Defectology Discon Discontin tinuit uity y divid divided ed in to to three three gen genera erall categories Inhe Inhere rent nt di disco scont ntin inui uity ty Pr Proce ocess ssin ing g Di Disc scon onti tinu nuit ity y Se Serv rvic ice e Disc Discon onti tinu nuit ity y
Defectology Inherent discontinuity are usually formed when the metal is molten. It is further subdivided in to Inherent wrought discontinuity and Inherent Cast discontinuity
Defectology Inherent wrought discontinuity Related to the melting and solidification of the original ingot before it is formed into slabs, Blooms and Bi Billets.
Defectology Inherent cast discontinuity Related to the melting, casting and solidification of a cast c ast article. Usually caused by, In Inad adeq equa uate te fe feed edin ing, g, Gating, Exce Excessi ssive ve pou pourin ring g temp tempera eratur ture e and and entrapped gases.
Defectology
Processing Discontinuity are usually related to the various manufacturing processes such as, Machining Forming Extruding Rollin Rol ling, g, weldi welding, ng, heat heat trea treatin ting g and plat plating ing
Defectology
Service Discontinuity are related to the various service condition such as, Stress Corrosion Fatigue And Erosion
Defectology Remember Discontinuity are not necessarily Defects. Any Indication that is found by the Inspector is called a Discontinuity until it can be identified and evaluated as to the effect it will have on the service of the part or to the requirements of the specification
Defectology
Inherent Inhere nt wrough wroughtt discont discontinu inuity ity Ing Ingot ot Discontinuities Inclusion Blow Holes Pipe and Segregations
Defectology Ingot Defects Pipe Non metallic Inclusion Porosity
Ingot
Defectology Ingot Defects Non Non met metal allilicc incl inclus usio ions ns su such ch as sla slag, g, ox oxid ides es,, and and sulphides Blo Blow w hole holess & poro porosit sity y are are form formed ed by gas gas trap trappe ped d Pip Pipes es due due to intern internal al shrin shrinka kage ge durin during g solidi solidific ficati ation on of ingot Se Segr greg egat atio ion n oc occu curr due to to non-e non-eve ven n dist distri ribu buti tion on of of the the various element.
Defectology
Inherent Inhere nt Cast Cast Disco Disconti ntinui nuity ty Cas Castin ting g Discontinuity Cold Shut Hot tears Shri Sh rink nkag age e Ca Cavi viti ties es Mic icrro shr hrin inka kag ge Blow Bl owho hole less an and d Po Poro rosi sity ty
Defectology Casting Discontinuity Co Cold ld Sh Shut ut Ca Caus used ed wh when en mo molt lten en me meta tall is is poured over solidification metal (not fused together)
Defectology Casting Discontinuity Ho Hott tea tears rs oc occu curs rs wh when en th ther ere e is is une unequ qual al shrinkage between light and heavy section
Defectology Casting Discontinuity Sh Shri rink nkag age e Cavi Caviti ties es Ar Are e usu usual ally ly cau cause sed db by y lack of enough molten metal to fill the space (similarly to pipe in the ingot)
Defectology Casting Discontinuity Mi Micr cro o shr shrin inka kage ge Us Usua ualllly y occu occurs rs as ma many ny small subsurface holes that appear at the gate of the casting.
Defectology Casting Discontinuity Bl Blow owho hole less ar are e smal smalll hol holes es at at the the sur surfa face ce of the casting caused by the gas which comes from the mold itself.
Defectology Casting Discontinuity Po Poro rosi sity ty is ca caus used ed by En Entr trap appe ped d gas gas.. Usually subsurface but can occur on the surface also.
Defectology Processing Process ing Disc Discont ontinu inuity ity are those those found found or produced by the forming or fabrication including Rolling, Forging, Grinding, Machining, Heat treating and Welding.
Defectology Processing Process ing Disc Discont ontinu inuity ity Non metal metallic lic inclusion and porosity may cause LAMINATION during flattening and spreading out of billets.
Defectology Processing Process ing Dis Discon contin tinuit uity y Rol Rollin ling g Non metallic inclusions are squeezed out into longer and thinner discontinuity called stringer.
Defectology Processing Process ing Dis Discon contin tinuit uity y For Forgin ging g Forging defects occur when metal is hammered or pressed into shape usually metal is very hot. Common discontinuity is Forging Lap and Forging Burst. Forgi For ging ng Lap Cau Caused sed by by folding folding the the metal metal Forgi For ging ng Burs Burstt Rup Ruptur ture e caused caused by by improper temperatures.
