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
