Case Study
geniSYS™ CNC machine provides
unique solution
Hydratight provided a unique solution to a significant obstacle in the
restoration of a US nuclear plant.
The Problem
A nuclear plant in Tennessee, where construction was suspended before
completion almost 25 years ago, is being brought into service in line with
the resurgence of US nuclear generating capacity.
The operator found serious thread corrosion on three out of 54 stud holes
on the cap head flange of one of the reactor vessels, which two decades
before had not been fully protected against the effects of weather and time.
This wasn’t a case of getting out the taps and cutting new threads. The
stud holes are 355.6 mm (14") deep and almost eight inches across. To
remake the holes would have required not only a specialist tap costing
tens of thousands of dollars, but also a vastly powerful and accurate motor
to turn it.
The Solution
The solution chosen by reactor maker, and approved by nuclear
regulators, was Hydratight’s unique geniSYS™ 220, a portable,
three‑dimensional milling and thread-cutting machine. In recent years
this machine has solved otherwise insurmountable problems in many
situations, from marine diesel engines to chemical and engineering plants.
Hydratight engineers re-engineered the
geniSYS™ and did extensive testing
Even this remarkable tool—portable enough to be operated by two
technicians—wasn’t suitable out of the box. Hydratight engineers had to
make extensive modifications to the feed screw, guide rails, milling head
and other elements of the computer-controlled device to extend its reach
from the standard 304.8 mm (12") to beyond the required 355.6 mm (14").
To gain rigidity the cutting tool was bolted to the head, rather than simply
clamping it in place with screws. The bearings were spread to reduce the
load and other small modifications were made. In the end the tool was
extended to 406.4 mm (16"), so it wouldn’t be at full reach during the cut—
which also meant it would be more accurate at 355.6 mm (14").
The control software then had to be rewritten: it was designed to allow travel
only to the machine’s designed spec and simply didn’t know how to go
beyond 304.8 mm (12").
After six weeks of design, problem-solving, machining and reprogramming,
the geniSYS was reassembled and started a long round of testing.
“The unique nature of the geniSYS™
is the reason we got the job—and
we believe only this tool could have
achieved this result.”
Knowing the machine was capable of making the cuts was one thing,
proving it could do so with great accuracy while bolted to the flange of a
reactor vessel on the reactor floor—three times—was still to be proven. An
error or inaccuracy during the work could cause hundreds of thousands of
dollars worth of damage and put the repair back to square one.
Todd Walstad,
Hydratight Field Service Manager
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continued from page 1
Hydratight technicians built the complete project in the workshop and ran
it several times, to prove the results were fully repeatable, before inviting
the vendor’s inspectors to see for themselves on a full-size mock-up. Then
they took the geniSYS to the customer’s plant and ran the repair through
twice more on full-scale mock-ups; once for the nuclear site engineers and
once for the Nuclear Regulatory Commission. With that demonstration
completed successfully, Hydratight received the green light to start work at
the plant.
After the long test period, one hole was cut in just three shifts. Anyone
involved in this kind of work will know how fast that is. It’s not just the
cutting: each one goes through many of quality control steps along the way.
In the end, both the customer and the plant operator were relieved and
delighted the repair had been a huge success: completed with extreme
accuracy and on time.
For more information, visit hydratight.com.
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