Presentation on theme: "TASK # 2: FLAWS/DISCONTINUITIES / DEFECTS WELDING INSPECTION AND QUALITY CONTROL WHY IS IT IMPORTANT FOR YOU TO LEARN THIS SKILL? UPON COMPLETION OF THIS."— Presentation transcript:
TASK # 2: FLAWS/DISCONTINUITIES / DEFECTS WELDING INSPECTION AND QUALITY CONTROL WHY IS IT IMPORTANT FOR YOU TO LEARN THIS SKILL? UPON COMPLETION OF THIS MODULE YOU WILL BE ABLE TO: 1.DIFFERENTIATE FLAWS, DISCONTINUITIES AND DEFECTS. 2.DEFINE THE MAJOR CLASSIFICATION OF WELD DEFECTS 3.IDENTIFY DEFECTS, ITS CAUSES AND ITS REMEDIES 4.ACCEPTANCE STANDARDS
All Welds have flaws. Another name for a flaw is a discontinuity Discontinuities are interruptions in the normal crystalline structure (or grain) of the metal. Discontinuities are NOT always defects Discontinuity Defect A flaw or flaws that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. The term designates rejectability.
Acceptance Standards a.CODE requirements b.Users standards Sample of Codes and Standards 1.AWS – American Welding Society 2.API – American Petroleum Institute 3.ASME – American Society of Mechanical Engineers 4.ABS – American Bureau of Shipping
The purpose of welding inspections is to locate and determine the size of any discontinuities Discontinuities that are too large or repeated too often within the weld become defects Defects will compromise the welds overall strength
What are some common defects? CLASSIFICATION SYSTEM AND TYPES A.DRAWING AND DIMENSIONAL B.STRUCTURAL DISCONTINUITIES IN WELDS C.PROPERTIES(Mechanical and Chemical) of weld metal and or base metal. A.Dimensional 1. Warpage-Longitudinal Distortion-Angular
b. Causes of warpage / distortion – 1. shrinkage of weld metal and overheating of joint, 2. faulty preparation 3. faulty clamping or weak tacking c. Controlling methods 1. proper bead sequence 2. correct preparation 3. intermittent welding 4. correct clamping, proper tack size, prewarp d. Correction method – straightening operation, heating, removal of welds and subsequent re-welding e. Effects 1. builds stress 2. failure to meet design dimensions
Joint Preparation Correct Bevel Angle Correct Root Gap Correct Root Face Proper Tack Weld Proper Alignment
2. Incorrect Joint Preparation a. Types 1. bevel angle 2. groove angle 3. root opening or root gap 4. root face b. Causes 1. improper methods used 2. failure to issue proper instructions 3. failure to follow instructions 4. use of improper symbols c. Controlling methods 1. use proper instructions 2. use of correct symbols 3. use correct techniques d. Corrections methods 1. prepare again using proper methods e. Effects–warpage/trapped slag/incomplete fusion/improper bead shape
Excessive Root Reinforcement Burn through Insufficient penetration Narrow root gap
4. Incorrect Weld Profile a.Type 1. excessive root reinforcement 2. excessive face reinforcement b.Causes 1. slow travel speed 2. excessive heat 3. incorrect root face 4. improper electrode angle c. Controlling methods 1. increase travel speed 2. reduce heat 3. use correct preparation 4. use correct electrode angle d. Correction methods 1. removal of excessive reinforcement 2. possible removal of welds and subsequent re-welding a.Effects – concentration of stress under load/notch effect
5. Incorrect Final Dimension a.Types 1. Too long / Too short b.Causes 1. incorrect tolerance on drawings or specifications 2. shrinkage of welds 3. incorrect joint preparation c. Controlling methods 1. inspect for correct dimensions or tolerances prior to fabrication d. Correction methods 1. possible removal of welds and subsequent re-welding e. Effects 1. will change dimensions of entire product
Structural Discontinuities Porosity Slag inclusion Tungsten Inclusion Poor penetration Undercut Cracks Lack of Fusion Burn Through Rollover or “Cold Lap”
Structural Discontinuities in Weld POROSITY- Gas entrapment
Sample of Defective Welds Porosity would likely to occur at starting the weld, Tie Ins. Over reinforcement
