Flange bolting issues top the list of critical-path threats during plant maintenance outages. But the right bolting solution can cancel those risks permanently.

1. 1
AVOIDING THE COSTLY
CHALLENGES OF SEIZED COUPLING
BOLTS IN HYDROPOWER PLANTS
Flange bolting issues top the list of critical-path threats
during plant maintenance outages. But the right bolting
solution can cancel those risks permanently.
By Peter Miranda
Business Development Director,
Power Generation
Nord-Lock, Inc./Superbolt, Inc.

2. 2
Introduction
Planned turbine outages are among the most ex-
pensive costs to power plants.1
Often, such costs to
hydropower facilities are compounded by the seizing
of conventional fitted bolts in turbine/generator (T/G)
coupling flanges. These seized bolts require extensive,
time-consuming labor, which may involve breakout
tongs, hammers, and chillers – though these solutions
typically fail. Drilling and boring are then employed
for bolt removal, but doing so for just one bolt can
require an entire shift. Remedial machining of bat-
tered flange bores adds cost and delay, and safety
issues related to brute-force removal and installation
methods can occur at every step.
Conventional Solutions vs. an Innovative Alternative
With conventional bolts so often implicated in extended
downtime, overrun costs, and increased personnel haz-
ards, why would a power company fall back on them
for reassembly? In nearly all cases, the main reasoning is
tradition: “This is how we’ve always handled it.” Tradition,
however, should not continue to cost millions of dollars in
productivity, particularly when a superior, innovative alter-
native is available. This alternative to dated, nut-and-bolt
connections is the mechanical expansion bolt.
Faster, safer, and easier to install and remove, mechanical
expansion bolts transfer forces more effectively than fitted
or interference bolts by combining radial expansion and
axial clamping forces. They save machining time, because
they accommodate looser tolerances. Once installed,
mechanical expansion bolts stay tight indefinitely ­­– and
when the next maintenance cycle comes around, simple
hand-held torque wrenches are the only requirement for
removal. Finally, they’re reusable: these bolts stand up to
repeated removal and handling, and they won’t damage
flange bores.
One mechanical expansion-bolt design in particular – EzFit
from Superbolt, Part of the Nord-Lock Group – has earned
numerous accolades from the power-generation industry.
In many cases, EzFit bolts have replaced traditional bolts in
hydropower facilities, saving time and money for those in-
corporating this technology (see “Case Study: Hydropower
Plant” sidebar for one such example).
Planning Guide for Outages
More often than not, planned outages for hydropow-
er plants uncover at least one immovably seized cou-
pling-flange bolt. Fortunately, such challenges can be
planned for in advance – with a few simple steps being
taken ahead of time to save major expenses, delays, and
damages later:
• Acknowledge the probability that “unexpected” faults
in conventional flange bolting will add downtime to
your next T/G disassembly.
• Build extra days into your outage schedule for bolt-
ing-related issues.
• Start researching alternatives to conventional bolting
now, so your next bolt-related incident is your last.
• Open a seized-bolt contingency file. Speed and clear
communications will be critical, so assemble all of the
operational and maintenance data, dimensions, and
specs that a bolting-tech supplier might need. Keep
it handy for the moment when it’s time to call for
backup.
EzFit mechanical expansion bolt by Superbolt
Example showing damaged coupling bore after stud removal

