A fire on an offshore installation has highlighted the risk of low
temperature spontaneous combustion from TEG soaked insulation. An
investigation has shown that spontaneous combustion of TEG soaked into
fibrous materials can occur at relatively low temperatures
(70oC). Therefore, specific precautions are required for stripping and
disposal, to avoid unexpected ignition and fire.
The incident occurred on the process deck and involved removal of
the aluminium cladding and TEG soaked insulation (Kaowool Ceramic) from
dehydration system pipework following a small leak of hot TEG from a
flange. The materials were temporarily stored,
with rags used to mop up excess TEG from the deck, in a plastic sack.
Spontaneous combustion subsequently caused a fire, which consumed the
sack and contents.
The TEG soaked insulation was at, or near, the pipework
temperature when it was placed in the plastic sack. The process of
stripping the insulation allowed air to be absorbed into the insulation.
In addition, dry hot insulation could have come into contact
with TEG soaked insulation after being removed from the pipework.
As the insulation cooled it was possible for an oxidation process
to have begun in the centre of the waste in the plastic sack, which
eventually gave rise to spontaneous ignition and combustion.
This incident is an example of a well-recognised phenomenon more
often observed in oil soaked rags in workshops and insulation soaked in
mineral oil. It is less common in relation to TEG but can occur in the
following circumstances: For spontaneous combustion
to occur, TEG must be absorbed into an insulating material which has
sufficient void spaces for air to be absorbed. The temperature will rise
if the temperature of the insulation is relatively high and the volume
sufficient to allow heat generated by an oxidation
process at its centre to be retained. The larger the volume of the
insulation, the greater the amount of heat retained and the lower the
temperature at which spontaneous combustion of the TEG will begin. High
temperatures can develop that could lead to a fire.
If the bulk of TEG soaked insulation is large enough, spontaneous
combustion could occur even if the insulation starts from cold. However,
the time taken before the initiation of the rapid heating process would
be much longer. TEG soaked rags are much less
reactive than insulation, but could still present a hazard. TEG
dehydration systems can run at temperatures up to 200oC and pipework is
often insulated with fibrous rock wool type material. This material has a
structure suited to the absorption of air into
the void spaces. In normal circumstances the insulation will be clad
with aluminium plate, which holds the insulation in a compressed state
and prevents the ingress of air. When cladding is removed and the
insulation stripped from the pipework, air will be
absorbed into the insulation. If the TEG and insulation are hot from
the process pipework and collected in bulk, the conditions within the
stripped material can be susceptible to spontaneous combustion.
SOURCE:IOGP