Shared Learning - Ignition of Compounds

                                                         What happened?

During a leak sealing operation in the UK on a high temperature application, the vapors given off by the compound spontaneously ignited and caused a small fire.

                                                         What went wrong?

The line contained flue gas at about 2 bar / 30psi and between 550oC/1022oF and 650oC/1202oF. The enclosure was injected with FSC-6C, as this is a suitable high temperature compound with a upper operating temperature of 850oC/1562oF.

The leak was sealed but when the technicians checked on the flange about 15 minutes later, a small pulsing flame was observed.

The flame was extinguished with a powder extinguisher but re-ignited itself shortly afterwards although the enclosure remained sealed. The flame was successfully extinguished by using a steam lance and to prevent re-ignition, the steam was left flowing over the enclosure for an extended period.

Whilst the line contents is essentially incombustible with no chance of it adding to the flames a different line content, a flammable atmosphere or combustible material in the vicinity could have resulted in a different outcome.

                                          Background/Additional Information

There is a risk when injecting at high temperatures, typically over 300oC/570oF, that some of the Furmanite compound ingredients or breakdown products, may be elevated above their auto-ignition temperatures. The Furmanite safety data sheets detail the specific temperatures for each compound in use.

When an auto-ignition temperature is reached spontaneous ignition, even without an external ignition source, such as a naked flame or a spark can occur.

In addition to the auto ignition risk most compounds contain process oils such as Dioctyl Adipate or Rubber Process Oil that can ignite when they are hot enough and if there is a source of ignition such as a spark. This “flash point” situation can theoretically occur at temperatures above 196oC/345oF and therefore it is essential when operating at temperatures above this that the potential for sparks is minimized.

Laboratory tests have generally found that the flash points of these constituents in the compound don’t ignite in the presence of an ignition source until temperatures above 430oC/806oF have been achieved

The compound use in this case doesn’t contain any process oils and is more stable but as previously stated, it does have a flash point and auto-ignition temperature that can be exceeded during its use.

Technicians should also be aware that any grease that has been added to the compound to aid the injection will have their own flash points and auto-ignition temperatures.

Particular care should be taken when using a compound on a cold or cool flange that will be heated up above 300oC/570oF after injection. In this instance flammable vapors may be emitted during the warming up process and if the pipe has been lagged these vapors can be trapped until they reach their auto-ignition temperature.
                                                         
                                                       Investigation Results 

Immediate Causes

FSC-6C compound was being injected at a temperature where the silicone rubber base was breaking down and vapors were being emitted from the flange.

The metal temperature was above the autoignition temperature of the vapors, causing them to ignite.

The emission of the vapors was not constant, causing the flame to pulse, as the level of vapor built up, ignited and was consumed, before building back up again.

Root Causes

Insufficient knowledge of the hazardous created during high temperature injection of Furmanite compounds.

Insufficient enforcement and compliance with good practices.

 

                                                               How do we prevent it from happening again?

In all cases* when attempting to seal high temperature leaks (above 300oC/570oF), a steam purge is recommended and the job should be monitored for a time following the completion of the injection. The length of time will vary and depends on the quantity of compound injected.

For high temperature leak sealing work (above 300oC/570oF) please contact engineering to discuss any additional safety measures that might be required.

* Even high temperature steam leaks may need a steam purge once the leak has been sealed

                                                                      What actions do I take?

·         All Furmanite Techs to be issued with this Safety Alert. (SDC Managers Globally)

·         All workshop supervisors / SDC Managers to ensure that leak sealing techs have access to a complete set of safety information on the compounds / substances that they use in their day-to- day operations and that their employees have been given suitable and sufficient information and instruction on their safe use. (SDC Managers Globally)

·         All Leak Sealing Procedures / risk assessments to be altered to reflect this safety alert. (Process Integrity Service Line Leadership)

·         All  leak  sealing  class  room  training  to  include  reference  to  flash  points  and  auto-ignition temperatures and where to get the relevant information. (Global Training Manager)

·         Chem-Check manual to be amended so that engineers have autoignition and flash point temperatures readily available to them. (Global Engineering Manager)

·         Engineering Teams providing chemchecks to make techs aware of the flash points and auto- ignition temps where applicable to the situation. (Engineering dept manager)