Oxyacetylene Welding (OAW)

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Oxyacetylene Welding (OAW)

• The oxyacetylene welding process uses a
  combination of oxygen and acetylene gas to
  provide a high temperature flame.

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Oxyacetylene Welding (OAW)

• OAW is a manual process in which the welder must
  personally control the the torch movement and
  filler rod application
• The term oxyfuel gas welding outfit refers to all
  the equipment needed to weld.
• Cylinders contain oxygen and acetylene gas at
  extremely high pressure.

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Typical Oxyacetylene Welding (OAW) Station
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Oxygen Cylinders

• Oxygen is stored within cylinders of various
  sizes and pressures ranging from 2000- 2640 PSI.
  (Pounds Per square inch)
• Oxygen cylinders are forged from solid armor
  plate steel. No part of the cylinder may be less
  than 1/4 thick.
• Cylinders are then tested to over 3,300 PSI
  using a (NDE) hydrostatic pressure test.

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Oxygen Cylinders

• Cylinders are regularly re-tested using
  hydrostatic (NDE) while in service
• Cylinders are regularly chemically cleaned and
  annealed to relieve jobsite stresses created by
  handling .

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Cylinder Transportation

• Never transport cylinders without the safety caps
  in place
• Never transport with the regulators in place
• Never allow bottles to stand freely. Always chain
  them to a secure cart or some other object that
  cannot be toppled easily.

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Oxygen Cylinders

• Oxygen cylinders incorporate a thin metal
  pressure safety disk made from stainless steel
  and are designed to rupture prior to the cylinder
  becoming damaged by pressure.
• The cylinder valve should always be handled
  carefully

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Pressure Regulators for Cylinders

• Reduce high storage cylinder pressure to lower
  working pressure.
• Most regulators have a gauge for cylinder
  pressure and working pressure.

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Pressure Regulators for Cylinders

• Regulators are shut off when the adjusting screw
  is turn out completely.
• Regulators maintain a constant torch pressure
  although cylinder pressure may vary
• Regulator diaphragms are made of stainless steel

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Pressure Regulators Gauges Using a Bourdon
movement

• Gas entering the gauge fills a Bourdon tube
• As pressure in the semicircular end increases it
  causes the free end of the tube to move outward.
• This movement is transmitted through to a curved
  rack which engages a pinion gear on the pointer
  shaft ultimately showing pressure.

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Regulator Hoses

• Hoses are are fabricated from rubber
• Oxygen hoses are green in color and have right
  hand thread.
• Acetylene hoses are red in color with left hand
  thread.
• Left hand threads can be identified by a grove in
  the body of the nut and it may have ACET
  stamped on it

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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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Acetylene Gas

• Virtually all the acetylene distributed for
  welding and cutting use is created by allowing
  calcium carbide (a man made product) to react
  with water.
• The nice thing about the calcium carbide method
  of producing acetylene is that it can be done on
  almost any scale desired. Placed in
  tightly-sealed cans, calcium carbide keeps
  indefinitely. For years, miners lamps produced
  acetylene by adding water, a drop at a time, to
  lumps of carbide.
• Before acetylene in cylinders became available in
  almost every community of appreciable size
  produced their own gas from calcium carbide.

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Acetylene Cylinders

• Acetylene is stored in cylinders specially
  designed for this purpose only.
• Acetylene is extremely unstable in its pure form
  at pressure above 15 PSI (Pounds per Square Inch)
  
• Acetone is also present within the cylinder to
  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.

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Acetylene Cylinders

• Cylinders are filled with a very porous substance
  monolithic filler to help prevent large pockets
  of pure acetylene form forming
• Cylinders have safety (Fuse) plugs in the top and
  bottom designed to melt at 212 F (100 C)

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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.
• Cylinder valve wrenches should be left in place
  on cylinders that do not have a hand wheel.

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Oxygen and Acetylene Regulator Pressure Settings

• Regulator pressure may vary with different torch
  styles and tip sizes.
• PSI (pounds per square inch) is sometimes shown
  as PSIG (pounds per square inch -gauge)
• Common gauge settings for cutting
• 1/4 material Oxy 30-35psi Acet 3-9 psi
• 1/2 material Oxy 55-85psi Acet 6-12 psi
• 1 material Oxy 110-160psi Acet 7-15 psi
• Check the torch manufactures data for optimum
  pressure settings

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Regulator Pressure Settings

• The maximum safe working pressure for acetylene
  is 15 PSI !

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Typical torch styles

• A small welding torch, with throttle valves
  located at the front end of the handle. Ideally
  suited to sheet metal welding. Can be fitted with
  cutting
• attachment in place of the welding head shown.
  Welding torches of this general design are by far
  the most widely used. They will handle any
  oxyacetylene welding job, can be fitted with
  multiflame (Rosebud) heads for heating
  applications, and accommodate cutting attachments
  that will cut steel 6 in. thick.
• A full-size oxygen cutting torch which has all
  valves located in its rear body. Another style of
  cutting torch, with oxygen valves located at the
  front end of its handle.

