Republic of the Philippines

Department of Education
REGION V
SCHOOLS DIVISION OFFICE OF SORSOGON CITY

SELF-DIRECTED LEARNING ACTIVITY SHEET IN SHIELDED METAL ARC WELDING 11

(WELD CARBON STEEL PLATE USING SMAW)
Grade: 11 Quarter: 2 Week: 1-2

Weld Defects, Causes and Remedies

I. INTRODUCTION:
Welding Defects can be defined as the irregularities formed in the given weld metal due to wrong welding
process or incorrect welding patterns, etc. The defect may differ from the desired weld bead shape, size, and
intended quality. Welding defects may occur either outside or inside the weld metal. Some of the defects may be
allowed if the defects are under permissible limits but other defects such as cracks are never accepted.

II. OBJECTIVES:
1. Identify causes and prevention of the different weld defects.
2. Mark and locate weld defects.
3. Remove defects and perform re-welding.

III. LEARNING ACTIVITY:

Welding defects are generated in a welding job due to the faulty or poor technique used by the
inexperienced or unskilled welder or due to fundamental difficulties in the welding operation. An ideal weld
or good weld should be such that adequate fusion exists between the filler metal and edge preparation
together with good penetration.
Types of Welding Defects
Welding defects are broadly classified into two categories, and these are:
1. External welding defects (Defects occur on the upper surface of the welded work).
2. Internal welding defects (Defects occur under the surface of the welded work).
I. External Welding Defects
The various types of external defects with their causes and remedies are listed below:
A. Weld Crack
This is the most unwanted defect of all the other welding defects. Welding cracks can be present at the
surface, inside of the weld material or at the heat affected zones.

Crack can also appear at different temperatures:

1. Hot Crack – It is more prominent during crystallization of weld joints where the temperature can rise
more than 10,000-degree Celsius.
2. Cold Crack – This type of crack occurs at the end of the welding process where the temperature is quite
low. Sometimes cold crack is visible several hours after welding or even after few days.
 Causes of Weld Crack:
1. Poor ductility of the given base metal
2. The presence of residual stress can cause a crack on the weld metal.
3. The rigidity of the joint which makes it difficult to expand or contract the metals.
4. If there is high content on sulphur and carbon then also the cracks may appear.
5. Using hydrogen as a shielding gas while welding ferrous materials.
Remedies for Weld crack:
1. Using appropriate materials may decrease the chances of crack.
2. Preheating the weld and reducing the cooling speed joint helps in reducing crack.
3. Reduce the gap between the weld joints by using reasonable weld joints.
4. While welding releases the clamping force slowly which increases fill to capacity of welding material.
B. Undercut
When the base of metal melts away from the weld zone, then a groove is formed in the shape of a notch,
then this type of defect is known as undercut. It reduces the fatigue strength of the joint.

Causes of Undercut:
1. If the arc voltage is very high then this defect may occur.
2. If we use the wrong electrode or if the angle of the electrode is wrong, then also the defect may
form.
3. Using a large electrode is also not advisable.
4. High electrode speed is also one of the reasons for this defect.
Remedies for Undercut:
1. Reduce the arc length or lower the arc voltage.
2. Keep the electrode angle from 30 to 45 degree with the standing leg.
3. The diameter of the electrode should be small.
4. Reduce the travel speed of the electrode.
C. Spatter
When some metal drops are expelled from the weld and remain stuck to the surface, then this defect is
known as spatter.

Causes of Spatter:
1. High welding current can cause this defect.
2. The longer the arc the more chances of getting this defect.
3. Incorrect polarity
4. Improper gas shielded may also cause this defect.
Remedies for Spatter:
1. Reducing the arc length and welding current
2. Using the right polarity and according to the conditions of the welding
3. Increasing the plate angle and using proper gas shielding
D. Porosity
Porosity refers to small cavities or holes resulting from gas pockets in weld metal.

Causes of Porosity:
1. It occurs when the electrode is not coated properly.
2. Using a longer arc may also increase its chances.
3. Increased welding currents.
4. Rust or oil on the welding surface.
Remedies for Porosity:
1. Proper selection of the electrode
2. Decreasing the welding current
3. Using smaller arc and slowing the process to allow the gases to escape
4. Remove rust or oil from the surface and use a proper technique
E. Overlap
When the weld face extends beyond the weld toe, then this defect occurs. In this condition the weld metal
rolls and forms an angle less than 90 degrees.

