Today, we ask what happens when a machine grows
old. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
We've built so much in the
last century. Bridges, dams, office buildings,
power plants, automobiles, computers. How do we go
about decommissioning all that stuff? We've become
pretty good at reclaiming material from old
bridges, buildings, and cars.
But computers, which grow obsolete in a few years,
pose disposal problems we've barely considered. We
think we know how to decommission nuclear plants,
but we don't have much experience doing it yet. The
first hydroelectric dams are just growing old. They
pose terrible dangers. Then there are offshore oil
Some 3800 platforms now line the Gulf of Mexico --
6500 world-wide. Only a fraction sit in less than
30 feet of water. Some are in water over a
half-mile deep. One in four is over 25 years old.
Most production equipment sits on the deck of an
underwater tower until the oil below is gone. Then
what becomes of that huge structure?
A few platforms could possibly be used by marine
scientists. Several have been toppled onto the
ocean floor where they continue to shelter marine
life -- growing coral and forming artificial reefs.
That, by the way, is what became of a huge part of
the Japanese Navy, long after it was sunk in Truk
Lagoon during WW-II.
But most towers have to be cut loose, turned on
their side, and floated off to land for recycling.
It's in that removal process that trouble arises. A
neutral panel of experts recently convened to
improve the federal regulation of those removals.
The worst problem is cutting the tower away from
the ocean floor. The cuts must be made well below
the mudline -- below water -- so currents that
scour the bottom won't expose the stumps.
Protruding steel can threaten fishing -- especially
The policy has been to cut the legs off 15 feet
below the mudline. That can be done by a diver
inside the legs of the tower, or by digging a great
pit around the footings -- then cutting the legs
off from outside. The cleanest way to sever the
metal is with oxyarc cutting torches. But that's
also the most dangerous. Divers have died from
oxygen explosions and they work in fear of shifting
It's far safer to lower explosive charges down the
hollow legs and fire them from above. It's safer,
but it's also far messier. On the wrong day,
thousands of fish might be killed by the blast --
the very fish that make their habitat in the tower
So engineers, out of the political limelight, work
to save people and fish alike. They ask how far
into the mud should we really cut the legs? Can we
shape explosive charges so they won't send killing
shock waves through the water? What's possible?
It's one more problem spawned by our ravenous
appetite for goods and energy. It'll be followed by
some new problem. All the while we wonder if we'll
ever learn to consider the death of a machine -- as
well as its life -- when we first design it.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
The Committee on Techniques for Removing Fixed
Offshore Structures and the Marine Board Commission
on Engineering and Technical Systems, National
Research Council, An Assessment of Techniques
for Removing Offshore Structures. Washington,
DC: National Academy Press, 1996.
I am grateful to Alan Powell, UH Mechanical
Engineering Department, for suggesting this episode
and providing the National Research Council report
along with other materials. I am also grateful to
him and to Era N. Ford, Twachtman Snyder &
Thornton, Inc. Consultants, for their critical help
with this episode. Ms. Ford also notes that Allan
G. Pulsipher, Center for Energy Studies, LSU, is a
primary expert on this problem.
For more on offshore oil, see Episode 1394.
From the cited NRC
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Offshore rigs photographed from Galveston with
600 mm lens. The left-hand one is in place. The
right-hand one is being moved.
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