Any weld professional, should know as much about
cutting steels, as you do about welding steels.

Although some of you may know Ed as an old fart, and think that's Ed on the left, in reality he is the one on the right in his roll as the Canadian training mgr for Linde (Praxair, Union Carbide, ESAB). Also when Ed worked as the weld product mgr for AGA and Airfgas, USA, Ed provided oxy-fuel, manual and mechanized cutting work shops to numerpous North American weld shops in the eighties and nineties. Those work shops, provided comparisons of oxy fuel equipment and the differences between the available fuel gases. Ed has had many articles published on both the weld and cutting processes, and he rewrote the Thermal Cutting Laser- Plasma - Oxy Fuel Cutting Section found in the ASM Handbook. Ninth Edition. 1988.

FUEL GASES WERE AND STILL ARE, SURROUNDED BY AS MUCH SALES BOVINE FECAL MATTER AS MIG GAS MIXES.

When evaluating the many different fuel gases available, companies will frequently look at the fuel gas price rather than on the the variables that influence the application.

Asking the right questions helps solve the choice of the correct fuel gas. There are five global fuel gases that warrant evaluation.
[1] Acetylen.
[2] Propylene.
[3] Propane.
[4] Natural Gas.
[5] Mapp Gas.

There are other fuel gases available, however like MIG welding Gas Mixes, you will find the information has more to do with product marketing spiel than real world BTU benifits with cutting steels

10 CUTTING GAS QUESTIONS DIRECTED AT PROVIDING SOLUTIONS FOR
CUTTING APPLICATIONS, CUTTING PRODUCTION AND SAFETY:

[1] Do the weight conversion of the fuel gas considered. When evaluating a specific fuel gas cost, examine how many cubic feet of gas a pound of the fuel that fuel gas delivers. (see fuel data below).

[2] Oxygen consumption is an important part of cutting costs. Examine the cutting oxygen requirements necessary for the fuel gas selected. Find out how much cubic feet of oxygen will you need for a cubic foot of fuel gas?

[3] With the parts you cut are you concerned with distortion. if distortion is an issue, you will less likely want a a fuel gas that has high heat in it's secondary flame?

[4] Depending on the thickness cut, the cut start times can eat up labor costs. A big influence on high volume cutting production, especially with thick parts, is the start times required to establish the cut. With this in mind you should look at the concentrated heat available in the primary flame.

[5] You will often loose cuts as there is not enough heat available. Cutting those steels over 1 inch, > 25 mm thick, and you may loose the cut because there is not enough heat available in the secondary flame.

[6] Some plants do both oxy fuel cutting and welding. Evaluate the fuel gas for its capability to do both welding and cutting.

[7] Perhaps you have safety concerns about the storage of the fuel gas at your facility. Examine how temperatures affect that fuel gas. Examine also the potential for flash backs, and how certain fuels decompose at relatively low working pressures.

[8] Possibly you will be cutting in a contained area with poor ventilation and you want to know how dangerous the fuel gas is. You should always be concerned about leaks from your equipment and hoses and its very important to be aware of which fuel gases are lighter or heavier than air.

[9] If you don't do a lot of cutting and cheap Nat gas is available in the building, well the fuel gas choice may be a no brainer. However if the nat gas is slowing down your production, perhaps it's time to do a cost analysis for a different fuel gas.

[10} If you are talking to a plasma or laser equipment sales rep, they may be biased in their cutting recommendations for the applications at your facility. Typically these reps and unfortunately too many companies that do cutting are ignorant of what oxygen with specific fuel gases and special cutting tips and operating pressures can achieve.

There are many considerations involved in cutting and I certainly don't intend to cover them all. It's the managers or engineers responsibility to look at the fuel gas data on this and other sites. Its also important to look at the oxy - fuel tip diiferences as the design of the tip will play a large role in cut productivity and quality, As with most processes involved in the weld industry, the weld - cutting management have a responsibility to cut through the sales hype that has immersed this important subject. T

Simply think about the questions you need to ask, and you are on the way to the selection of a cost effective fuel gas that will meet your budget, production and safety requirements.

