Welding in Shipbuilding
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PRESENTATION ONPRESENTATION ONWELDINGWELDING
BY
RISHIKESH KR. KAUSHIK
SEM.-VI
32nd BATCH
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A Brief History of WeldingA Brief History of Welding
• Late 19th Century• Scientists/engineers apply advances in electricity to
heat and/or join metals (Le Chatelier, Joule, etc.)• Early 20th Century
• Prior to WWI welding was not trusted as a method to join two metals due to crack issues
• 1930’s and 40’s• Industrial welding gains acceptance and is used
extensively in the war effort to build tanks, aircraft, ships, etc.
• Modern Welding• the nuclear/space age helps bring welding from an art to
a science
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INTRODUCTIONINTRODUCTION
• A welding is a permanent joint which is obtained by the fusion of the edges of the two parts to be joined together, with or without application of pressure and a filler material.
• The heat required for the fusion of material may be obtained by burning of gas or by an electrical arc.
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Weldability of a MetalWeldability of a Metal
• Metallurgical Capacity• Parent metal will join with the weld metal without
formation of deleterious constituents or alloys
• Mechanical Soundness• Joint will be free from discontinuities, gas
porosity, shrinkage, slag, or cracks
• Serviceability• Weld is able to perform under varying conditions
or service (e.g., extreme temperatures, corrosive environments, fatigue, high pressures, etc.)
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Welding ProcessesWelding Processes
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BROAD CLASSIFICATIONBROAD CLASSIFICATION
• Welding processes that use heat alone e.g., fusion welding
• Welding processes that use combinat-ion of heat and pressure
e.g., forge welding
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Types of WeldingTypes of Welding
Fusion Welding Pressure Welding
Homogeneous Heterogeneous
Brazing Soldering
Thermit Welding
Gas welding
High Energy Beam
Electric Arc
MIG
TIG
Shielded Metal Arc – “Stick”
Forge welding
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Fusion Welding PrinciplesFusion Welding Principles
• Base metal is melted
• Filler metal may be added
• Heat is supplied by various means• Oxyacetylene gas• Electric Arc• Plasma Arc• Laser
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Fusion WeldingFusion Welding
BASE METAL
WELD
SOLIDIFIED SLAG
ARC POOL
WELDING ATMOSPHERE
CORE WIRE
ELECTRODE COATING
ARC STREAM
PENETRATION DEPTH
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Types of Fusion WeldingTypes of Fusion Welding
HOMOGENEOUS
• Thermit welding
• Gas welding
• Electrical arc welding
(i) Oxyacetylene Cutting/Welding
(ii)Shielded Metal Arc (“Stick”)
(iii)Metal Inert Gas (MIG)
(iv)Tungsten Inert Gas (TIG)
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THERMIT WELDINGTHERMIT WELDING
• Mixture of iron oxide and aluminium called thermit is used.
• Weld section are molten at same time and weld cools uniformly, so minimum problem with residual stresses.
• Used in joining iron and steel parts that are too large to be manufactured in one piece.
e.g., rails,stern and rudder frames.
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GAS WELDINGGAS WELDING
• Made by applying flame of gases like oxy-acetylene or hydrogen from a welding torch.
• A flux is being used to remove slag.
• Heating is slow so used on thinner materials.
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ELECTRICAL ARC ELECTRICAL ARC WELDINGWELDING
• Work is prepared in same manner as in case of gas welding.
• Filler metal is supplied by metal welding electrode.
• An arc is strike by touching work of base metal with the electrode.
• Slag is brushed off after joint is cooled.
• Extensively used due to greater speed of welding.
• Protection of eye and face is reqd.
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Oxyacetylene WeldingOxyacetylene Welding
• Flame formed by burning a mix of acetylene (C2H2) and oxygen
• Fusion of metal is achieved by passing the inner cone of the flame over the metal
• Oxyacetylene can also be used for cutting metals
Inner Cone: 5000-6300 deg F Combustion Envelope 3800 deg F
2300 deg FTORCH TIP
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Shielded Metal Arc (Stick)Shielded Metal Arc (Stick)
• An electric arc is generated between a coated electrode and the parent metal
• The coated electrode carries the electric current to form the arc, produces a gas to control the atmosphere and provides filler metal for the weld bead
• Electric current may be AC or DC. • Used for welding of lighter steel structures
and Al-alloys.
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Shielded Metal Arc (contd.)Shielded Metal Arc (contd.)
• Process:
• Intense heat at the arc melts the tip of the electrode
• Tiny drops of metal enter the arc stream and are deposited on the parent metal
• As molten metal is deposited, a slag forms over the bead which serves as an insulation against air contaminants during cooling
• After a weld ‘pass’ is allowed to cool, the oxide layer is removed by a chipping hammer and then cleaned with a wire brush before the next pass.
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Inert Gas WeldingInert Gas Welding
For materials such as Al or Ti which quickly form oxide layers, a method to place an inert atmosphere around the weld puddle had to be developed
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• Uses a consumable electrode (filler wire made of the base metal)
• Inert gas is typically Argon
• As argon is very costly, CO2 is used for shielding gas specially for mild steel
• Used in AL-deckhouses, liq. Methane gas tanks.
