/ News & Press / Video / Animation of Explosion at Tesoro's Anacortes Refinery

Animation of Explosion at Tesoro's Anacortes Refinery

WEBVTT
Kind: captions
Language: en

00:00:07.567 --> 00:00:12.728
Narrator: April 2, 2010,
the Tesoro Refinery in Anacortes, Washington.
00:00:12.728 --> 00:00:20.975
A nearly 40-year-old heat exchanger violently ruptures,
causing an explosion and fire that kills seven workers,
00:00:20.975 --> 00:00:25.703
the largest loss of life
at a U.S. refinery since 2005.
00:00:25.703 --> 00:00:28.607
The Chemical Safety Board
launched an investigation
00:00:28.607 --> 00:00:31.896
and determined that the heat exchanger
catastrophically failed
00:00:31.896 --> 00:00:38.335
due to long-term damage from what is
known as high temperature hydrogen attack.
00:00:38.335 --> 00:00:46.759
The Tesoro Refinery in Anacortes is an 800-acre facility
located approximately 70 miles northwest of Seattle.
00:00:46.759 --> 00:00:54.447
The refinery produces a variety of products
including gasoline, diesel, jet fuel and asphalt.
00:00:54.447 --> 00:00:58.736
Within the refinery's naphtha
hydrotreater unit, raw naphtha,
00:00:58.736 --> 00:01:05.271
a light component of crude oil, is treated to
remove nitrogen, sulfur and oxygen impurities.
00:01:05.271 --> 00:01:07.280
Before entering the unit's reactor,
00:01:07.280 --> 00:01:13.112
the raw naphtha and hydrogen and preheated
inside pressure vessels called heat exchangers.
00:01:13.112 --> 00:01:19.279
The unit contains two banks of three heat exchangers
supported by a three-level steel structure.
00:01:19.279 --> 00:01:24.375
Each heat exchanger consists of a
bundle of tubes inside a steel shell.
00:01:24.375 --> 00:01:28.304
Hot fluid exiting the reactor
flows through the heat exchanger shell
00:01:28.304 --> 00:01:33.951
while cool fluid headed for the reactor
flows inside the tubes.
00:01:33.951 --> 00:01:37.503
Heat is exchanged
through the walls of the tubes.
00:01:37.503 --> 00:01:42.279
Every six months the heat exchangers are
taken offline to be cleaned because of fouling,
00:01:42.279 --> 00:01:46.463
a common occurrence when operating
heat exchangers in this type of service.
00:01:46.463 --> 00:01:52.551
As the raw naphtha is heated, a scale-like
material forms and deposits onto the inside of the tubes,
00:01:52.551 --> 00:01:57.943
hindering the transfer of heat
in the exchangers.
00:01:57.943 --> 00:02:04.767
On March 28, 2010, one bank of heat exchangers
was taken offline and disassembled for cleaning
00:02:04.767 --> 00:02:07.551
while the other bank
remained in service.
00:02:07.551 --> 00:02:11.254
This allowed the unit
to continue to operate.
00:02:11.254 --> 00:02:14.791
By mid-afternoon on April 1,
the cleaning was complete
00:02:14.791 --> 00:02:21.007
and operators initiated the startup
of the offline bank of heat exchangers.
00:02:21.007 --> 00:02:27.390
The procedure required an inside board operator
monitoring the control console and one outside operator
00:02:27.390 --> 00:02:31.438
opening and closing
large manually-operated valves.
00:02:31.438 --> 00:02:35.189
But the heat exchangers had a
history of developing leaks during startup,
00:02:35.189 --> 00:02:39.357
something that refinery personnel
had come to see as normal.
00:02:39.357 --> 00:02:44.325
Additional operators from other nearby units
were called upon to assist with the startup,
00:02:44.325 --> 00:02:47.333
including mitigation
of potential leaks.
00:02:47.333 --> 00:02:53.509
By 10:30 p.m. the outside operator was joined by
six workers from other units within the refinery.
00:02:53.509 --> 00:02:59.821
The seven workers were located around the heat
exchangers where startup activities continued past midnight.
00:02:59.821 --> 00:03:05.286
But unknown to the workers, the steel shells of
the middle vessels in both banks of heat exchangers
00:03:05.286 --> 00:03:10.957
had been severely weakened due to cracking
caused by high temperature hydrogen attack.
00:03:10.957 --> 00:03:16.005
This occurs when tiny hydrogen atoms
diffuse into steel at a high temperature,
00:03:16.005 --> 00:03:20.262
then react with carbon in the steel
to form methane gas.
00:03:20.262 --> 00:03:25.454
The larger methane molecules, unable
to diffuse out of the steel, accumulate,
00:03:25.454 --> 00:03:29.220
stressing the steel and
over time causing fissures.
00:03:29.220 --> 00:03:35.781
In both of the middle heat exchangers the fissures grew
and connected to form large internal cracks.
00:03:35.781 --> 00:03:40.669
One such crack was 48 inches long and
extended more than one-third of the way
00:03:40.669 --> 00:03:43.206
through the vessel's
one-inch thick shell.
00:03:43.206 --> 00:03:48.805
Shortly after midnight the temperature of the fluid
exiting the tubes of the online bank of exchangers
00:03:48.805 --> 00:03:52.710
increased about 75 degrees
over the span of three minutes,
00:03:52.710 --> 00:03:56.797
a temperature increase that was typical
and observed in previous startups.
00:03:56.797 --> 00:04:01.557
But the middle heat exchanger was so severely
weakened from high temperature hydrogen attack
00:04:01.557 --> 00:04:06.854
that it likely could not withstand the
stress caused by the rapid temperature increase.
00:04:06.854 --> 00:04:12.573
At 12:35 a.m. employees working at a
nearby process unit heard a loud hissing noise,
00:04:12.573 --> 00:04:17.437
and vapor began to leak as the heat exchanger
cracked at its weakest point.
00:04:17.437 --> 00:04:21.397
Seconds later the
exchanger violently ruptured.
00:04:21.397 --> 00:04:28.285
Hot hydrogen and naphtha vapor rapidly vented from the
exchanger and spontaneously ignited upon contact with air,
00:04:28.285 --> 00:04:33.349
resulting in a massive fire that
consumed the heat exchanger structure.
00:04:33.349 --> 00:04:36.253
Three of the seven operators
died at the scene.
00:04:36.253 --> 00:04:40.735
The other four operators were transported
to local burn centers with severe injuries.
00:04:40.735 --> 00:04:42.717
Two died within hours.
00:04:42.717 --> 00:04:45.653
The other two
succumbed within days.

Sales phone