 

INDUSTRIAL GAS DATA FOR CUTTING STEELS

NATURAL GAS (NG)

[] NATURAL GAS (CH4 METHANE) IS RARELY TOXIC

[] TO USE NATURAL GAS FOR CUTTING HEATING OR BRAZING AT YOUR PLANT YOU WILL NEED NAT GAS PRESSURE BOOSTERS.

[] NG CAUSES ASPHYXIATION OVER 50% VOLUME IN AIR

[] USING NATURAL GAS (NG) INSTEAD OF ACETYLENE, THE NG CAN REDUCE GAS INSTALLATION AND INSURANCE COSTS.

[] FRACTURING OCCURS IF LIQUID NG HAS CONTACT WITH CARBON STEELS.

If you cut steels inside a vessel and a leak occurs,
it's better to use a cutting gas that lighter than air.

[] NATURAL GAS IN CONTRAST TO PROPANE IS LIGHTER THAN AIR SO IF LEAKS OCCUR THE GASES DISSIPATE UPWARDS.

[] NAT GAS CAN BE USED AT HIGHER PRESSURES THAN ACET.

[] LIQUID NATURAL GAS CAN CAUSE FREEZE BURNS

 

A good application for NG, as it's lighter than air.

If Propane or Propylene was used on the above ship application, and hose leaks occurred which are common. The leaking fuel gases would build up in the base of the ship. Combine the fuel gases with the oxy in the atmosphere and wait around for a fitter or welder to ignite a torch or start a weld and bang, we have another preventable catastrophic accident.

[] NATURAL GAS . 1-lb NG = 23.6 cf. // 1kg NG = 1.47 cu m

[] NG FLAME TEMPERATURE WITH OXYGEN 4600oF (2538oC)

[] ACETYLENE (C2H2) FLAME TEMPERATURE WITH OXYGEN 5900oF (3260oC). THIS TEMPERATURE IS FOCUSSED IN THE INNER CONE. THE HEAT CONCENTRATION AND HIGHER TEMPERATURE IS WHY ACETYLENE CUTS FASTER THAN NAT GAS. THE HIGHER TEMP ACETYLENE "STARTS THE CUT SOONER". SO ACETLENE CUTS FINISH QUICKER

NOTE: ALL FUEL GASES CUT AT THE SIMILER CUTTING SPEEDS, AS OXYGEN IS PRIMARILY RESPONSIBLE FOR THE CUT.

[] NATURAL GAS FLAME VELOCITY IN OXY 13.6 ft/sec.

 

Multi-torch Oxy Fuel Cutting = lowest cost.

Propane or Nat Gas multi-torch equipment,
will often offer a much lower cost alternative to
costly plasma cutting equipment

ACETYLENE

 

[] ACETYLENE NORTH AMERICA CYL VALVE COMMERCIAL CGA 300

[] ACETYLENE HAS MOST BTUs CONCENTRATED IN THE INNER FLAME RESULTING IN THE QUICKEST PRE HEAT TIMES. THIS IS ESPECIALLY BENEFICIAL FOR HIGH VOLUME CUTS . REMEMBER THE SOONER YOU START A CUT THE QUICKER YOU FINNISH, THIS IS THE ADVANTAGE ACETYLENE HAS OVER ALL COMMON FUEL GASES. IN TERMS OF THE HEAT OF SECONDARY FLAMES, TAKE A LOOK AT PROPYLENE.

[] AS ACETYLENE HAS LESS HEAT IN THE OUTER FLAME THAN LOWER COST GASES LIKE PROPANE, ACETYLENE IS NOT COST EFFECTIVE FOR CUTTING / HEATING APPLICATIONS WHICH BENEFIT FROM WIDE SPREAD HEAT. HOWEVER, ACETYLENE WHICH IS THE HOTTEST FUEL GAS, CAN REDUCE DISTORTION ON THIN APPLICATIONS TO DUE TO IT'S LOWER HEAT IN THE SECONDARY FLAME.

 

[] ACETYLENE (C2H2) MOLECULAR WEIGHT 26.036

[] HYDROGEN CONTENT IN C2H2 = 7.7%

[] CARBON CONTENT IN C2H2 = 92.3%

[] SPECIFIC GRAVITY GAS C2H2 = 0.9056. NOTE AIR=1

Note how Acetylene concentrates
those BTUs at the tip of the inner flame.

