Welding 10 - Oxy-Fuel Welding Safety
Oxy-Fuel Welding Safety - Objective
Recognize hazards associated with oxy-acetylene welding equipment (i.e.,
tanks, hoses, gauges) and take the necessary measures to avoid unintentional
injuries, including those caused by flashback and backfire
The oxyacetylene
welding process uses
a combination of
oxygen and acetylene
gas to provide a high
temperature flame.
Oxyacetylene Welding (OAW) Outfit
The term oxyacetylene gas-welding outfit refers to all the equipment needed to
weld.
Typical Oxyacetylene
Welding (OAW) Station
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Quiz Time
In your own words describe the objective for this unit.
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Oxygen Cylinders
Oxygen is much more dangerous than many
people believe. We generally encounter oxygen
as a gas and in this state it is colorless,
odorless, and tasteless. Oxygen will not
explode or burn, however oxygen increases
the flammability of almost everything.
Oxygen will also cause anything that is
burning to burn hotter and faster. Fires in
atmospheres enriched oxygen are very hard to
extinguish, and these fires will spread rapidly.
The normal oxygen content in air is around 21
percent but at slightly higher oxygen
concentrations, for example 25 percent,
combustible materials, including clothing
fabrics, ignite more easily and burn much
faster. Nearly all materials including textiles,
rubber and even metals will burn vigorously in
oxygen
Oxygen is not the same thing as air. Pure oxygen will react with materials like steel
and oil in a completely different way than air. Oxygen is very reactive. Pure oxygen,
at high pressure, such as from a cylinder, can react violently with common materials
such as oil and steel. For example oil may catch fire spontaneously and when
exposed to pressurized oxygen and contained, it may explode.
See YouTube video of steel wool burning in an enhance oxygen environment.
http://supporting-paa.wikispaces.com/Oxygen+-+steel+cutting
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Oxygen cylinders are filled to an extremely high pressure. Oxygen is stored within
cylinders of various sizes and pressures ranging from 2000-2640 PSI. (Pounds Per
square inch) In order to accommodate these extreme pressures, oxygen cylinders
are forged from solid armor plate steel. No part of the cylinder may be less than
6.35mm (1/4”) thick
Under normal operating conditions
pressurized gas cylinders are quite
safe, but when a gas cylinder is
inadvertently exposed to fire or
high temperatures. The pressure
inside the cylinder will increase
dramatically, leading to the
possibility of a violent explosion.
Pressure-relief devices are
installed on most cylinders to
prevent the rupture of the cylinder.
Oxygen cylinders incorporate a thin metal
“pressure safety disk” made from stainless steel.
This disk is called a rupture disk. These disks are
designed to rupture prior to the cylinder becoming
damaged by an extreme increase in pressure. Care
should be taken when handling and storing
cylinders to prevent damage to the pressure-relief
devices.
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Quiz Time
The type of safety device is used on a oxygen cylinder.
a. A fusible plug
b. A check valve
c. A pressure safety disk
d. A spring-loaded plug
A slight increase in the percentage of oxygen in air will result in
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Mixing Oil and pressurized oxygen may result in an __________________.
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Gas Cylinder Transportation
Never transport cylinders
without the safety caps in
place
Cylinder caps must be securely in place when
transporting cylinders.
Always chain cylinders to a secure cart or some other object
that cannot be toppled easily. When unsecured, and
uncapped cylinders are knocked over and the cylinder valve
may break releasing and high-pressure gas. Damaged
cylinders can become uncontrolled rockets or pinwheels
Rocketing cylinders have caused severe injury and damage.
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Quiz Time
Failure to transport gas cylinders safely may cause
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Pressure Regulators for Cylinders
Pressure regulators for cylinders reduce high cylinder pressure to lower working
pressure. Most regulators have two gauges.
One gauge shows the
cylinder pressure and the
second gauge shows the
working pressure (line
pressure)
Regulators are shut off
when the adjusting screw
is turned out completely.
