DH: Downward Welding with High-
Cellulose Electrodes Is Fastest in Root
Pass Welding
In the construction of cross-field pipelines, the highly
efficient spread method is used worldwide, in which a
series of combined operations proceed continuously in a
certain order at a constant speed: leveling the land,
ditching, placing the pipe, machining, welding,
inspecting, coating, and burying the pipe. In this case,
root pass welding efficiency is believed to be a key
factor that determines how fast a pipeline is constructed.
High-cellulose electrodes offer superior welding speeds
as shown in
. This is the main reason for thepredominant use of high-cellulose electrodes.
However, the weld metal of high-cellulose electrodes
contains higher amounts of diffusible hydrogen than that
of low-hydrogen electrodes.
As the content of diffusible hydrogen increases, the
weld metal becomes more susceptible to cold cracking.
In addition, high-cellulose weld metals contain more
oxygen than low-hydrogen weld metals. Because of its
higher oxygen content, the high-cellulose weld metal
exhibits lower impact values compared with the lowhydrogen
weld metal at low temperatures
Therefore, the DH procedure is very useful
particularly in comparatively low-strength, thin-section
pipes for which the impact requirement is not strict and
the crack susceptibility is not high. With this procedure,
stricter controls of preheating and interpass temperatures
are needed to prevent cold cracking than with the
procedures using low-hydrogen electrodes.
Dear all,
What r advantages & dis-advantages of cellulose electrodes.
Pl. reply.
psp
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K.Muzip ur Rahuman.
QA/QC Coordinator.
BLNG - PROJECTS
Adinin Works Engg.
Brunei
Mob;006737170703
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