Fundamentals of Transitioning Inline Deflagration to Detonation

In the realm of combustion processes, an in-line deflagration is an accelerated flame within a pipe that moves through a flammable mixture along the axis of the pipe. This type of explosion propagates at subsonic velocity, a trait that differentiates it from a detonation, which travels faster than the speed of sound.

The in-line deflagration can potentially develop into an in-line detonation, a process known as Deflagration to Detonation Transition (DDT). This transition, occurring in a spatially limited area, is influenced by factors such as operating pressure, operating temperature, pipe diameter, pipe configuration, test gas, and explosion group. The position of this transition zone can be expressed as an L/D ratio, where L is the distance between the ignition source and the installation location of the flame arrester, and D is the pipe diameter.

The international standards defining these combustion processes for flame arresters in in-line deflagrations include ISO 16852 and EN 12874. These standards specify testing methods and performance requirements for flame arresters under deflagration conditions.

In-line deflagration flame arresters play a crucial role in preventing the propagation of deflagrations and stable detonations. These devices must not be installed too far from the ignition source to avoid being subject to a detonation due to a long starting distance. The allowable L/D for in-line deflagration flame arresters is stated in the manufacturers' manual of the flame arrester.

One such manufacturer is PROTEGO, a company that offers PROTEGO® In-line flame arresters. These devices protect against deflagration and stable or unstable detonations in pipes. Brad Luckman, the Senior Vice President of Global Sales at PROTEGO, leads the development of technical sales teams and shapes the company's worldwide sales and marketing strategy. He has deep expertise in process safety applications across various industries.

Figure 1 represents the Deflagration to Detonation Transition (DDT) and its effect on velocity and pressure during the cycle of a deflagration-to-detonation event along a length of pipe. This figure provides a visual representation of the transition from a deflagration to a detonation, a process that can be dangerous if not controlled.

It's essential to understand the mechanics of in-line deflagrations and the role of flame arresters in preventing their propagation. With the right knowledge and the right tools, we can ensure safety in various industries where these phenomena occur.