By Tim Heston, Senior Editor
Afull-penetration root pass in an open bevel joint represents the epitome of pipe weld- ing skill, and this applies in the fabrication
of pipe spools; that is, a subassembly of pipes and
fittings welded in pipe shops and then sent into the
field. If the welder deposits metal too far above the
weld pool, it sinks and cools prematurely, so fusion
is incomplete. But if the welder keeps the arc in
front of the weld pool, and at just the right height,
hot metal flows toward the root and, voila! he gets a
full-penetration root pass that should pass muster.
To perform the root pass, an expert welder must
“read” the weld pool carefully and react instantaneously to any changes, and it’s this skill that
piqued Francois Nadeau’s curiosity in the 1980s. At
that time Nadeau headed the welding automation
group of the National Research Council (NRC) of
“This was a period when a lot of vision systems
were being developed,” Nadeau said. “If you went
to the welding tradeshows at the time, you often
saw about 15 companies that were putting together
vision systems for welding automation.” He added
that many of these vision-system companies aren’t
around anymore, mainly because manufacturers
found it more cost-effective to adapt processes to
automation by making weld preparations more
But pipe spool fabrication is different. “It’s not
practical to have a perfect, repeatable prepara-
tion,” Nadeau said. “You’d have to remachine all the
flanges and pipe ends. It’s a delicate operation with
a [weld] preparation that by nature will vary.”
This is where Nadeau and his team saw opportu-
nity. For years pipe welding operations had installed
automated systems for the cover and cap pass, but
they had yet to automate the root pass successfully.
If the fabricator had any automation at all, it re-
quired additional handling between the hand weld-
ing and automated station.
“So we focused on this,” he said, “and developed
a vision system and control strategy that varies the
welding parameters dynamically to control the pen-
etration of the root pass.”
From this came a new pipe welding automa-
tion technology. To commercialize it, Nadeau left
the NRC in 1989 and launched Tecnar Automation,
Saint-Bruno, Quebec, Canada. The company soon
released the first iteration of Rotoweld, a DOS-based
mechanized system with separate root and fill pass
Last year the company released the third iteration of the technology, Rotoweld 3.0, which uses a
custom robot to perform 1G girth welds. The robot
arm performs the root, fill, and cap passes with one
welding gun, though the system still can be configured with multiple processes. For instance, a thick-walled pipe might call for gas metal arc welding
(GMAW) for the root pass and submerged arc welding (SAW) for the fill and cap passes.
Most spool welding jobs rarely consist of only
straight pipe-to-pipe connections, but instead involve
one curved elbow piece, a flange, or other shape that
needs room to spin as the pipe is rotated under the
welding gun. The robot and the rotary positioning
system provide the necessary clearance so the pipe
elbows and similar shapes can spin freely without hitting either the floor or the welding carriage.
Near the end of the robot arm is a vision camera
that focuses on the arc at about a 90-degree angle.
The welding gun approaches the joint at a 45-degree
down-hand angle with an additional 30-degree gun
angle, emulating a downhill pipe weld. The camera
sees heat distribution in the weld pool, which correlates to how metal circulates within it. When the
gap changes, so does the distribution of heat and
the weld pool characteristics. Like a human pipe
welder, the automation reacts by adapting weld parameters on-the-fly.
“It reacts by adjusting the travel speed, wire feed
rate, arc voltage, and oscillation width,” Nadeau
said, “so that everything is kept at the right level in
relation to the weld pool, and it pushes the hot metal
to the bottom.”
The adaptation calls for some complex control al-
gorithms, because one parameter doesn’t necessar-
ily relate in direct proportion to another parameter.
Getting to the root of pipe welding automation
Adaptive welding spurs automation in spool fabrication
In this automated setup, a robot arm performs the root, fill and cap passes of a pipe will, adjusting parameters on-the-fly.
The system continuously analyzes an image of the root weld pool, as recorded by a video camera incorporated into
the end of the robot arm.