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
