POWER March 2021 - 14

O&M
Bolting Tools Important for
Operation, Maintenance of
Wind Turbines
There is a trend churning in the wind
power industry; it involves upgrading
wind turbines with newer, more powerful
generation systems. Thanks to higher-capacity
turbines and more efficient
components, repowered turbines can
produce up to 20% more energy annually.
At a time when future tax credits
for wind power are uncertain, choosing
to repower fleets is an efficient way to
increase wind energy productivity and
help ensure maintenance costs don't
exceed profits.
Although
beneficial,
repowering
is
not as straightforward as it may sound.
It requires bigger, more exacting equipment,
and may result in larger nuts and
bolts that are placed closer together
than in the past. Whether you are considering
upgrading your wind turbines
or looking for safer and more efficient
tools for your current fleet, now is a
great time to review wind turbine maintenance
and bolting tool options.
A wind turbine can contain somewhere
around 25,000 bolts, each of
them under precise bolt load and up
against a variety of forces in nature.
Once a wind turbine is commissioned
for service, a maintenance schedule dictated
by the original equipment manufacturer
(OEM) must be maintained to
have the tower covered by the warranty.
One of those regular maintenance tasks
is checking that bolt loads are within
the variation specified by the OEM. In
a worst-case scenario, if too many bolts
become loose, a catastrophic failure
could occur.
Technicians must check the load on a
certain percentage of bolts, as directed
by the OEM's specifications. One example
might be a 10% check: Check 10%
of the bolts for 10% of variance. Over
time, small variances can occur because
things shift and push. Or a technician
could accidentally overstress a bolt and
stretch the metal beyond a yield point.
During maintenance, the technician
will check whether a bolt is still as tight
as it was a year ago, and either tighten
it or replace it if it went past its yield. If
too many variations are found, the OEM
specification may require that 100% of
the bolts must be tested.
14
1. Maintenance schedules for wind turbines are dictated by the turbine's original equipment
manufacturer. This turbine, on an installation in the North Sea, northwest of the German island
of Borkum, is among those using Enerpac systems and equipment. Courtesy: Enerpac
Maintenance Frequency
Maintenance schedules are dictated by
the turbine OEM, and must be maintained
and documented for the warranty.
The schedule varies based on the age of
the wind tower (Figure 1) or number of
hours in use. For bolting, maintenance
may need to occur every three months,
six months, or annually. If there was zero
variation in the bolted joints from the last
maintenance check, the wind tower operator
can ask for an exemption on the next
service, which saves time and money.
Controlled bolting is the process of applying
an accurate bolt load to a mechanical
joint to meet design specifications.
Bolt load can be measured directly using
hydraulic bolt tensioners, ultrasonics,
or calculating torque values determined
by the bolt material, size, and friction of
the stud and nut. Having the means to
measure bolt load during or immediately
following the bolting process is essential
for joint integrity and safety.
Torque wrenches apply rotational
force onto a nut to stretch, not yield,
the bolt to achieve bolt load. A hydraulic
torque wrench, when coupled with a
specially designed torque pump, creates
the torque output, or torque load, necessary
to create the clamping force to secure
bolted-joint integrity.
While torque wrenches and bolt tensioners
work to accomplish the same objective-to
clamp nuts and bolts together
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for joint integrity-tensioning directly
stretches the bolt against the flange rather
than nut rotation from the torque wrench.
Tensioning typically creates a more accurate
load often required on larger bolts. The
decision of which to use is driven by the
engineer. As wind towers get repowered
with bigger equipment, more exacting and
reliable tools are required.
New features are available on torque
wrenches that set a higher standard in
safety, versatility, simplicity, and performance.
For example, when it comes to
safety, a built-in, work-at-height safety
tether connection, such as that on the
Enerpac DSX-Series aluminum torque
wrenches, helps prevent injuries to workers
below. Meanwhile, a fully enclosed
square drive keeps technicians' hands
protected from moving parts, and its optimized
weight-to-output ratio and slim
design help prevent operator fatigue.
Versatility is a benefit of this modular
torque wrench. The module drive units
and hex cassettes are interchangeable
with a wide range of hex- and squaredrive
cassettes from several manufacturers,
while the combination of superior
alloys makes it one of the most durable
wrenches in its class.
Items to consider when selecting
torqueing tools include handle options,
size, and material strength. Some designs
allow handles to mount on both
sides of a square-drive torque wrench,
POWER | March 2021

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POWER March 2021

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