[] 1-lb ACETYLENE = 14.6 cubic feet.
[] 1-lb PROPYLENE = 9.7 cubic feet.



Note: Remember when you work out the cost of oxy - fuel gases that a pound of acetylene provides 50% more gas than a pound of propylene or propane

Note. Acetylene requires less oxy than any other fuel gas.

[] 1-lb C2H2 = 0.4134 cu/m

[] C2H2 AUTO IGNITION TEMP IN AIR 1 atm 101.3kPa = 581oF 305oC

[] C2H2 AUTO IGNITION TEMP OXY 1 atm 101.3kPa = 565oF 296oC

[] C2H2 CRITICAL DENSITY 14.4 lb/CF 231 kg/cum

[] C2H2 CRITICAL TEMPERATURE 95.31oF 35.15oC.

Acetylene / Propylene first choice.

[] ACETYLENE (C2H2) CRITICAL VOLUME 0.00398 CF/mol 0.1128 cum/Kmol

[] C2H2 1-lb = 14.7 CF 1kg = 0.9 cu m 917 CF

[] C2H2 SUBLIMATION POINT 1 atm 101kPa = -119oF -83.8oC.

Remember with fuel gases ask the right questions. Does the application require high BTUs in the secondary flame like propane. Will the application make do with the lower cost, lower BTUs from nat gas, or is the application better served with higher, concentrated inner flame energy available from acet or propylene

[] ACETYLENE HEAT VALUE PRIMARY FLAME 507 Btu/CF
[] ACETYLENE SECONDARY 963 Btu/CF
[] C2H2 Btu/lb = 21387 / C2H2 Btu/CF = 1488.

[] COMPARE NG PRIMARY FLAME WITH OXYGEN 11 Btu / CF 0.4 MJ/cum
[] COMPARE NG SECONDARY FLAME WITH OXYGEN 989 Btu / CF 37 MJ/cum

[] COMPARE PROPANE. PRIMARY FLAME HEAT 255 Btu/CF 10 MJ/cum
[] COMPARE PROPANE OUTER FLAME HEAT 2243 Btu/CF 94 MJ/cum

[] COMPARE PROPYLENE. PRIMARY FLAME HEAT 433 Btu/CF 16 MJ/cum
[] COMPARE PROPYLENE SECONDARY FLAME HEAT 1938 Btu/CF 72 MJ/cum

Working out fuel - oxy gas costs. Look at how much
cuft oxygen is required per lb of fuel gas.

Note the oxy requirements for the different fuel gases. In contrast to acetylene, gases such as propane and propylenes can require approx 200% more oxgen when cutting.


[] C2H2 HEAT VALVE PRIMARY FLAME 19 MJ/cm SECONDARY 36 MJ/cum

[] C2H2 FLAME VELOCITY IN AIR 11 CF/sec 182.9 cm/sec

[] C2H2 FLAME VELOCITY IN OXY 22.7 CF/sec 6.91 m/sec

[] C2H2 1 CF GAS = .069 lb C2H2 (1cu/m GAS = 1.09 lb)

Gas velocity and concentrated high heat in the primary flame
are two of the reasons acetylene is for many applications
well suited for welding and brazing.

[] ACETYLENE (C2H2) FLAME TEMPERATURE WITH OXYGEN
5900oF (3260oC)

[] COMPARE PROPANE PLUS OXYGEN TEMPERATURE 4579oF (2526oC)

[] COMPARE NG FLAME TEMPERATURE WITH OXYGEN 4600oF (2538oC).

Cutting speeds depend on
oxy flow and nozzle design.

Divergent tips provide less cut width and
therefore can provide faster cutting speeds.

 

 

Oxy Acet Cuts:

With correct tips, techniques gas pressures and speed, oxy / acet
multi- torch applications can out perform plasma on
parts thicker than > 1/4 inch, > 6 mm.

[] C2H2 FLAMMABLE LIMITS 68oF 20oC 1 atm AIR 2-82% OXY 2-93%

[] STORE ACETYLENE (C2H2) IN NO FLAME AREA PROTECTED FROM HOT SUN, AWAY FROM OXIDIZING GASES.

