4. 4/19/2024
SKG 4
FAILURE DUE TO WELDING DEFECT ON %AGE
BASIS
According to the American Society of Mechanical
Engineers (ASME) welding defect causes are broken
down into the following % age:-
•41% poor process conditions
•32% operator error
•12% wrong technique
•10% incorrect consumables and
•5% bad weld grooves
5. 4/19/2024
SKG 5
WHAT IS A WELDING DEFECT ?
The defects in the weld can be defined as
irregularities in the weld metal produced due
to incorrect welding parameters or wrong
welding procedures or wrong combination of
filler metal and parent metal. It can simply be
defined as:
“Defects introduced during welding beyond the
acceptance limit that can cause a weld to fail”.
A defect does not allow the finished joint to
withstand the required strength (load).
6. Effect of Welding parameters
A- Proper amperage, arc length,
travel speed
B- Amperage - too low
C- Amperage - too high
D- Arc Length - too short
E- Arc Length - too long
F- Travel Speed - too slow
G- Travel speed - too fast
6
8. DEFECT PREVENTION
SELECT CORRECT WELDING PROCESS
SELECT CORRECT WELDING PROCEDURE
1. DESIGN THE JOINT PROPERLY
2. KNOW THE MATERIAL
3. SELECT CORRECT ELECTRODE
4. SELECT CORRECT CURRENT
5. SELECT A SKILLED WELDER
6. PREHEAT IF REQUIRED
7. WELD WITH CORRECT SPEED AND WEAVING
8. CHECK THE WELD AND RECTIFY.
8
11. Weld Spatter Causes
Welding current too high
Welding voltage too low
Using too large an electrode
Using incorrect shielding gas
Using a blocked nozzle
Using wrong polarity
11
14. Undercut Causes
Welding current too high
Travel speed too slow
Voltage too high
Improper electrode manipulation
Improper torch angle (low)
Using too large an electrode
14
15. 4/19/2024
SKG 15
CRACKS
•A hair line separation in the BM/BM-WM-bdy /
WM/HAZ
•May appear:
–at the root or
–middle or
–In the crater
–surface or
–subsurface
•Most dangerous of all defects
•Occurs in the WM when localized stresses exceed the
UTS of material.
•May be of microscopic or macroscopic sizes.
16. 4/19/2024
SKG 16
HOT CRACKS
•Crack in the weld that occurs just after the
welds are completed and some- times while the
welds are being made.
–Develops at high temperatures
–Propagates between the grains of the material
(intercrystalline)
–Occurs in the weld metal & sometimes in
HAZ.
•“solidification crack ” (weld metal)
•“liquation crack” (HAZ)
19. Cracks Causes
Poor weldability of base metal
Improper design of weld joint
Improper joint preparation
Incorrect welding procedure
Unsuitable welding process
19
20. 20
Hydrogen cracking also known as cold
cracking or delayed cracking. The main
feature of this type of crack is that it
occurs in ferritic weldable steels, and
generally occurs immediately on
welding or after a short time after
welding, but usually within 48 hrs.
Hydrogen cracking
21. 21
Visual appearance of Hydrogen Cracking
Hydrogen cracks can be usually have the following
characteristics:
Cracks may also occur in the weld bead, normally
transverse to the welding direction at an angle of 45 to the
weld surface. They are near straight, follow a jagged path.
In low alloy steels, the cracks can be transverse to the
weld, perpendicular to the surface of the weld, but do not
branch and are planar (Planar Defect).
Identification
22. 22
There are three factors,
which can cause hydrogen cracking:
Hydrogen generated by the welding process, or
by contamination of the weld area (paint?).
A hard brittle structure, which is susceptible to
cracking.
Residual tensile stresses acting on the welded
joint (restraint). Cracking is caused by the
diffusion of hydrogen to the highly stressed,
hardened part of the weldment
Possible Causes
25. Poor Fusion Causes
Too low a current to melt the parent
metal
Using wrong size electrode
Too low a travel speed
Striking the arc against a fusion face and
letting the molten weld pool to run onto
the other cold face
25
28. 28
Effect of electrode size on root fusion
a)Large
diameter
electrode
) Small
diameter
electrode
b
29. Slag Inclusion Causes
Improper manipulation of electrode,
torch, filler rod
Non removal of slags after each bead
deposit
Non melting down of slags on beads
previously deposited
Too fast a travel speed for the sealing runs
29
30. Porosity Causes
Arc atmosphere contamination with high hydrogen
Electrode unsuitable for base metal
Incorrect electrode manipulation
Incorrect current setting
Improper selection of shielding gas.
Excessively oxidized work piece surfaces.
Inadequate deoxidizing alloys in the wire
The presence of foreign matter 30
.
31. 31
Porosity is a group of small voids, where
as blow holes are comparatively bigger
hole or cavity caused by entrapment of
gases [gases:H2,CO,CO2,N2 &O2 from
coating ingredients in the electrode or
moisture, oil, grease, rust, etc on BM]
within the solidified weld”.
POROSITY/BLOW HOLES
33. 33
Atmospheric contamination can be caused
by:
1) Inadequate shielding gas flow.
2) Excessive shielding gas flow. This can
cause aspiration of air into the gas stream.
3) Severely clogged gas nozzle or damaged
gas supply system (leaking hoses, fittings,
etc.)
4) An excessive wind in the welding area.
This can blow away the gas shield.
POROSITY
35. Irregular Weld Shape Causes
Current too high
Electrode/wire wander
Improper electrode manipulation
Incorrect shielding gas use
Travel speed not uniform
Excessive gas flow
Using wrong electrode for position
welding
35
36. Electrodes used in KGPW as per RDSO Classification.
1.M.S.Electrodes- A1 to C2-for general purpose,static load
condition & Boiler
class quality type.
2.Low Alloy Steel Electrodes:- D to E class-depending on
Carbon %,Dynamic
load condition & type of Low Hydrogen.
3.S.S Electrodes:-M class(M1 to M6)
4.Hard Facing:-H Class(H3a,H4b & H)
5.C.I:- F class-Non Machinable. G class-Machinable
(GREY,NODULAR & WHITE C.I are also available)
6.AL & AL Alloys:-L class
7.Copper & Bronze:-K class.
8.Cutting & Piercing:-N1 Class
9.Gouging:-N2 class
36
37. Welding machines should have voltmeter and
ammeter in working condition
Proper earthing is to be done .
No girder earthing is to be provided.
4/19/2024
SKG 37
39. Suggestions
The electrodes should be baked properly to avoid
dampness,blow holes,porosity,hydrogen cracking.
Portable baking oven may be used.
Proper Tightening of wire by means of terminal
jointer.
4/19/2024
SKG 39
40. SUGGESTION
One welding plant is used by more than one welder at a
time.This should be avoided for good quality weld.If so
required multi console operator welding machines may
be procured.
Welder are to be sent for R.C training and gradation of
welders.
40
