Joint Design, Testing, and Inspection

Joint Design, Testing, and Inspection
Chapter 28

Objectives Describe various types of weld joint designs.
Understand implications of doing code welding. Describe various nondestructive weld test methods. Describe various destructive weld test methods. Demonstrate ability to do groove and fillet weld soundness tests.

Objectives Describe and conduct visual weld inspection.
Explain the various gauges used for weld inspection.

Welding First used as means of patching and repairing
As use switched to fabrication, it was essential for welded joints to be strong Meet service requirements (fitness for purpose) Methods for testing quality of weld, ability of welder, and ability of inspector devised Visual inspection Need to inspect within weld to determine reliability of welded joint

Joint Design Five basic joints Types of welds applied to these joints
Butt Corner Edge Lap T Types of welds applied to these joints Fillet Groove

Open and Closed Roots Open roots
Spaces between edges of member to be welded Used to secure complete root penetration in butt joints and to secure attachment to backing member Penetration refers to depth to which base metal melted and fused with metal of filler rod or electrode Closed roots No space between members to be welded

Factors When Choosing Open or Closed Root Set Up
Thickness of the base metal Kind of joint Nature of the job Position of welding Type and size of electrode Structural importance of the joint in fabrication Physical properties required of weld

Closed and Open Roots Closed Roots Open Roots
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Edge Joints and Edge Weld
Economical for noncode work Cost of penetration low Not suitable for sever load conditions Not be used if either member subject to direct tension or bending at root Very deep penetration impossible Used only on 1/4 inch metal or thinner Edge weld completely consumes edges of edge joint

Closed Square-groove Butt Joint
Can be welded in several different ways Preparation requires only butting together of plate edges CJP of base metal necessary if used for code edges Welding one side does not secure complete joint penetration and joint weak at root Can be done on metal 1/8" or thinner Welding both sides increases joints strength Used on metal 3/16" or thinner

For complete joint penetration Shielded metal arc welding used on metal 1/4" thick Submerged arc welding used on metal 5/8" thick On metal more than 3/16" thick, recommended that root of first pass be chipped or gouged out from the reverse side to sound metal before depositing second weld

Open Square-groove Butt Joints
Penetration easier than on closed square-groove butt joints Heavier sections can be welded One sided up to 3/16" material Both sides up to 1/4" Shielded metal arc process for metal 3/8" thick Submerged arc welding for metal 3/4 thick Root of first pass must be chipped out to sound metal before depositing second weld

Open Square-groove Butt Joints
Material up to 1/4" Material 1/16" or less If joint penetration not achieved, joint not any stronger than closed type and has same possibility of failure under load. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Single V-groove Butt Joint
Superior to square-groove butt joints Provide 100% penetration and better plate edge preparation than square-groove butt joints Metal preparation more costly and greater amount of electrode deposit used in welding Used on plate thicknesses from 1/4" to 5/8" Joints welded from both sides with complete joint penetration provide full strength and meet requirements of code welding

Single V-groove Butt Joint
Welding from both side accomplished only where work will permit operator to weld from both sides of plate Backing strip can be used Weld faster and use larger electrodes Removable back used when welding from one side with submerged arc process Can weld up to 1 1/2" in thickness

Proportions for Single V-groove Butt Joints

Single V-groove Butt Joints

Double V-groove Butt Joint
Suitable for most severe load conditions Used on heavier plate 3/4 to 1-1/2 inch thick Cost of joint preparation greater than single V-groove butt joint, but amount of filler metal needed less Essential that complete root penetration be achieved Work must permit welding from both sides, and back side of the first pass must be chipped before applying second pass from other side

Double V-groove Butt Joint
May be less with wider root opening Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Beveled-groove Butt Joints
Suggested for work where load demands greater than can be met by square butt joints and less than V-groove butt joints Join metal up to 3/4 inch thick, and less filler metal required than for V-groove butt joint, thus reducing number of electrodes needed Cost of preparation less than V-groove butt joints since necessary to bevel only one plate edge For full strength root of first pass should be chipped to sound metal before depositing second pass

Beveled-groove Butt Joints
May be less with wider root opening Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Double Bevel-groove Butt Joint

Single Bevel-groove Butt Joints

Single U-groove Butt Joint
Used for very important work Cost of preparation greater than bevel and V-groove butt joints, but fewer electrodes needed Used on plate thicknesses from 1/2" to 3/4" Complete penetration necessary Easier to obtain when welded from both sides and on joints with backup strip Joint usually welded with free-flowing electrodes

Single U-groove Butt Joint

Double U-groove Butt Joint
Used on work of same nature as single U-groove butt joints but when plate thicknesses are greater Plate thicknesses range up to 3/4" Cost of preparation greater than single U-groove butt joints Double joints may be welded with fewer electrodes Welding from both sides permits more even distribution of stress and reduces distortion Choice between double-U and double V-groove made on basis of relative costs of metal preparation and welding Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Double U-groove Butt Joint

