What do Hose Colors Mean When Welding?

I reme,ber the first time I had a torch in my hands. I turned on the gas, struck some sparks and a little blue flame slickered into life. Magic. But how did that happen. What was coming from those tanks. And what did these colors mean? They came in a variety of colors, and I did not know if that was just for decoration or if there was some reason for those particular blacks, reds, and greens.

After doing some research, I discovered that the colors of the hoses when welding were actually very important. It was not just for decoration. Knowing which hoses contained particular gases was critically important to doing the job right, and it could even be a matter of personal safety. Each type of welding requires special gas. In the US, hoses for acetylene, propane and other gases used as fuel must be red, and oxygen must be green. In addition to the differing colors, the red fuel hoses have a left-hand thread, and the green oxygen hoses have a right-hand thread. Inert gases, which are used for “shielding” in some types of welding, are black. It is very important to remember that these colors can vary in different countries.

This article mainly deals with the color scheme for welding gases in the US.

Hoses for welding gases many times come in pairs for fuel and oxygen. However, just because the outside of the hoses may be attached as a pair to help keep your work area organized, they are still separate hoses. This keeps the different gases from mixing. It is always very important that the proper gas goes into the proper hose. Again, it is red for the fuel in the US and green for the oxygen. The hose for the inert gas is in black. 


Spark welding by Chetan Bisariya, on Flickr
Spark welding” (CC BY 2.0) by Chetan Bisariya

The oldest and simplest type of welding is called Oxy-fuel welding. This type has been in use since the early 1900s. At that time oxygen was not used to increase the flame’s temperature, so there was no need to be concerned about different colors of hoses. As they name implies, oxy-fuel welding uses acetylene or other types of flammable gas as fuel, which is found in the red hose. In addition to being less efficient than other type of welding, oxy-fuel welding is more dangerous than more modern varients. The heat in oxy-fuel welding is produced by burning acetylene or other flammable gas for fuel, and is the only type of welding which uses an open flame. Currently, although it is still used in some places, oxy-fuel welding is utilized far less frequently than in the past. Although industry has largely given up on oxy-fuel welding, hobbyists are much more likely to still use this simpler and cheaper form of welding. Oxygen, which is blended with the fuel gas to increase heat, has green hoses in the US.

Largely due to the dangers from oxy-fuel’s open flame, commercial welders now mainly use the different types of arc welding. Rather than the open flame used in oxy-fuel welding, the different type of arc welding use electricity which travels through an electrode to heat the base metal being welded.

Arc Welding

Arc welding has replaced gas in popularity for industrial and commercial processes. This is due to its comparative safety, improved precision and the ability to properly weld many types of metals. While the electric arc welding has the advantages of safety and a more stable heat source, it requires using an additional gas source.

A number of different gases are used as “shielding” gases in industrial environments. The purpose of shielding gas is to prevent exposure of the molten metal to various substances in the atmosphere which would cause it to oxidize and weaken/damage the weld.

Shielding gases are either inert of active gases. Inert gases have no effect, or reaction to, the welding process. They only displace the air surrounding the weld which might have contaminated the new weld. Argon and helium are the best-known inert gases used for welding.

Active gases, on the other hand, do affect the welding process. Carbon dioxide, oxygen, nitrogen and hydrogen are well-know active shield gases. These different active gases have different effects, depending on the material being welded. For example, certain active gases may become slightly electrically conductive. This will raise the arc voltage which increases penetration, effecting how the molten metal is deposited. Another way the active gases increase penetration is by sometimes breaking the surface tension of the molten metal. This allows the weld to flow or flatten slightly, which allows the metal to be deposited correctly. Many types of welding use a combination of inert and active shielding gases.

Whether they are inert or active, all shielding gases except for oxygen will be found in black hoses.  

SMAW – (Shielded Metal Arc Welding)

The simplest type of arc welding is usually called Shielded Metal Arc Welding or SMAW. It is also frequently referred to as ‘Stick” welding. The welding stick uses electric current to create an electric arc between the stick and the metals to be joined. In SMAW welding the electrode is covered with inert materials that vaporize from the heat.

The shielding gases used for Shielded Metal Arc Welding are created as the electrode melts. We include it here for completeness but you won’t need to worry about gas lines for SMAW.

MIG (Metal Inert Gas) Welding or GMAW (Gas Metal Arc Welding)

MIG (Metal Inert Gas) sometimes known as GMAW (Gas Metal Arc) uses an center fed wire shielded by gas that is consumed by the heat it creates. MIG welding is considered to be one of the easier forms of arc welding to learn and the equipment is usually less expensive than the other types of arc welding(stick welding reigns supreme for cheapness). These are many reasons why it is most often preferred by everyone from amateurs to professionals.