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Typical startup procedures

• Verify that equipment visually appears safe IE
  Hose condition, visibility of gauges
• Clean torch orifices with a tip cleaners (a
  small wire gauge file set used to clean slag and
  dirt form the torch tip)
• Crack (or open) cylinder valves slightly allowing
  pressure to enter the regulators slowly
• Opening the cylinder valve quickly will Slam
  the regulator and will cause failure.

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Typical startup procedures

• Never stand directly in the path of a regulator
  when opening the cylinder
• Check for leaks using by listening for Hissing
  or by using a soapy Bubble solution
• Adjust the regulators to the correct operating
  pressure
• Slightly open and close the Oxygen and Acetylene
  valves at the torch head to purge any atmosphere
  from the system.

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Typical startup procedures

• Always use a flint and steel spark lighter to
  light the oxygen acetylene flame.
• Never use a butane lighter to light the flame

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Flame Settings

• There are three distinct types of oxy-acetylene
  flames, usually termed
• Neutral
• Carburizing (or excess acetylene)
• Oxidizing (or excess oxygen )
• The type of flame produced depends upon the ratio
  of oxygen to acetylene in the gas mixture which
  leaves the torch tip.

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Pure Acetylene and Carburizing Flame profiles
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Neutral and Oxidizing Flame Profiles
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Flame definition

• The neutral flame (Fig. 4-1) is produced when the
  ratio of oxygen to acetylene, in the mixture
  leaving the torch, is almost exactly one-to-one.
  Its termed neutral because it will usually
  have no chemical effect on the metal being
  welded. It will not oxidize the weld metal it
  will not cause an increase in the carbon content
  of the weld metal.
• The excess acetylene flame (Fig. 4-2), as its
  name implies, is created when the proportion of
  acetylene in the mixture is higher than that
  required to produce the neutral flame. Used on
  steel, it will cause an increase in the carbon
  content of the weld metal.
• The oxidizing flame (Fig. 4-3) results from
  burning a mixture which contains more oxygen than
  required for a neutral flame. It will oxidize or
  burn some of the metal being welded.

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Quiz time

• The regulator diaphragm is often made from
  _______?
• A reinforced rubber
• B malleable iron
• C tempered aluminum
• D stainless steel

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Quiz time

• The hose nuts for oxygen and acetylene differ
  greatly, because the acetylene hose nut has.
• A a left hand thread.
• B has a grove cut around it. C may have
  ACET stamped on it.
• D All of the above.

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Quiz time

• An oxygen cylinder must be able to withstand a
  ________ pressure of 3300 psi (22753 kPa) to be
  qualified for service. A atmospheric
• B hydrostatic
• C hydroscopic
• D vapor

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Quiz time

• Why is the area above 15 psig often marked with a
  red band on a acetylene low pressure regulator ?
• Answer
• Acetylene pressure above 15 psig is unstable and
  should not be used

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Quiz time

• True or False ?
• A flint and steel spark lighter is the generally
  used to light the oxyacetylene flame.
• Answer True

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Quiz time

• Acetylene cylinder fuse plugs melt at a
  temperature of ________ F or 100C
• Answer
• 212F

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Quiz time

• What is the maximum safe working gauge pressure
  for acetylene gas?
• A 8 psig (55 kPa)
• B 15 psig (103 kPa)
• C 22 psig (152 kPa)
• D 30 psig (207 kPa)

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Quiz time

• The color of and oxygen hose on a oxyacetylene
  welding outfit is ______?
• Answer
• Green

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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

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Quiz time

• True or False ?
• The regulator is closed when the adjusting screw
  is turned out.
• Answer True

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Quiz time

• The color of and acetylene oxygen hose on a
  oxyacetylene welding outfit is ______?
• Answer
• Red

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Quiz time

• No part of an oxygen cylinder walls may be
  thinner than _______?
• A 1/4in (6.4 mm)
• B 3/8in (9.5 mm)
• C 3/16in (4.8 mm)
• D 7/32in (5.6 mm)

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Quiz time

• To prevent the occurrence of flashbacks, a
  ________ should be installed between either the
  torch and hoses or regulators and hoses.
• A a two way check valve.
• B flame screen.
• C flashback arrestor.
• D three way check valve.

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Quiz time

• What type of safety device is used on a acetylene
  cylinder.
• A A spring loaded plug
• B A pressure safety disk
• C A fusible plug
• D A check valve

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Quiz time

• Mixing _______ and water will produce acetylene
  gas.
• A calcium carbide
• B potassium carbonate
• C carbon dioxide
• D acetylene carbide

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Modern WeldingYork County School of Technology