Welding B

What is the color and odor of oxygen?

Oxygen is colorless and odorless.

Is oxygen flammable by itself?

No, O2 is not flammable by itself, but it may combine violently with other materials.

How can oxygen be produced?

Oxygen can be produced via air liquefaction, water electrolysis, and chemical processes.

For welding/cutting purpose it is minimum 99.5% pure.

What should you do if your oxygen hose breaks and catches fire?

Stop oxygen flow, stop fuel flow, and extinguish the fire.

What materials should be kept away from oxygen regulators?

Oil or grease should be kept away as they may catch fire or explode.

What is acetylene represented as in chemical form?

Acetylene is represented as C2H2.

What is a notable characteristic of acetylene's odor?

Acetylene is colorless with a strong and irritating odor.

What is the maximum safe pressure for acetylene?

The maximum safe pressure for acetylene is 15 psig.

How is acetylene gas generated?

Acetylene gas is generated by bringing calcium carbide with water.

What are the LEL and UEL percentages for acetylene?

LEL is 2.5% and UEL is 80% in air, 3% and 93% for O2. Acetylene has the widest flammable range.

What factors affect heating/cutting for torch cutting? (4)

-High flame temp

-High flame propagation speed

-Adequate heat content

-Little to no chemical reaction iwth base mental.

Acetylene meets most of these most closely so it’s widely used

Why is acetylene considered unstable?

Acetylene becomes unstable at its critical point at 28psig and 21C. Max safe pressure is 15psig. If acetylene hits the critical point it may autoignite in air.

MAPP Gas (Methylacetylene-Propadiene Stabilized) Adv/Disadv for cutting?

Adv:

• MAPP gas has high BTU and is good for cutting 6” or thicker plates.

• acetylene equipment can usually be used with MAPP gas

Disadv:

• Needs about 2x the volume oxygen compared to acetylene.

Propane (C3H8) Adv and Disadv for cutting:

Adv:

• High BTU for 6” or thicker plate

• Cutting tips interchangeable with nat gas.

Disadv:

• Needs 4.5 times the volume of oxygen compared to acetylene.

Natural Gas (CH3) Adv and Disadv for cutting:

Adv:

• Affordable and available

• Cutting tips interchangeable with propane.

Disadv:

What are the 5 fuel gases most common in the industry for cutting torch operations? Which one has highest flame temps? Which on costs the most? Which one has highest BTU?

Acetylene

• 1470 BTU/ft3

• 3090C Flame Temp (highest)

• Most expensive

MAPP

• 2460 BTU/ft3

• 2871C Flame Temp

• Needs 2x volume O2 compared to acetylene

Propane

• 2498 BTU/ft3 (highest)

• 2526C Flame Temp

• Needs 4.5x volume O2 compared to acetylene.

Propylene

• 2400 BTU/ft3

• 2871C Flame Temp

• Needs 2.6x it’s own volume of O2.

Natural Gas.

• 1000 BTU/ft3

• 2538C Flame Temp

• 2 or 1 volumes of it’s own volume of O2.

How is propylene produced?

-Byproduct of crude oil refining.

What 4 factors do you consider when selecting a fuel gas for cutting?

1. Cost

2. Oxygen needed for combustion

3. Heat Content

4. Flame Temp

What does BTU stand for?

BTU stands for British Thermal Unit.

Why is it important to use the right type of fittings with acetylene?

Using copper or red brass fittings with acetylene can cause an explosion.

What type of cylinder is used to store liquid oxygen?

• A liquid oxygen cylinder is constructed like a thermos bottle. It has a outer and inner vessel.

• Reduces size and weight of container when comparing to gaseous.

• Stored liquified at pressure less than 240psig.

• Liquid draws from inner vessel and passes through outer vessel. Absorbs heat and helps turn it into gaseous state.

What type of cylinder is used to store gaseous oxygen?

• Hot Drawng single piece of hot steel with no girth or longitudinal seams. Bottom is concave and top is hemispherical.

• Top is thicker since it gets threaded for a regulator.