Regulators maintain a
constant torch pressure
even when cylinder
pressure vary.
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Oxyacetylene Regulator Hoses
Hoses are fabricated from
nylon mesh sandwiched
between two rubber tubes.
Oxygen hoses are green in
color and have right hand
thread.
Acetylene hoses are red in
color with left hand thread.
Acetylene (fuel) gas connections
have left hand threads Left hand
threads can be identified by a
grove in the body of the nut
Oxygen gas fittings have right hand
threads. These fittings do not have a
groove in the body of the nut
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Quiz Time
The hose nuts for oxygen and acetylene differ greatly, because the acetylene hose
nut has:
a. a right hand thread.
b. a grove cut around it.
c. the words “Fuel Gas” stamped on it.
d. all of the above.
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Check Valves & Flashback Arrestors
Check valves allow gas flow in
one direction only
Flashback arrestors are designed to eliminate the
possibility of an explosion at the cylinder.
Combination Check/ Flashback Valves
can be placed at the torch or regulator.
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Victor Torch Safety YouTube video
Some manufactuers of oxyacetylene torches have fashback arrestors built into the
handle
Quiz Time
Describe the purpose of an oxyacetylene check valve.
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Describe the purpose of an oxyacetylene flashback arrestor.
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Calcium Carbide
Calcium carbide mixed with water is
used to produce virtually all acetylene
gas..
For many years, miners’
lamps produced
acetylene by adding
water, a drop at a time, to
lumps of carbide.
Acetylene mixed with
oxygen produces the
hottest flame for welding
and cutting.
Unfortunately, acetylene
gas is highly volatile, and
it is very unstable.
Acetylene, which is not
stored in an approved
cylinder, is extremely
unstable at pressures
above 15 PSI (Pounds per
Square Inch)
If acetylene gas is handled improperly it may explode!
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Quiz Time
Acetylene, which is not stored in an approved cylinder, is extremely unstable at
pressures above ________PSI.
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Acetylene Cylinders
Pressurized acetylene is
stored in cylinders
specially designed to
safely store the gas.
Acetylene tanks produced
before 1984 often
incorporated small
amounts of asbestos, to
add stability without
flammability.
Acetylene cylinders are
filled with a very porous
substance and a solvent
called acetone. The filler
and the acetone absorb
and stabilize the
acetylene.
Acetylene cylinders
should always be stored
in the upright position to
prevent the acetone form
escaping thus causing the
acetylene to become
unstable.
Acetylene
Cylinder
Label
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Acetylene cylinders are protected
from explosion by fusible metal
plugs. These fusible plugs are
designed to melt at 212° F (100
°C).
Fusible plugs are located on top and
bottom of the cylinder. These devices are
an integral part of the cylinder, rather
than being installed in the cylinder valve.
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Some small acetylene
cylinders are equipped
with fusible plugs in the
valve body.
Acetylene Valves Acetylene cylinder shut off valves should only be opened 1/4 to
1/2 turn. This will allow the cylinder to be closed quickly in case of fire.
Oxygen and Acetylene
Regulator Pressure
Settings
Regulator recommended
pressure varies with
different torch styles and
tip sizes. Always be sure
to check the torch
manufactures data for
optimum pressure
settings.
Regulator Pressure
Settings The maximum safe
working pressure for
acetylene is 15 PSI!
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Quiz Time
Acetone helps to absorb and _____________________________ acetylene.
The device that protects an acetylene cylinder from explosion is called
______________________.
Why should acetylene cylinders only be opened ¼ to ½ turn?
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Why is the area above 15 psi often marked with a red band on an acetylene pressure
regulator?
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Further Reading
http://www.aws.org/educators/Library/0000/000631.ppt.
http://www.ccohs.ca/oshanswers/chemicals/compressed/compress.html
http://www.airproducts.com/~/media/Files/PDF/company/safetygram-15.pdf
http://www.victortechnologies.com/index.php/victor/breaking-news/552.html
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