Liquid Flashback Arrestors and Their Role in Fuel Gas Pipelines Discussed

Oxy-acetylene torches and fuel pipelines are used for welding, cutting, heating, and brazing in metal fabrication workshops and several other industrial facilities. The design of these torches has evolved over the years. Today, you will see oxy-acetylene torches in safety-centered designs; still, they can cause serious accidents. Flashback is one of the common causes of accidents in these torches. Backflow, backfire, and sustained backfire are a few other causes. To avoid these, flashback arrestors are used. How do these devices work? Why are they important for any metalworking facility? Read this post to know the answers.

Definitions of Different Fire Discrepancies You Must Be Aware Of

Flashback, backfire, and sustained backfire are a few confusing terms. Knowing their differences would help immensely in keeping the situation under control.

• Backflow: If the gas is operated at high pressure for a long time, it may flow back into the hose through the torch. However, this transversal occurs at low pressure. This may lead to the mixing of gases in the hose, which would cause severe fire or explosion.
• Flashback: This occurs when the gases flowing upstream reverses their flow back to the equipment or hose. This flashback can be caused due to several issues such as ambient operating conditions, improper use of a check valve, and so on. The gas that flows back to the hose may damage it and separate from the pipelines spread in other areas leading to fire and major explosion.
• Backfire and Sustained Backfire: Backfire occurs when the fire flame enters into the torch with a violent sound and fizzles out quickly. The backfire usually sustains for a few seconds. It is not considered a dangerous situation. However, in some conditions, the flame may continue to burn in the nozzle for a long time producing a smoky flame and a whistling sound. If this happens, the users need to immediately close all the valves in the vicinity, else the flame may damage the torch and other torches, too. In most dangerous cases it may lead to a fire.

Going by definition, you can easily identify why flashback is dangerous, and why it needs to be prevented. The next section introduces you to flashback arrestors that can be used to contain the fire in oxy-acetylene torches and acetylene cylinders.

A General Discussion on Flashback Arresters

A flashback arrester or arrestor is a device that helps in stopping the reverse flow of fire in oxy-acetylene torches. Flashback arrestors are of two types – dry and wet flashback arrestors.

• Dry Flashback Arrestors: These devices use dry materials such as ceramic cartridges and sintered metal to stop the reverse flow of the fire through the torch. The dry material is usually powdered and it creates an effective barrier for the fire.
• Liquid Flashback Arrestors: These devices are also known as hydraulic flashback arrestors or wet flashback arrestors and they use liquids like ethylene glycol to reverse the flow of fire. Typically, non-absorbing liquids are considered for the purpose.

Dry flashback arrestors are suited for small applications, while hydraulic flashback arrestors are a common sight in industrial facilities. Hydraulic flashback arrestors are more popular among the two owing to certain advantages they offer. These flashback arrestors are used in gas pipelines, torch inlets, as well as fuel gas piping system regulators to curb fire. The next section introduces you to the working and efficiency of one of the popular flashback arrestors by Rexarc.

An Overview of Rexarc’s Liquid Flashback Arrester Parts and Its Working

Rexarc is one of the leading manufacturers of liquid flashback arresters for oxygen and acetylene applications. They also provide a flashback arrester for acetylene cylinder. They comprise several components, which assure effective fire quenching. The following pointers will help you understand the working of these devices in industrial setups.

• Rexarc’s liquid flashback arrestor (FBA) features the following components:
  • Inlet pipe with check valve
  • Outlet pipe
  • Flow diverter
  • Relief valve
  • FBA liquid
• The gas enters into the equipment through the inlet pipe at in-line pressure.
• The pressure of the gas in the torch or cylinder may vary between 5 and 200 PSI depending on the type of gas used. In typical applications, the pressure of acetylene gas is maintained at 10–15 PSI.
• The gas next passes through the check valve and the flashback fluid. The check valve and flashback fluid both create a double barrier between the high-pressure gas in the cylinder and downline users.
• Next, the gas escapes from the FBA chamber and helps protect the application.
• If a flashback occurs, the flame will enter into the device through the outlet pipe and enter the chamber filled with liquid at high velocity. The fluid quenches the flame and the check valve prevents the fluid from pushing upwards. Thus, the flashback is prevented from reaching the gas in the cylinder.

In addition to this, there is another interesting aspect of this system. The relief valve used in the system doesn’t open fast to relieve the pressure, which was created during the flashback. This valve prevents the systems from over-pressuring during the regular operating conditions. Also, it aids to vent the system during maintenance. These flashback arrestors have been in use for more than 60 years. Would you be interested in knowing how these flashback arrestors work in real? If yes, visit our Youtuve video on flashback arrestors to know more.