J-groove Butt Joints Single and double used on work similar to that requiring U-groove butt joints Load conditions would not be as demanding Cost of preparation less since only one plate edge must be prepared Less filler metal required to fill groove Difficult to secure good fusion and thorough penetration because of perpendicular wall

J-groove Butt Joint Double J-groove butt joint
Single J-groove butt joints Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lap Joints Used frequently on all kinds of work
No plate preparation involved Single-fillet not as strong as double-fillet Used on noncode work and when joint not subjected to bending Fusion to the root is necessary Never used to replace butt joint on work under severe load

Lap Joints Single Fillet Double Fillet

Slot and Plug Welds on a Lap Joint
Used infrequently Joint one plate or bracket to another when desirable to conceal weld or when lack of edge to weld on Requires series of these welds in order to withstand heavy load Cost of preparation high Difficult to make welds free or porosity and slag inclusions if slots small

Slot and Plug Welds on a Lap Joint

Flush Corner Joints Used on light gauge sheet metal (under 12 gauge)
No edge preparation needed and fitup simple Can weld heavier plate if no bending action at root Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Half-open Corner Joints
Used on 12-gauge to 7-gauge plate Forms groove and permits weld penetration to root and good appearance No edge preparation required Fitup usually simple Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Full-open Corner Joints
Can be used on any plate thickness Welded one side, penetration must be secured through root Welded both sides, joint suitable for severe loads Good stress distribution No edge preparation required Plates must be cut absolutely square Used in production welding Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Square-groove T-Joint
Used on plate thicknesses up to 1/2" Preparation of plate not necessary Fitup can be fast and economical Electrode costs are high Single-fillet T-joint will not withstand bending action at roof of weld If possible, weld from both sides and joint will withstand high load conditions

Single Bevel-groove T-joint
Can withstand more severe loads than square-groove Used on plate thicknesses ranging from 3/8 to 5/8 inch Plate of greater thickness welded with submerged arc Cost of preparation greater than for square-groove T-joint, and fitup likely to take longer Electrode costs less because these are groove welds not fillet welds If possible to weld from one side only, full penetration must be obtained so bending does not cause failure Done from both sides, load resistance of joint materially increased

Double Bevel-Groove T-Joint
Used for heavy plate thicknesses up to 1" Done from both sides of plate May be used for severe loads Must make sure fusion obtained with both flat and vertical plates Complete joint penetration necessary More expensive than square groove T or single bevel-groove joint – weld time and electrode costs less Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Single J-groove T-joint
Used for most severe load conditions Generally used on plates 1 inch or heavier If welding from one side, great care should be taken to secure good root penetration If welding from both sides possible, efficiency of joint can be increased materially by putting bead on side opposite J Reduces tendency of failure at root as result of load at this point Cost of plate edge preparation higher than for bevel-groove T-joint, but saving in weld time and electrode costs

Double J-groove T-joint
Will withstand most severe load conditions Used on plates 1-1/4" or heavier Must be able to weld from both sides of plate Complete joint penetration and surface fusion essential to prevent failure Plate edge preparation higher than V-groove T-joints and single J-groove joints Electrode costs lower Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Code Welding Code – set of regulations governing all elements of welded construction in certain industry Provide for human safety and protect property against failure of weldment No universal testing procedure Pressure piping conforms to Code for Pressure Piping of American Standards Association Boiler piping conforms to Code for Boilers and Pressure Vessels, Section IX by ASME

Code Welding Welding of pipelines conforms to Standard for Welding Pipelines and Related Facilities Developed by American Petroleum Institute Generally these standards set by federal, state, and local governments, insurance companies, and various professional organizations AWS Structural Welding Code – Steel Food and Hygienic Welding Industry Aerospace and Ground Support Systems

Code Welding Employer (engineering and production dept.) makes sure work meets standards Welder should have good understanding of weld tests and how to do visual inspection Two broad categories of welding tests Procedure qualification Purpose to determine correctness of method of welding Welder qualification or performance qualification Purpose to see if welder has knowledge and skill

Code Welding Methods of testing determine quality of weld divided into three very broad classifications Nondestructive testing Does not damage weld or finished product Destructive testing or mechanical testing Requires test specimen be taken from fabrication Weld damaged beyond use Visual testing Surface of weld and base metal observed for visual imperfections Which should be the first inspection method used

Code Welding Example Recommended dimensions of grooves for shielded metal arc welding, gas metal arc welding, and gas welding (except pressure gas welding). Note: Dimensions marked * are exceptions that apply specifically to designs for gas metal arc welding. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Code Welding Example Recommended dimensions of grooves for gas tungsten arc welding processes to obtain controlled and complete penetration. Note: for steel except as noted. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