Defectology Processing Process ing Dis Discon contin tinuit uity y For Forgin ging g Forgi For ging ng Lap Cau Caused sed by by folding folding the the metal metal Forgi For ging ng Burs Burstt Rup Ruptur ture e caused caused by by improper temperatures.
Defectology Processing Process ing Dis Discon contin tinuit uity y Gri Grind nding ing Grinding crack caused by stresses which are built up from Excess heat created between grinding wheel and metal.
Defectology Processing Process ing Disc Discont ontinu inuity ity Hea Heatt treatin treating g Heat treating crack caused by the stresses built up during heating and cooling.
Defectology Processing Discontinuity Weld Defects and Discontinuities
Defect A fla flaw w or or flaw flawss tha thatt by nat natur ure e or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. The term designates rejectability.
Discontinuity An inte interru rrupti ption on of the the typic typical al struc structur ture e of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect.
Weld Joint Discontinuities
Porosity
Uniformly Scattered Cluster Linear Piping
Cracks
Inclusions lag g Sla Wagont gontracks racks Tung ngssten Spatter Arc Craters
(hi-lo) o) Misalignment (hi-l
Undercut
Underfill
Concavity or Convexity
Excessive reinforcement
Improper reinforcement
Heat-affected zone microstructure alteration Base Plate laminati laminations ons
Longitudinal Transverse Crater Throat Size or dimensions Toe Root Base Metal Discontinuiti Discontinuities es Underbead and Lamellar tteari Lamellar earing ng Heat-affected zone Lamin Lami nation onss and and Hot Delamin Delami nation onss Cold or delayed Laps and and Seams
Overlap Burn-through Incomplete or Insufficient Penetration Incompletee Fusion Incomplet Surface irregularity ± Overlap
Arc Strikes
Cracks
Longitudinal Lon Transverse Crater Throat Toe Root Underb Und erbead ead and Hea Heat-af t-affect fected ed zon zone e Hot Cold or or de delaye yed d
Longitudinal
Crack
Definition: A crack running in the direction of the weld axis. May be f ound in the weld or base metal. Cause: Preheat or fast cooling pr o blem. Als o caused by shrinkage stresses in high constraint areas. Prevention: Weld towar d areas of less constraint. Also preheat to even out the cooling rates. Repair: Remove and reweld
Transverse
Crack
Definition: A crack running into or inside a weld, transverse to the weld axis direction. dness pr o blem Cause: Weld metal har dn
Prevention: Repair:
Crater Crack Definition: A crack , generally in the shape of an ³X´ which is f ound in a crater er.. Cra Crater cracks are hot cracks. Cause: The center of the weld pool becomes solid bef ore th outside of the weld pool, pulling the center apar t during cooling Prevention: Use crater fill, fill the crater at weld termination and/or preheat to even out the cooling of the puddle Repair:
Throat
Crack
Definition: A longitudinal crack located in the weld thr oat area. Cause: Transverse Stresses, pr o bably fr om shrinkage. Indicates inadequate filler metal selection or welding pr ocedure. May be due to crater crack pr o pagation. Prevention: Correct initial cause. Increasing preheat may prevent it. be sure not to leave a crater er.. Use a more ductile filler material. Repair: Remove and reweld using appr o priate pr ocedure. Be sure to correct initial pr o blem first.
Toe
Crack
Definition: A crack in the base metal beginning at the toe of the weld Cause: Transverse shrinkage stresses. Indicates a HAZ brittleness pr o blem. Prevention: Increase preheat if possible, or use a more ductile filler material. Repair:
oot R oot
Crack
oot. Definition: A crack in the weld at the weld r oot
Cause: Transverse shrinkage stresses. Same as a thr oat crack. Prevention: Same as a thr oat crack Repair:
Underbead Crack Definition: A crack in the unmelted parent metal of the HAZ. ogen embrittlement Cause: Hydr og odes and/or preheat Prevention: Use Lo/Hi electr od
Repair: (only f ound using NDT). Remove and reweld.
Hot Crack Definition: A crack in the weld that occurs during solidification. Cause: Micr o stresses fr om weld metal shrinkage pulling apar t weld metal as it cools fr om liquid to solid temp. Prevention: Preheat or use a low tensile filler material. Repair: Remove and reweld, correct pr o blem first, preheat may be necessary, increase weld size.
Cold Crack Definition: A crack that occurs af ter the metal has completely solidified Cause: Shrinkage, Highly restrained welds, Discontinuities Prevention: Preheat, weld towar d areas of less constraint, use a more ductile weld metal Repair: Remove and reweld, correct pr o blem first, preheat may be necessary.
