Thermal Expansion Hazard
Recommended Measures
The sequence of events that led to catastrophic failures could have
been avoided by the following measures:
1.
Identify thermal expansion hazards (e.g. trapped liquid
between two valves) in Process Hazardous Analysis (PHA).
2.
Design equipment, heat exchanger tubes and piping to
withstand thermal expansion and contraction.
3.
Design to include thermal pressure relief for overpressure
protection. If any equipment or line can be isolated with full of
liquid, a relief valve should be provided for preventing
overpressure of the contained liquid.
4.
Lock-open thermal relief path and avoid blocked-in conditions,
e.g. through Lock-Out-Tag-Out (LOTO) procedure, safe work
practice, Pre-Startup Safety Review (PSSR) and MOC.
5.
Conduct training and improve competency of personnel on
awareness of thermal expansion effects.
Williams Geismar Olefins Plant, Louisiana, June 2013
Liquid contained within process vessels or piping will expand when heated up due-to the
increase in its specific volume. Liquid that is unintentionally blocked-in and then heated by
different source of heat such as process heat, heat tracing, external fire, solar radiation or
ambient temperature, will expand and may generate an overpressure that could lead to
equipment damage including vessels and piping systems. Typical situations of thermal
expansion in the industry are:
1.
2.
Cooling coils (in reactor) which are filled with liquid and are accidentally blocked-in;
Liquid-filled piping in an isolated valve section due to heat or solar radiation and may
cause the line to fracture or leakage from flanges;
One of the past accidents due to liquid thermal expansion involved a reboiler at Williams
Geismar Olefins Plant, Louisiana, in June 2013. The consequential explosion and fire
resulted in 2 fatalities and 167 injuries. The incident occurred during non-routine
operational activities that introduces heat to a reboiler which was offline and partially
liquid filled, unknown to the operating team, creating an overpressure event as the vessel
was isolated from its pressure relief devise. The introduced heat increased the
temperature of the liquid propane mixture confined within the reboiler shell, resulting in a
dramatic pressure rise within the vessel. A BLEVE (Boiling Liquid Expanding Vapour
Explosion) occurs as the reboiler shell catastrophically ruptured, caused a fire.
References | Additional Notes | Distribution List |
1. U.S. Chemical Safety and Hazard Investigation Board, Case Study
on Williams Geismar Olefins Plant, 2016