[] C2H2 NON TOXIC MILD ANESTHETIC. NOTE. 75% IN AIR CAUSES SUFFOCATION

[] ABOVE 29 psi 200 kPa C2H2 CAN DECOMPOSE - PRODUCE ENERGY . WATCH THAT WORKING PRESSURE, WHAT'S GOOD FOR OXY IS NOT GOOD FOR ACETYLENE

[] MAXIMUM C2H2 CYLINDER PRESSURE NORTH AMERICA 15 psi 103 kPa TYPICALLY SET 5 TO 10 psi.

 

Which flame is carburizing, oxidizing and Neutral?

Setting that cutting, brazing or welding flame, the operator
needs to understand what is neutral, oxidizing or carburizing
flame and how the temperatures change with the different flame types.

THE OXY - ACETYLENE FLAME

 

Acet burning in air 1500F. / Strongly Carburizing 5700F. / Slight Excess 5800F./ Neutral 5900F. / Oxidizing 6000F

The above oxy Acet flame pictures are taken from Ted Jefferson's 17th Edition Welding Encyclopedia. When Ted Died I went to his house to see his widow. The Encyclopedia was no longer being published. His wife gave me the last edition he was working on which was full of the notes where he wanted to make changes.. I informed the president of the AWS that this important book was no longer being published and it's a book that the AWS should publish. Later the AWS reprinted the book. If you like weld history, the encyclopedia is a treat.

[] C2H2 HIGHLY FLAMMABLE AND EXPLOSIVE IF CYLINDER HEATED

[] C2H2 IN EVENT OF FIRE USE CO2 OR POWDER EXTINGUISHERS

[] AVOID C2H2 CONTACT WITH Cu SILVER MERCURY.

Remember the fuel gas gets the cut started.
The hotter the inner flame and more concentrated the
inner flame heat, the faster the cut starts.

The oxygen and tip design are responsible for the cut.

[] USE STEEL OR WROUGHT IRON IN C2H2 PIPE INSTALLATION

[] USE BRASS WITH LESS THAN 70% Cu CONTENT FOR REGULATOR FITTINGS

[] SILVER ALLOYS USED FOR BRAZING MAX CONTENT SILVER 43% Cu 21%

 

PROPANE

[] PROPANE NORTH AMERICA CGA CYL VALVE 510

[] PROPANE DATA C3H8 LIQUID PETROLEUM GAS LPG

[] BEST ALL ROUND "CYLINDER" GAS FOR PREHEAT AND CUTTING PARTS >12 mm.
MORE BTUs IN OUTER FLAME THAN ACETYLENE.

High Btu in Secondary Flame is beneficial
when cutting thick steels..

Gases such as Propane and Propylene all very high BTU in outer flame.

 

Cutting in confined places and tat Gas Gravity is
very important. Always be wary of equipment leaks.

 

[] PROPANE FLAMMABLE LIMITS AIR 68oF 20oC. 1 atm 101.3kPa = 3.4-13.8%

[] PROPANE FLAMMABLE LIMITS OXY 68oF 20oC. 1 atm 101.3kPa = 2.5-55%

[] PROPANE FLAME VELOCITY AIR 1 atm. 101.3kPa = 1.48 ft/sec 0.45 m/sec

[] PROPANE FLAME VELOCITY IN OXY 12.2 ft/sec 3.7 m/sec.

 

 

[] PROPANE HEAVIER THAN AIR 60oF 15.6oC PROPANE = 1.5 AIR = 1

[] PROPANE VAPORIZATION PRESSURE 70oF 21oC = 109.7 psi 756.6 kPa

[] TOTAL HEAT AFTER VAPORIZATION 2498 Btu/CF 104 MJ/cum.

 

[] PROPANE TOTAL HEAT AFTER VAPORIZATION 21800 Btu/lb 51000 KJ/kg

[] PROPANE PLUS OXYGEN TEMPERATURE 4579oF 2526oC

[] PROPANE PRIMARY FLAME HEAT 255 Btu/CF 10 MJ/cum
[] PROPANE OUTER FLAME HEAT 2243 Btu/CF 94 MJ/cum

[] COMPARE NG PRIMARY FLAME WITH OXYGEN 11 Btu / CF 0.4 MJ/cum
[] COMPARE NG SECONDARY FLAME WITH OXYGEN 989 Btu / CF 37 MJ/cum