  • Ease of use to quality of result
  • Very gental learning curve
  • Relatively cheap hardware

100% argon,is usually involved in some way for shielding. In some cases, various combinations that may include the inert gases of argon or helium, with active gases of carbon dioxide, magnesium or titanium that can be used for shielding. Like all other shielding gases, they will be in the black hoses. Your choice of shielding gases is determined by the type of metal being welded.

TIG (Tungsten Inert Gas) or GTAW (Gas Tungsten Arc Welding)

TIG welding by humbert15, on Flickr
TIG welding” (CC BY 2.0) by humbert15

Tungsten Inert Gas, usually abbreviated TIG welding or Gas Tungsten Arc Welding (GTAW) is another important type of arc welding. The type of electrode used for TIG produces the necessary heat by using a non-consumable electrode made of tungsten. TIG welding can be used for the highest quality work and it provides a superior finish. This is particularly useful for delicate projects. However, it is one of the most difficult types of welding to learn and perform, so it can only be used by experts. For shielding, the inert gases of argon and helium are used.

FCAW (Flux-Cored Arc Welding)

If you want to avoid the cost of shielding gases and the need for one more hose to keep track of, Flux-Cored Arc Welding (FCAW) might be your choice for arc welding. FCAW is very similar to the MIG or GMAW process. Because FCAW uses a special tubular wire filled with flux for protection, shielding gas is not always needed and you may not need the black hose. This type of welding is also known for being very inexpensive and easy to learn. The lack of needing shielding gas makes FCAW the best choice for working outdoors, since there is no shield gas to blow away in the wind.

However, as they say, nothing is perfect. While self-shielded FCAW remains the obvious choice for outdoors, gas-shielded FCAW is often used inside to improve the weld quality. The most frequently used shield gas for FCAW is carbon dioxide. FCAW also has a number of limitations regarding what metals it can be used for and the results might not look as nice as those from other welding processes. So, do not throw out your black hose.

Colors Can Differ In Other Countries 

Now that you know the proper colors for welding hoses in the US, this may all seem simple. However, those colors are not always the same in different countries. In the UK, red is also the color for the fuel gases of acetylene and hydrogen. When LiquifiedPetroleum Gas (LPG) fuel, such as propane, is used the fuel hose should be orange. This indicates that the hose is compatible with LPG. LPG will damage an incompatible hose. This includes most acetylene hoses.

Additionally, in the UK blue hoses are for oxygen. Another potential source of confusion in the UK is the fact that oxygen hoses may also be black, particularly older equipment. When using this older equipment, the best way to differentiate between oxygen and shielding gases would be to put some blue tapes around the ends on the hose, and maybe one more piece in the middle for good measure.

It is always important to remember that these color codes are supposed to be accurate. Unfortunately, there may be instances when hoses are hooked up to the wrong gas supplies, leading to potentially serious problems. Never just assume they are correct and be sure to check every hose before getting started.

Welding Gas Tank Colors

Although welding gas cylinders are supposed to be certain colors, they are far less uniform than the colors of gas hoses. This is particularly true between different countries This makes checking the contents of your gas cylinders even more important than checking your hoses. Some gas tanks even have a disclaimer on them warning you not to assume the color is accurate, and just read the printed label, instead. So, the only safe way to determine what gas is in the cylinder would be to follow this suggestion and read. The actual rules, such as they are, vary greatly. For example, oxygen is sometimes said to be green, but you might see it in any color or even just gray. Acetylene is often said to be red, but it may be purple, blue, gray or many other colors.

Pressure Regulators

Gauges and Valves by kevingessner, on Flickr
Gauges and Valves” (CC BY 2.0) by kevingessner

As the name implies, a pressure regulator is designed to control the pressure of gases, most importantly those used in oxyfuel welding. One example of its absolute necessity is the fact that the pressure of acetylene gas in the tank is typically more than seven time as great as that in the torch. You do the math and figure out how much danger you might be in without a good pressure regulator.

The first way to determine what type of regulator is to determine whether it is for flammable or non-flammable gas. The screw threads on the valves of flammable gas regulators like acetylene or propane should have left-hand threads. One the other hand, (pun intended) the regulators for non-flammable gases like argon of carbon dioxide have right hand threads.

However, just determining whether your regulator is for flammable or non-flammable gas is not enough. There are several different types of pressure regulators, designed for different gases. It is very important to be using the correct regulator. For example, while acetylene and propane gases are both fuel, propane gas will corrode the internal components of an acetylene regulator, almost certainly leading to leakage and failure.

One Quick Note about Flashback Arrestors

A flashback arrestor, also known as flash arrestor, could become one of the most important pieces of equipment in your welding kit. Particularly when you are using an oxy-fuel welder. The flashback arrestor, which is installed near the pressure regulator, is a safety device that is designed to stop a flashback or reverse flow of gas. If a flame would get into a pressurized oxygen tank, your welding career may be short and unpleasant. At the very least, an explosion could seriously damage or destroy your equipment.


Always check with your local welding shop if you are confused. They should be able to test your equipment and get you all sorted out.


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