NDT Magnetic Particle Testing
One of most easily used nondestructive tests Used to inspect plate edges before welding for surface imperfections Tests welds for surface cracks, incomplete fusion, porosity, undercut, incomplete root penetration, and slag inclusions Method limited to only magnetic materials Often referred to as Magnaflux® method Name of particular brand of testing equipment

Detects presence of internal and surface cracks too fine to be seen by naked eye Depth of 1/4" to 3/8" below surface of weld Part prepared must be smooth, clean, dry and free from oil, water, and excess slag Wire brushing and sandblasting Part magnetized by using electric current Magnetized surface covered with thin layer of magnetic powder Another method uses fluorescent powder that glows in black light

Layer of powder can be blown off surface when no defects Defect shows because powder held to surface at defect – “flux leakage” Magnetic field in workpiece sets up north pole at one end of defect and south pool at other Cracks must be at angle to magnetic lines of force in order to show Transverse (crosswise) crack would not show because lines of force would be parallel with crack

Circular Magnetization

Magnetic Particle Testing Units
Portable magnetic particle testing unit can be used in shop and field. Shown here checking critical welds during construction of a Detroit bank building. Note use of magnetic powder as unit applied. Magnaflux Corp. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Example of Circular Magnetism
Circular magnetism is when current passed through workpiece, the magnetic lines of force are at right angles to current, and discontinuities that are angled against lines of force will create flux leakage needed to produce magnetic poles on the surface. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Longitudinal Magnetism
Magnetic field is produced with a coil, the lines of force are parallel and longitudinal. A longitudinal crack will not show, but a crack angles against the lines of force is indicated. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Direct magnetization may also be used with alternating current Limited to detection of surface discontinuities only Indirect magnetization method Uses electrically supplied coil wrapped around soft iron core to produce electromagnet

Direct Magnetization Using D.C. Prods
American Welding Society, AWS B1.10 Guide for Nondestructive Examination of Welds, Fig. 14, p. 15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Indirect Magnetization Using a Yoke
American Welding Society, AWS B1.10 Guide for Nondestructive Examination of Welds, Fig. 14, p. 15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Radiographic Inspection
Nondestructive test method that shows presence and type of microscopic defects in interior of welds Utilizes either X-ray or gamma ray Source of X-rays is X-ray tube Gamma rays have shorter wavelengths and produced by atomic disintegration of radium or commercial radioisotopes Can penetrate deep, but exposure time longer than X-rays

Radiographs Film produced by X-rays or gamma rays Can establish presence of variety of defects and record their size, shape, and relative location Size of X-ray equipment rated on basis of its electric energy Voltage controls wavelength and penetrating power Gamma rays come from radioisotopes that are constantly emitting radiation – caution

Radiographic Testing Photograph taken of internal condition of weld metal Photographic film placed on side opposite source of radiation Distance between film and surface of workpiece not greater than 1 inch Rays penetrate metal and produce image on film Different materials absorb radiation at different rates Slag absorbs less radiation than steel and permits more radiation to reach film – thus slag shows up darker

Typical Arrangement of Radiation Source and Film in Weld Radiography
American Welding Society, AWS Bi.10 Guide for Nondestructive Examination of Welds, Fig. 14, p. 15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Orientation of Discontinuities With Radiographic Inspection
American Welding Society American Welding Society Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Weld Discontinuities as Indicated on Radiographic Film
Porosity as indicated by the dark areas in lighter denser weld metal Slag inclusion indicated by darker less dense areas Transverse cracks Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Weld Discontinuities as Indicated on Radiographic Film
Incomplete fusion, less dense area along edge of weld Incomplete penetration in root pass Undercut as shown by less dense areas along toe of cap pass Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Penetrant Inspection Nondestructive method for locating defects open to surface; cannot detect interior defects Red dye penetrant method Surface must be clean Sprayed with dye penetrant which penetrates into cracks and other irregularities Excess wiped clean with solvent Part sprayed with highly volatile liquid that contains fine white powder (developer) Evaporation of liquid leaves dry white powder that draws out red dye so defects marked clearly

Spotcheck® Dye penetrant test for defects open to surface
Relies on penetration of defect by dye, removal of excess dye, and development of indication Highly sensitive process Small cracks show up against white developer background Locates cracks, pores, leaks, and seams invisible to unaided eye (shows in red) Used on almost all materials

Spotcheck® Advantages
Complete portability for critical inspection at remote shop or field locations Fast inspection of small, critical sections suspected of being defective Ease of application and dependable interpretation of results Low initial investment and low per part cost in moderate volume uses

Spotcheck® Visible Penetrant
Applying Spotcheck® Magnaflux Corp. Spotcheck® visible penetrant kit which includes penetrant, developer, and cleaner Magnaflux Corp. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fluorescent Penetrant
Technique similar to that used in dye method Treated metal surface examined under ultraviolet or black light in semidarkness Florescent penetrant inspection Sharp contrast between fluorescent material and base background indicates cracks or other defects in metal Useful for leak detection in lined or clad vessels Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Magnaflux Corp.

