DEFINITIONS.
Lack of fusion. Lack of union in a weld. a. between weld metal and parent metal. b. between parent metal and parent metal. c. between weld metal and weld metal. Lack of sidewall fusion. Lack of union between weld metal and parent metal at a side of a
Lack of inter-run fusion. Lack of union between adjacent runs of weld metal in a multi-run joint.
Inclusion. Slag or other foreign matter entrapped during welding. The defect is more irregular in shape than a gas pore.
Oxide inclusion. Metallic oxide entrapped during welding.
Tungsten inclusion. An inclusion of tungsten from the electrode during TIG welding. Copper inclusion. An inclusion of copper due to the accidental melting of the contact
tube or nozzle in self adjusting or controlled arc welding or due to pick up by contact between the copper nozzle and the molten panel during TIG welding.
Puckering. The formation of an oxide covered weld run or bead with irregular surfaces and with deeply entrained oxide films, which can occur when materials forming refractory oxides (e.g. aluminium and its alloys) are being welded.
Porosity. A group of gas pores.
Elongated cavities. A string of gas pores situated parallel to the weld axis. (Linear porosity.)
Blowhole. A cavity generally over 1.5mm in diameter formed by entrapped gas during the solidification of molten metal.
Wormhole. An elongated or tubular cavity formed by entrapped gas during the solidification of molten metal.
GENERAL CAUSES
Porosity. Is the result of gas being entrapped within the solidifying weld metal. Porosity will be present in a weld if the welding technique, materials used or condition of the weld joint promotes gas formation. If the molten weld metal cools slowly and allows all gas to rise to the surface before solidification, the weld would be virtually free of porosity.
Isolated or uniform porosity: The cause of this form of singular porosity is generally faulty welding technique or defective material or both.
Cluster or group porosity: Is a localised group of pores that may result from improper initiation or termination of the welding arc.
Linear porosity: Always forms a straight line along a run of weld and is caused by gas evolving from contaminants.
Overlap. (Cold lap/roll over.) Usually caused by incorrect manipulation of welding
procedures i.e. low current combined with wrong travel speed. This defect can occur on the fusion face as well as the cap run if the fusion face contains tightly adhering oxides. (This would only be detected by NDT and probably interpreted as lack of
fusion.) Overlap may be defined as a surface connected discontinuity that forms a severe mechanical notch parallel to the weld axis.
Tungsten Particles of tungsten trapped in the weld metal deposited with the TIG process. Inclusion. Usually occurs when the operator dips the tungsten electrode tip into the molten
pool. A second reason for this defect, not generally recognised, is that if the
operating current is set too high the electrode tip will melt and droplets of tungsten will be fired into the molten pool by the shielding gas.
SPECIFIC CAUSES AND REMEDIES.
CAUSE REMEDY
Porosity.
Excessive hydrogen, nitrogen or Use low hydrogen welding process; filler metals oxygen in welding atmosphere high in deoxidisers; increase shielding gas flow High solidification rate Use preheat or increase heat input
Dirty base metal Clean joint faces and adjoining surfaces
Dirty filler wire Use specially cleaned and packaged filler wire and store in a clean area
Improper arc length, welding current Change welding conditions and techniques or electrode manipulation
Volatisation of zinc from brass Use copper-silicon filler metal; reduce heat input Galvanised steel Use E7010 electrodes and manipulate the arc heat
to volatilise the galvanised zinc ahead of the molten weld pool
Excessive moisture in electrode covering Use recommended procedures for baking and or on joint surfaces storing electrodes; preheat the base metal High sulphur base metal Use electrodes with basic slagging reactions
Inclusions
Failure to remove slag Clean surface and previous weld bead Entrapment of refractory oxides Power wire brush the previous bead Tungsten in the weld metal Avoid contact between the electrode and
workpiece; use larger electrode Improper joint design Increase bevel angle of joint
Oxide inclusions Provide proper gas shielding Weld metal cracking
Highly rigid joint Preheat; relieve residual stresses mechanically; minimise shrinkage stresses using back step or block welding sequence
Excessive dilution Change welding current and travel speed; weld with covered electrode negative; butter the joint faces prior to welding
Defective electrodes Change to new electrode; bake electrodes to remove moisture
Poor fit-up Reduce root opening; build up the edges with weld metal
Small weld bead Increase electrode size; raise welding current; reduce travel speed
High sulphur base metal Use filler metal low in sulphur
Angular distortion Change to balanced welding on both sides of joint Crater cracking Fill crater before extinguishing the arc; use a
welding current decay device when terminating the weld bead
Base metal cracking
Hydrogen in welding atmosphere Use low hydrogen welding process; preheat and hold for two hours after welding or post weld heat treat immediately
Hot cracking Use low heat input; deposit thin layers; change base metal
Low ductility Use preheat; anneal the base metal High residual stresses Redesign the weldment; change welding
sequence; apply intermediate stress relief heat treatment
High hardenability Preheat; increase heat input; heat treat without cooling to room temperature
Brittle phases in the microstructure Solution heat-treat prior to welding