Presentation on theme: "WELDING INSPECTION AND QUALITY CONTROL"— Presentation transcript:
1 WELDING INSPECTION AND QUALITY CONTROL TASK # 2:FLAWS/DISCONTINUITIES / DEFECTSWHY IS IT IMPORTANT FOR YOU TO LEARN THIS SKILL?UPON COMPLETION OF THIS MODULE YOU WILL BE ABLE TO:DIFFERENTIATE FLAWS, DISCONTINUITIES AND DEFECTS.DEFINE THE MAJOR CLASSIFICATION OF WELD DEFECTSIDENTIFY DEFECTS, ITS CAUSES AND ITS REMEDIESACCEPTANCE STANDARDS
2 DiscontinuityAll Welds have flaws.Another name for a flaw is a discontinuityDiscontinuities are interruptions in the normal crystalline structure (or grain) of the metal.Discontinuities are NOT always defectsDefectA 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.
3 Acceptance Standards CODE requirements Users standards Sample of Codes and StandardsAWS – American Welding SocietyAPI – American Petroleum InstituteASME – American Society of Mechanical EngineersABS – American Bureau of Shipping
4 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 defectsDefects will compromise the welds overall strength
5 What are some common defects? CLASSIFICATION SYSTEM AND TYPESDRAWING AND DIMENSIONALSTRUCTURAL DISCONTINUITIES IN WELDSPROPERTIES(Mechanical and Chemical) of weld metal and or base metal.Dimensional1. Warpage-Longitudinal Distortion-Angular
6 b. Causes of warpage / distortion – 1 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
19 Excessive Root Reinforcement Insufficient penetrationBurn throughNarrow root gap
20 4. Incorrect Weld Profile Type1. excessive root reinforcement2. excessive face reinforcementCauses1. slow travel speed2. excessive heat3. incorrect root face4. improper electrode anglec. Controlling methods1. increase travel speed2. reduce heat3. use correct preparation4. use correct electrode angled. Correction methods1. removal of excessive reinforcement2. possible removal of welds and subsequent re-weldingEffects – concentration of stress under load/notch effect
21 5. Incorrect Final Dimension Types1. Too long / Too shortCauses1. incorrect tolerance on drawings or specifications2. shrinkage of welds3. incorrect joint preparationc. Controlling methods1. inspect for correct dimensions or tolerances prior to fabricationd. Correction methods1. possible removal of welds and subsequent re-weldinge. Effects1. will change dimensions of entire product
22 Structural Discontinuities PorositySlag inclusionTungsten InclusionPoor penetrationUndercutCracksLack of FusionBurn ThroughRollover or “Cold Lap”
23 Structural Discontinuities in Weld POROSITY- Gas entrapment
24 Sample of Defective Welds Porosity would likely to occur at starting the weld, Tie Ins.Over reinforcement
25 Sample of Defective Welds A. PorosityCauses:1.Welding speed too rapid2.Current too low3.High sulphur or other impurities4.Faulty electrodes
26 PorosityTypes1. uniformly scattered porosity2. cluster porosity3. linear porosityb. Causes1. dirt, grease, rust, oil, moisture on base metal2. excessive current3. moisture in shielding gas4. moisture in filler metalsc. Controlling methods1. clean base metal properly2. dry base metal and/or filler materials3. proper welding techniqued. Corrective methods1. removal of defective area and subsequent re-weldinge. Effectdepending on nature and type can propagate into a crack
27 2. Slag InclusionsType1. slag at root of joint2. slag at bond area3. scattered slag inclusionsb. Causes1. improper joint preparation2. improper cleaning of welds3. improper techniques – wrong current setting- wrong travel or speedc. Controlling methods1. proper joint preparation2. proper cleaning before welding another bead3. use proper technique – adjust current setting,- adjust travel or speedd. Corrective methods1. removal of defective area and subsequent re-weldinge. Effect – weld is weak and cause cracking
28 Sample of Defective Welds B. Slag InclusionCauses:1.Joint design: sharp V-shaped recess2.High viscosity of molten metal, rapid chilling, too low a weld temperatureSlag are not complete remove before depositing another bead.
30 3. Tungsten InclusionsType1. Scattered inclusionsb. Causes1. touching the electrode to the work or molten weld metal2. incorrect current type and or current setting3. incorrect type and or size of tungsten electrodec. Controlling methods1. use proper welding technique2. use correct type and current setting3. use correct type and size of tungsten electroded. Correction method1. removal of defective area and subsequent re-weldinge. Effects1. creates brittle area2. can cause crackingNote: can be seen as white image in x-ray film.
