The document discusses the process of welding pipes for oil and gas pipelines. It begins with an introduction stating that welding is crucial for constructing pipelines and connects pipes to form a conduit. It then describes the uphill and downhill welding methods, with downhill being more common for thinner pipes. The main steps of pipeline welding are outlined as laying the initial root bead, adding a hot pass bead for reinforcement, and then filler and cap beads to complete the weld. Semi-automatic welding is also mentioned as using a wire electrode and inert gas for thicker pipes.
3. Introduction
• Welding is the pivotal operation in the
construction of a pipeline.
• The technique of welding pipes to form an
integral conduit for oil and gas transmission.
• The time taken for completion of the pipeline
directly depends on the speed at which the
welding crew works.
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4. Welding method
• The methods of the pipe depends on the
direction of welding in the vertical plane
established by the pipe ends.
• The two methods are i) Vertical up or uphill
ii) Vertical down or down hill
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5. i) Uphill method
• This weld is made with the arc progressing
from bottom towards top. Welder makes
settings of voltage and current on the welding
machine so that he can able to increase &
decrease the current rapidly.
• There by increasing the welding current &
deposition rate to achieve good penetration.
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7. ii) Downhill method
• Welding is vertically down. Welder has to
maintain the proper angle between the
electrode and the metal.
• It utilize higher welding current and faster
welding speeds is advantageous for pipes with
thickness of ½ inch.
• Majority of the pipelines have thickness of less
than ½ inch , so downhill technique is
commonly used.
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9. Steps involved in pipeline welding :
Root or Stringer bead : Once the alignment
has been completed , the joint is ready for initial
weld.
• The initial weld is known as root or stringer
bead. It is the most important bead of the pipe
weld.
• Two welders work on opposite sides of the
pipe , each is responsible for welding portion.
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10. • The pressure on the internal clamp is to
maintain untill root bead to completed. The
clamp is then carefully released & withdraw.
• In case of external clamp being used, the
clamp can be removed after the root bead is
50% completed.
• For pipe diameter 8” or less, one welder may
be used.
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11. Hot Pass ( higher weld currents ) :
The hot pass bead follows the root bead.
Normally a second crew follows behind the
root bead crew.
• The hot pass weld before the stringer weld
has cooled & it prevent the cracking of
stringer bead .
• The stringer bead is cleaned thoroughly before
the hot pass is applied.
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12. Filler and cap beads :
Proper cleaning of slag, scale and dirt after
application of each bead is essential for
obtaining high quality weld.
• Following completion of stringer and hot pass
beads, another welding crew takes over.
• They build on the another material already in
place. These additional beads are known as
‘Filler beads’.
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14. Semi automatic welding :
• It uses bare wire electrode shielded by an
inert gas, usually carbondioxide.
• The arc heats the pipe and melts the electrode
which provides filler metal for joint.
• Apparatus consist of spool of coiled wire, a
pair of driving rolls, control switch & gas
supply.
• It is favoured for heavy-walled metals.
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