Sample of Defective Welds A. Porosity Causes: 1.Welding speed too rapid 2.Current too low 3.High sulphur or other impurities 4.Faulty electrodes
1.Porosity a.Types 1. uniformly scattered porosity 2. cluster porosity 3. linear porosity b. Causes 1. dirt, grease, rust, oil, moisture on base metal 2. excessive current 3. moisture in shielding gas 4. moisture in filler metals c. Controlling methods 1. clean base metal properly 2. dry base metal and/or filler materials 3. proper welding technique d. Corrective methods 1. removal of defective area and subsequent re-welding e. Effect depending on nature and type can propagate into a crack
2. Slag Inclusions a.Type 1. slag at root of joint 2. slag at bond area 3. scattered slag inclusions b. Causes 1. improper joint preparation 2. improper cleaning of welds 3. improper techniques – wrong current setting - wrong travel or speed c. Controlling methods 1. proper joint preparation 2. proper cleaning before welding another bead 3. use proper technique – adjust current setting, - adjust travel or speed d. Corrective methods 1. removal of defective area and subsequent re-welding e. Effect – weld is weak and cause cracking
Sample of Defective Welds B. Slag Inclusion Causes: 1.Joint design: sharp V-shaped recess 2.High viscosity of molten metal, rapid chilling, too low a weld temperature Slag are not complete remove before depositing another bead.
3. Tungsten Inclusions a.Type 1. Scattered inclusions b. Causes 1. touching the electrode to the work or molten weld metal 2. incorrect current type and or current setting 3. incorrect type and or size of tungsten electrode c. Controlling methods 1. use proper welding technique 2. use correct type and current setting 3. use correct type and size of tungsten electrode d. Correction method 1. removal of defective area and subsequent re-welding e. Effects 1. creates brittle area 2. can cause cracking Note: can be seen as white image in x-ray film.
4. Incomplete Fusion a.Type 1. incomplete fusion at the root of the weld or adjacent layers of weld metal b. Causes 1. inadequate amount of heat (low current setting) 2. incorrect electrode angle 3. travel speed too fast 4. incorrect joint preparation c. Controlling Methods 1. increase amount of heat (increase current setting) 2. reduce travel speed 3. use correct electrode angle 4. use proper joint preparation d. Correction methods 1. possible back gouge and re-weld 2. removal of defective area and subsequent re-welding e. Effect – weak joint and can cause cracking
4. Incomplete fusion at the root of the weld Corner edge of the joint is not melted
5. Incomplete joint penetration a.Type 1. lack of complete fill at the root of the joint / either butt joint or tee joint. b. Causes 1. groove design not suited for the process 2. root face dimension is too great (thick) 3. root opening is too small 4. fast travel speed 5. insufficient welding current c. Controlling methods 1. use proper joint design 2. reduce travel speed 3. increase current setting d. Correction method 1. possible back gouge and re-weld 2. removal of defective area and subsequent re-welding e. Effects – notch effect possible start cracks
Defective Root Penetration Lack of penetration: Causes: 1.Too long arc 2.Wrong fit-up or root gap 3. Low current rating 4. Faulty electrode size 5. Wrong travel speed
Keyhole = root gap + 1/16” on both sides is the recommended size. Burn Through / Melt through Defective Root Penetration keyhole
Defective Root Penetration Lack of Penetration In tie ins
Insufficient Fill on the Root Side (suckback) Definition: The weld surface is below the adjacent surfaces of the base metal at the weld root. Cause: Typically improper joint preparation or excessive weld pool heat. Prevention: Correct cause. Repair: Backweld to fill. May requireremoval of weld section by grinding for access to the joint root.
