In Mechanical Engineering Welding is one of the most important Metal joining process. As we know that in Casting we some defects are always there and similarly in welding defects are there. welding defects is very common problem but need to solve it because it lead to failure to the material. In this article we will Identifying common welding defects or types of welding defects and welding defects remedies
Preventing and fixing problems with your welds
If I could wave my magic filler rod and make it so that all your welds would be strong, clean, and sharp-looking, I’d certainly do it. But the last time I went to the welding supply shop and asked to buy a magic filler rod, they looked at me like I was nuts, so for now you just have to live with the fact that some of your welds will be imperfect. Don’t worry about it too much; after all, no welder is perfect, and welding can be a tricky endeavor. What I can do is fill you in on some of the most common weld flaws so that when they show up, you realize that you’re dealing with the same kinds of challenges that hundreds of thousands of welders have cursed and spat about since the first guy figured out how to strike an arc. These are the kinds of defects that you’re likely to notice only after you’ve finished a weld (either a single pass or a complete weld, depending on the defect). Most are pretty easy to detect, and — thankfully — relatively easy to adjust for and prevent. To help prevent welding defects before they happen, be sure your welding materials are clean and in good shape before you start a project. The metal you’re planning to weld should be free of any material that may contaminate the weld. Remove any grease, paint, or oil from the metal. You should also
put the pieces to be welded in place to make sure they fit together and line up properly.
WELDING DEFECTS: CAUSES AND REMEDIES
|Arc Strike Cracking|
|Improper welding technique||Use proper welding technique|
|Rapidly Cooling of welding area||Proper Cooling of welding area|
|high thermal severity||Preheat as per Welding Procedure Specification|
|Hydrogen in the weld metal||Welding consumables must be hydrogen controlled|
|Presence of impurities||Remove impurities|
|Weld of insufficient sectional area||Proper weld of sufficient sectional area|
|High welding speeds and low current density||As per requirement Use of welding speeds and current density|
|Unfilled Crater||Filler crater with proper technique|
|Crater crack in sub-merged arc welding||Utilize run out tab|
|high welding current||Medium welding current|
|poor joint design that does not diffuse heat||Proper weld joint design|
|impurities (such as sulphur and phosphorus)||Remove impurities|
|speed fast & long arcs||Speed medium & medium arcs|
|Base metal contamination||Avoid contamination of base metal|
|Not enough speed||Increase welding speed|
|Much voltage||Proper voltage|
|Under Bead Crack|
|More presence of Hydrogen||Reduce presence of Hydrogen|
|Unequal contraction of base metal & weld metal||Equal contraction of base metal & weld metal|
|Rapid cooling of weld||Use Proper or matched electrode|
|Improper joint preparation||Reduce Rigidity of weldment|
|High restraint of joint||Use higher ductile welding filler metal|
|Use Preheat or Reduce cooling rate|
|Less cooling rate||Increase cooling rate|
|Improper Preheating||Proper Preheating|
|Improper coating on the electrode.||Use low hydrogen welding process|
|Improper Preheating||Use preheat|
|Longer arcs||Increase heat input|
|Too low and too high arc currents||Clean joint surfaces and|
|Faster arc travel speeds||Reduce arc travel speeds|
|Incorrect welding technique||Use proper welding technique|
|Unclean job surface||Adjacent surfaces|
|Improper base metal composition||Reducing excessive moisture|
|Excessive layers & faulty joint preparation||Tack weld parts with allowance for distortion|
|Improper bead sequence||Use proper bead sequence|
|Improper set-up and fixture||Tack or clamp parts securely|
|Excessive weld size||Make weld of specify size|
|Over-heating of base metal (thin plate)|
|high sulphur content in the work piece or electrode||Reduce sulphur content|
|excessive moisture from the electrode or workpiece||Avoid moisture|
|too short of an arc||Use proper welding current or polarity|
|wrong welding current or polarity|
|Improper cleaning||Proper cleaning|
|Presence of grease & dirt||Avoid grease & dirt|
|Incomplete slag removal from previous bead||Complete remove slag from previous bead|
|Gap & Improper preparation of groove||Avoid more Gap|
|Lack of Fusion|
|Improper manipulation of welding electrode||Minimum heat input to be maintained|
|Weld joint design.||Avoid molten pool flooding the arc|
|Improper heat input||Proper cleaning of oxides slag|
|Surface contamination which leads slag formation prevents fusion||Correct Electrode angle
|Lack of Penetration|
|Improper joint ( U joint give better than J butt joint )||Use proper joint geometry|
|Less welding current||Follow current WPS ( welding procedure specification )|
|Root gap too small||Use small electrode in root|
|Too large root face||Increase root opening|
|Faster arc travel speed||Reduce arc travel speed|
|Large electrode diameter||Medium electrode diameter|
|Poor ductility of weld metal||Use the base metal which has higher ductility|
|High Sulphur content of the base metal||Low sulphur & Low inclusions in base metal|
|Hydrogen in the weld||Use low hydrogen in welding|
|Tensile stresses in thickness direction||Decrease the stress by Modification|
|Excessive welding current||Use the right adequate welding current|
|Wrong electrode angle||Proper electrode angle|
|Excessive side manipulation|
Welding Defects #1: Incomplete Penetration
Here’s a list of the most common causes of incomplete penetration welding defects.
