Basic Civil Engineering first year Notes- Chapter 4 Building.pptx
Electrode & welding defects
1. ELECTRODES & FLUX
- Can welding be done by bare electrodes ?
- Why do we require coating at all ?
- Reasons are instability of arc, lack of
shielding, poor mechanical properties
- What are the different type of coating
TYPE OF COATING
Cellulose material - It is made by hard or soft wood,
pulp & similar substance. Washing, drying &
grading into different mesh sizes.
- High arc force, large volume of gas mostly
hydrogen
2. RUTILE
- It is a crystalline form of titanium dioxide.
Available in beach sand. Concentration - 87% App.
- Arc Stabilizer.
- Good Slag remover.
BALL CLAY – It is a compound of silica &
alumina commonly known as alumino silicate.
- Slag remover
- Gives plasticity in the wet paste.
IRON POWDER – Sometimes added to flux
coating to add strength to weld
- Gives good mechanical strength, arc stabilizer.
3. PURPOSE OF FLUX COATING
- Gas shielding of arc.
- Stabilizer of the arc (potassium silicate).
- Provides slag blanket.
- Alloying elements will improve mechanical
properties (Iron oxide, Ferro manganese).
- Gives good penetration.
- Welding in all positions becomes easy.
- Compensate oxidation loss.
4. ELECTRODE CLASSIFICATION
BASED ON COVERING
- Rutile Electrode – Quite & smooth arc, Excellent
slag removal, fine ripples, medium penetration, thick
slag.
- Cellulose electrode – forceful & noisy arc, coarse
slag, deep penetration, more gas shield, thin slag
cover.
- Basic Electrode – Adequate penetration, slag
removal is good, contains more iron powder, good
mechanical properties.
5. BASED ON APPLICATIONS
- Stainless steel electrode
- Low alloy electrodes
- Copper & copper alloy electrode
- Aluminum & alloy electrodes
- Hard facing electrodes.
WHAT IT INDICATES
E6010
E – Electrode
60 – min tensile strength 60000 psi (410 mpa)
1- Welding position
0 – Coating current & condition.
6. AWS ELECTRODE CLASSIFICATION SYSTEM
FOR CARBON & LOW - ALLOY STEEL
ELECTRODES (SMAW)
AWS Specification A5.1
E 60 1 0 Type of Coating
& Current
Electrode
Strength in PSI Position
7. E 80 1 8 - B1
Electrode
80 PSI Min.
All Position
For AC or DCEP
Chemical Composition of
Weld Metal Deposit
8. POSITION
DIGIT POSITION
1 Flat, Horizontal, Vertical, Overhead
2 Flat & Horizontal Only
3 Flat, Horizontal, Vertical down,
Overhead
9. TYPE OF COATING & CURRENT
DIGIT TYPE OF COATING CURRENT
0 Cellulose Sodium DCEP
1 Cellulose Potassium AC or DCEP or DCEN
2 Titania Sodium AC or DCEN
3 Titania Potassium AC or DCEP
4 Iron Powder Titania AC or DCEP or DCEN
5 Low Hydrogen Sodium DCEP
6 Low Hydrogen Potassium AC or DCEP
7 Iron Powder Iron Oxide AC or DCEP or DCEN
8 Iron Powder Low Hydrogen AC or DCEP
10. CHEMICAL COMPOSITION OF WELD DEPOSIT
Suffix %Mn %Ni %Cr %Mo %V
A1 1/2
B1 1/2 1/2
B2 1-1/4 1/2
B3 2-1/4 1
C1 2-1/2
C2 3-1/4
C3 1 0.15 0.35
D1&D2 1.25-2.00 0.25-0.45
G 0.50 0.3Min 0.20Min 0.10Min
11. AWS ELECTRODE CLASSIFICATION SYSTEM
FOR CARBON STEEL ELECTRODES (GMAW)
Chemical
Composition
ER 70 S- X & Shielding
Electrode
or rod
Strength in PSI Solid Electrode Wire
12. SPECIFICATIONS FOR GMAW ELECTRODES
BASE MATERIAL TYPE AWS
SPECIFICATION
Carbon Steel A5.18
Low Alloy Steel A5.28
Al Alloy A5.10
Cu Alloy A5.7
Magnesium A5.19
Nickel Alloys A5.14
Stainless Steel A5.9
Titanium A5.16
13. AWS CLASSIFICATIONS FOR GTAW
ELECTRODES
AWS COMPOSITION COLOR
CLASS. CODE
EWP Pure Tungsten Green
EWCe-2 97.3% Tungsten, 2% Cerium Oxide Orange
EWLa-1 98.3% Tungsten,1% lanthanum Oxide Black
EWTh-1 98.3% Tungsten,1% lanthanum Oxide Yellow
EWTh-2 97.3% Tungsten,2% lanthanum Oxide Red
EWZr-1 99.1% Tungsten,0.25%Zirconium Oxide Brown
EWG 94.5% Tungsten,remainder not specified Gray
14. ALLOY STEELS
Steel is considered to be alloy - steel when the
maximum of the range given for the content of alloying
elements exceeds one or more of the following limits
Manganese 1.65%
Silicon 0.60%
Cu 0.60% or
in which the limits of any of the following elements is
specified or required
Al, Boron, Cr 3.99%
Cobalt, Columbium, Mo, Ni, Ti, Tungsten, Vanadium or
any other element added to obtain the desired alloying
element.
