 |
CAUSES AND REMEDIES FOR FUSION WELD DISCONTINUTIES
| CAUSES | CORRECTIVE ACTION | |
| A. | POROSITY | |
| 1. | Contamination of work piece | Clean joint area |
| 2. | Excessive moisture pickup in electrode covering | Follow manufacturers recommended rebaking procedure. |
| 3. | Moisture on work surfaces | Use preheating/warm up work piece. |
| 4. | High Sulphur content of | Use basic coated base metal electrodes. |
| 5. | a) A long arc length b) Excessive current c)Higher travel speed |
Change welding parameters and technique. |
| 6. | High solidification rate |
Use preheat |
| B. | INCLUSIONS | |
| 1. | Improper cleaning procedure | Clean work surfaces and each weld run throughly. Whereever necessary use power wire brush, grinders, chisel to ensure through removal of slag. |
| 2. | Improper welding technique a) Long arc length b) High travel speed c) Slag flooding ahead of welding arc. |
Improve welding technique. Reposition work to prevent loss of slag control wherever possible Restrict weaving to minimum |
| 3. | Narrow, inaccessible joints | Increase groove angle. |
| C. | INCOMPLETE FUSION | |
| 1. | Improper joint design | Increase includes
angle of groove joint. Change the groove design to 'J' or a 'U' type |
| 2. | Presence of slag or oxide film | Clean weld surfaces prior to welding. |
| 3. | Incorrect electrode position and operating current | Maintain proper electrode position and current. |
| 4. | Improper manipulation of arc | Use correct manipulation
techniques to melt the joint faces properly. |
| D. | INADEQUATE PENETRATION | |
| 1. | Improper joint preparation. a) Excessively thick root face. b) Insufficient root opening c) Bridging of root opening |
Use proper joint geometry. Reduce root face height. Use wider root opening. |
| 2. | Electrode diameter too large | Use smaller electrode
in root. Increase root opening. |
| 3. | Inadequate current | Follow correct welding
current and technique. |
| E. | CRACKS | |
| 1. | High rigidity of joint | Use preheating Relieve residual stresses minimises shrinkage stresses, using backstep or block welding sequences. |
| 2. | Poor joint fit up | Adjust root opening all alignment. |
| 3. | Higher carbon content of weld metal and/or hardenable base material | Use proper electrode. Use buttering layers wherever necessary. |
| 4. | Too small a weld bead | Decrease travel speed
to increase cross section of bead. Increase electrode size. |
| 5. | High sulphur content in base level of sulphur of weldmetal element like Mn. | Use filler with high level of sulphur fixing element like Min. |
| 6. | Hot cracking | Reduce the heat input. Minimum joint restraints. |
| 7. | Cracking at the crater | Filling up the crater
before withdrawing the electrode. Use taper poer control device. Use back step welding technique. |
| 8. | High hardenablity | Preheat the job. Post weld heat treatment without cooling to room temperature. |
| 9. | Hydrogen induced cracking/Delayed cracking | Use low hydrogen welding
electrode. Use suitable preheat and post weldheat treatment. |
| 10. | Presence of brittle phases in the micro-structure of the base material | Soften the material before welding |
| 11. | Low ductility of the base material | Use preheat Anneal the base metal. Use ductile weldmetal. |
| 12. | High residual stresses | Redesign the weldmetal
and reduce restraints. Change welding sequence. Use intermediate stress-relief heat treatment. |
| 13. | Excessive dilution | Change welding current. Use buttering technique wherever possible. |
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