reach the bottom of the joint.
don’t melt together on the first pass.
✓ You’re welding a joint with a V-shaped groove and the angle of the
groove is too small (less than 60 to 70 degrees), such that you can’t
manipulate your electrode at the bottom of the joint to complete
✓ Your electrode is too large for the metals you’re welding.
✓ Your speed of travel(how quickly you move the bead) is too fast, so
not enough metal is deposited in the joint.
✓ Your welding amperage is too low.If you don’t have enough electricity
going to the electrode, the current won’t be strong enough to melt the
Welding Defects #2: Incomplete Fusion
✓ You’re using the wrong electrode for the material that you’re welding.
✓ Your speed of travel is too fast.
✓ Your arc length is too short.
✓ Your welding amperage is set too low.
If you think your incomplete fusion may be because of a low welding amperage, crank up the machine! But be careful: You really need only
enough amperage to melt the base metal and ensure a good weld.
Anything more is unnecessary and can be dangerous.
✓ Contaminants or impurities on the surface of the parent metal(the metal
you’re welding) prevent the molten metal (from the filler rod or elsewhere
on the parent metal) from fusing.
Welding Defects #3: Undercutting
✓ Your electrode is too large for the base metal you’re welding.
✓ Your arc is too long.
✓ You have your amperage set too high.
✓ You’re moving your electrode around too much while you’re welding.
Weaving your electrode back and forth is okay and even beneficial, but if
you do it too much, you’re buying a one-way ticket to Undercutting City
(which is of course the county seat for Lousy Weld County).
Welding Defects #4: Slag Inclusions
Common causes of slag inclusions include
✓ Failure to clean a welding pass before applying the next pass
Be sure to clean your welds before you go back in and apply a second weld bead.
✓ Slag running ahead of your weld puddle when you’re welding a V-shaped
groove that’s too tight
✓ Incorrect welding angle
✓ Welding amperage that’s too low
Welding Defects #5 Flux Inclusions
✓ Clean your weld joints properly after each pass.This task is especially
important when you’re brazing.
✓ Don’t go overboard with your use of flux.
✓ Make sure you’re using enough heat to melt the filler or flux material.
Welding Defects #6: Porosity
✓ Make sure all your materials are clean before you begin welding.
✓ Work on proper manipulation of your electrode.
✓ Try using low-hydrogen electrodes.
Welding Defects #7: Cracks
✓ Hot cracks:
quickly or cools down too quickly. If you’re having problems with hot cracking, try preheating your material. You can also postheat your material, which means that you apply a little heat here and there after you’ve finished welding in an effort to let the metal cool down more
✓ Cold cracks:
weld.) It generally happens only in steel, and it’s caused by deformities in the structure of the steel. You can guard against cold cracking by
increasing the thickness of your first welding pass when starting a new weld. Making sure you’re manipulating your electrode properly, as well as pre- and postheating your metal, can also help thwart cold cracking.
✓ Crater cracks:
electrode. The really annoying part about crater cracks is that they can cause other cracks, and the cracking can just kind of snowball from
there. You can control the problem by making sure you’re using the appropriate amount of amperage and heat for each project, slowing your
speed of travel, and pre- and postheating.
Welding Defects #9: Warpage
Say you’re welding a Tjoint. The vertical part of the Tsometimes pulls itself toward the weld joint. To account for that movement, simply tilt the vertical part out a little before you weld, so that when it tries to pull toward the weld joint, it pulls itself into a nice 90-degree angle!
The more heat you use, the more likely you are to end up with warpage, so be sure to use only the amount of heat you need. Don’t overdo it. Opting for a slower speed of travel while welding can also help to cut down on warpage.
Welding Defects #10: Spatter
You can keep spatter to a minimum by spraying with an anti-spatter compound (available at your welding supply store) or by scraping the spatter off the parent metal surface.