Repairs
to
Cracks
Determ Dete rmin ine e th the e ca caus use e Corr Co rrec ectt th the e pro probl blem em Take Tak e preca precauti utions ons to to preven preventt reoccur reoccurren rence ce Genera Gen erally lly req requir uired ed to rep repair air usi using ng a smaller electrode
Porosity
Single Pore Unif Un ifor orml mly y Sc Scat atte tere red d Cluster Linear Piping
Single
Pore
Separa Separated ted by by at leas leastt their their own own diam diamete eterr along the axis of the weld
SINGLE POR E
Uniformly Scattered
Porosity Typi Typical cally ly judg judged ed by by diame diamete terr and and proximity to a start or stop oft often en caus caused ed by by low low amper amperage age or shor short t arc gap or an unshielded weld start
Cluster
Porosity
Typical Typically ly view viewed ed as a sing single le larg large e discontinuity
Linear
Porosity
being being line linear ar great greatly ly affects affects the sever severity ity of of this discontinuity
Porosity preh prehea eatt wil willl hel help p elim elimin inat ate e ma may y need need an an elect electro rode de wit with h more more deoxidizers Us Use e ru runn-on on/r /run un-o -off ff ta taps ps res restar tartt on top of prev previou iouss weld and gri grind nd off lump
Inclusions
Slag Wagontracks Tungsten
Slag Inclusion Definition: Slag entrapped within the weld Cause: Low amperage, impr o per technique, Trying to weld in an area that is too tight. Slow travel in Ver tical Down Prevention: Increase amperage or preheat, grind out tight areas to gain access to bottom of joint. Repair: Remove by grinding. Reweld.
Tungsten
Inclusion
Definition: A tungsten par ticle embedded in a weld. (Typic (T ypically ally GT GTA AW only) ode too small, amperage too high, Cause: Tungsten electr od ode tip not AC balance on +, Upslo pe too high, electr od ode dipped into the weld pool or touched snipped, electr od od, electr od ode split. with the fill r od, Prevention: Eliminate the cause
Repair: Grind out and reweld
Inclusions
Fix whe when n you you see see it. it. Otherw Otherwise ise gri grind nd out out & fix.
SLAG INCLUSION AT COR NE NER BETWEEN BACKING BAR & PLATE PR OCES O CESS S - FCA FCAW-g
Incomplete
or Insufficient
Penetration Definition: When the weld metal does not extend to the oot required depth into the joint r oot oot o pening, fast Cause: Low amperage, low preheat, tight r oot travel speed, shor t arc length.
Prevention: Correct the contributing factor(s). Repair: Back gouge and back weld or remove and reweld.
Incomplete
Fusion
Definition: Where weld metal does not f orm a cohesive bond with the base metal. ode angles, fast travel Cause: Low amperage, steep electr od ode too small, speed, shor t arc gap, lack of preheat, electr od unclean base metal, arc off seam. Prevention: Eliminate the potential causes.
Repair: remove and reweld, being careful to completely remove the defective area. This is sometimes extremely difficult to find.
Undercut oove cut at the Definition: A gr oo toe of the weld and lef t unfilled. ode Cause: High amperage, electr od angle, long arc length, rust
Prevention: Set machine on scrap metal. Clean metal bef ore welding.
epair: Weld R epair:
ode, sometimes must be with smaller electr od ogen with preheat. Sometimes must gouge first. low hydr og
Undercut (cont......)
Undercut typically has an allowable limit. Different codes and standards vary greatly in the allowable amount. Plate Pla te - the less lesser er of of 1/32 1/32 or 5% 5% (typ.) (typ.) ODOT OD OT - 0. 0.01 010 0 ( <1 <1/6 /64 4))
Insufficient
Fill
Defin Definiti ition: on: The weld weld surfac surface e is below below the the adjac adjacent ent surfaces of the base metal Cause: Impr o per welding techniques Prevention: Apply pr o per welding techniques f or the weld type and position. Use stripper beads bef ore the cover pass. Repair: Simply weld to fill. May require preparation by grinding.
Reinforcement The amo amount of a gr oove oove weld weld which ext extend ndss beyond beyond the surface of f tthe plat plate
Excessive Insuffi fici cie ent Improper contour
Face
Reinf orceme Rein rcement nt
R oot oot Rei Rein nf orceme rcement nt
Excessive Reinforcement Definiti Definition: on: Speci Specifica fically lly define defined d by by the the standa standard. rd. Typi Typicall cally, y, Reinforcement should be flush to 1/16(pipe) or flush to 1/8 (plate or structural shapes).
