* Chemical reaction weakened steel, led to blast
* Company revising inspection procedures
* Other investigations ongoing
(Adds detail, background, adds byline)
By Kristen Hays
HOUSTON, July 21 Damage to a heat exchanger
that couldn't be seen by the naked eye caused an explosion that
killed seven workers at a Washington state refinery last year,
an investigation by workers and Tesoro Corp (TSO.N) showed.
The final report of a joint investigation by the company
and the local chapter of the United Steelworkers union released
late Thursday said the blast at the 120,000 barrel-per-day
(bpd) refinery in Anacortes, Washington, stemmed from a
chemical reaction involving steel exposed to atomic hydrogen at
high temperatures and pressures.
That reaction, called "high temperature hydrogen attack,"
or HTHA, allows cracks to form and weakens the steel. The
damaged heat exchanger in a naphtha hydrotreater subsequently
could not handle operating pressures and exploded, the report
Tesoro shut the plant for nearly six months after the April
2010 explosion, which was the worst refinery disaster since a
2005 explosion killed 15 workers at BP Plc's (BP.L) (BP.N)
437,080-bpd refinery in Texas City, Texas.
Tesoro is appealing a $2.4 million fine and 44 violations
levied against the company for the blast by Washington state's
Department of Labor & Industries.
The state regulator issued the fine and violations last
October after a six-month investigation found that the
explosion could have been prevented by proper inspection and
maintenance of the heat exchanger. The regulator said it had
not been properly inspected in 12 years.
Tesoro said on Thursday that the HTHA damage was visible in
highly magnified samples of the steel, but such a specialized
inspection was not done before the blast.
"Corrosion experts did not recommend the failed exchanger
for an HTHA inspection in any of the five corrosion reviews
conducted between 1990 and 2008," the company said in a
Tesoro spokesman Mike Marcy declined comment on the appeal,
citing company policy against discussing pending litigation.
Tesoro said it is building new heat exchangers designed to
minimize HTHA risk. The company also said it now surpasses
industry standards for determining what equipment needs HTHA
testing and has a new plan for enhanced corrosion reviews.
The U.S. Chemical Safety Board is investigating the
explosion, as is the criminal division of the U.S.
Environmental Protection Agency.
Tesoro has cooperated with the investigations, and said it
provided copies of Thursday's report to those agencies.
(Editing by Lisa Shumaker)