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Welder’s Handbook
Cracks
Cause
Prevention
Weld Metal
Highly Rigid Joint
Preheat Relieve residual stresses mechanically Minimize shrinkage stresses using back-step or block welding sequence Change welding current and travel speed Weld with covered electrode, DCEN; butter the joint faces prior to welding Change to new electrode; properly store and maintain electrodes
Excessive Dilution
Detective Electrodes
Poor Fit-Up
Reduce root opening; build up edges with weld metal
Small Weld Bead
Increase electrode size; raise welding current; reduce travel speed
High-Sulfur Base Metal
Use low-sulfur filler metal
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
Heat Affected Zone (HAZ)
Hydrogen in welding atmosphere
Use low-hydrogen welding process; preheat and hold for 2 hr after welding or post-heat immediately Use low heat input; deposit thin layers; change base metal
Hot cracking
Low Ductility
Use preheat; anneal base metal
High Residual Stresses
Redesign the weldment; change welding sequence; apply immediate stress-relief heat treatment Preheat; increase heat input; heat treat without cooling to room temperature
High Hardenability
Brittle phases in the microstructure
Solution heat treat prior to welding
Effects
Reduces static, fatigue and impact strengths, corrosion performance and leak resistance; all leading to joint failure.
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