Chapter 9 Flashcards
Discontinuities Def?
Types?
Groups types?
- Irregularities in weld or weldment
- Interruption in the uniform nature of an item
- Types: Cracks, porosity, undercut, incomplete fusion, etc
Linear and nonlinear Discontinuities
Defect
specific discontinuity which can impair the suitability of that structure for its intended purpose
“Rejectable Discontinuity”
“Rejectable Discontinuity”
defect
Linear Discontinuities
critical?
lengths which are much greater than their widths
Far more critical - can cause failure
nonlinear Discontinuities
critical?
lengths and widths that are the same
less critical
End condition
specific sharpness at its extremities - more likely to propagate the sharper it is
Discontinuities in order of sharpest
Cracks, incomplete fusion incomplete joint penetration, slag inclusion porosity,
Cracks
characteristics?
linear or nonlinear ?
causes?
- Most critical discontinuities
- Linear
- Very shard end conditions
- Tendency to grow or propagate is a stress is applied
- if a metal is overloaded
Cold Cracks
- occur after metal has cooled to ambient temp
- cracks resulting from hydrogen
- ## intergranular or transgranular (between or through Individual grains
Hot Cracks
- Usually occur as metal solidifies at an elevated temp.
- Intergranular (cracks occur between individual grains
- -
Transverse Cracks
Cause ?
Those lying in a direction perpendicular to the longitudinal axis
Caused by the longitudinal shrinkage stresses of welding acting on the low ductility of the weld or bas metal
longitudinal cracks
Cause?
Those lying in a direction parallel to the longitudinal axis
Transverse shrinkage stresses of welding or stresses associated with service conditions
Throat cracks? longitudinal or Transverse ? hot or cold? other name? Causes?
- cracks along the weld throat
- longitudinal &
- hot cracks
- Also called centerline cracks
causes - Weld cross section is small - thin root pass - concave fillet welds their reduced cross section may not be sufficient to withstand the transfers weld shrinkage stresses
Root cracks
longitudinal or Transverse ?
hot or cold?
Causes?
- cracks along the weld root
- longitudinal
- hot cracks
- weld shrinkage stresses from welding
- Improperly fitted or prepared joints
- Large root openings
Toe cracks
hot or cold?
Causes?
- Cracks at the toe
- cold cracks
- from weld reinforcement or convexity may provide a stress riser at the welds’ toes
- transverse shrinkage stresses of welding, or service stresses
- Fatigue loading of weld components
Crater cracks
Other name?
hot or cold?
occur at the TERMINATION POINT of individual weld passes.
“star cracks” technique and arc does not provide for complete filling of the molten weld puddle -will result in a crater or shallow spot
- Also a result of filler material having flow characteristics which produce concave profiles when solidified.
considered hot cracks since they occur at the solidification of the molten puddle.
Underbead
other name?
Causes
- cracks located in HAZ instead of weld metal
- parallel to fusion line
- delayed cracks (final inspection 48-72hr after weld has cooled. (effect high strength steal)
- usually sub-surface but could propagate to the surface
- form from the presence of hydrogen in the weld zone- during welding their is room for hydrogen atoms but as it cools there is less room for them and the metal attempts to much it out causing a crack.
or filler material, surrounding atmosphere or surface contaminants.
Incomplete fusion
Other name?
Causes
discontinuity that occurs between weld metal and fusion face or weld beads
also called cold lap
- fusion is less than specified
- significant weld discontinuity
- often because of slag inclusion from insufficient cleaning
- not enough concentrated heat to melt metal
- improper manipulation of welding electrode by welder
- configuration of the weld joint
- insufficient groove angle
- extreme contamination or mill scale
Incomplete joint penetration
Other name?
Causes?
- associated only with groove welds
- weld metal does not extend entirely through the joint thickness when complete penetration is required
- some codes/specs allow incomplete joint penetration some don’t.
- also called partial joint penetration or lack of penetration
- improper technique, or joint configuration ot excessive contamination.