• All connections right hand threads.

• 2 sizes usually: 244ft3 full, 122ft3 half.

• serial number stamped near top.

What is the purpose of a metal rupture disk in oxygen gas cylinders?

It provides controlled relief from extreme pressure due to temperature rise.

What distinguishes the construction of oxygen cylinders compared to acetylene cylinders?

• Oxygen cylinders are high-pressure vessels; acetylene cylinders are designed to operate at lower working pressures.

• Oxygen cylinders have the “metal rupture disk” operating based on pressure and installed in the reg. >3200psig.

• Acetylene cylinders have a “fusible metal plug” based on temperature >100C and is built into the cylinder.

• No draw off limit for oxygen, acetylene has it.

• Acetylene cylinders also use porous material inside.

What is the purpose of a backseating spring and seal in a regulator?

To prevent leaks by sealing against the top of the valve stem.

What is the importance of hydrotesting gas cylinders?

Cylinders are hydrotested to ensure they can safely handle their rated pressure.

Periodically hydrotested at 1.5x working press. Retested after 10 years and then 5 after that.

What should you do if an oxygen cylinder is empty?

Mark it with an MT to indicate it is empty and put it in storage.

What should you do if an acetylene cylinder is empty?

-Ensure the cylinder does not weight less than the stamped weight on shoulder of cylinder. If it weighs less than 40% it means it drew off some acetone. This must be refilled with acetone until the weight is the same.

Why should acetylene cylinders be used in a vertical position?

To prevent acetone from being drawn off.

Old style vs New style acetylene cylinders?

• Older styles used shredded asbestos, balsa wood, portland cement, charcoal porous materials inside, about 75-80% porous.

  • These would be susceptible to crushing on impact.

• New styles use billions of microscopic pores made of “calciun silicate” and are designed to withstand 400psig crushing force.

Why is acetone added into acetylene cylinders?

-Acetone is added up to make up about 40% of volumetric capacity because above 15psig the acetylene is unstable and may ignite. The cylinder is usually stored at pressures much higher than this.

The acetone will absorb the gas into the solution to break it up and keep it dissoved. Acetylene can only stay dissolved in small spaces. If more pressure is applied, the acetylene will stay dissolved even better.

Why do draw off limits exist on acetylene cylinders?

What is the draw off limit?

How can you avoid it?

-To prevent acetone from being drawn.

-Limit is usually cannot be emptied faster than 1/7th of the total volume of the cylinder.

-Draw off may happen with larger tips, you can usually avoid it by manifolding multiple cylinders so each one draws less at a time.

What are the key parts of a typical regulator?

The main parts are spring, diaphragm, and valve/seat.

What does 'regulator creep' refer to? How can it be caused?

It refers to the high pressure side of the reg leaking past the seat, raising pressure above normal.

-Ruptured diaphragm, valve seat contamination

What are the main advantages of using a manifold system?

A manifold system allows for drawing off large volumes of acetylene gas safely without draw off occuring.

Are compressed gas cylinders color coded? Who identifies them?

NO. Identified according to ANSI.

What is the role of flashback arrestors? Where can they be located?

Flashback arrestors extinguish flames and prevent them from traveling back into the equipment.

They can be located at the torch and/or cylinder connections. Preferably both.

What is a common use for heavy-duty cutting torches?

They are used for cutting materials 6” or greater in rough service. Commonly in demolition.

What should be monitored when using cutting torches?

Monitor lag or draglines, excessive slag buildup, and melting of the top edge.

What happens if an acetylene cylinder is drawn off too quickly?

The flame temperature drops and the flame appears pale blue with orange flecks.

What is a two-stage regulator used for?

To reduce pressure first to an intermediate level and then further to a useable level.

Why should you not repair oxyfuel hoses?

Hoses should not be repaired as they are high-pressure and could fail.

What color are fuel gas hoses?

Fuel gas hoses are red with left-hand threads.

What are common types of cutting torch tips?

Common tips include straight, scarfing, gouging, and heavy duty rivet/bolt cutting tips.

