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Dive crews make repairs underwater at Horse Mesa Dam

Dive crews make repairs underwater at Horse Mesa Dam

Horse Mesa Dam is located
approximately 70 miles east of the Metropolitan Phoenix area on
the Salt River. The installed megawatt
capacity of Horse Mesa is
greater than the other 3 Salt River dams
combined, so it’s our most valuable
hydrogeneration site. The 12th of June 2012, while the unit was undergoing a start-up, the operators noticed
some unusual noises that were quite evident. At that time they
shut down the unit, realizing something was
not quite right. The unit was then inspected, at which point
we found that a piece of the intake structure had lodged
itself in the turbine. SRP put together a
multidisciplinary team. The team met numerous times to develop different
options and evaluate those. Throughout that long process, it was determined that
the best-evaluated option would be to complete the
repairs using diving. Throughout the design
process, sophisticated computerized
fluid dynamics models were used, to evaluate the hydraulics
and improve upon those. In order to maintain
the tight schedule we had, which was
to put the unit back in service as quickly as possible, we engaged in our
Mechanical C&M group, to have them fabricate
the main pieces that
went back into place. So MCM was critical
to complete the work on time. It was roughly 10 days to get
everything in, just because permits in Arizona
and trucking, logistically it was one of the
tougher jobs that we had to do. We were working 24
hours a day, 7 days a week. Total, there was
22, 23 guys. Each shift was about 12 men. The divers get
into the bell. There’s 2 divers at a time. They take this
elevator to their work, and they are at that
depth where they’re going
to be working at. So as soon as you reach
that ambient depth, the hatch opens, you pull up
the hatch, and you know you’re there. One diver runs out, does
5 hours of work, he comes back, the next diver comes out
and does another 5 hours of work and that’s your bell
run, which equals about 12 hours. You have to plan every step out, 10 steps ahead, before you do it
because you’re the only guy down there. And if you don’t,
well, then it’s not going to work out. But it’s a great thrill in that, to be able to have
everybody at your disposal
and be able to work. We can lift things underwater, and you can move
things a lot easier underwater. On the other hand, you also have the restriction of
a hose and your hat, and all the gear
that you have to wear. But you do get used
to it after awhile. And my last dive was
rolling in the second
guidevein. It was hairy. I’m not gonna lie. It’s a lot of weight
that you’re dealing with there, and you just take it slowly. Constant communication
with the supervisor and everything is done at the level
that you’re comfortable with. This thing was extremely
intense. It was 24 hours a
day, 7 days a week. Holidays, there was no down
time on this job.

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