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Flame arrester – deflagration and detonation

Posted On : Wednesday 13th June

Elmac Technologies, the leading manufacturer of flame arrester technology is providing you with this useful guide to deflagration and detonation pipeline explosions.

When the gas is ignited the flame begins to accelerate. This acceleration results in the build-up of a pressure wave ahead of the flame. Given enough run up distance, this pressure wave can build into a shock wave as the flame speed reaches sonic velocity. This first phase is known as a deflagration.

Once the shock wave reaches a pressure to auto-ignite the gas through which it is travelling the flame front and shock wave couple together forming an unstable detonation.

This deflagration to detonation transition (DDT) is the most severe phase of a pipeline explosion, which can generate flame speeds of >3000m/s and high pressures, over 100bar in some cases.

In short, the deflagration flame arrester is designed to stop the initial phase of the explosion and is shorter and lighter than the unstable detonation arrestor, but the deflagration flame arrester has restrictions on its placement within the pipework regarding distance from the source of ignition.

Explosion characteristics

If you’re unsure about deflagration and detonation flame arresters, this brief guide to explosion characteristics is designed to help. Of course, for further advice or clarification in any way, please get in touch with one of our experts.

Explosion DescriptionExplosion TypeFlame Arrester RequiredNotes
Caused by ignition of a flammable vapour cloud.Unconfined deflagrationEnd of line deflagration arresterHere, there is no physical restriction on the associated expansion of volume - the flame front travels below the speed of sound due to the quick dissipation of the heat and pressure into atmosphere.

Caused by ignition of a flammable gas mixture within a pipe.Confined deflagrationIn line deflagration arresterHere, gas is compressed resulting in higher pressure, accelerating the flame front. The initial stages are sub sonic.
Caused by acceleration of a deflagration flame front and transition of pressure wave to shock wave within a pipe.Confined detonationUnstable detonation arresterWith Deflagration to Detonation Transition (DDT), flame speed reaches sonic velocity resulting in auto ignition of the gas at overdriven detonation stage. Here we see flame speeds of >3000m/s and high pressures, over 100bar in some cases.

Flame arresters – what can go wrong?

A flame arrester may not function correctly if:

  • It is incorrectly specified in the first place
  • It is incorrectly installed
  • It is not maintained properly
  • It becomes damaged or distorted
  • It is blocked or contaminated
  • The process conditions are changed
  • Plant modifications are made

Maintenance and Health & Safety law

HS(G)158 states, “Health and safety law requires that plant and equipment is maintained in a safe condition. It is essential that flame arresters are well maintained. They should be covered by a program of regular inspection and maintenance so they continue to be effective.”

It also goes on to say, “Keep records of the specification of each arrester, its location and its maintenance history.” These records help to identify if the arrester is suitable for the media that it is protecting. Should the process conditions be changed it can then be easily identified if the flame arrester fitted remains suitable for the new conditions.

So how can Elmac help?

Many issues can be identified easily through simple inspection regimes but all too often flame arresters are not serviced regularly.

Elmac Technologies can assist with all aspects of flame arrester effectiveness, from initial inspection reports to on-going maintenance or simply the supply of spare parts.

Standards Compliance

All Elmac flame arresters have been tested and certified in accordance with national or international standards. Actual device performance is verified in the Elmac Technologies state-of-the-art in-house test facility.

 

 

 

 

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