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Orbital welding

Author : Mahesh Ugale

Orbital welding is Automatic Tunguston inert gas welding. It
eliminates chances of manual errors in welding. It produces
identical welds for hundred of times hence accuracy in welding.

Orbital welding was first used in the 1960's when the aerospace
industry recognized the need for a superior joining technique
for aerospace hydraulic lines. A mechanism was developed in
which the arc from a tungsten electrode was rotated around the
tubing weld joint. The arc welding current was regulated with a
control system thus automating the entire process. The result
was a more precision and reliable method than the manual welding
method it replaced. Orbital welding became practical for many
industries in the early 1980's when combination power supply /
control systems were developed that operated from 110 V AC and
were physically small enough to be carried from place to place
on a construction site for multiple in-place welds. Modern day
orbital welding systems offer computer control where welding
parameters for a variety of applications can be stored in memory
and called up when needed for a specific application. The skills
of a certified welder are thus built into the welding system,
producing enormous numbers of identical welds and leaving
significantly less room for error or defects.

Orbital Welding Equipment

In the orbital welding process, tubes / pipes are clamped in
place and an orbital weld head rotates an electrode and electric
arc around the weld joint to make the required weld. An orbital
welding system consists of a power supply and an orbital weld
head.

Power Supply: The power supply / control system supplies and
controls the welding parameters according to the specific weld
program created or recalled from memory. The power supply
provides the control parameters, the arc welding current, the
power to drive the motor in the weld head and switches the
shield gas (es) on / off as necessary.

Weld Head: Orbital weld heads are normally of the enclosed type
and provide an inert atmosphere chamber that surrounds the weld
joint. Standard enclosed orbital weld heads are practical in
welding tube sizes from 1/16 inch (1.6mm) to 6 inches (152mm)
with wall thickness' of up to 0.154 inches (3.9mm) Larger
diameters and wall thickness' can be accommodated with open
style weld heads.

The Physics of the GTAW Process

The orbital welding process uses the Gas Tungsten Arc Welding
process (GTAW) as the source of the electric arc that melts the
base material and forms the weld. In the GTAW process (also
referred to as the Tungsten Inert Gas process - TIG) an electric
arc is established between a Tungsten electrode and the part to
be welded. To start the arc, an RF or high voltage signal
(usually 3.5 to 7 KV) is used to break down (ionize) the
insulating properties of the shield gas and make it electrically
conductive in order to pass through a tiny amount of current. A
capacitor dumps current into this electrical path, which reduces
the arc voltage to a level where the power supply can then
supply current for the arc. The power supply responds to the
demand and provides weld current to keep the arc established.
The metal to be welded is melted by the intense heat of the arc
and fuses together.

Reasons for Using Orbital Welding Equipment

There are many reasons for using orbital welding equipment. The
ability to make high quality, consistent welds repeatedly at a
speed close to the maximum weld speed offer many benefits to the
user:

� Productivity. An orbital welding system will drastically
outperform manual welders, many times paying for the cost of the
orbital equipment in a single job.

� Quality. The quality of a weld created by an orbital welding
system with the correct weld program will be superior to that of
manual welding. In applications such as semiconductor or
pharmaceutical tube welding, orbital welding is the only means
to reach the weld quality requirements.

� Consistency. Once a weld program has been established an
orbital welding system can repeatedly perform the same weld
hundreds of times, eliminating the normal variability,
inconsistencies, errors and defects of manual welding.

� Orbital welding may be used in applications where a tube or
pipe to be welded cannot be rotated or where rotation of the
part is not practical.

� Orbital welding may be used in applications where access space
restrictions limit the physical size of the welding device. Weld
heads may be used in rows of boiler tubing where it would be
difficult for a manual welder to use a welding torch or view the
weld joint.

� Many other reasons exist for the use of orbital equipment over
manual welding. Examples are applications where inspection of
the internal weld is not practical for each weld created. By
making a sample weld coupon that passes certification, the logic
holds that if the sample weld is acceptable, that successive
welds created by an automatic machine with the same input
parameters should also be sound.

Industries and Applications for Orbital Welding

Aerospace: As noted earlier, the aerospace industry was the
first industry to recognize the requirement for orbital welding.
The high-pressure systems of a single plane can have over 1,500
welded joints, all automatically created with orbital equipment.

Boiler Tube: Boiler tube installation and repairs offer a
perfect application for orbital welding. Compact orbital weld
heads can be clamped in place between rows of heat exchanger
tubing where a manual welder would experience severe difficulty
making repeatable welds.

Food, Dairy and Beverage Industries: The food, dairy and
beverage industries require consistent full penetration welds on
all weld joints. Most of these tubing / piping systems have
schedules for cleaning and sterilization in place. For maximum
piping system efficiency the tubing must be as smooth as
possible. Any pit, crevice, crack or incomplete weld joint can
form a place for the fluid inside the tubing to be trapped and
form a bacteria harbor.

Nuclear Piping: The nuclear industry with its severe operating
environment and associated specifications for a high quality
weld has long been an advocate of orbital welding.

Offshore Applications: Sub-sea hydraulic lines use materials
whose properties can be altered during the thermal changes that
are normal with a weld cycle. Hydraulic joints welded with
orbital equipment offer superior corrosion resistance and
mechanical properties.

Pharmaceutical Industry: Pharmaceutical process lines and piping
systems deliver high quality water to their processes. This
requires high quality welds to ensure a source of water from the
tubes that is uncontaminated by bacteria, rust or other
contaminant. Orbital welding ensures full penetration welds with
no overheating occurring that could undermine the corrosion
resistance of the final weld zone.

Semiconductor Industry: The semiconductor industry requires
piping systems with extremely smooth internal surface finish in
order to prevent contaminant buildup on the tubing walls or weld
joints. Once large enough, a build up of particulate, moisture
or contaminant could release and ruin the batch process.

Tube/Pipe Fittings, Valves and Regulators: Hydraulic lines and
liquid and gas delivery systems all require tubing with
connector fittings. Orbital systems provide a means to ensure
high productivity of welding and improved weld quality.
Sometimes the tubing may be welded in place to a valve or
regulator body. Here the orbital weld head provides the ability
to produce high quality welds in applications with restricted
access to the weld joint.

A manual weld taken from an operating plant. This weld has
defects that include lack-of- penetration, misalignment, a huge
crevice, and discoloration due to poor ID purge. This weld would
be considered unacceptable by any standard

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