What is a characteristic of solid one-piece tips?

They are typically used with acetylene.

Can you mix different fuel gases with the same cutting tips?

No, mixing tips and fuels can destroy the tips.

What is the maximum burst pressure for oxyfuel hoses?

Maximum burst pressure for oxyfuel hoses is 400psig.

What should you do if you detect leaks in a gas system?

Turn off the gas supply immediately and address the leaks before proceeding.

What device is often installed at the torch end of the oxyfuel setup?

Reverse flow check valves are installed to prevent backflow.

How is acetylene stored in the cylinder?

Acetylene gas is dissolved in acetone and the cylinder contains porous material.

What is the purpose of the back pressure check valve in a gas system?

To prevent potential backflow of gas from the torch into the system.

What factor affects the stability of acetylene gas in the cylinder?

The pressure in the vessel affects the absorption of acetylene in acetone.

What do the terms 'LEL' and 'UEL' mean?

LEL stands for Lower Explosive Limit and UEL stands for Upper Explosive Limit.

What is the main function of the regulator when working with gas cylinders?

To control the delivery pressure of gas from the cylinder.

What minimum wall thickness is required for gaseous oxygen cylinders?

The minimum wall thickness is 0.260 inches.

How does one determine the appropriate size of the oxyfuel hose?

The size of the hose is determined based on the flow needed (usually size of the torch tip). Sizes come in 3/16”, 1/4”, 3/8”.

Usually 1/4” is most common.

What happens to acetylene above its critical pressure?

It may break down, release heat, and potentially autoignite.

What is the primary use of the pipe beveler in oxyfuel equipment?

To bevel round pipe in place for welding or piping applications.

What information is typically found on a gas cylinder label?

The identification must conform to ANSI standards.

What essential safety practice should be followed when using regulators at high pressures?

Store regulators with the adjustment screw engaged slightly inward to prevent seat corrosion.

What color and labeling differences exist between fuel gas and oxygen hoses?

Fuel gas hoses are red and have left-hand threads; oxygen hoses are green and have right-hand threads.

What pressure is typically set for acetlyene and oxygen when cutting?

3psig acetylence

30 psig oxygen

What is the function of a one-way check valve in a manifold system?

To prevent gas from flowing back into the cylinder.

What is the primary concern with using large tips on acetylene cylinders?

They may exceed the draw limit and draw acetone. Changing flame temperature and potentially unsafe fuel gas bottle conditions.

What must be adhered to when transporting oxygen or acetylene cylinders?

Always transport in an upright position and secured to prevent tipping.

What reaction does acetylene have when mixed with incompatible materials?

It can form a residue and cause an explosion.

How often should oxygen gaseous cylinders be hydrotested?

Cylinders must be hydrotested every 10 years and then every 5 years following the first retest.

What type of flashback prevention is not relied upon for safety?

Reverse flow check valves should not be used as a replacement for flashback arrestors.

Why is it critical to properly understand the use of each type of cutting torch tip?

Using the wrong tip can lead to inefficiency or damage to the material or equipment.

When using combination weld and cutting torch - explain how the hand valves for fuel and oxygen are set.

There are 3 hand valves. 1 - fuel at torch handle, 2 - oxygen at torch handle, 3 - oxygen at cutting handle

1. Fuel at torch handle is adjusted as typical, usually 1 or 2 turns.

2. Oxygen at torch handle is wide open - this ensure adequate cutting oxygen is delivered

3. Oxygen at cutting handle is adjusted for appropriate preheat oxygen required.

Explain the 2 different types of machine cutting torches.

1. Radiagraph:

   1. Runs on a track to produce straight lines

2. Pipe Beveler:

   1. Used to bevel round pipe in place.

-Always ensure adequate preheat is used

-Adjustments available for both: travel speed, preheater distance, torch angle, torch inclination and machine base distance.

-Never leave a cutting torch unattended

-Monitor lag or draglines and adjust if excessive slag buildup or melting occurs.