[] COMPARE PROPYLENE. PRIMARY FLAME HEAT 433 Btu/CF 16 MJ/cum
[] COMPARE PROPYLENE SECONDARY FLAME HEAT 1938 Btu/CF 72 MJ/cum

[] COMPARE ACETYLENE. PRIMARY FLAME HEAT 507 Btu /CF
[] COMPARE ACETYLENE SECONDARY FLAME 963 Btu/CF

[] PROPANE AUTO IGNITION TEMP AIR 1 atm 101.3kPa = 919oF 493oC

[] PROPANE AUTO IGNITION TEMP OXY 1 atm 101.3kPa = 874oF 468oC

[] PROPANE CRITICAL DENSITY 13.5 lb/CF 217 kg/cum

[] PROPANE CRITICAL PRESSURE 616 psi 4246 kPa abs

[] PROPANE CRITICAL TEMPERATURE 206.3oF 96.8oC

[] PROPANE MILD ANESTHETIC CAN CAUSE SUFFOCATION 50% IN AIR

[] PROPANE LIQUID CAN CAUSE FREEZE BURNS

[] DON'T STORE PROPANE & OXIDIZING GASES TOGETHER - LEAKS SEEK LOW LEVELS

[] USE CO2 POWDER EXTINGUISHERS ON FLAME - STORE IN NO FLAME AREA

[] PROPANE IS NON CORROSIVE CAN BE USED WITH MOST METALS.

PROPYLENE

PROPYLENE (C3H6) LP GAS BY PRODUCT OF OIL REFINING. THIS FUEL GAS HAS PROPERTIES IN WHICH A GOOD INNER AND OUTER FLAME HEAT IS GENERATED. SUPERIOR TO PROPANE AND NAT GAS. AND SAFER THAN ACETYLENE. YOU WILL USE MORE OXYGEN WITH THIS GAS THAN ACETYLENE DOES.

 

 

[] PROPYLENE NON TOXIC WITH MILD ANESTHETIC EFFECT

[] DON'T STORE PROPYLENE WITH OXIDIZING GASES

[] AVOID OZONES CHLORINE GAS FLUORINE HYD CHLORIDE

[] AVOID NITROGEN PEROXIDE NEAR PROPYLENE

[] PROPYLENE IN AIR ABOVE 50% VOLUME SUFFOCATION MAY OCCUR

[] PROPYLENE LIQUID CAN CAUSE FREEZE BURNS

[] PROPYLENE IN OXY FLAME TEMPERATURE 5193oF 2867oC

[] PROPYLENE PRIMARY FLAME HEAT 433 Btu/CF 16 MJ/cum
[] PROPYLENE SECONDARY FLAME HEAT 1938 Btu/CF 72 MJ/cum

[] COMPARE NG PRIMARY FLAME WITH OXYGEN 11 Btu / CF 0.4 MJ/cum
[] COMPARE NG SECONDARY FLAME WITH OXYGEN 989 Btu / CF 37 MJ/cum

[] COMPARE PROPANE. PRIMARY FLAME HEAT 255 Btu/CF 10 MJ/cum
[] COMPARE PROPANE OUTER FLAME HEAT 2243 Btu/CF 94 MJ/cum

[] COMPARE ACETYLENE. PRIMARY FLAME HEAT 507 Btu /CF
[] COMPARE ACETYLENE SECONDARY FLAME 963 Btu/CF.

 

[] PROPYLENE FLAME VELOCITY IN OXY 15 ft/sec

[] HEAT VALUE AFTER VAPORIZATION 2371 Btu/CF 88 MJ/cum

[] HEAT VALUE AFTER VAPORIZATION 21000 Btu/lb 49000 KJ/kg

[] PROPYLENE AUTO IGNITION TEMP AIR 1 atm 101.3kPa 851oF 455oC

[] PROPYLENE CRITICAL DENSITY 14.5 lb/CF 232 kg/cum

[] PROPYLENE CRITICAL PRESSURE 670.3 psi 4620 kPa

[] PROPYLENE CRITICAL TEMPERATURE 197.5oF 91.9oC

[] PROPYLENE FLAMMABLE LIMITS AIR 68oF 20oC 1 atm = 2-11%

[] PROPYLENE FLAMMABLE LIMITS OXY 68oF 20oC 1 atm = 2-53%

[] PROPYLENE HEAVIER THAN AIR AIR=1 PROPYLENE = 1.48

[] PROPYLENE = 4.35 lb/GAL 1-lb = 9.7 CF 0.27 cu m

[] PROPYLENE VAPORIZATION PRESSURE 70oF 21oC = 132.8 psi 915.7 kPa

[] MAXIMUM PROPYLENE REGULATOR PRESSURE IS CYLINDER PRESSURE.

