POWER April 2014 - 82

PLANT SAFETY
were at the hydroelectric plant and immediately
available for rescue on the day of the
incident. " The CSB investigation determined
that the closest community rescue service
was approximately 75 minutes away. Rescue
workers talked with the trapped workers on
hand-held radios for 45 minutes before they
died from smoke inhalation. There were no
fire extinguishers located inside the tunnel.
The owner and contractor subsequently
failed to cooperate fully in the CSB investigation,
particularly with providing requested
documentation. In fact, the CSB eventually
had to request the assistance of the U.S. Attorney's
Office to obtain requested documentation
from the parties. Several contractor
managers even " asserted their constitutional
right against self incrimination. "
When the CSB was ready to release its final
report, the owner and contractor, each facing
criminal charges in relation to the fatalities,
unsuccessfully went to federal court in an attempt
to block its release. The CSB's August
2010 final report is available at www.csb.gov.
In June 2011, the owner was acquitted
in the criminal case of willfully violating
OSHA regulations causing death, pleading
the accident " was not foreseeable. "
However, the owner paid an OSHA fine of
$150,000 to settle the citations issued after
the investigation and paid millions to the
dead workers' families to settle civil lawsuits.
The contractor paid $1.55 million
to satisfy workplace safety violations, and
criminal charges are pending.
Pressure Pipe Explodes
The plant maintenance staff at a power plant
was charged with replacing a high-pressure
steam piping spool piece that connects the
main steam stop valve to the non-return
valve. The piping configuration at this particular
plant interconnects the high-pressure
steam piping across four boilers.
On the day work began, workers noticed
that the main steam stop valve on an adjacent
boiler was leaking steam. The workers were
unfamiliar with the steam piping arrangement
and dismissed its importance. In addition,
because the welders were very experienced,
the company elected not to test the welders
prior to beginning the work or follow welding
procedure inspections required by the
American Society of Mechanical Engineers
(ASME) Piping and Boiler and Pressure Vessel
Codes.
The welders began fabricating the new
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spool piece in place on a Friday afternoon,
completing the first 3/32-inch circumferential
welding root pass connecting the pipe
to flanges located on both ends of the pipe.
The root pass filled in about one-fifth of the
pipe thickness, which was sufficient to seal
the spool piece. The crew then secured their
work and left for the weekend. Unbeknown
to the crew, the leaking valve on the adjacent
boiler slowly filled the new spool piece
with steam. The steam condensed into water
as the pipe cooled over the weekend. A
drain line on the spool piece was left closed,
causing hot water to slowly accumulate instead
of drain.
The crew returned to their work on Monday
morning and none of the workers or
plant staff thought to open the drain valve to
ensure the spool piece was dry inside. The
welder went to work to complete the four
remaining welding passes on one end of
the pipe spool. The pipe heated from welding
(the heat-affected zone ranged from
1,200F up to the weld puddle temperature of
3,000F) caused the trapped water to evaporate
and superheat, thus pressurizing the
pipe spool. The welders next began making
the final 1/16-inch passes on the other end
of the pipe spool.
The welder was about two-thirds of the
CIRCLE 38 ON READER SERVICE CARD
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POWER | April 2014
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POWER April 2014

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