Cause: Travel speed too slow, amperage too low Prevention: Set amperage and travel speed on scrap plate. Repair: Remove excessive reinf orcement and feather the weld toes to a smooth transition to the base plate.
Insufficient R einforcement einforcement Definition: S pecifically defined by the standar d. Typic Typically ally, Underfill may be up to 5% of metal thick ness not to exceed 1/32´ as long as the thick ness is made up in the o pposite reinf orcement. Not applied to fillet welds. oot reinf orcement - Too little filler metal will Cause: On r oot cause thinning of the filler metal. In OH position, too hot or too wide will cause dr oo oo ping of the o pen r oot oot puddle. Prevention: Use pr o per welding technique. Use backing or consumable inser ts. Use back weld or backing.
Repair: Possibly simply increase the face reinf orcement. If backwelding is not possible, must remove and reweld.
Improper Weld Contour Definition: When the weld exhibits less than a 1350 1350 transition angle at the weld toe. Cause: Poor welding technique Prevention: Use pr o per techniques. A weave or whip motion can of ten eliminate the pr o blem. Repair: The weld face must be feathered into the base plate.
Overlap
Definition: When the face of the weld extends beyond the toe of the weld ode Cause: Impr o per welding technique. Typically, electr od angles and travel speed.
Prevention: Overlap is a contour pr o blem. Pr o per welding technique will prevent this pr o blem. Repair: Overlap must be removed to blend smoothly into the base metal. Be careful of deep grind marks that run transverse to the load. Also be careful of fusion discontinuities hidden by grinding. Use NDT to be sure.
Overlap Overlap is measured measure d wi witth a square edg edgee such as a 6´ rule. No No am amo ount of overlap is typically allo all owe wed d.
Burn-through
(non-standard)
Definition: When an undesirable o pen hole has been completely melted thr ough the base metal. The hole may or may not be lef t o pen. Cause: Excessive heat in put. Prevention: Reduce heat in put by increasing travel speed, use of a heat sink , or by reducing welding parameters. Repair: Will be defined by standar ds. Filling may suffice. Otherwise, removal and rewelding may be required. Some standar ds may require special filler metal and/or PWHT HT..
rc
Strike
Definition: A localized coalescence outside the weld zone. Cause: Carelessness Prevention: In difficult areas, ad jacent areas can be otected using fire blankets. pr ot Repair: Where applicable, arc strikes must be sanded smooth and tested f or cracks. If f ound, they must be remove and repaired using a qualified repair pr ocedure and inspected as any other weld.
Spatter
Definition: Small par ticles of weld metal expelled fr om the welding o peration which adhere to the base metal surface. ode angles, high Cause: Long arc length, severe electr od amperages. otected Prevention: Correct the cause. Base metal can be pr ot with coverings or hi-temp paints.
Repair: Remove by grinding or sanding. Sometimes must b tested as if it were a weld.
rc
Craters
Definition: A depression lef t at the termination of the weld where the weld pool is lef t unfilled. Cause: Impr o per weld termination techniques Prevention: Repair: If no cracks exist, simply fill in the crater. Generally welding fr om beyond the crater back into the crater er..
Base
Metal Discontinuities
Lame Lamellllar ar te tea ari ring ng La Lami mina nati tion onss and Dela Delami mina nati tion onss Laps and Seams
Laminations Base Met Metal Discont Discontiinui uitty May require repair prio prior r to weld to wel ding Forme rmed d duri uring ng the milling milling pr ocess
Lamination effects can be reduced by joint design:
Delaminations
Laps
and
Seams
A mill-ind mill-induce uced d disc iscont ontiinui uitty in in which result results fr om a lump of met metal being bei ng squeeze squeezed d over into into the surface of f tthe mat material. If beyond beyond accep accepttable limit limits, mus mustt be remo remove ved d and repaire repaired d or discar ded.
Heat-affected
zone microstructure alteration
grain grai n re refi finem nemen ent t grai gr ain n gr growt wth h hard ha rden ened ed ar area eass soft so ften ened ed ar area eass precip pre cipita itate te suscep susceptib tible le areas areas..
Radiographic
defects
Porosity
Excessive
Penetration
Incomplete
Penetration
Burn
Through
Internal Concavity
Internal Root Undercut
Root
Pass Aligned Porosity
Internal Root Undercut
Lack
of Sidewall Fusion
Slag Inclusions
External Undercut
External Concavity
Miss-match
Miss-Match with penetration
Lack
of
Transverse
Cracking
Tungsten Inclusion