15. ALLOY STEELS
AWS Filler Metal Specifications
Suffix Letter designate the chemical composition
of the deposited weld metal
Suffix Letter indicate the following chemistry
Suffix Letter Chemistry
A C - Mo Steel
B Cr - Mo Steel
C or NI Ni Steel
D Mn - Mo Steel
NM Ni - Mo Steel
G, K, M and W Other Low Alloy Steel
16. ALLOY STEELS
To Weld Alloy Steel successfully four factors
must be considered
1. Always use a low - hydrogen welding procedure,
process & filler metal
2. Select a filler metal that matches the strength
level of the alloy steel
3. Select a filler metal that comes close to
matching the composition of alloy steel
4. Use proper welding procedure
19. LOW - ALLOY STEELS
Low Nickel Steel AISI 2315, 2515, 2517
Carbon 0.12 - 0.30%
Mn 0.40 - 0.60%
Si 0.20 - 0.45%
Ni 3.25 - 5.25 %
Electrode With the C-1, C - 2 Suffix
if C < 0.15% No preheat, except for heavy
section
if C > 0.15% Preheat up to 260o C
Stress Relieving Advisable
20. LOW - ALLOY STEELS
Low Ni - Cr Steel AISI 3120, 3135, 3140, 3310, 3316
Carbon 0.14 - 0.34%
Mn 0.40 - 0.90%
Si 0.20 - 0.35%
Ni 1.10 - 3.75 %
Cr 0.55 - 0.75%
Electrode E80XX & E90XX
if C < 0.15% No preheat, except for heavy
section
if C > 0.20% Preheat up to 316o C
Stress Relieving Advisable
21. LOW - ALLOY STEELS
Low Manganese Steel AISI 1320, 1330, 1335, 1340, 1345
Carbon 0.18 - 0.48%
Mn 1.60 - 1.90%
Si 0.20 - 0.35%
Electrode E80XX & E90XX With A-1, D-1 or
D-2 Suffix
Low Range of C & Mn No preheat
if C >= 0.25% Preheat desirable(121o C- 149o C)
High Range Mn Mandatory
Thicker Section (240o C- 290o C)
Stress Relieving Advisable
22. LOW - ALLOY STEELS
Low Alloy Cr Steel AISI 5015 to 5160
Carbon 0.12 - 1.10%
Mn 0.30 - 1.00%
Si 0.20 - 0.30%
Cr 0.20 - 1.60%
Electrode E80XX & E90XX With B Suffix
Low Range of C & Cr No preheat
High Range C & Cr 399o C
Thicker Section (240o C- 290o C)
Stress Relieving Advisable
23. LOW - ALLOY STEELS
Low Alloy Cr Steel AISI 5015 to 5160
C.E. = C% + Mn% + Ni% + Cr% + Mo% + Cu%
6 20 10 40
if C.E. < 0.40% Material is readily weldable
C.E. > 0.40% Special Controls Required
Preheating
Low Hydrogen Processes
Procedure Should be Qualified
24. STAINLESS STEELS
Also called Corrosion - Resistant Steels
They do not rust
Strongly resist attack by great many liquids, gases
& chemicals
Good low - temperature toughness & ductility
Good Strength & Resistance to High Temp.
Iron as main element
Chromium - 11 to 30 %
25. STAINLESS STEELS
AISI Identification System
Three Digit Number e.g. AISI 304
First Digit indicates Group
Last Two indicates specific alloy
Series Metallurgical Principle Magnetic
Design. Group Elements
2XX Austenitic Cr-Ni-Mn Non Magnetic
3XX Austenitic Cr-Ni -do-
4XX Martensitic Cr Magnetic
4XX Ferritic Cr -do-
5XX Martensitic Cr-Mo -do-
26. LOW HYDROGEN ELECTRODES
These electrodes are having covering that is
low in hydrogen bearing compound.
- Hydrogen has limited solubility in steel.
