To Pressure Equipment Owners and Operators
Rig Boiler Fatality
A worker was checking a rig boiler when a ball valve on the blow-off
line came apart releasing high pressure hot water and steam into
the area. The worker received severe burns and later died in
hospital.
Failure analysis suggests that the ball valve involved in the incident
failed as a result of damage caused by water freezing in the valve.
Experimental tests conducted as part of the failure analysis showed
that ball valves were irreparably damaged when subjected to
freezing temperatures with water retained in ball valves in the
closed position. On freezing, water became ice and expanded,
exerting tremendous force on the valve body. The valve failed
when the threaded nut section on one side of the valve dislocated
from the main valve body. Examination revealed that the valve
body had increased in diameter and the thread crests on the nut
section were deformed or sheared off. Based on the results of the
tests, damage would have been expected to have occurred upon
freezing.
With the low temperature conditions in our Province in winter,
there is potential for severe damage to pressure-retaining
components from the freezing of water or other fluids.
Pressure equipment subject to the freezing of accumulated and
retained moisture or water or other fluids may incur damage that
would result in the equipment’s being unfit for pressure service,
together with a significant potential safety hazard when under
pressure.
Any pressure equipment that has been subject to freezing of the
contained fluid should be taken out of service. If freezing has been
suspected or observed, the pressure equipment of fittings involved
must not be placed back in pressure service without proper
inspection and integrity evaluation. The use of damaged
components in pressure service can be highly hazardous and
components damaged by freezing can not likely be repaired.
K. T. Lau, Ph.D., P.Eng.
Chief Inspector and Administrator Pressure Equipment
Province of Alberta
First published in March/April 2004 Steamlines.
Home