Inclusion
entrapped foreign solid material , such as slag, flux, tungsten, or oxide
when the welding process uses some type of flux shielding
causes
improper manipulation of welding electrode
insufficient cleaning
undesirable weld profile that hinders cleaning
A lot of Tungsten inclusion (white on radiograph)
, spatter, overheating of electrode, inadequate or improper shielding gas, excessive electrode size or current, to small of electrode.
Porosity
- Cavity-type discontinuities formed by gas entrapment during solidification
- voids or gas pockets within the solidified weld metal
- least detrimental discontinuity unless id pressure lines
- spherical in shape
- caused by contaminants or moisture
Uniform scattered porosity
numerous cavities which occur throughout the weld in no particular pattern
Cluster porosity
specific patterns of several cavities in a group
linear porosity
specific patterns of several cavities in a straight line
Undercut
- surface discontinuity at the base metal adjacent to the weld
- the BASE METAL has been melted away during welding & insufficient filler metal deposited to fill the depression
- detrmental to fatigue load structures
causes - improper technique
- welding to fast
- weld heat is too high, causing excessive melting of BM
Underfill
also alled
causes
- surface discontinuity in WELD METAL - loss of material in cross section
- not sufficient filler metal deposited
- can occur and the face and root
- also called suck back or internal concavity
- caused by incomplete welds / not understanding perimeters / excessive heat / excessive travel speed
- visually detected
Overlap
-protrusion or overflow of the weld metal beyond the weld toe or root
-visually detected
- significant discontinuity
- can hide cracks that will come out later
causes
-travel speed to low - too much time to metal to melt
- more weld metal without fusing
Convexity
causes
discontinuity of fillet welds only
- bulging wels
- uses excessive material
causes sharp edges causing problem with fatigue
- slight convexity is ok and desirable but not too much
causes
travel speed too slow / not enough heat / improper technique
Weld reinforcement
Similar to convexity but for groove welds only
- face reinforcement / root reinforcement
- the greater the reinforcement angle the less fatigue resistance
uses excessive material
causes sharp edges causing problem with fatigue
causes
travel speed too slow / not enough heat / improper technique
Arc Strikes
the arc in initiated on the base metal away from the weld joint
- detrimental
- base metal is melted and rapidly cooled due to the massive heat sink
Spatter
issues with spatter
causes
- metal particles expelled during fusion welding that do not form a part of the weld.
- some globules may have enough heat to cause localized HAZ on the base metal similar to an ark struck
- can be a local stress riser
cause problems for coatings
causes - high welding currents (turbulence)
- some welding applications cause more than others
GMAW - FCAW
Lamination
Delimitation
- Base metal flaw
- nonmetallic inclusion which occur in steel when being produced (form of oxide)
________________________ - the separation of a lamination under stress
Lamellar Tear
3 conditions that must exists ?
- Terrace like fracture in the base metal - parallel to the rolled surface and weld.
- occurs with high stress in the Z direction or thickness direction
- resulting from weld shrinkage
- the thicker the material the higher the inclusion content, the greater the possibility of experiencing tearing
- 3 conditions that must exist
1- Through-thickness direction
2- susceptible joint configuration
3 material with high inclusion content
Seams & Laps
Base metal discontinuity during steel making
- opened to the rolled surface of the metal instead of the edge
seems - straight line longitudinal crevices or openings that may appear on the surface of steel - caused by imperfections in steel ingot
laps - result from overfilling in the rolling mill passes that cause fins or projections
Dimensional discontinuities
Dimensional irregularities in size or shape imperfections
inspect by taking measurements of weld sizes and lengths to insure there is sufficient weld metal to transmit the applied load
make suer heat didn’t cause distortion or warpage
Discontinuities (laser & Electron Beam welding)
Missed joint
root porosity
inconsistant penetration or spiking
Missed joint
Discontinuities (laser & Electron Beam welding)
Beam is deflected off the joint - caused by axis of the laser is not aligned with the joint root
root porosity
Discontinuities (laser & Electron Beam welding)
Formation of void at the bottom of the weld
caused by gasses that didn’t have time to escape through deep weld metal
inconsistant penetration or spiking
Discontinuities (laser & Electron Beam welding)
mainly in high power deer penetrating welds
Caused by variations in power density
