120101h Oxyfuel Equipment

Question 1

Which gas is produced using the air liquefaction process?
a) acetylene
b) oxygen
c) propane
d) hydrogen

Answer 1

b) oxygen

Question 2

Explain why oxygen is dangerous.

Answer 2

Oxygen readily supports combustion and may react violently with some materials.

Question 3

For efficient heating and cutting operations, oxygen must have a minimum purity of:
a) 80%.
b) 93%.
c) 98.6%.
d) 99.5%.

Answer 3

d) 99.5%.

Question 4

Oil or grease in contact with pure oxygen can _____________________.

Answer 4

Oil or grease in contact with pure oxygen can react violently and cause an explosion.

Question 5

Explain how acetylene gas is produced.

Answer 5

by mixing calcium carbide and water in an acetylene generator

Question 6

Define acetylene generator.

Answer 6

A machine used to produce acetylene gas (C2H2) by bringing specific amounts of
granulated calcium carbide and water together under strictly controlled conditions. The vaporous acetylene gas is collected from the generator as it is produced, and it is placed into specially designed cylinders for storage and use.

Question 7

Fill in the blanks with the correct numbers associated with acetylene.
a) The critical pressure is _____kPa (____psi).
b) The maximum safe working pressure is _____kPa (____psi).
c) The explosive limit in air is from_____% to _____%.
d) The explosive limit in pure oxygen is from _____% to _____%.

Answer 7

a) The critical pressure is 193 kPa (28 psi).
b) The maximum safe working pressure is 103 kPa (15 psi).
c) The explosive limit in air is from 2.5% to 80%.
d) The explosive limit in pure oxygen is from 3.0% to 93%.

Question 8

List four (4) fuel gases used for heating and cutting.

Answer 8

a) acetylene
b) propane
c) natural gas
d) propylene

Question 9

List two (2) methods used for storing oxygen

Answer 9

a) They may be stored as a liquid in a cryogenic container (like a thermos bottle).
b) They may be stored as a gas in high-pressure cylinders.

Question 10

Name the safety device used on oxygen cylinders. What is its bursting pressure

Answer 10

It is a metal rupture disc that has a bursting pressure of about 22 000 kPa (3200 psi).

Question 11

Compare the pressures and contents of a full-size oxygen cylinder with a half-size cylinder.

Answer 11

The pressure is the same for both cylinders, but the volume of gas in the half-sized cylinder is half that of the full-size cylinder.

Question 12

Explain why fuel gas cylinders have left-hand threads and non-fuel gas cylinders have right-hand threads.

Answer 12

This is a safety feature that ensures the equipment is not interchanged.

Question 13

Explain why an acetylene cylinder is filled with a porous material.

Answer 13

The porous material prevents a large volume of free acetylene gas from accumulating under high pressure to keep the acetylene stable.

Question 14

State the location and purpose of fusible metal plugs.

Answer 14

Fusible plugs are located on the top and bottom of acetylene cylinders. In case of fire they melt at approximately 100°C (212°F) providing a controlled release of gas which helps to prevent an explosion of the cylinder.

Question 15

State two (2) safety precautions used to prevent acetone loss.

Answer 15

a) Keep acetylene cylinders in a vertical position during storage and use.
b) Do not exceed the draw limit.

Question 16

What should be done before the cylinder valve protective caps are removed?
a) Cylinders should be pressure-tested.
b) Cylinders should be secured.
c) Cylinder valves should be cracked.
d) Equipment should be lubricated and ready for installation.

Answer 16

b) Cylinders should be secured.

Question 17

In order to protect the regulator gauges from being damaged:
a) only use regulators with a pre-set stage.
b) release the adjusting screw before you open the cylinder valve.
c) engage the adjusting screw to allow unrestricted gas flow.
d) use only gauges equipped with heavy-duty Bourdon tubes.

Answer 17

b) release the adjusting screw before you open the cylinder valve.

Question 18

Which type of regulator fitting requires a fibre washer?

Answer 18

a flat-faced fitting found on some acetylene regulator/cylinder valves

Question 19

Why are the cylinder valves cracked before the regulators are attached?