Ultrasonic Inspection
Nondestructive test method Rapid and has ability to probe deeply without damaging weldment (200 inches) Able to supply precise information without elaborate test setups Can detect, locate, and measure both surface and subsurface defects in weld and base metal Needs experienced operator

Done by means of electrically timed wave similar to sound wave but higher pitch and frequency Ultrasonic – frequencies above human hearing Waves passed through material being tested and reflected back by any density change Three basic types of waves Shear (angle) beams, longitudinal (straight) beams for surface and subsurface flaws, and surface waves for surface breaks and cracks Reflected signals appear on screen as vertical reflections of horizontal baseline

Transducer Search unit containing piezoelectric device that converts electric energy into mechanical energy (sound) and then converts sound back to electric Signal displayed on CRT or LCD Coupled to part to be inspected Two reference pips appear on screen, first pip echo from surface called main bang; second pip echo from bottom Distance between pips calibrated When defect picked up by search unit, produces third pip Distance between pips and relative height indicate location and severity of discontinuity

Portable ultrasonic weld flaw detector with built-in trigonometric flaw location calculations with curvature correction and AWS D1.1 weld rating calculation. It has a 480-inch measurement range in steel, 0.25 to 25-megahertz frequency capability. The SmartView feature displays the most relevant shot for critical scanning. Agfa Corporation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Ultrasonic Testing Ultrasonic testing bond of copper liner to base metal of copper-clad reactor. The welds were X-rayed with gamma rays, and chemical analysis was made of weld deposit. Nooter Corp. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Ultrasonic Testing Using portable
ultrasonic instrument to check a structural weld on the seventy-sixth floor of the John Hancock Building in Chicago. Magnaflux Corp. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

This video clip shows the RT inspection of a weld.

Eddy Current Testing Makes use of electromagnetic energy to detect defects in material When coil has been energized with alternating current at high frequency brought close to conductive material, will produce eddy currents Secondary currents induced in conductor Caused by variation in magnetic field Search coil used and connected to meters, recorders which pick up signals from weldment Defect in material distorts magnetic field and indicated Size shown by amount of change

Eddy Current Testing Suitable for both ferrous and nonferrous materials Used extensively in testing welded tubing, pipe, and rails Can determine physical characteristics of material, wall thickness in tubing and thickness of various coatings Only good up to 3/16 inch thickness and calibration blocks required for all types of welds Two areas that limit its use

Eddy Current Testing Eddy current control and rotating probe. The control is compact and portable. This single-channel test instrument incorporates all the features required for automatic testing. Forster Instruments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Eddy Current Testing Core
American Welding society, AWS B1.10 Guide for Nondestructive Examination of Welds, Fig. 28, p.25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Leak Tests Made by means of pneumatic or hydraulic pressure
Load applied that is equal to or greater than expected in service Usually used to test pressure vessels and pipelines If used as destructive method, pressure applied until unit bursts Water usually used to test for leaks Hydrogen, oil, and helium also used Weld seam painted with liquid soap when testing with air and bubbles appear where leaks

Hardness Tests Important to know harness of weld deposit if weld going to be machined or subject to surface wear Number of nondestructive hardness tests Brinell Rockwell Vickers Knoop

Brinell Hardness Test Consists of impressing hardened steel ball into metal to be tested at given pressure for predetermined time Diameter of impression measured and indicates Brinell number on chart Ball 10 ± millimeters forced into specimen by hydraulic pressure of 3,000 kilograms for 15 sec. Brinell hardness number (BHN) can be related to actual tensile strength of carbon steel Multiply DHN by 500

Rockwell Hardness Test
Similar to Brinell system, but differs in that readings obtained from dial Measures depth of residual penetration made by small hardened steel ball or diamond cone Minor load of 10 kg applied, which seats penetrator (ball or cone) in surface of speciment Then full load of 150 kg applied After major load removed, hardness number indicated on dial gauge Numbers based on difference of penetration between major and minor loads

Rockwell Hardness Test
Two Rockwell scales C-scale Cone-shaped diamond penetrator used instead of ball Applied at load of 150 kg B-scale Used for softer metals Penetrator is hardened steel ball 1/8" or 1/16" in diameter applied at lesser load of 100 kg

Microhardness Testing
Uses range of loads and diamond indenters to make indentation Measured and converted to hardness value Two types of indenters Square base pyramid-shaped diamond (Vickers) Narrow rhombus shaped indenter (Knoop tester) Typically light loads Used to test metals, ceramics, and composites

Microhardness Testing: Vickers Method
Testing of very thin materials like foils Measuring surface of part Small parts or small areas Measuring individual microstructures Measuring depth of case hardening by sectioning part and making series of indentations to describe profile of change in hardness

