WELD DEFECTS

DISCONTINUITY IN WELD DEFECTS ::

  • AN INTERUUPTION OF THE TYPICAL STRUCTURE IN THE MECHANICAL OR METALLURGICAL OR PHYSICAL CHARETERESTICS OF MATERIAL OR WELDMENT
  • DISCONTINUITY IS A DEFECT WHEN IT DOES NOT MEET THE PRODUCT REQUIREMENT

TYPES OF DEFECTS:

  • PLANAR

CRACKS, LAMELLAR TEARS

LACK OF FUSION

LACK OF PENETRATION

  • VOLUMINAR

POROSITY

SLAG

TUNGSTEN INCLUSION

INSPECTION METHOD IN  WELD DEFECTS:

JOINT RT UT PT MT VT
BUTT A A A A A
CORNER O A A A A
TEE O A A A A
LAP U O A A A
A – APPLICABLE O –   Marginally applicablity U- Not applicable

POROSTY – Types

  • SCATTERED POROSITY
  • CLUSTER POROSTY
  • LINEAR ALIGNED POROSITY
  • WORMHOLE – ELONGATED POROSTY

Porosity – Causes

  • Due to dissolved gases ( mostly H2 ) in the weld metal > the solubility limits when weld solidifies
  • H2 is supplied by gas shield, moisture in atmosphere, flux, coating, or water in the area of welding
  • Excess arc length
  • Moisture pickup in the low hydrogen electrodes
  • Surface contamination
  • Moist flux
  • Magnetic arc blow
  • Welding speed too high
  • Crater pipes
  • In TIG , MIG process loss of shielding, impure gas may causes porosity
  • More tendency in vertical & overhead position
  • At start and stop points due to unstable heat flow condition

SLAG & SOLID INCLUSIONS

  • Oxides and other non metallic solid materials entrapped between weld and base metal, or between weld metal and base metal

CAUSES

  • Loss of slag control due to poor manipulating technique and slag flooding advance of the arc because of the arc positioning
  • Incomplete inter-pass cleaning
  • Poor previous bead
  • Heavy mill scale or rust
  • Piece of unfused flux from electrodes with damaged coatings

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