31 4. Incomplete FusionType1. incomplete fusion at the root of the weld or adjacent layers of weld metalb. Causes1. inadequate amount of heat (low current setting)2. incorrect electrode angle3. travel speed too fast4. incorrect joint preparationc. Controlling Methods1. increase amount of heat (increase current setting)2. reduce travel speed3. use correct electrode angle4. use proper joint preparationd. Correction methods1. possible back gouge and re-weld2. removal of defective area and subsequent re-weldinge. Effect – weak joint and can cause cracking
32 4. Incomplete fusion at the root of the weld Corner edge of the joint is not melted
34 5. Incomplete joint penetration Type1. lack of complete fill at the root of the joint / either butt joint or tee joint.b. Causes1. groove design not suited for the process2. root face dimension is too great (thick)3. root opening is too small4. fast travel speed5. insufficient welding currentc. Controlling methods1. use proper joint design2. reduce travel speed3. increase current settingd. Correction method1. possible back gouge and re-weld2. removal of defective area and subsequent re-weldinge. Effects – notch effect possible start cracks
36 Defective Root Penetration Lack of penetration:Causes:1.Too long arc2.Wrong fit-up or root gap3. Low current rating4. Faulty electrode size5. Wrong travel speed
37 Defective Root Penetration keyholeKeyhole = root gap + 1/16” on both sides is the recommended size.Burn Through / Melt through
38 Defective Root Penetration Lack of Penetration In tie ins
39 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.
41 6. UndercutTypes1. side wall undercut2. surface toe line undercutb. Causes1. excessive current (too high current)2. too long arc length3. magnetic arc blow (DC welding)4. excessive travel speed (travel too fast)5. incorrect electrode anglec. Controlling methods1. reduce current2. adjust arc length3. use AC welding4. reduce travel speed5. observe electrode angle
42 d. Correction methods1. grinding or removal of defective area and subsequent re-welding.e. Effects1. reduces strength of the joint2. can cause slag inclusion
43 UndercutDefinition: A groove cut at the toe of the weld and left unfilled.Cause: High amperage, electrode angle, long arc length, rustPrevention: 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.
45 Undercut D. Undercutting Causes: 1.Current too high 2.Arc length too long3.Improper manipulation of the electrode4. Welding speed too rapid
46 Undercut typically has an allowable limit 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)
47 7. CracksTypes1. transverse and longitudinal weld cracks2. crater cracks3. base metal crackingb. Causes1. localized stress exceeds the ultimate strength of the material2. lack of pre heat3. poor crater fill techniquec. Controlling methods1. use pre heating2. use low hydrogen electrodes3. sequence welds to balance shrinkage4. use proper crater fill technique5. avoid quenching and cooling conditions
48 d. Correction method1. grinding / removal of defective area and subsequent re-weldinge. Effects1. weld failure2. cracks progress in length (increase of crack length)
50 CRATER CRACKSINSUFFICIENT FILLING AT THE END OF THE WELD
51 8. Surface irregularities Types1. depressions2. varying surface welds3. varying reinforcement4. non uniform weld ripples5. spatterb. Causes1. inexperienced welder2. restricted positioning while weldingc. Controlling methods1. proper training of welders2. workmanship samplesd. Correction methods1. grinding or chipping before depositing succeeding weldse. Effects1. could result in slag entrapment or other discontinuities
53 Insufficient FillDefinition: The weld surface is below the adjacent surfaces of the base metalCause: Improper welding techniquesPrevention: 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.
58 Properties (Mechanical and Chemical) of Welded Metal and/or Base Metal Tensile strength – ultimate strength of a material subjected to a tensile loadYield strength – indication of maximum stress that can be developed in a material without with out plastic deformation.Ductility – extent to which a material can sustain palstic deformation without ruptureHardness – measure of a materials resistance to localized plastic deformationImpact – energy required to fracture a part subjected to shock loadingChemical Composition – the structure and properties of substances and of the changes they undergo.
59 How would you find these faults ? TWO METHODS OF DETERMINING WELD FAULTS1. Non Destructive Examination2. DESTRUCTIVE TESTING
60 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.
61 Florence-Darlington Technical College Excerpts from:Tim TurnerElizabethtown Technical CollegeWanda S. BentonFlorence-Darlington Technical College