Describe the 4 different cutting tip styles:

1. Straight: normal and bevel cuts

2. Scarfing: remove minor imperfections during casting work

3. Gouging: gouging

4. Heavy Duty/Rivet Cutting: Cuts bolt or rivet heads without damage to parent material.

Define how aceylene vs nat gas/propane tips are constructed. Can they be interchanged?

Acetylene - Solid 1 piece

Nat Gas/Propane - 2 Piecem, splined with a cup to anchor the flame.

You cannot mix the tips between acetylene and nat/propane tips. If you use acetylene on a nat/propane tip it will destroy it because the acetylene flame speed is high.

You can interchange propane and natural gas tips unless the manufacturer states otherwise.

Kerf draglines on a properly performed shape cut are:

Perpendicular to plate surface.

What is “Kerf”

width of a cut or width of material that is being removed by a cut.

If your cut is rough and slag is accumulating, what is the likely cause?

Dirty cutting torch tip.

Hose nuts for oxygen vs acetylene

O2:

No groove cut

Right hand thread

Acetylene:

Groove cut on outside

Left hand thread

May have ACET stamped on it.

What is the likely problem if kerf edges melt back together behind cut?

Tip is too large for material thickness

Never light torch using a ___ of oxygen AND acetylene.

Mixture. Always light acetylene on its own first.

What standard must a manifolded acetylene system follow?

CGA Standard (Compressed Gas Association)

What must be ensured when connecting cylinders to the manifolded acetylene system?

Ensure equal pressures across all cylinders, otherwise draw limit may be reached as the cylinders equalize. This can cause a temp rise and potential explosion.

Key type vs Wheel type hand valves on acetylene cylinders

Key type: Needs a T wrench

Wheel type: Can open by hand

Never open the hand valve more than 1 to 1.5 turns of the spindle!

When Oxy acetylene flame feather and cone is equal. The flame is a ___ flame.

2 X flame

Explain how to light off a combination torch and shut it down.

• open combination torch oxygen handle fully first

• Purge both oxygen and fuel gas lines individually- ensures no debris or trace gas

• With preheat oxygen closed, open acetylene 0.5 turn and ignite flame. Creep open acetylene valve more until there’s smoke.

• Begin adding pregeat oxygen via the oxygen torch valve that was closed

• To cut- depress cutting lever.

Shutting it down you want to shut off oxygen first and then fuel.

Explain how to start the acetylene torch cut

• Place torch at starting point and preheat with the inner flame cone about 1/16” away from material surface. Always try to start your cut on a sharp edge. If it’s a solid roundshape, you can also try drilling a hole or use a chisel to nick the material where you want to start your cut.

• When starting point is red hot it means it is over 1600F. At this point you can introduce the cutting oxygen. Keep torch still until you penetrated the material.

• Maintain a 1/16 to 1/8” distance from preheat cones to workpiece. Do not allow flame cones to touch the workpiece.

Define “Drag” when torch cutting

• Amount of Drag is the offset distance between where slag should exit theoretically vs where it actually exits.

• Drag can be expressed as % of the cut thickness (15% would mean that the exit of the cut lags behind the entry point of the cut by a distance equal to 15% of the material thickness).

Define Travel Speed and why it’s important, and the way to tell if you’re going too slow or too fast when cutting.

• Torch travel speed affects the drag in the kerf line.

• Use drag lines to determine your travel speed.

• Slow: ragged kerf because the cutting stream wanders into the plate in irregular fashion

• Fast: slag bubbles up to surface because cutting jet stream cannot blow fully through. This can also happen if the tip is too small or insufficient oxygen pressure.

Explain Torch Inclination, which way do you want it if thin vs thicker material?

• Angle relative to direction of travel.

• Correct torch angle affects travel speed and cut quality

• Thinner material : more forehand inclination

• Thicker material : less inclination, on 3” or thicker you may want slight backhand inclination.

• Shape cutting : no angle at all

Explain 2 ways or piercing holes with the torch cutter to avoid slag getting into the tip:

• Can cause backfire or plug orifices if slag blows back up into tip. 2 methods help avoid this:

  • Still Torch method:

    • Best for small holes in thicker plate.

