies: Weid Metal Cracking Preheat Relieve residual stresses mechani
13、cally (peening) Minimize shrinkage stresses using backstep or block welding sequence Change welding current and travel speed Weld with covered electrode neeative: butter the ioint faces prior to welding Defective electrodes Poor fit-up Small weld bead High sulfur base metal Angular distortion Crater
14、 cracking I 1 Change to new electrode; bake electrodes to remove moisture Reduce root opening; build up the edges with weld metal. Increase root opening. Increase electrode size; raise welding current; reduce travel speed Use filler metal low in sulfur Change to balanced welding on both sides of joi
15、nt Fill crater before extinguishing the arc; use a welding current decay device when - Causes: Heat-Affected Zone Hydrogen in weiding atmosphere Hot cracking Low ductility High residual stresses terminating the weld bead Use low-hydrogen welding process; preheat and hold for 2 hour after welding or
16、postweld heat treat immediately Use low heat input; deposit thin layers; change base metal and/or filler metal Use preheat; anneal base metal prior to welding Redesign weldment; change welding sequence; apply intermediate stress-relief Remedies: Heat-Affected Zone High hardenability Brittle phases i
17、n the microstructure heat treatment Preheat; increase heat input; heat treat without cooling to room temperature Solution heat treat prior to welding Inclusions Inclusions are defined as “Entrapped foreign solid material, such as slag, flux, tungsten, or oxide.” The inclusions may be found as single
18、 particles, aligned particles, or clustered particles. Slag inclusions are fre- quently found on the weld surfaces, or along the toes of the weld due to improper cleaning techniques. Tungsten inclusions are usually subsurface. Examples of inclusions are shown below. Inclusions on the surface can be
19、detected by VT; subsurface inclusions require UT or RT. Slag Inclusions (darkened areas) Repairs of inclusions on the surface require removal by gouging or grinding, welding if required, and reinspec- tion by appropriate NDT method. Subsurface inclusions require removal by gouging or grinding, follo
20、wed by weld repair and reinspection. Common Causes and Remedies of Slag Inclusions Tungsten in the weld metal Improper joint design Causes I Avoid contact between the electrode and the work use larger electrode Increase groove angle of joint Remedies Slag flooding ahead of the welding arc Poor elect
21、rode manipulative technique Failure to remove slag I Clean surface and previous weld bead Reposition work to prevent loss of slag control Change electrode or flux to improve slag control Entrapment of refractory oxides I Power wire brush the previous weld bead Entrapped pieces of electrode covering
22、Use undamaged electrodes Oxide inclusions 1 Provide proper gas shielding II Incomplete Fusion Incomplete fusion is defined as “A weld discontinuity in which fusion did not occur between weld metal and fusion INCOMPLETE r CI 5/16 in. TO W 1 in. (25 mm) W 2 1 in. 1/16 in. (1.6 mm) 118 in. (3 mrn) 3/16
23、 in. (5 mm) (C) UNACCEPTABLE FILLET WELD PROFILES INSUFFICIENT EXCESSIVE EXCESSIVE OVERLAP INSUFFICIENT INCOMPLETE THROAT CONVEXITY UNDERCUT LEG FUSION 23 (D) ACCEPTABLE GROOVE WELD PROFILE IN BUTT JOINT BUTT JOINT- BUTT JOINT (TRANSITION)- EQUAL THICKNESS PLATE UNEQUAL THICKNESS PLATE NOTE: REINFOR
24、CEMENT R SHALL NOT EXCEED 1/8 in. (3 mm). (E) UNACCEPTABLE GROOVE WELD PROFILES IN BUTT JOINTS EXCESSIVE INSUFFICIENT EXCESSIVE OVERLAP 24 REINFORCEMENT THROAT UNDERCUT Fillet Weld Measurement How to Use Weld Fillet Gage PLACEMENT CONVEX WELDS CONCAVE WELDS BE CERTAIN BLADE EDGE IS SQUARE WITH WELDE
25、D PARTS. FOR CONVEX WELDS: USE BLADE WITH SINGLE ARC AT APPROPRIATE SIZE. FOR CONCAVE WELDS: USE BLADE WITH DOUBLE ARC AT APPROPRIATE SIZE. 25 Dimensional Considerations An important aspect of VT is the measurements for size, geometry, and assembly of welded structures. The manufacturing drawings wi
26、ll show the required lengths, widths, thicknesses, diameters, etc., of the various components, as well as weld sizes. The inspector should determine the dimensional tolerances for each of the measurements specified, and consider them during component measurement for conformance. If the tolerances ar
27、e not stated, the inspector should ask for clarification. Often, these tolerances are noted as minimums.“maximums, or a dimensional range such as “I .5 - 1.750 inches.“ The inspector should also be aware that measurements can be given in the US. Customary units, or in the S.I. or metric units. Dimen
28、sional Defects Incorrect Joint Preparation I. Incorrect joint penetration subject to visual inspection, generally before welding is started. includes out-of-tolerance welding bevel or groove dimensions, base metal misalignment, and undesirable weld joint fit up conditions. 2. Included in the require
29、ments for weld joint preparation shall be inspection for removal of scale, paint, oil, etc., from the weld joint. 3. Partial penetration weld joint preparations shall be visually inspected prior to welding to assure proper weld throat dimensions. Incorrect Weld Size I. Incorrect weld size subject to
30、 visual inspection includes undersized fillet weld leg dimensions and underfilled groove weld throat dimensions. 2. Fillet weld size shall be determined by means of a fillet weld gage. Incorrect Final Dimensions Incorrect final dimensions subject io visual inspection include all conditions of dimens
31、ional inaccuracies, distortion, and lack of conformity to design requirements. 26 Thickness and Weight of Steel Plates: 1/32-1 inch Gage 22 16 Fraction Decimal mm lb/ft2 1/32 0.031 0.794 1.275 1/16 0.063 1.588 2.550 I 13 I 3/32 1 0.094 1 2.381 I 3.825 I II 9 I18 0.125 3.175 5.100 5/32 0.156 3.969 6.
