|
Storage Tank Inspection Above Ground Tanks
For more information on the Maverick robot see this story on the INEEL web site. Buried Tanks
|
|
 |
|
|
Storage Tank Inspection Above Ground Tanks
For more information on the Maverick robot see this story on the INEEL web site. Buried Tanks
|
|
|
|
Large
chemical and petroleum product storage tanks can be found at chemical
processing plants, refineries, and industrial locations. They are huge
metal structures 150 feet in diameter and 50-60 feet tall and can easily
hold more than two million gallons of gas or other hazardous liquids.
Most tanks are made of steel plate that is welded together to form the
structure. The material and the welds are inspected for manufacturing
defects when constructed but must also be periodically inspected throughout
their service life for signs of damage. The carbon steel is prone to
attack by corrosion and in some circumstances cracks can form over time.
NDT personnel use visual, X-ray, ultrasonic and other inspection methods
to search for flaws and service-induced damage.
Inspections
and thickness measurements of the tank walls can be made manually with
the inspector in a man lift or hanging down from the top. However a
much safer way to make an inspection is to use a crawling robot. These
robots have magnetic wheels that allow them to cling to the tank walls.
Using remote controls, an operator guides them into positions and makes
the necessary measurements. They work great on the side walls, however,
getting to a tank floor is a different story since it is not accessible
from the outside. The floor is particularly prone to thinning due to
corrosion attack and tank owners must find the weak spots in the floors
before they breach the tank's integrity. This often involves the costly
process of draining the contents, removing the layer of sludge from
the bottom and cleaning the tanks so inspection personnel may enter
it.
However,
researchers at the Department of Energy's Idaho National Engineering
and Environmental Laboratory and Solex Robotics in Idaho Falls, Idaho,
have developed a new robot to enter filled tanks and make the inspections.
His name is Maverick and he is designed to go where no person can or
would want to go. He's a remote-controlled, submersible robot who will
immerse himself in gasoline and other hazardous liquids to do his job.
He looks like a suitcase on steroids and is packed with an array of
cameras, sonar and ultrasonic devices. The inspectors lower him with
a pulley to the bottom of as full a tank as possible. A 500-foot umbilical
cord connects him to the command trailer outside the tank. Maverick
has bright red spotlights that provide light for his infrared eyes,
and he constantly pings out his position to external sonar beacons as
he searches the floor for flaws with his ultrasonic array. In the command
trailer, separate computers control Maverick's position, his cameras
and the ultrasonic inspection system for the tank floor. Maverick's
automated ultrasonic array takes millions of measurements and makes
a 3-D map of the inspected tank floor.
Not
all tanks are built above ground. A very special inspection situation
involves the tanks used to store nuclear waste. Weapons, space, medical,
and other research and production programs in the United States have
generated millions of gallons of radioactive waste. This waste has been
stored in approximately 280 underground tanks, which are located primarily
at five Department of Energy sites in the US. These tanks were built
from the 1940's to the 1980's and have capacities ranging from 13,000
to over 1,000,000 gallons. Many of these tanks have exceeded their original
design life, and as the tanks age concerns about their leaks continue
to increase. 
What
makes these inspections especially difficult is that the tanks are buried
underground to help shield the radiation. Since the waste is particularly
hazardous, special precautions must be taken to limit exposure to personnel
to the radiation and chemical hazards. This extraordinary situation
has resulted in many innovative technologies being developed to inspect
the tanks. Visual examinations of the tanks are conducted using remote
video cameras. These cameras are mounted on robotic arms that are lowered
into the tanks. The images to the right show what is know as the light-duty
utility arm fitted with the video inspection system inside a tank and
being deployed down into a tank from above. Some of the tanks are manufactured
with two shells and there is a small space between the walls of the
shells. The robotic crawlers can be lowered down into this space and
used to perform ultrasonic inspections of welds and to make thickness
measurements of the tank walls.