Page 185 - CITS - Welder - Trade Practical

WELDER - CITS

3 Lap joint
4 Angle joint
5 Composite joint
6 Pipe flange joint

7 Y joint
8 Elbow joint
9 Welding of pipe butt joints: Normally joints in pipes
10 And tubes cannot be welded from the inside of the bore.

11 Hence before starting to learn pipe welding, a person should
12 Be proficient in welding in all positions i.e. flat, horizontal,
13 Vertical and overhead.
14 All these positions are used to weld pipes.
15 Pipes welding positions
1G - Pipe weld in flat (roll) position i.e. pipe axis is parallel to the ground.

2G - Pipe weld in horizontal position i.e. pipe axis is perpendicular to the ground.
5G - Pipe weld in flat (fixed) position i.e. pipe axis is parallel to the ground.
6G - Pipe weld in including (fixed) position i.e. pipe axis is including to both horizontal and vertical planes.
During the welding of butt joints the pipe may be

1 Rolled or rotated (1G position)
2 Fixed (2G, 5G and 6G position).
Welding of pipe butt joints by arc can be done in 1G position by a Continuous rotation method and b Segmental
method.
1a Pipe welding by arc (in 1G position) by continuous rotation method: Satisfactory welding of butt joints in
pipes depends upon the correct preparation of pipe ends and careful assembly of the joint to be welded. Ensure
that the bores and root faces are in correct alignment and that the gap is correct.
Clean the edges. Prepare an angle of bevel 35° by gas cutting and filing. A root face 1.5 to 2.5 mm is to be
provided.

Setting the pipes for welding: Tack weld together with 4 small equally spaced tacks. The gap should be equal to
the root face dimension plus 0.75 mm. Support the tacked assembly on V blocks or rollers so that the assembly
can be rolled or rotated with the free hand.
Select a 2.5 mm rutile electrode for 1st run and a 3.15 mm rutile electrode for 2nd run.
Set a current of 70-80A for 1st run and 100-110 for the 2nd run.
Rotate the assembly as welding proceeds. keeping the welding arc within an area between vertical and 10° from
the vertical in the direction of welding.
(Use a helmet type screen).
– Direct the electrode centrally at the root of the joint and in line with the radius of the pipe at the point of welding.
– Strike the arc near the top dead center and hold the arc length as short as possible. Continue to weld as the
pipe is rotated manually at steady speed.
– Deposit first run by weaving the electrode very slightly from root face to root face.
– Adjust the speed of rotation to obtain full fusion of the root faces without excessive penetration.
– Chip out tack weld as they are approached. Do not weld over tacks otherwise loss of penetration at the tacking
points may occur.

168

CITS : C G & M - Welder - Exercise 46