Metal Inert Gas (MIG)Metal Inert Gas (MIG)
BASE METAL PUDDLE
POWER SOURCE
DRIVE WHEELSCONSUMABLE ELECTRODE
ARC COLUMNSHIELDING GAS
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• Tungsten electrode acts as a cathode which is non consumable• A plasma is produced between the tungsten cathode and the
base metal which heats the base metal to its melting point• Filler metal can be added to the weld pool
• Plate(generally of Al) of thickness less than 6mm is welded by this process
Tungsten Inert Gas (TIG)Tungsten Inert Gas (TIG)
BASE METAL PUDDLE
POWER SOURCE
ARC COLUMNSHIELDING GAS
TUNGSTEN ELECTRODE
+ +
BASE METAL (ANODE)
TUNGSTEN ELECTRODE
(CATHODE)
- - -
+ +
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Types of Fusion WeldingTypes of Fusion Welding
HETEROGENEOUS
• Soldering
• Brazing
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SOLDERINGSOLDERING
• Produces coalescence of materials by heating them to a suitable temperature.
• Uses a filler metal having a liquidus not exceeding 450oC (840oF) and below the solidus of the base materials.
• The filler metal is distributed between the closely fitted surfaces of the joint by capillary action.
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BRAZINGBRAZING
• Same as soldering only difference is that it uses a filler metal, having a liquidus above 450oC and below the solidus of the base materials.
• A braze is a very special form of weld, the base metal is theoretically not melted.
• Relates to welding processes using brass or bronze filler metal, where the filler metal is not distributed by capillary action.
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Weld Metal ProtectionWeld Metal Protection
• During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation
• Must protect weld puddle (arc pool) from the atmosphere
• Methods• Weld Fluxes• Inert Gases• Vacuum
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Weld FluxesWeld Fluxes
• Typical fluxes• SiO2, TiO2, FeO, Go, Al2O3
• Produces a gaseous shield to prevent contamination
• Act as scavengers to reduce oxides• Add alloying elements to the weld• Influence shape of weld bead during solidification
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Inert GasesInert Gases
• Argon, helium, nitrogen, and carbon dioxide
• Form a protective envelope around the weld area
• Used in• MIG• TIG• Shield Metal Arc
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Vacuum Vacuum
• Produce high-quality welds
• Used in electron beam welding
• Nuclear/special metal applications
• Reduces impurities by a factor of 20 versus other methods
• Expensive and time-consuming
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Welding PositionsWelding Positions
FLATFLAT
HORIZONTALHORIZONTAL
VERTICALVERTICAL
OVERHEADOVERHEAD
INCREASING DIFFICULTY
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Weld DefectsWeld Defects
• Undercuts/Overlaps
• Grain Growth• A wide T will exist between base metal and HAZ. Preheating
and cooling methods will affect the brittleness of the metal in this region
• Blowholes• Are cavities caused by gas entrapment during the
solidification of the weld puddle. Prevented by proper weld technique (even temperature and speed)
• HAZ is transition between liquid recrystalisation and base (usually cold-worked) metal most shrinkage occurs here, so most brittle →This is where welds usually fail.
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Weld Defects(contd.)Weld Defects(contd.)
• Inclusions• Impurities or foreign substances which are forced into the weld
puddle during the welding process. Has the same effect as a crack.
Prevented by proper technique/cleanliness.
• Segregation• Condition where some regions of the metal are enriched with an
alloy ingredient and others aren’t. Can be prevented by proper heat treatment and cooling.
• Porosity• The formation of tiny pinholes generated by atmospheric
contamination. Prevented by keeping a protective shield over the molten weld puddle.
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Residual StressesResidual Stresses
• Rapid heating and cooling results in thermal stresses detrimental to joint strength.
• Prevention• Edge Preparation/Alignment – beveled edges and space between
components to allow movement• Control of heat input – skip or intermittent weld technique• Preheating – reduces expansion/contraction forces (alloys) and
removes moisture from the surface• Peening – help metal stretch as it cools by hitting with a hammer.
Use with care since it may work harden the metal• Heat Treatment – “soak” the metal at a high temperature to relieve
stresses• Jigs and Fixtures – prevent distortion by holding metal fixed• Number of Passes – the fewer the better.
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Joint DesignJoint Design
BUTT JOINTBUTT JOINT
STRAP JOINT
LAP JOINT
FILLET JOINT
CORNER JOINT
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Generalized Welding SymbolGeneralized Welding Symbol
FAR SIDE DETAILS
ARROW SIDE DETAILS
Field weld symbol
Weld all-around for pipes, etc.
L1-L2
L1-L2
D = Weld Depth (usually equal to plate thickness)
L1 = Weld Length
L2 = Distance between centers for stitched welds
The Field Weld Symbol is a guide for installation. Shipyardsnormally do not use it, except in modular construction.
ElectrodeMaterial
D
D
Weld Geometry
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Example of Welding SymbolExample of Welding Symbol
1/2” 1/2”
1/2
1/2
One-sided welds are max 80% efficientTwo sided are 100% efficient
Geometry symbol for V-groove
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Weld Symbols (Butt Joints)Weld Symbols (Butt Joints)
Backing
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Weld Symbol (Fillet Joints)Weld Symbol (Fillet Joints)
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Weld Symbol (Corner Joints)Weld Symbol (Corner Joints)
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WELD TESTINGWELD TESTING• For economic reasons much of the weld
testing in shipbuilding is carried out visually by trained inspectors.
• For important welds radiographic equipment is used for spot check in merchant ships.
• Welding material undergoes coprehe- nsive tests by classification society before approval.
• But for accuracy in the test NDT is used.
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ADVANTAGES OF ADVANTAGES OF WELDINGWELDING
FOR SHIPBUILDERWelding lends itself to the prefabrication
techniques.Easier to obtain water tightness and oil
tightness. Joints produced more quickly.Less skilled labor is required.
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ADVANTAGES OF ADVANTAGES OF WELDING(contd.)WELDING(contd.)
FOR SHIPOWNERReduced hull steel weight ;so more
deadweight.Less maintenance.Smoother hull reduced skin friction
resistance which reduces fuel costs.
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THANK YOU!!!!!
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QUESTIONS???