    • Tip is one size larger than normal for material

    • Set O2 pressure at min 25 psig.

    • Use heavy preheat

    • squeeze lever and RAISE the torch - allows slag to blow clear. Lower tip to continue the cut once fully pierced.

  • Travelling torch method:

    • preferred on materials 1/2” thick or less.

    • Normal pressure

    • Hold torch with slight forehand incline and preheat.

    • once at temp, squeeze cutting lever and slowly advance torch - this allows slag to blow clear. keep travelling until cut is through.

Explain common cutting faults with acetylene torch.

• Examine the kerf lines. This is critical to knowing which variable needs correcting.

  • Dirty tip - rough cut with large slag on bottom

  • Fast ravel speed - slag bubbles to surface and cutting stops

  • Preheat flames too small or too long

  • Oxygen pressure too low or too high

  • Cutting tip too small or too large

  • Unsteady torch movement

  • Improperly executed stop/starts

What are 4 factors in helping determine type of tip to use when cutting with torch?

• Depth of cut = larger tip for deeper cut

• Type of material to be cut

• Condition of material - rust may make it harder

• Type of cut needed: 4 hole preheat is adequate for square cutting but 6 hole versions give a faster and more even preheat.

What are the 2 methods of cutting with acetylene torch (techniques when cutting)

• Across Cut:

  • Hold torch at 90deg to the cut line.

  • Pivot with your free hand, roll your pivot hand as the cut progresses

• Push/Pull:

  • Free hand becomes balance point. Use it to push or pull torch.

Explain the differences between backfire, burnback, flashback.

• Backfire:

  • Flame backs up into the tip. May re-establish with a pop

  • Susceptible at the cutting attachment.

  • Too little gas speed, dirty tip, partial obstructions, loose seat connections, hot tips may cause it.

• Burnback:

  • combustion steadily takes place in the tip and mixer.

  • Susceptible at the cutting attachment.

  • Black smoke, red sparks, screeching sound from tip.

  • Must close both torch valves quickly.

  • Hot tip, tip orifices that are enlarged, faulty torch body seats allowing mixing before mixer.

• Flashback:

  • Hose contains lower pressure and can burn back all the way into the cylinder.

  • Most serious malfunction.

  • Close O2 cylinder, Close Acetylene, Extinguish Fire. (In Order)

  • Grossly unequal pressures, mildly unequal pressures + obstruction, faulty operation (lighting with a mixture of acetylene and oxygen at the same time), failing to purge each line individually before lighting torch. Attempting to light with a mixture will almost certainly cause a flashback.

Explain the differences between Gas Speed vs Flame Propagation speed.

• Gas Speed:

  • speed of premix gases leaving tip

  • lineal ft/sec

• Flame propagation speed:

  • speed of flame travel or spread

  • Usually 17 - 25 ft/s for O2 and Acetylene. If the Gas speed is less than the flame speed, the flame burns back and backfires will occur. If gas speed is much higher, the flame will lift off the nozzle.

Define the 3 types of Flames and how to distinguish them for acetylene torches.

• Flame Types:

  • Carbonizing Flame:

    • Rich in fuel

    • Less flame temp than a neutral flame

    • Will show a feather on the end of the cone of the preheater. This feather determines the amount of excess acetylene. If the feather is the same length as the cone - then it is a 2X flame (because the feather is 1X the cone plus another 1X. If you cannot see the feather then it is X or 1X [same thing]). X means the length of the neutral cone that would be formed if the feather were removed by adding oxygen

  • Neutral Flame:

    • No excess O2 or fuel

    • Flame temp with acetylene and O2 would be 3090C

    • Occurs when the feather disappears into the cone as oxygen is added.

  • Oxidizing Flame:

    • rich in oxygen

    • Flame temps can reach 3470C

    • Cone becomes shorter, sharper, and pale blue.

    • Oxygen in the flame first attacks the carbon in the steel and burns it out, then the iron.

    • When cutting, your are mainly oxidizing the material.