Microhardness Testing: Knoop Method
Closely spaced requirements Testing close to an edge due to the narrow shape of the indentation More resolution due to the width of the Knoop indentation Thinner materials because indentation is less deep

Impact Hardness Tester
Done with portable machine Easy to operate and extremely accurate Takes 1 second to perform Hardnesses displayed digitally Permits testing in any direction, automatically adjusted for gravity Unit coverts electronically to Brinell, Rockwell Ba and C, Shore, and Vickers scales Uses comparative method of evaluating hardness

Impact Hardness Tester
Equipment does not need to be zeroed or adjusted Typical metals tested Cast steel, irons, tool steel, aluminum, yellow metals, stainless steel Designed for use on all metallic materials from 80 Brinell to about 68 Rockwell C Accuracy is in the ± 0.5%

Compact Portable Sonic Hardness Tester
Micro Photonics, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Destructive Testing Mechanical testing of weld samples to determine strength and other properties Relatively inexpensive and highly reliable Usually performed on test specimens taken from welded plate that duplicates material and weld procedures used on job Certain general test procedures developed by AWS that are standard for industry and various code-making bodies

Groove Welds Reduced-section tension test Free-bend test
Determines tensile strength, yield strength, and ductility; used for procedure qualification Free-bend test Determines ductility; used for procedure qualification Root-bend test Determines soundness; used widely for welder qualification; also used for procedure qualification

Groove Welds Face-bend test Side-bend test Nick-break test
Determines soundness; used widely for welder qualification; also used for procedure qualification Side-bend test Nick-break test Determines soundness; at one time used widely for welder qualification; used infrequently today

Fillet Welds Longitudinal and transverse shear tests
Determines shear strength; used for procedure qualification Fillet weld soundness test Determines soundness; used extensively for welder qualification Fillet weld break test Determines soundness; used infrequently today Fillet weld fracture and macro test Determines soundness; ASME test for procedure qualification and welder qualification

General Requirements All codes require essentially same qualifying procedures for plate or pipe Each position of welding, type of joint, and weld has designated number for identification Generally, face-, root-, and side-bend test specimens required for groove welds in plate or pipe T-joint break or macro-etch test specimens required for fillet welds in plate Required number and type of test specimens vary with thickness of material

General Requirements Under most welding codes, tests remain in effect indefinitely unless: Welder does not work with welding process for which he/she qualified for period of more than 6 months Requalification required only on 3/8" thick plate Reason to be dissatisfied with work of welder Immediate retest consists of two test welds of each type failed (All specimens must pass) Complete retest if welder has had further training or practice since last test

Procedure Qualification Tests
Conducted for purpose of determining correctness of welding method Should cover: Filler metals Joint preparation Position of welding Welding process Base metal specifications Techniques and characteristics Current setting Electrode size Electrode manipulation Preheat and postheat

Procedure Qualification Tests
Groove weld Specimens required given in Table 28-9 in text Fillet welds Longitudinal shear test Transverse shear test Bend and soundness test Two root-bend tests Table covers requirement for fillet well soundness test for WPS

Welder Qualification Tests
Also referred to as performance qualification test Conducted for purpose of determining whether welder has knowledge and skill to make sound welds and to follow and apply procedure of welding for class of work General practice for code welding to qualify on groove weld tests in 3G and 4G positions Time limits imposed by specific codes on how long a welder remains qualified AWS D1.1 it is indefinitely If they are using the welding process and procedures continuously If six months transpire between use Or if the welders ability is being questioned they will have to take a requalification test

Welder Qualification Tests
Groove welds Table covers various complete joint penetration groove weld tests Based on various plate thicknesses Fillet welds Two different kinds of fillet weld specimens Figure 28-63, welds made in each position for which welder is to be qualified; two root-bend tests made Figure 28-65, welds subjected to fracture test and etched

Preparation of Test Specimens
Selecting and preparing plates Test plate and backup strip, if used, are weldable, ductile low carbon steel Test designed so both plate and weld will bend and stretch during test Welding plates First step proper electrode selection Important on first pass to get good penetration, fusion, and sound weld metal on root beads No preheat or postheat treatment permissible to pass test

Preparation of Test Specimens
Finishing the specimen All grinding and machining marks must be lengthwise on sample Surface should be smooth, with no low or irregular spots Edges of specimen should have smooth 1/8" radius Do not quench in water when done grinding After test specimens have been bent, outside surface visually examined for surface discontinuities

Acceptable Test Specimens
Surface shall contain no discontinuities exceeding the following dimensions 1/8" measured in any direction on surface 1/8" as sum of all discontinuities exceeding 1/32" but less than 1/8" 1/4" maximum corner crack, except when results from visible slag inclusion or other fusion-types in which case 1/8" maximum size applies If corner crack exceeds 1/4" and no evidence of slag or fusion type discontinuities, then it shall be discarded

