![]() PPT – Introduction to Welding Technology Power. Point presentation | free to download. Title: Introduction to Welding Technology 1. Introduction to Welding Technology. The Weld. Net CONSULTANT ENGINEERS - METALLURGY AND WELDING 2. Welding processes. Fusion welding Involves melting solidification Solid phase welding Explosive bonding Diffusion welding Friction welding 3. ![]() Fusion welding. Most commonly used processes Heat source electric arc, gas flame, laser Filler metal From electrode, rod, wires, powder, fluxes Independently added filler No filler (autogenous welding) 4. Weld. The AWS definition for a welding process is A materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone and with or without the use of filler material". Filler (if used) has a melting temperature similar to the parts being joined 5. Weldability. The capacity of a material to be welded under the imposed fabrication conditions into a specific, suitably designed structure and to perform satisfactorily in intended service. ANSI / AWS A3. 0) 6. Factors affecting weldability. Weldability is often considered to be a material property. However the effect of other variables should not be ignored. · Real Threat or Not? Do you ever download full version software that is accompanied by a crack? Do you obtain illegal copies online, or make a copy from. If you have a broken LCD LED TV Screen that has any type of damage such as lines running vertically, spots or patches, cracks or breaks, this page will give you tips. · Welcome to the Samsung forum on CNET! Samsung worked with CNET to create a forum where people can ask questions and talk about all Samsung products and get help with. ![]() Weldability is also affected by Design of a weld Service conditions Choice of welding process 7. Design. Weld joint design and execution Thickness, location, access, environment Restraint Weldment size, assembly sequence Service stresses Safety factor for welds 8. Physical properties. Melting and vaporisation temperatures Electrical and thermal properties Conductivity, expansion coefficient, thermal capacity, latent heat Ionisation potential of electrode Magnetic susceptibility Reflectivity 9. Solidification of weld metal. Dendritic or cellular growth Segregation Depends on composition Cooling rate Can lead to solidification cracking 1. Dilution. Proportion of weld metal that comes from the base material Must be considered for each weld run Affects composition, properties, risk of defects Greatest effect when filler composition is different to either or both base metals 1. Chemical properties. Affinity of weld metal for O, N and H Susceptibility to porosity, embrittlement Presence of a surface film on base metal Oxide films Paint or metallic surface coating Fluxing / De- oxidising properties of a slag 1. Contaminant gases. Nitrogen and oxygen from air Hydrogen from Moisture in air Moisture in consumables or surface contaminants Organic materials (grease, oil, paint etc) 1. Gas- metal reactions. Liquid metal may react with air or other gases Depends on Liquid metal composition Gas composition Consequences Porosity - gas released on solidification Formation of compounds Embrittlement 1. Metallurgical properties. Strengthening mechanism of base material Weld versus base material strength Freezing range Susceptibility to solidification cracking Susceptibility to detrimental phases forming during welding Embrittlement or corrosion 1. Service environment. Extreme environments Corrosive Low temperature (brittle failure) High temperature (oxidation, creep, embrittlement) Others (wear, fatigue, nuclear) The more extreme the environment The more difficult it is to find suitable materials The more restricted the welding procedure becomes to avoid service failure (arc energy) 1. Welding variables. Arc energy (heat input) Preheat and interpass temperature Filler metal composition 1. Arc energy. Q arc energy in k. J/mm I welding current E arc voltage v travel speed in mm/min. Low arc energy Small weld pool size Incomplete fusion High cooling rate Martensite and hydrogen cracking. High arc energy Large weld pool size Low cooling rate Increased solidification cracking risk Low ductility and strength Precipitation of unwanted particles (corrosion and ductility) 1. Preheat and interpass. Preheat is applied independently Gas torches Gas radiant heaters Electric resistance heaters Interpass temperature Temperature before next pass is added Controlled by a cooling time, or air or water cooling 1. Raising PH/IP temperature. Slows cooling rate Reduces HICC in steels Can increase risk of solidification cracks Can increase tendency to embrittlement Improves fusion Reduces temperature gradient Minimises distortion and residual stress 2. Fusion weld structure 2. Thermal gradients in HAZFusion line Fusion line 2mm Fusion line 5 mm. Temperature. Time 2. Thermal HAZ regions 2. HAZ Structure. Weld. Coarse grain region. Disturbed microstructure. Grain refining. Original base material 2. Weld positions and joints 2. Welding positions - plate. Flat 1. GHorizontal 2. GVertical 3. G Up or Down. Overhead 4. G 2. 