In case of welded connection in steel structures, during welding, a defect is caused by coating of the parent metal with a foreign matter and because the groove is not kept clean. This defect is known as:
- Aincomplete penetration
- Boverlap
- Cslag inclusion
- Dlack of fusionCorrect
Solution
Concept
Lack of fusion means the weld metal does not fuse with the parent metal. It is often caused by dirty surfaces such as oxide, scale or foreign coating.
Step-by-step solution
1. The defect is caused by foreign matter on the parent metal and an unclean groove. 2. Foreign matter stops the weld metal from melting into and joining the parent metal. 3. Failure of weld metal and parent metal to join is called lack of fusion (incomplete fusion). 4. So the answer is (D).
Explanation
When the parent metal is coated with oxide, scale or other foreign matter, the weld metal cannot fuse properly with it. This defect is called lack of fusion or incomplete fusion. Low heat input can also cause it.
Why the other options are wrong
A: Incomplete penetration means the weld does not reach the root of the joint, mainly due to poor groove design or high speed. B: Overlap means weld metal flows over the parent metal surface without fusing, mainly due to low speed or a wrong electrode angle. C: Slag inclusion means slag is trapped inside the weld, mainly due to poor cleaning between passes.
Shortcut
Dirty surface plus no bonding with parent metal means lack of fusion.
Common mistake
Choosing slag inclusion just because the word 'not clean' appears. Slag inclusion is trapped slag inside the weld, not a coating on the parent metal.
Correct answer: D) lack of fusion