Reduced-section Tension Test
Purpose Determine tensile strength of weld metal Used only for procedure qualification tests Suitable for butt joints in plate or in pipe Usual size and shape of specimens Figures through in text

Method of testing Subjecting specimen to longitudinal load great enough to break it or pull it apart Before testing, least width and corresponding thickness of reduced section measure in inches Cross sectional area = width x thickness Tensile strength in pounds per square inch obtained by dividing maximum load by cross-sectional area

Usual test results required Specimen shall have tensile strength equal or greater than Minimum specified tensile strength of base material Lower of minimum specified tensile strengths of dissimilar materials Specified tensile strength of weld metal if weld metal is of lower strength than base metal 5% below specified minimum tensile strength of base metal if specimen breaks in base metal outside of weld

Root-, Face-, and Side-bend Soundness Test
Purpose Revealing incomplete soundness, penetration, and fusion in weld metal Procedure and welder qualification tests applied to groove welds in both plate and pipe Face-bend test checks quality of fusion to side walls and face of weld joint, porosity, slag inclusion, porosity, and measures ductility Root-bend test checks penetration and fusion throughout root of joint Side-bend test checks for soundness and fusion

Usual size and shape of specimens Refer to Figures through in text Method of testing Each specimen bent in jig having the contour Manual, mechanical, electrical, or hydraulic means may be used for moving male member in relation to female member Specimen place on female member of jig with weld at midspan

Method of testing, cont. Face-bend specimens placed with face directed toward gap Root-bend specimens placed with root directed toward gap Side-bend specimens placed with side showing greater discontinuity, if any, toward gap Two members of jig force together until curvature of specimen such that 1/32" diameter wire cannot be passed between curved portion of male member and specimen Specimen then removed from jig

Usual test results required Convex surface of specimen visually examined To be acceptable, no discontinuities exceeding: 1/8 inch in any direction on surface 3/8 inch as sum of all discontinuities exceeding 1/32 inch but less than 1/8 inch 1/4-inch maximum corner crack, except when corner crack results from visible slag inclusion or other fusion type discontinuities, in which case 1/8-inch maximum size shall apply If corner crack exceeds 1/4 inch and no evidence of slag or fusion type discontinuities, then it is discarded

Nick-break Test Purpose Usual size and shape of specimens
Determining soundness of weld Usual size and shape of specimens Refer to Figures and in text Method of testing Weld reinforcement not removed from specimen Specimen notched in sides by saw, supported and struck with quick, sharp blows by hammer or heavy weight

Nick-break Test Usual test results required
Fractured surface does not have any discontinuities exceeding these limits: Greatest dimension of porosity shall not exceed 1/16 inch Combined area of all porosity not exceed 2% of exposed surface area Slag inclusions hall not be more than 1/32" in depth and not more than 1/8" or one-half nominal thickness in length No incomplete fusion allowed At least 1/2-inch separation between adjacent discontinuities

Longitudinal and Transverse Shear Tests
Purpose Determining shearing strength of fillet welds Used for procedure qualifications Usual size and shape of specimens Refer to Figures through for standard specifications Figures and show prepared longitudinal weld specimens

Longitudinal and Transverse Shear Tests: Method of Testing
Specimen ruptured by pulling in tensile testing machine and maximum load in pounds determined Transverse welds Before pulling, width of specimen measured in inches and size of fillet weld recorded Pounds per linear inch obtained by dividing maximum force by twice width of specimen Shearing strength of weld in pounds per square inch obtained by dividing shearing strength (p.s.i.) by average theoretical throat dimension Theoretical throat dimension = fillet weld times 0.707

Longitudinal and Transverse Shear Tests: Method of Testing
Longitudinal welds Before pulling, length of each weld measure in inches Shearing strength of welds in pounds per linear inch obtained by dividing maximum force by sum of lengths of welds that ruptured Usual test results required Longitudinal shear: shearing strength (p.s.i.) cannot be less than 2/3 minimum specified tensile range of base material Transverse shear: shearing strength of welds in pounds per square inch cannot be less than 7/8th of minimum specified tensile range of base material

Fillet-weld Break Test
Purpose Determining soundness of fillet weld Several different tests, one by AWS Method of testing Fillet welding one flat plate or bar at right angles to another in form of T-joint Specimen removed (6") with one start or stop Specimen fractured by application of pressure from press, testing machine, or hammer Fractured at root, and fractured material examined

Fillet-weld Break Test
Usual test results required (AWS) Weld must fracture through throat of weld Visual examination shall show Uniform appearance Uniform weld size, not varying over 1/8 inch No overlap No cracks No undercut greater than inch No visible surface porosity

Etching Reveals penetration and soundness of weld cross section Objectives of test: Determine soundness of weld Make visible boundaries between weld metal and base metal and between layers of weld metal Determine location and depth of penetration of weld Determine location and number of weld passes To examine metallurgical structure of heat-affected zone Inspected with polarizing microscope or photographed with metallograph

