Poor Fusion
Causes of poor fusion: Low welding current; improper weaving technique; improper electrode diameter; poor joint preparation; hurried welding speed.
Corrections: The electrode should be small enough to reach the bottom of the joint; for a given electrode, current should increase with plate thickness to properly deposit metal and penetrate the plates; weaving should sweep outward enough to melt sides of the joint; deposited metal should fuse into the plates, not curl away.
Causes of porosity: Excessive arc length; insufficient puddling; unsound base metal; moisture in electrode coating.
Corrections: Shorter arc required, especially on stainless steels; sufficient puddling of molten metal to allow trapped gas to escape; proper weaving technique; appropriate welding current; sound base metal selection; dry electrodes.
Incomplete Penetration
Causes of incomplete penetration: Improper joint preparation; electrode too large; insufficient welding current; hurried welding speed.
Corrections: Allow proper free space at bottom of weld; use electrodes of appropriate diameter in narrow groove; use sufficient welding current and proper welding speed; use a backup bar; chip or cut out the back of the joint and deposit a backing bead.
Causes of brittleness: Air-hardening of base metal; improper heating; unsatisfactory electrodes.
Corrections: Preheating of medium-carbon and certain alloy steels at 150 to 260°C (300 to 500°F); proper preheating; controlled cooling. Multiple-layer welds tend to anneal hard zones; stress relieving at 600 to 650°C (1100 to 1200°F) after welding generally softens hard areas formed during welding. Austenitic electrodes are sometimes desirable on air-hardening steels; the increased weld ductility compensates for the brittleness of the heat-affected areas in the base metal.
Causes of arc blow: Magnetic fields force the arc in a different direction than the point at which it is directed, particularly at the ends of joints and in comers when welding with direct current.
Corrections: Place the workpiece connection in the direction of arc blow; clamp the workpiece cable to the work at two or more locations; weld toward the direction of the blow; hold a short arc; change the magnetic path around the arc by using steel blocks, or magnetic shunts; use a-c welding.
Undercutting
Causes of undercutting: Excessive welding current; improper electrode technique; mismatch between electrode design and weld position.
Corrections: Use a moderate welding current and proper welding speed; use an electrode that produces a puddle of the proper size; proper weaving technique; proper positioning of the electrode relative to a horizontal fillet weld. See UNDERCUT.
Causes of distortion: Improper joint preparation or clamping; non-uniform heating of the parts; improper welding sequence.
Corrections: Clamp or tack parts properly to resist shrinkage; pre-form parts to compensate for weld shrinkage; distribute welding deposit to avoid localized overheating; preheat heavy structures; remove rolling or forming strains before welding; proper welding sequence, determined by a study of the structure. See DISTORTION.
Cracked Welds
Causes of cracked welds: Joint too rigid; welds too small for size of parts joined; poorly executed welds; improper joint preparation; unsuitable electrode.
Corrections: Design the structure and develop a welding procedure to eliminate rigid joints; design weld size appropriate to parts; make a full size weld in short sections; develop a welding sequence that leaves the ends of the joint free to move as long as possible; proper fusion; preheating; prepare uniform joints.
Irregular Surface
Causes of irregular surface: Excessive welding current; improper weaving technique; improper voltage; overheating of the workpiece; inherent characteristics
of the electrode.
Corrections: Change to proper welding technique; use proper welding current; use proper voltage; use proper welding speed.
Irregular Weld Quality
Causes: Wrong electrode: improper technique; excessive current; electrode used in wrong position; improper joint design.
Corrections: Prepare the joint properly; match the electrode to the weld position; weld with uniform weave, proper rate of travel, and proper welding current.
Residual Stresses
Causes of residual stress: Joints are too rigid; improper welding sequence.
Corrections: Make the weld in several passes; peen each deposit; stress relieve finished product at 600°C to 650°C (1100°F to 1200°F) for one hour per inch of thickness; develop procedure that permits all parts to be free to move as long as possible.
Causes of corrosion: improper type of electrode diminishes corrosion resistance of the weld compared to the parent metal; improper weld deposit for the corrosive media; the metallurgical effect of welding; and improper cleaning of the weld.
Corrections: Use electrodes that provide equal or better corrosion resistance than the parent metal; when welding austenitic stainless steel the analysis of the steel and the welding procedure should be correct to avoid carbide precipitation: this condition can be cor rected by heating to 104°C-115O°C (1900 to 2100°F) followed by quenching; proper cleaning of materials such as aluminum to prevent corrosion.
Causes of spatter: The inherent properties of certain electrodes; excessive welding current; the type or diameter of rod used; an excessively long arc; arc blow.
Corrections: Use proper type of electrode; proper welding current; proper arc length; reduce arc blow; use anti-spatter adjacent to the weld to prevent the welding of spalls to the work.
Warping of Thin Plates
Causes of warping: Shrinkage of the deposited weld metal; local overheating at the joint; improper joint preparation; unsuitable clamping of the parts.
Corrections: Select electrode with high welding speed and moderate penetrating properties; weld rapidly to prevent over-heating of the plates adjacent to the weld; do not permit excessive space between the parts; clamp parts adjacent to the joint; use a back-up bar to cool them rapidly; use a welding sequence such as the backstep or skip procedure; peen the joint edges thinner than the body of the plate before welding. The elongated edges will pull back to the original shape when the weld shrinks.