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Undesirable Events
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Introduction
Most threats to safety from the production process involve the release of
hydrocarbons. Thus the analysis and design of a production platform safety
system should focus on preventing, stopping, and minimizing the effects of
hydrocarbons that are released.
Undesirable Events
An undesirable event is an adverse occurrence in a process component that
poses a threat to safety. The undesirable events discussed are those that might
develop in a process under worst-case conditions of input and output. An
undesirable event may be indicated by one or more process variables ranging out
of operating limits.
UNDESIRABLE EVENTS
Listed below are the eight (8) undesirable events stating the cause of the
event, the effect of the event, and the detectable abnormal condition, the
primary and secondary protection that should prevent or react to its occurrence
and the location of the safety devices.
|
Event |
Cause |
Effect |
Detectable Condition |
Primary Protection |
Secondary Protection |
Device Location |
|
Overpressure |
Fluid input exceeds output |
Rupture/leak |
High Pressure |
PSH |
PSV |
Gas/vapor section |
|
Leak |
Corrosion, erosion, mech. Failure, rupture, external damage |
Release of hydrocarbons |
Low pressure, backflow, and low level |
PSL, FSL, LSL |
ESS |
PSL/gas-vapor LSL/below oper. level and above liquid outlet pipe |
|
Liquid Overflow |
Liquid input exceeds liquid output |
Overpressure, high level downstream or release to atmos. |
High level |
LSH |
ESS |
Above opr. Level and below gas outlet pipe |
|
Gas Blowby |
Failure of level control |
Overpressure downstream |
Low level |
LSL |
PSH downstream |
Below opr. Level and above liquid outlet pipe |
|
Underpressure |
Fluid withdrawal exceeds fluid input |
Collapse and leak |
Low pressure |
Vent or gas make-up |
PSV (atmos) PSL (press vessel) |
Gas/vapor section as high as possible |
|
Excess Temperature |
Excess fuel, extraneous fuel in firing chamber, low level, insufficient
volume heat transfer fluid |
Reduction of working pressure, overpressure of circulating tubes |
High temperature, low flow, low level |
Fluid/stack TSH, TSL, LSL, low flow sensor |
Stack TSH, fluid TSH, ESS |
TSH in thermwell in liquid section |
|
Direct Ignition Source |
Flame emission, spark emission, hot surface |
Fire or explosion |
High temperature, low air flow |
Flame arrestor, air intake PSL, stack arrestor TSH |
TSH, blower motor interlock, ESS |
Flame/stack arrestor fixed, natural draft TSH downstream of flame
arrestor, TSH in fluid |
|
Excess Combustible Vapors in the Firing Chamber |
Failure of fuel of air control equipment, improper operating procedure |
Explosion or rupture |
Flame failure, high or low fuel supply, low air, blower failure in
forced draft burners |
Flame failure sensor (BSL) |
PSH, PSL, motor interlock |
Fuel line and air intake |
01/13/2009
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