Answer 19

to remove dust or dirt from the cylinder valve

Question 20

How should you check for leaks on oxyfuel equipment?
a) Use an open flame.
b) Use a spark lighter.
c) Spray with anti-spatter solution.
d) Apply a suitable leak detection fluid.

Answer 20

d) Apply a suitable leak detection fluid.

Question 21

When shutting down an oxyfuel outfit you should:
a) close the cylinder valves and bleed the system.
b) close the torch valves and bleed the system.
c) back off the regulator screws and bleed the system.
d) roll up the hoses and remove the welding tip.

Answer 21

a) close the cylinder valves and bleed the system.

Question 22

Regarding shutting down an oxyfuel outfit, answer true or false to the following.

a) Hoses are rolled up.
b) Torch valves are closed.
c) Regulator adjusting screws are disengaged.
d) Cylinder valves are closed.
e) Shutdown is done at the end of each work shift.

Answer 22

All statements (a - e) are true.

Question 23

Why are regulators used for oxyfuel heating and cutting operations?

Answer 23

Regulators reduce source pressure to a working pressure and maintain a constant
delivery pressure.

Question 24

What precaution should be taken when regulators are to be stored for extended
periods of time?

Answer 24

Turn in the working pressure adjusting screw enough to release the spring pressure on the diaphragm to move the valve stem off the valve seat.

Question 25

List the two (2) types of regulators and briefly explain the operation of each type.

Answer 25

a) Single-stage regulators reduce source pressure to working pressure in one step.
b) Two-stage regulators reduce source pressure to working pressure on two steps.

Question 26

What does creep mean as it relates to welding equipment regulators?

Answer 26

Creep is a condition where the high-pressure valve is not seated, so gas leaks into the
low-pressure side and causes an uncontrolled pressure rise in the low-pressure chamber.

Question 27

How would you safely repair an acetylene hose?

Answer 27

Cut out the damaged area and splice using CGA approved fittings of yellow brass, iron or steel.

Question 28

What colour is the oxygen hose?

Answer 28

The oxygen hose is green.

Question 29

Which hose fittings have a left-hand thread?

Answer 29

Fuel gas fittings have a left-hand thread.

Question 30

List two (2) tools that may be used to properly clean a dirty tip.

Answer 30

a) tip cleaners
b) tip drills

Question 31

Label the oxyfuel equipment components in Figure 28.

Answer 31

Figure 30 shows the correctly labelled diagram.

Question 32

Label the gas cylinder components in Figure 29.

Answer 32

Figure 31 shows the correctly labelled diagram.

Question 33

What is the difference between a backfire and a flashback?

Answer 33

A backfire occurs in the mixer and tip. A flashback occurs beyond the mixer into the
hose and regulator on the low-pressure side.

Question 34

List four (4) causes of backfires.

Answer 34

a) too little gas speed
b) obstruction of gas flow
c) loose or faulty connections between the tip and mixer
d) a hot tip

Question 35

List four (4) causes of flashbacks.

Answer 35

a) grossly unequal pressures
b) mildly unequal pressures plus an obstruction of the tip
c) failing to purge the lines
d) faulty manipulation of valves

Question 36

Describe a burnback.

Answer 36

A burnback is combustion that takes place steadily in the tip and mixer of the torch.

Question 37

Why do you purge each line individually on an oxyfuel outfit before lighting the torch?

Answer 37

To prevent flashbacks, you purge the lines of any air or explosive mixture that may be present.

Question 38

When changing heating tips to a different size, why is there a need to rebalance gas pressures?
a) to ensure the tip is free of dirt
b) because the orifice size is different
c) to prevent a burnback
d) to ensure the proper gases are in their respective hoses

Answer 38

b) because the orifice size is different

Question 39

Why should the acetylene torch valve always be set so the flame is above the smoke range?

Answer 39

This ensures that adequate gas flow is maintained and reduces the possibilities of
backfires and burnbacks.

Question 40

Define speed of flame propagation.

Answer 40

This is the speed that a flame travels in premixed gases.