Naveed Habib Khan Mechanical Department 6th August 2009

1. WELDING Naveed Habib Khan Mechanical Department 6th August 2009

2. Contents • Welding Basics • Types of Weld Joints • Welding Positions • Welding Types • Welding Processes • Welding Symbols • Welding Safety

3. What is Fabrication / Welding? • Fabrication “Metal Fabrication is the forming of metal, usually steel plate, into various forms either by welding or other forms of metal joining processes • Welding “A fabrication process that joins materials, usually metals by causing coalescence” Coalescence means “Fusion”

4. Welding Terms • Weldments • Weld puddle • Slag • Weld Bead • Backing • Tack Weld • Heat Affected Zone (HAZ)

5. Parts of a Weld Joint and Weld Heat Affected Zone 5

6. Fillet Weld Fillet welds should: Have a flat to slightly convex face Be uniform in appearance Have equal leg size 6

7. Types of Weld Joints There are 5 types of joints … B – Butt Joint L – Lap Joint T – Tee Joint E – Edge Joint C – Corner Joint 7

8. Fillet and Groove Welds Groove and fillet welds can be made on many types of joints 8

9. Types of Joints 9

10. WELDED JOINT CATEGORY • ASME Code defines welded joints by category. • The term “Category” defines the location of a joint in a vessel. • The joints included in each category are designated as joints of Categories A, B, C, and D. • The “Categories” established by UW-3 are for use in specifying special requirements (based on Service, Material, and Thickness) regarding joint type and degree of inspection for certain welded pressure joints. • Weld joint efficiency “E” • It is a measure of weld quality and accounts for stress concentrations. • E is needed in component thickness calculations

11. Figure illustrates typical joint locations included in each category.

12. Category A: Longitudinal welded joints within the main shell or nozzles; any welded joint within a formed or flat head; circumferential welded joints connecting hemispherical heads to main shells, to transitions in diameters. • Category B: Circumferential welded joints within the main shell, nozzles, or transitions in diameter; circumferential welded joints connecting formed heads other than hemispherical to main shells, to transitions in diameter. • Category C: Welded joints connecting flanges, tubesheets, or flat heads to main shell, to formed heads, to transitions in diameter, to nozzles. • Category D: Welded joints connecting nozzles to main shells, to spheres, to transitions in diameter, to heads.

13. Weld joint efficiency vs. Joint Type, Category & Radiographic Examination

14. Welding Positions There are various positions that a weld can be made in: 14

15. Weld Passes Fill Pass Cover Pass Root Pass Hot Pass

16. ENERGY BEAM

17. Welding Process • Arc Welding “Arc welding process use electric power supply to create & maintain an electric arc b/w an electrode and the base material to melt metals at the welding point”.

18. How an arc is formed? • The arc is like a flame of intense heat that is generated as the electrical current passes through a highly resistant air gap.

19. The Arc Welding Circuit The electricity flows from the power source, through the electrode and across the arc, through the base material to the work lead and back to the power source 19

20. Basic Steps of Arc Welding Choose the right welding process Preparation of Welding Prepare the base materials: remove scale, rust, oil, grease and any foreign material Qualified Welders Welding Procedure Tack Welds Choose the right filler material Pre-heating Connections Welding & Removal of Temporary Attachment Assess and comply with safety requirements Use proper welding techniques and be sure to protect the molten puddle from contaminants in the air Inspect the weld 20

21. Factors Affecting the Welding • Welding Procedure • Thickness • Electrode extension • Angle of bevel • Travel speed • Cleanliness • Type of joint • Polarity, Current & Voltage • Root Opening distance • Welding Position

22. Types of Arc Welding • Shielded Metal - Arc Welding (SMAW) • Gas Metal - Arc Welding (GMAW) • Gas Tungsten - Arc Welding (GTAW) • Submerged - Arc Welding (SAW) • Plasma - Arc Welding (PAW) • Flux Cored - Arc Welding (FCAW) • GAS WELDING • Oxyacetylene Welding (OAW)

23. Gas Tungsten Arc Welding (GTAW) Also called Tungsten inert gas (TIG) This uses a similar inert gas shield to MIG, but the tungsten electrode is not consumed. Filler metal is provided from a separate rod fed automatically into the molten pool

24. Equipment for GTAW Welding

25. Type of Current & polarity • Direct Current • Direct current straight polarity (DCSP) • Direct current reverse polarity (DCRP) • Alternating Current • Type of Power Source • Generator • Transformer

26. Tungsten Electrode • Non consumable • Melting point = 6170°F • Tungsten Alloys : Thoria, Zirconia, Ceria, Lanthana or a combination of oxides. • Length = 3 to 24 inches • Diameter = .01 to .25inches • Extension & Shape

27. GTAW Shielding Gases • Argon, Helium or mixture of Gases • Inert gases don't form compound with other elements. • These gases protect the tungsten electrode and weld metal from contamination.