Etching Transverse section cut from welded joint
Face of weld and base material filed to smooth surface and polished with fine emery cloth Surface exposed to one of the following: Iodine and potassium iodide Nitric acid Hydrochloric acid Ammonium persulphate

Etching Macroetch test (less than 10x magnification)
Visual test Fillet weld macroetch test shall have: No cracks No incomplete fusion Weld profiles that blend smoothly into base metal No convexity or concavity exceeding 1/16" No undercut exceeding 0.010" No porosity or inclusions greater than 1/32" No acceptable porosity or inclusions exceeding 1/4"

Objectives of Etching To determine soundness of weld
To make visible boundaries between weld metal and base metal and between layers of weld metal To determine location and depth of fusion and penetration of weld To determine location and number of weld passes To examine metallurgical structure of heat-affected zone

Impact Testing Determines impact strength of welds and base metal in welded products Impact strength is ability of metal to withstand sharp, high velocity blow Compares toughness of weld metal with base metal Two standard methods of testing Izod and Charpy tests Specimen broken by single blow Impact strength measured in foot-pounds

Impact Testing Both types of tests make in impact-testing machine
Difference between tests mainly the position of the notch in the test specimen Amount of energy in falling pendulum known Distance through which pendulum swings after breaking specimen indicates how much of total energy used in breaking it Shorter the distance, the higher reading on scale

Impact Testing Izod Test Charpy Test
The Lincoln Co. The Lincoln Co. Typical impact test specimens and methods of holding and applying the test load. The V-notch specimens shown have an groove angle of 45º and a bottom radius of 0.010" in the notch. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fatigue Testing Purpose is to find out how well weld can resist repetitive stress as compared to base metal Improperly made welds that contain defects like porosity, slag inclusions, and cracks don't blend smoothly into base metal Two principal methods of testing Specimen bent back and forth in regular fatigue-testing machine Specimen rotated under load in testing machine

Corrosion Testing Weld metal and base metal subjected to corrosive conditions similar to environmental conditions weldment will be exposed Materials compared for resistance to corrosion Defect shows as difference in rate of corrosion when compared to base metal Weld metal must be equal to or better than base material in corrosion resistance

Specific Gravity Used to make sure no fine porosity exists
Performed in laboratory Test specimen Cylinder of all-weld metal 5/8" in diameter and 2" long taken from weld bead Specific gravity obtained by dividing weight in grams by volume in cubic centimeters High quality weld will have specific gravity of 7.80 grams per cubic centimeter

Visual Inspection Most widely used of all inspection methods
Quick and does not require expensive equipment Good magnifying glass (10x) recommended Required before more expensive NDE methods applied Should be employed by welder, welding inspector, and supervisor from beginning to end of welding job

Principal Defects Incomplete penetration Incomplete fusion
Undercutting Inclusions Porosity Cracking Brittle welds Dimensional defects

Incomplete Penetration
Failure of filler and base metal to fuse together at root of joint Root-face sections of welding groove may fail to reach melting temperature for entire depth or not reach root of fillet joint Leaves void caused by bridging of weld metal from one plate to another Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Will cause weld failure if weld subjected to tension or bending stresses When welded from one side, following conditions likely to cause incomplete penetration Root-face dimension too big even though root opening adequate Root opening too small Groove angle of V-groove too small

Will result from following error in technique even if joint design adequate Electrode too large Rate of travel too high Welding current too low

Incomplete Fusion Failure of welding process to fuse together layer of weld metal or weld metal and base metal Overlap Weld metal just rolls over plate surfaces May occur at any point in welding groove Very often good fusion at root and plate but toe of weld does not fuse (heat conduction and poor technique)

Incomplete Fusion Caused by:
Failure to raise temperature of base metal or previously deposited weld metal to melting point Electrode too small Rate of travel too fast Arc length too close Welding current too low Improper fluxing which fails to dissolve oxide and other foreign material from surfaces which deposited metal must fuse

Avoiding Incomplete Fusion
Making sure that surfaces to be welded are free of foreign material Selecting proper type and size of electrodes Selecting correct current adjustment wire-feed speed, and voltage Using good welding technique

Undercutting Burning away of base metal at toe of weld Caused by:
On multilayer, occur at juncture of layer with wall of groove Caused by: Poor technique Type of electrode used Current adjustment too high Arc length too long Failure to fill up crater completely Very serious defect Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Undercutting To prevent serious effect, correct before depositing next bead Rounded chipping tool used to remove sharp recess If at surface of joint, should not be permitted Reduces strength of joint If weld part of primary member and transverse to tensile stress, undercut can be no more than 0.010" in depth Special undercut gauge made for this precise measurement Visible inspection used