32、375 I 3 I 114 I 0.250 I 6.350 1 10.200 1 7, 3/16 51 7/32 I 11 9/32 1 0.281 1 7.144 I 11.475 0.188 4.763 7.650 0.219 5.556 8.925 5/16 I 0.313 I 7.937 I 12.750 11/32 0.344 8.731 I 14.025 Applicable 15/32 I 0.469 1 11.906 1 19.125 1/2 1 0.500 I 12.700 1 20.400 27 Gage I Fraction 1 Decimal I mm 1 ib/f2
33、I 17/32 1 0.531 I 13.494 21.675 9/16 I 0.563 I 14.287 1 22.950 I 19/32 I 0.594 I 15.081 1 24.225 I I 5/8 I 0.625 I 15.875 I 25.500 1 21/32 1 0.656 1 16.669 1 26.775 11116 1 0.688 1 17.463 1 28.050 Not 13/16 I 0.813 I 20.638 I 33.150 27/32 I 0.844 I 21.431 1 34.425 I -I I 718 I 0.875 I 22.225 1 35.70
34、0 I 29/32 I 0.906 1 23.019 36.975 15/16 I 0.938 I 23.813 I 38.250 31/32 1 0.969 I 24.606 I 39.525 I) 1.ooO I 25.400 I 40.800 Thickness and Weight of Steel Plates: 1-2 inch 28 Nominal Nominal Wall Thicknesses in inches for Pipe Sched. Sched. Stan- Sched. Sched. Sched. Sched. XX Size 5s 10s dard2 40 x
35、s3 80 120 160 Strong 1/8 0.405 - 0.049 0.068 0.068 0.095 0.095 - - - 114 0.540 - 0.065 0.088 0.088 0.119 0.1 19 - - - 3/8 0.675 - 0.065 0.09/ 0.091 0.126 0.126 - - - 1/2 0.840 0.065 0.083 0.109 0.109 0.147 0.147 - 0.188 0.294 3/4 1.050 0.065 0.083 0.113 0.113 O./% 0.154 - 0.219 0.306 I 1.315 0.065 0
36、.109 0.133 0.133 0.179 0.179 - 0.250 0.358 1-1/4 1.660 0.065 0.109 0.140 0.140 0.191 0.191 - 0.250 0.382 I-l/2 1.900 0.065 0.109 0.145 0.145 0.200 0.200 - 0.281 0.400 2 2.375 0.065 0.109 0.154 0.154 0.218 0.218 - 0.344 0.436 2-1/2 2.875 0.083 0.120 0.203 0.203 0.276 0.276 - 0.375 0.552 3 3.5 0.083 0
37、.120 0.2/6 0.216 0.300 0.300 - 0.438 0.600 3-1/2 4.0 0.083 0.120 0.226 0.226 0.3/8 0.318 - - - 4 4.5 0.083 0.120 0.237 0.237 0.337 0.337 0.438 0.531 0.674 5 5.563 0.109 0.134 0.258 0.258 0.375 0.375 0.500 0.625 0.750 6 6.625 0.109 0.134 0.280 0.280 0.432 0.432 0.562 0.719 0.864 - 29 mass (weight) pressure tensile strength pounds kilograms 0.454 psi kilopascal (kPa) 6.895 kPa psi O. 145 psi megapascal (MPa) 6.895 x lW3 kilograms pounds 2.205 1.450 x 10 MPa psi