- Solubility is high in liquid state
- Beyond solubility limit, it retained in weld
called traps.
- Localization of hydrogen takes place which
creates under bead crack, Hydrogen
induced crack.
27. SELECTION OF ELECTRODES
- Composition & strength of BM
- Penetration requirement
- Position of welding.
- Fit up condition
- Skill of welding personnel
- Cost of welding operation.
- Service requirement of weld joint.
28. PREHEATING & POST HEATING
It is to elevate base metal temp before or after
welding operation.
Purpose - to reduce cooling rate
- To avoid cold cracks
- To avoid hydrogen entrapment
- To remove moisture
Carbon equivalent = C+Mn/6+(Cr+Mo+V)/5 +
(Ni+Cu)/15
29. 0.40 Below – Preheating optional
0.40 - 0.60 – Preheating 150 to 200 deg c
0.60 & above – Preheating & Post heating –
200 – 370 deg C
POST WELD HEAT TREATMENT
- Rate of heating
- Soaking & soaking time
- Rate of cooling
30. WELDING DEFECTS
In the correct sense, a defect is a rejectable discontinuity
or a flaw of rejectable in nature. Certain flaws acceptable
in one type of product need not be accepted nature in
another product. A defect is definitely a discontinuity but
a discontinuity need not necessary be a defect.
ACCEPTANCE / REJECTION CRITERIA
- Stress to which the parts will be subjected.
- Type of material used.
- The temp & pressure to which the parts will be
stressed & Its thickness
- Consequence of failure & cost &accessibility of
repair.
31. DEFECT CHARACTERISTICS
- Size of defect
- Sharpness or notch effect
- Orientation of defect
- Location of defect (surface, root, weld metal, HAZ,
Parent metal.
BROAD CLASSIFICATIONS
Planer defect (two dimensional) - cracks, lack of fusion,
lack of penetration, lamination
Voluminar defect (three dimensional) – Slag inclusion,
Porosity, cavity, root concavity.
32. Geometric defects
Misalignment, undercut, concavity , convexity,
excessive reinforcement, improper reinforcement,
overlap, burn through, incomplete penetration, lack of
fusion, surface irregularity
Incomplete penetration – Lack of penetration &
excessive penetration.
- Excessive thick root face or insufficient root opening
can be avoided by use proper joint geometry.
- Insufficient heat input.
- Slag flooding ahead of welding – Use small
electrodes in root .
33. - Misalignment - id matching
- Bridging or root opening.
INCOMPLETE FUSION
- Insufficient heat input, wrong size of electrode,
improper joint design – follow correct WPS
- Incorrect electrode position – maintain correct
position.
- Weld metal running ahead of arc – lower the current
& speed
SLAG INCLUSION
- Improper joint design-increase groove angle of joint.
- Oxide inclusions – proper gas shielding.
- Poor electrode manipulative techniques.
- Change electrode or flux to improve slag control.
- Failure by welder to remove slag
34. POROSITY
- Improper arc length, welding current, electrode
manipulation – change welding condition &
techniques.
- Excessive moisture in electrode-use correct baking
& holding temp.
- Excessive Hydrogen & nitrogen in weld atmosphere
by use low hydrogen electrodes.
- High solidification rate – use preheat
- Dirty metal or filler metal.
46. EFFECT OR VARIATION OF PARAMETERS
CURRENT TOO LOW
• Poor penetration
• Slag inclusion
• Irregular ripples
• Uneven bead height
CURRENT TOO HIGH
• Excessive penetration
• More spatter
• Poor ripple appearance
• Porosity
• Undercut
47. ARC TOO SHORT
• Irregular ripples
• Electrode freezing the job
ARC TOO LONG
• Wide ripples
• More spatters, blow holes
TRAVEL TOO FAST
• Narrow width of bead
• Porosity
TRAVEL TOO LOW
• More width & height of bead
• Slag inclusion
48. DISTORATION & RESIDUAL STRESS
• Distortion or residual shape change occur during
welding.
• These imperfections adversely affect further assembly.
• Designers are often constrained to design structure free
from distortion
• Distortion control is often tackled by shop floor
engineers.
• This is a after effect of welding that remains permanent
in the component till the equilibrium is disturbed.
49. PROCESS – Localized application of heat causes
plastic deformation. As a result thermal shrinkage occur
near that zone & the metal or weldment changes its
shape during cooling.
METHOD TO PREVENT
• Minimizing weld joints.
• Minimizing weld sizes.
• Minimizing unsupported length
• Selection of appropriate edge preparation
• Use of intermittent welding.
• Using proper jigs & fixtures
• Using welding sequence
• Minimizing heat input rate