6. Undercut a.Types 1. side wall undercut 2. surface toe line undercut b. Causes 1. excessive current (too high current) 2. too long arc length 3. magnetic arc blow (DC welding) 4. excessive travel speed (travel too fast) 5. incorrect electrode angle c. Controlling methods 1. reduce current 2. adjust arc length 3. use AC welding 4. reduce travel speed 5. observe electrode angle
d. Correction methods 1. grinding or removal of defective area and subsequent re-welding. e. Effects 1. reduces strength of the joint 2. can cause slag inclusion
Undercut Definition: A groove cut at the toe of the weld and left unfilled. Cause: High amperage, electrode angle, long arc length, rust Prevention: Set machine on scrap metal. Clean metal before welding. Repair: Weld with smaller electrode, sometimes must be low hydrogen with preheat. Sometimes must gouge first.
Undercut D. Undercutting Causes: 1.Current too high 2.Arc length too long 3.Improper manipulation of the electrode 4. Welding speed too rapid
Undercut typically has an allowable limit. Different codes and standards vary greatly in the allowable amount. Plate - the lesser of 1/32” or 5% (typical)
7. Cracks a.Types 1. transverse and longitudinal weld cracks 2. crater cracks 3. base metal cracking b. Causes 1. localized stress exceeds the ultimate strength of the material 2. lack of pre heat 3. poor crater fill technique c. Controlling methods 1. use pre heating 2. use low hydrogen electrodes 3. sequence welds to balance shrinkage 4. use proper crater fill technique 5. avoid quenching and cooling conditions
d. Correction method 1. grinding / removal of defective area and subsequent re- welding e. Effects 1. weld failure 2. cracks progress in length (increase of crack length)
CRATER CRACKS INSUFFICIENT FILLING AT THE END OF THE WELD
8. Surface irregularities a.Types 1. depressions 2. varying surface welds 3. varying reinforcement 4. non uniform weld ripples 5. spatter b. Causes 1. inexperienced welder 2. restricted positioning while welding c. Controlling methods 1. proper training of welders 2. workmanship samples d. Correction methods 1. grinding or chipping before depositing succeeding welds e. Effects 1. could result in slag entrapment or other discontinuities
Insufficient Fill Definition: The weld surface is below the adjacent surfaces of the base metal Cause: Improper welding techniques Prevention: Apply proper welding techniques for the weld type and position. Use stripper beads before the cover pass. Repair: Simply weld to fill. May require preparation by grinding.
Properties (Mechanical and Chemical) of Welded Metal and/or Base Metal 1.Tensile strength – ultimate strength of a material subjected to a tensile load 2.Yield strength – indication of maximum stress that can be developed in a material without with out plastic deformation. 3.Ductility – extent to which a material can sustain palstic deformation without rupture 4.Hardness – measure of a materials resistance to localized plastic deformation 5.Impact – energy required to fracture a part subjected to shock loading 6.Chemical Composition – the structure and properties of substances and of the changes they undergo.
How would you find these faults ? TWO METHODS OF DETERMINING WELD FAULTS 1. Non Destructive Examination 2. DESTRUCTIVE TESTING
Standard Acceptability of welding defects: 1. Undercut should not exceed 1/32” inch(0.8mm) width and depth or must not exceed to 5% thickness from base metal. 2. No porosity shall exceed 1/16 inch (1.6mm) or in addition no square inch of weld metal shall exceed 1/16 inch(1.6mm) in greatest dimensions. 3. No gas pocket on square inch of weld metal area shall contain more than 6 gas pocket exceeding 1/16 inch (1.6mm) in greatest dimensions. 4. No slag inclusion shall exceed 1/8 inch (3.2mm) in every 6 inches of weld.
Tim Turner Elizabethtown Technical College Excerpts from: Wanda S. Benton Florence-Darlington Technical College