Causes of Overlap:
1. Improper welding technique
2. By using large electrodes this defect may occur.
3. High welding current.
Remedies for Overlap:
1. Use a proper technique for welding.
2. Use small electrode.
3. Less welding current
F. Distortion
Distortion means contraction of weld metal during welding that forces base metal to move.

Causes of Distortion:
1. A great number of passes with small diameter electrodes
2. Slow arc travel speed
3. High residual stresses in the plate to be welded
4. Using improper welding sequences
 Remedies of Distortion:
1. Use the proper amount of weld metal as per the requirement of the joint. It will reduce the
contraction forces.
2. Use an appropriate number of weld passes.
3. Place the weld near the neutral axis.
4. Use proper welding sequences.
G. Burn-Through
Burn- Through refers to weld metal melting completely through base metal resulting in holes where no
metal remains.

Cause of Burn-Through:
1. Excessive heat input
Remedies of Burn-Through:
1. Select lower amperage. Use smaller electrode.
2. Increase and/or maintain steady travel speed.
II. Internal Welding Defects
The various types of internal defects with their causes and remedies are listed below:
A. Slag Inclusion
If there is any slag in the weld, then it affects the toughness and metal weldability of the given material. This
decreases the structural performance of the weld material. Slag is formed on the surface of the weld or
between the welding turns.

Causes of Slag:
1. Slag is formed if the welding current density is very small, as it does not provide the required
amount of heat for melting the metal surface.
2. If the welding speed is too fast then also slag may occur.
3. If the edge of the weld surface is not cleaned properly then also slag may form.
4. Improper welding angle and travel rate of welding rod
Remedies for Slag Inclusion:
1. Increase the current density.
2. Adjust the welding speed so that the slag and weld pool do not mix with each other.
3. Clean the weld edges and remove the slags of previous weld layers.
4. Have a proper electrode angle and travel rate.
B. Incomplete Fusion
Incomplete fusion occurs when the welder does not accurately weld the material and the metal pre solidifies
which leads to a gap which is not filled with the molten metal.
 Causes of Incomplete fusion:
1. It occurs because of the low heat input.
2. When the weld pool is very large and runs ahead of the arc.
3. When the angle of the joint is too low.
4. Incorrect electrode and torch angle may also lead to incomplete fusion.
5. Improper bead position
Remedies for Incomplete Fusion:
1. Increasing the welding current and decreasing the travel speed helps in removing the chances of
incomplete fusion.
2. Reducing the deposition rate.
3. Increasing the joint angle.
4. Try to position the electrode and torch angle properly so that the edges of the plate melt away.
5. Positioning the bead properly so that the sharp edges with other beads can be avoided.
C. Incomplete Penetration or Incompletely Filled Groove
These defects occur only in the butt welds where the groove of the metal is not filled completely. It is also
called as incomplete penetration defect.

Causes of an Incomplete Penetration or Incompletely Filled Groove:

1. Less deposition of the weld metal
2. Use of improper size of the electrode
3. Improper welding technique
Remedies for Incomplete Penetration or Incompletely Filled Groove:
1. More deposition of the weld metal.
2. Use a proper size of the electrode.
3. By using a proper welding technique.

IV. PRACTICE TASK:

Directions: Read and answer the given activities. Write your answer in a separate sheet of paper.
1. What are the types of External Weld Defects?

V. EVALUATION
Directions: Multiple Choice: Choose the letter of the correct answer.

1. ____________________ is a group of small voids and blowholes are comparatively bigger isolated
holes or cavities.
a. Spatter b. Porosity
c. Penetration d. Welding Defects
2. ____________________ is the small metal particles that are thrown out of the arc during welding and
get deposited on the base metal around the weld bead along its length.
a. Spatter b. Penetration c. Porosity d. Welding defects
 3. __________________ is the change in the shape and difference between the position of two plates
before and after welding due to the temperature gradient present at various points along the joints.
a. Groove b. Hot tear
c. Distortion d. Undercut
4. _________________ is a kind of weld defect which forms a groove in the parent metal along with the
sides of the weld bead.
a. Groove b. Hot tear
c. Distortion d. Undercut
5. ________________________ reduces the thickness of the plate and also reduces the strength of the
weld.
a. Groove b. Hot tear
c. Distortion d. Undercut

Acknowledgement:
Shielded Metal Arc Welding – Grade 11
Alternative Delivery Mode
Modified by: Jay-Ar N. Bustamante - TI Content Editor: Marilyn c. Hular, MT1, Amalia H. Domdom, Asst. School Principal I

RIZAL INTEGRATED NATIONAL SCHOOL

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