MAPP GAS

IF I REMEMBER CORRETLY, THIS FUEL GAS CAME ABOUT BECAUSE DOW CHEMICAL WANTED A SALES SOURCE FOR SOME OF ITS BY PRODUCTS.

THE BOTTOM LINE. I DON'T BELIEVE THE WELD INDUSTRY NEEDS THIS FUEL GAS MIX. MAPP WORKS, BUT IT'S COMPOSITION COMPLEXITY AT THE END OF THE DAY, PROVIDES FEW IF ANY BENEFITS IN CONTRAST THE MUCH LOWER COST PROPANE.

TALKING ABOUT SALEMANSHIP, YOU MAY HAVE HEARD OF A FUEL GAS CALLED FLAMEX. HOW SHOULD I DESCRIBE FLAMEX. TAKE A GALLON OF PROPANE AND MIX IN AN OUNCE OF MUSTARD AND GIVE IT A UNIQUE NAME THAT ENDS WITH AN X. THEN YOU TELL A GULLABLE INDUSTRY YOUR FUEL GAS HAS UNIQUE CUTTING CAPABILITY AND WELD SHOPS SNAP IT UP. WELL THAT SURELY COULD NOT HAPPEN IN THE USA AND CANADA NOW COULD IT?

[] MAPP C3H4 METHYLACETYLENE PROPADIENE

[] MAPP IS STABILIZED WITH PROPANE ISOBUTANE ISOBUTYLENE

[] MAPP 1-lb = 9.06 CF 0.25 cu/ m 1kg = 19.9 CF 0.56 cu m

[] MAPP MOLECULAR WEIGHT 42.3 VAP. HEAT 227 Btu/lb 0.53 MJ/kg

[] MAPP TOTAL HEAT OF COMBUSTION 21700 Btu/lb 50.5 MJ/kg

[] MAPP BOILING RANGE 1 atm 101.3kPa = -36 -4oF / -38 -20oC

[] MAPP FLAME TEMPERATURE IN OXY 5301oF 2927oC.

[] MAPP FLAME VELOCITY 15.4 ft/sec 4.69 m/sec

[] MAPP AUTO IGNITION TEMPERATURE IN AIR 851oF 455oC

[] MAPP FLAMMABLE LIMITS IN OXY 2.5-60%

[] MAPP FLAMMABLE LIMITS IN AIR 2.5-11%

[] MAPP VAPORIZATION PRESSURE 70oF 21oC = 94 psi 645 kPa

[] MAPP SPECIFIC GRAVITY GAS 60oF 15.5oC = 1.48 AIR=1

[] STORAGE EQUIPMENT FOR MAPP SAME AS PROPANE

[] MAPP SERVICE LINES IRON - STEEL ALLOY -

[] DON'T USE Cu CONTAINING MORE THAN 60% Cu

[] REGULATORS TORCH MANIFOLDS VAPORIZERS - USE MAPP APPROVED

 

 

Note on Laser and Oxy Fuel Cut Edges and Scale:

Laser cut surfaces with oxygen assist gas can influence weld quality.

When oxygen is used as the laser assist cutting gas, the oxygen causes the formation iron oxides. The laser oxy assist gas accelerates the formation of oxidation, similar to oxy - fuel cutting. The laser cut surface scale is similar to rust.

Typically the laser cut surface is made up of black magnetite (ferrous oxides). Keep in mind also that carbon can migrate to the laser cut edge. This carbon can increase the carbon content of the future welds. When nitrogen is used as the assist gas, the amount of oxidation is minimal. Oxy assist gas laser cutting provides faster cutting speeds than nitrogen on carbon steels. Nitrogen is used for stainless.

The laser scale is brittle it can be detrimental to the weld and is also a poor surface for paint or coatings.


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