Theory of welding joint, types, advantages, disadvantages, symbols, arrow symbol, interpretation of symbol of welding in drawing, piping layout, types, duct layout

1. Mechanical Drafting
Welding Joints, Piping and Duct
Layout
Gaurav Mistry
AssistantProfessor
Diwaliba Polytechnic, UTU.

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 Welded Joints MechanicalDrafting
Welding
 For joining metal parts permanently, welding is used in Engineering Field.
 Welding is an effective method of making permanent joints between two or more
metal parts.
 Cast iron, steel and its alloys, brass and copper are the metals that may be welded
easily.
 Production of leak proof joints that can withstand high pressures and temperatures
are made possible with advanced welding technology.
 For this reason, welding is fast replacing casting and forging wherever possible.
 When compared to riveting, welding is cheaper, stronger and simpler to execute at
site with considerable freedom in design. Hence, it is widely used in ship building
and structuralfabrication in place of riveting.
 There are different types of welding. It is necessary to have the information
regarding the type and size of weld that should be used to carry out required
welding work.

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 Welded Joints MechanicalDrafting
Advantages and Disadvantages of Welding joint over Rivet joint.

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 Welded Joints MechanicalDrafting
 Types of Weld joints.
1. Lap or FilletJoint.
The lap joint or the fillet joint is obtained by overlapping the plates and then welding
the edges of the plates. The cross-section of the fillet is approximatelytriangular.
A single transverse fillet joint has the disadvantage that the edge of the plate which is
not welded can buckle or warp out of shape.

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 Welded Joints MechanicalDrafting
 Types of Weld joints.
2. Butt Joint.
The butt joint is obtainedby placing the platesedge to edge as shown in Fig.
In butt welds, the plate edges do not require bevelling if the thickness of plate is less
than 5 mm.
On the other hand, if the plate thickness is 5 mm to 12.5 mm, the edges should be
bevelled to V or U-groove on both sides.

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 Welded Joints MechanicalDrafting
 Types of Weld joints.
3. OtherTypes of Weld.
The othertype of welded joints are corner joint, edge joint and T-joint.
The main considerations involvedin the selectionof weld type are:
1. The shape of the welded component required,
2. The thickness of the plates to be welded, and
3. The direction of the forces applied.

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MechanicalDrafting
 Welded Joints
Weld Nomenclature

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MechanicalDrafting
 Welded Joints
Standard location of Welding Symbol used to show complete
info. in drawing.
Elements of a Welding Symbol
A welding symbol consists of the following eight elements:
1. Reference line, 2. Arrow, 3. Basic weld symbols, 4. Dimensions and other data,
5. Supplementary symbols, 6. Finish symbols, 7. Tail, and 8. Specification, process or other
references.

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MechanicalDrafting
 Welded Joints
Designation of welding processes in welding symbol

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MechanicalDrafting
 Welded Joints
(i) An arrow line (1) per joint,
(ii) A dual reference line,
consisting of two parallel lines;
one continuous and one dashed
(2a, 2b) and
(iii) A certain number of
dimensions (4) and conventional
signs (3).
In addition to the weld symbol of the joint to be made, the two
conventional signs used for welding as per BIS are
(1) A circle at the elbow connecting the arrow and the reference
line to indicate welding all around and,
(2) (2) A filled-in circle at the elbow indicate welding on site, as
shown in Fig

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MechanicalDrafting
 Welded Joints
 Elementary/Basic welding symbols

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MechanicalDrafting
 Welded Joints
 Elementary/Basic welding symbols

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MechanicalDrafting
 Welded Joints
 Elementary/Basic welding symbols

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MechanicalDrafting
 Welded Joints
 Supplementary welding symbols

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MechanicalDrafting
 Welded Joints
 Combination of Basic and Supplementary welding symbols

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MechanicalDrafting
 Welded Joints
 Some Examples showing Representation of Welding symbols

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MechanicalDrafting
 Welded Joints
 Methods to show the weld by arrow. (arrow side and other side)

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MechanicalDrafting
 Welded Joints
 Welding symbol in relation to the reference line.

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MechanicalDrafting
 Welded Joints
 Welding symbol shown by an arrow.

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MechanicalDrafting
 Welded Joints
 Dimensions of Weld.

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MechanicalDrafting
 Welded Joints
 Illustration to give meaning of Weld symbol.

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MechanicalDrafting
 Piping
 Pipe Types and Symbols of pipelines carrying different fluids
Pipe Types:
1. Steel Tubes
2. Steel Pipes
3. Cast iron pipes
4. Brass Pipes
5. Copper Pipes
6. Lead Pipes
7. Brass Tubes
8. Aluminium Pipes
9. AluminiumAlloy Pipes
10.Copper AlloyPipes
11.Low Pressure Pipes
12.High Pressure Pipes
13.Drawn Pipes
14.Fabricated Pipes

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MechanicalDrafting
 Piping
 Pipe Fittings

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MechanicalDrafting
 Piping
 Pipe Fittings

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MechanicalDrafting
 Piping
 Pipe FittingsApplications:
Applications:
1. Nipple:To increase the length of pipe line.
2. Elbow 90/45 deg: To bend the piping at an angle of 90/45deg.
3. Elbow – reducer: To join the smaller pipe at right angle to the bigger pipe.
4. Reducer tee: To join the small branch pipe with the larger pipe.
5. Coupling:To join two pipes of equal diameter in a straight line.
6. Union: To join the pipes creating the facility of replacing the pipe if required to
do so at the time of maintenance.
7. Plug: To close the pipe end having internal threads.
8. Cap: To close the pipe end having external threads.
9. Bend: To give bend to pipe at an angle of 90 deg or more.

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MechanicalDrafting
 Piping
 Standard symbols for flanged and threaded pipe fittings and
valves

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MechanicalDrafting
 Piping
 Line diagram of piping drawing

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MechanicalDrafting
 Piping
 Scale layout of piping drawing

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MechanicalDrafting
 Piping
 Line diagram of above (scale layout) piping drawing

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MechanicalDrafting
 Duct Layout
 Types of Duct and its application
 Types of ducts are as under:
1. Ducts with threadedjoints
2. Ducts with flanged joints
3. Welded ducts
 Application of ducts:
1. In water supplyservice.
2. In water line, casing line and line pipes in industries.
3. In refinery service.
4. In boilers and superheaters.
5. As a pressure duct.
6. Low and high temperature applications.
7. In pipe line of water wells.
8. In automobilefor radiator pipe lines and in fuel lines.
9. In heat exchangers and condensers.
10. In refrigerators and air conditioners.

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MechanicalDrafting
 Duct Layout
 Flanged type fabricated bends.

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MechanicalDrafting
 Duct Layout
 Welded type
fabricated bends.

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REFERENCES:
1. Machine Drawing, K. L. Narayan, NewAge Int. Pub.
2. Mechanical Drafting, S. V. Gosai, Atul Prakashan.
3. A text book of Machine Design, R. S. Khurmi, S. Chand Pub.
MechanicalDrafting