Inclusions Entrapped foreign solid materials in weld
Slag, flux, tungsten, or oxides Usually elongated or globular in shape Most can be prevented by: Preparing groove and clean properly before each bead deposited Taking care to avoid leaving any contours that will be difficult to penetrate fully with arc Making sure all slag has been cleaned from surface of previous bead

Porosity Presence of pockets that do not contain any solid material
Gases forming in voids derived from: Gas released by cooling weld metal Gases formed by chemical reactions in weld Excessive porosity can effect the mechanical properties of joint Porosity may be scattered uniformly, isolated in small groups or concentrated at root

Porosity Best prevented by avoiding:
Overheating and underheating of weld metal Excess moisture in covered electrode Contaminated base metal or consumables Too high current setting Too long an arc Code specifies maximum size acceptable

Cracking Linear ruptures of metal under stress
Occur in weld metal, in plate next to weld or in heat-affected zone Three major classes of cracking Hot cracking Cold cracking Microfissuring

Hot Cracking Occurs at elevated temperatures during cooling shortly after weld deposited and started to solidify Stress must be present to induce cracking Slight stress causes very small cracks detected only with some of nondestructive testing techniques such as radiographic and liquid penetrant inspection Most welding cracks hot cracks

Cold Cracking Cracking at or near room temperature
May occur hours or days after cooling Usually start in base metal in heat-affected zone May appear as underbead cracks parallel to weld or as toe cracks at edge of weld Occurs more often in steels than other metals

Microfissures (Microcracks)
May be either hot or cold cracks Too small to be seen with naked eye Not detectable at magnifications below 10 power Usually do not reduce service life of fabrication

Weld Metal Cracking Three different types Transverse cracks
Run across face of weld and may extend into base metal Usually caused by excessive restraint during welding Longitudinal cracks Usually confined to center of weld deposit If not eliminated, crack will progress through entire weld Crater cracks Usually proceed to edge of crater and may be starting point for longitudinal crack

Longitudinal Cracking
Corrected by Increasing thickness of the root pass deposit Controlling heat input Decreasing speed of travel to allow more weld metal to build up Correcting electrode manipulation Preheating and postheating May be continuation of crater cracks or cracks in first layer of welding

Cracks in Welded Joints
Examples of crater cracks Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cracks in Welded Joints

Base Metal Cracking Usually occur along edges of weld and through heat-affected zone into base metal Possibility of cracking increases when working with hardenable materials Underbead crack (mainly in steel) Base metal crack usually associated with hydrogen Toe cracks caused by hot cracking in or near fusion line Arc strikes (accidental touching of electrode to work) may cause small cracks Can also be started as result of undercutting

Base Metal Cracking Root cracks often produce cracking in plate on side opposite weld Nonfused area may crake if area subject to tensile strength Improper design with little regard for expansion and contraction contributes to cracking Care must be taken in type of steel selected and electrode chosen for welding

Brittle Welds Has poor elongation, very low yield point, very poor ductility, and poor resistance to stress and strain Highly subject to failure and may fail without warning any time during life of weldment Principle cause is use of excessive heat which burns metal Avoid by using multilayer welds and careful selection of material and electrode

Dimensional Defects Caused by improper welding procedure and/or technique and include: Longitudinal contraction Transverse contraction Warping Angular distortion Controls that help prevent Welding jigs, proper welding sequences, correct welding procedure, suitable joint design, and preheat and postheat

Weld Gauges Tools used to make sure completed weld within limits specified by engineering design and weld procedure Two designs: concave and convex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Method of Using Weld Gauge
Size of Convex Fillet Maximum Convexity General Electric Co. General Electric Co. Two Examples Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Weld Gauge Method of using fillet weld gauge to determine size
of a convex fillet weld Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Laser Scanners New stage in weld inspection handheld devices
Can be used for preweld inspection to determine if joint design meets specification Can select type of inspection, view measurement and results on bright color display Data stored in memory or downloaded to computer

Summary Welding demands constant visual examination during entire operation Many variables to adjust continuously Special attention given to root pass Tables 28-5 and 28-6 summarize various weld and base metal defects that may be encountered Table 28-7 gives the recommended inspection methods for evaluating fillet and butt joints

Summary Visual inspection most convenient method
Radiographic inspection permits looking into weld for defects that fall within sensitivity range of the process Magnetic particle inspection outstanding for detecting surface cracks and used to advantage on heavy weldments and assemblies Dye penetrant easy to use for detecting surface cracks

Summary Ultrasonic inspection excellent for detecting subsurface discontinuities, but requires expert interpretation Hydrostatic testing determines tightness of welds in fabricated vessels Hardness tests indicate approximate tensile strengths of metals and show whether or not base metal and weld metal strengths matched Destructive testing gives absolute measure of strength of sample tested

Joint Design, Testing, and Inspection

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Joint Design, Testing, and Inspection

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