28. Properties Of Inert Gases

29. Filler Metals • Selection of Filler metal depends upon chemical composition of base metal. • To increase the tensile strength, ductility, and corrosion resistance. • Filler metal is kept in “HOT OVENS” for preheating for smooth operation. • Classification of Filler metals in AWS • Stainless steel A5.9 • Carbon steels A5.18 • Low alloy steel A5.28 • Deposition Rate E R 70 1 8 A1 Allow Constituent of Filler Current Condition Position of Welding (1 6) Tensile Strength in Ksi Type of Covering (usually for GTAW only) Electrode

30. Cost of GTAW • Labor (20% to 40%) • Overhead cost (Major Cost) • Filler metal cost • Shielded gas cost • Electric power cost (Minor cost) • Tungsten Electrode cost (4%of Shielding gas cost) • Welding Torch

31. Advantages • High Quality Weld • No Flux or Slag • Used for both Ferrous & Non-Ferrous metals • No Smokes or Fumes • Welding can be done in all position • Filler metal is not always required • The arc & weld pool is clearly visible to the welder • For many application, it is the best method • Excellent for welding thin metals and pipeline welding

32. Limitations • Welding speed is slow • Electrode is easily contaminated • Not efficient for welding thick sections • Thickness should not exceed ¾”. • Lower filler metal deposition rate • Not Economical • Hand eye co-ordination skill is required • Highly skilled labor needed for this process

33. Shielded Metal Arc Welding (SMAW) • This is the most commonly used technique. There is a wide choice of electrodes, metal and fluxes, allowing application to different welding conditions. • The gas shield is evolved from the flux, preventing oxidation of the molten metal pool. • Also referred to as “Stick Welding” • Used for everything from pipeline welding, farm repair and complex fabrication. • Uses a “stick” shaped electrode. • Can weld: steel, cast iron, stainless steel, etc.

34. Shielded Metal Arc Welding (SMAW)

35. Gas Metal Arc Welding (GMAW) • Electrode metal is fused directly into the molten pool. The electrode is, therefore, consumed rapidly, being fed from a motorized reel down the centre of the welding torch • Also referred to as “MIG” welding • Uses a shield gas and a continuous wire electrode • Used for all types of fabricatio • Great for thin metals up to ¼” • Excellent speed of deposition • Used for metals such as: steel, aluminum and stainless steel.

36. Gas Metal Arc Welding (GMAW)

37. MIG Welding Benefits •  Higher deposition rates than SMAW •  All position capability • Less operator skill required •  Long welds can be made without starts and stops •  Minimal post weld cleaning is required

38. Submerged arc welding (SAW) • Instead of using shielding gas, the arc and weld zone are completely submerged under a blanket of granulated flux. • A continuous wire electrode is fed into the weld. This is a common process for welding

39. Flux-cored arc welding (FCAW) • This is similar to the MIG process, but uses a continuous hollow electrode filled with flux, which produces the shielding gas. • The advantage of the technique is that it can be used for outdoor welding, as the gas shield is less susceptible to draughts.

40. Plasma - Arc Welding (PAW) • Plasma welding is similar to the TIG process. • A needle-like plasma arc is formed through an orifice and fuses the base metal. • Shielding gas is used. Plasma welding is most suited to high-quality and precision welding applications.

41. Oxygen/ Fuel Welding • Utilizes oxygen and a fuel gas to heat metal until it is in a molten state and fuse multiple pieces of metal together. Can be used with or without a filler rod. • Great for brazing dissimilar metals together. • Older technology that can be replaced by GTAW

42. Welding Symbols Welding symbols contain information about the weld to be made 42

43. Welding symbols give the welder specific instructions about the weld including: Placement, Size, Length, Process Any other special notes Welding symbols are Universally used Governed by the AWS Found on engineering drawings 43

44. Reference Line Reference Line (Required element) Always Horizontal

45. Arrow Line Reference Line (Required element) Arrow

46. Tail Reference Line (Required element) Arrow Tail

47. Reference Line must always be horizontal, Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area. Reference Line (Required element) Arrow Tail The tail of the welding symbol is used to indicate the welding or cutting processes, as well as the welding specification, procedures, or the supplementary information to be used in making the weld.

48. Reference Line must always be horizontal, Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area. Basic components of aWELDING SYMBOL Arrow connects reference line to arrow side member of joint or arrow side of joint Reference Line (Required element) Arrow Tail omitted when reference not used Tail The tail of the welding symbol is used to indicate the welding or cutting processes, as well as the welding specification, procedures, or the supplementary information to be used in making the weld.

49. All the way Around A circle at the tangent of the arrow and the reference line means welding to be all around.

50. Field Weld Symbol A flag at the tangent of the reference line and arrow means Field Weld.