6Welding positions - pipe. Axis vertical 2. GAxis horizontal 5. GAxis inclined 4. G 2. 7Weld joints. Butt. Tee. Lap. Corner. Cruciform 2. 8Weld Types 2. Weld types. Butt weld Between mating members Best quality High weld preparation cost Fillet weld Easy preparation Asymmetric loads, lower design loads 3. Butt welds. Joint types Double welded butt Permanent or temporary backing Single welded butt Lower stress concentration Easier ultrasonic testing or radiography Expensive preparation 3. Butt weld types. Single vee can be single or double welded. Double vee. Single bevel. Backed butt (permanent or temporary) 3. Butt weld terms 3. J Preparations. Single U preparation. Root radius. Land. Double U butt 3. 4Fillet welds. Simple to assemble and weld Stress concentrations at toes and root Notch at root (fatigue, toughness) Critical dimension is throat thickness Root gap affects throat thickness Radiography and ultrasonic testing is of limited use Large fillets are uneconomic 3. Fillet weld terms. Gaps shall be taken into account for minimum leg length 3. Weld preparation dimensions. Standard preparations AS/NZS1. AS/NZS3. 99. 2 AWS D1. ASME B3. 1. 3 Non Standard (Compromise at fabricators risk) Weld cross sectional area Cost Ease of welding (risk of defects) 3. Weld Defects and. Discontinuities 3. Welding discontinuities. Discontinuities are essentially defects that fall within the limitations of the welding standard requirements Cracks Never a discontinuity !! Porosity Most common complying weld defect Incomplete fusion / Inclusions Some allowed by most welding standards Defective profile Under- weld, over- weld, lack of root bead, burn through, undercut, spatter etc. Most client specifications limit these types 3. Welding defects- Causes. Cracks HACC / HICC, solidification, liquation causes Porosity Gas entrapment / ejection, poor shielding Incomplete fusion Sidewall, inter run, root pass, weld toes ( cold lap ) Electrode angle implicated or poor joint profile Inclusions Slag, oxide, tungsten Usually operator induced Defective weld profile / finish Under- weld, over- weld, lack of root bead, burn through, undercut Usually operator induced 4. Some weld defects. Undercut. Cold lap. Incomplete penetration. Slag inclusion. Incomplete sidewall fusion. Incomplete root fusion 4. Solidification cracking. Low melting point constituents Sulphur, Phosphorus, Tin, Lead, Niobium Undesirable eutectics Grain boundary segregation Segregation of sulphides etc. Lowering ductility and raising crack sensitivity Strains arising during solidification Solidification range Material types, contamination Base material dilution, lowering weld strength Expansion coefficient Differing between base material and weld material Clad materials Weld pool shape and size Depth- to- width ratio Surface concavity Arc energy 4. Solidification cracks. Crater crack. Longitudinal crack. Centreline Crack 4. Weldability of structural steel. Benchmark against which other materials are judged Risk of hydrogen induced cold cracking. Only occurs in ferritic, bainitic or martensitic steel 4. Hydrogen induced cold cracks. HACC Hydrogen assisted Presence of hydrogen Susceptible microstructure Tensile Stress Temperature Below 1. C HICC Hydrogen induced Hydrogen embrittlement Susceptible microstructure / stress not always required 4. Susceptible microstructure. Weld metal or HAZ Martensite or upper bainite Composition Hardenability and hardness - carbon equivalent TTT diagrams Cooling rates Cooling time between 5. C and 3. 00. C Section thickness Preheat temperature 4. Sources of tensile stress. Residual stress Restraint Through thickness in thick sections Applied stress Excessive peening Lifting Presetting Fairing and straightening operations 4.
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