3. 3
The Superbolt Solution
Innovative Superbolt EzFit mechanical expansion bolts re-
place large fitted or interference-fit bolts without modifica-
tions to onsite equipment. No traditional system is easier,
faster, or safer to install and remove, thanks to a unique
combination of technologies:
• Multi-jackbolt tensioners (MJTs) that impart tremen-
dous axial forces for unmatched joint-clamping power,
but require only simple hand tools for installation and
disassembly.
• A patented split expansion sleeve that mates solidly
and accurately with the bore to transfer radial forces
in shear.
- It saves critical machining time, because it
accommodates looser tolerances than
interference-fit bolts require.
- It eliminates slippage during operation – essential
in high-speed rotating couplings or alignment
systems.
- It’s trouble-free – much less likely to hang up
during removal than conventional close-tolerance
solid sleeves.
Validated Worldwide
EzFit has been tested and approved by the American
Bureau of Shipping, Det Norske Veritas, and Lloyd’s
Register of Shipping.
EzFit at a Glance
• Easy installation: Loose-fit sleeves (up to .020”
through-hole clearance) can be inserted by hand, even
in holes misaligned due to rotation.
• Fast adjustment: Tightening requires only minutes per
assembly, using hand tools alone.
• Safety: No special high-powered tools, improvised
rigging, or deep-freezing required. Installation/removal
torque normally measures less than 100 ft-lb.
• Economy: Lower time and tooling costs.
• Reusability: Split sleeves spring back to original
diameter, use after use.
• Less machining: No bore reaming or honing. No
coupling-face machining at nut positions. No onsite
sleeve finish machining.
• Easy flange assembly: Axial and radial forces combine
to pull coupling halves together.
Custom Designs
• Using the latest FEA technology, our engineers can
custom-design EzFit mechanical expansion bolts for
any coupling built for bolts 1” (28 mm) DIA or larger.
• If required, we can combine the features and
advantages of hydraulic and mechanical
expansion-sleeve coupling bolts.
Typical Bolting Replacement Cost and Time
Machining/repairs for one bolt
With conventional technology With EzFit Expansion Bolts
3 - 6 hours per hole
$1,000 - $2,500 per hole
$2,000 per bolt/stud for
every outage
10 - 15 minutes per hole
$100 per hole
One-time investment of $3,600
Labor & equipment rental
OEM replacement

4. 4
EBA: Anchor (dowel), radial preloading
EBC: Coupling, access both sides
EBB: Blind hole, access one side
Product Range
Case Study: Hydropower Plant
During a recent planned outage, a hydropower plant in
North America experienced the usual issues while disassem-
bling nuts and fitted studs on the turbine shaft coupling.
The customer reached out to Nord-Lock Group to proactively
investigate the best tensioning options for securing this joint.
During these discussions, Nord-Lock Group learned the fol-
lowing points were of critical importance:
1. worker safety;
2. reduced installation and removal times; and
3. the ability to downsize tooling needs due to limited access.
Application requirements: the fitted holes are three inches in
diameter, and calculations based on coupling operating pa-
rameters showed that 150,000 lbs of preload was needed to
safely secure the coupling connection. Also, due to necessary
safety covers installed over the flange bolts, space for the
bolting elements was restricted.
After review, Nord-Lock Group recommended EzFit expan-
sion bolts, which provide the required axial and radial forces
to keep the joint secure. Keeping in mind the customer’s
critical points, the tensioners were designed with a final
jackbolt torque of only 78 ft-lbf to meet the required load
requirements. This final jackbolt torque can now be achieved
using only a hand-held calibrated torque wrench. Quick-
ly recognizing the benefits of safety, total cost, and labor
savings, the customer purchased 14 EzFit assemblies for
their application. After delivery, Superbolt visited the site for
product training and to assist with installation, resulting in a
very happy customer.
©
Copyright 2019 Nord-Lock Group. NORD-LOCK, SUPERBOLT, BOLTIGHT, and
EXPANDER SYSTEM are trademarks owned by different companies within the Nord-
Lock Group. All other logos, trademarks, registered trademarks, or service marks
used herein are the property of the Nord-Lock Group. All rights reserved.
Reference
1 “Guidelines for Reducing the Time and Cost of
Turbine-Generator Maintenance Overhauls and
Inspections – 2014: Supplemental Addition.”
Electric Power Research Institute, 3 December
2014, https://www.epri.com/#/pages/prod-
uct/3002003441/.
Nord-Lock, Inc./Superbolt, Inc.
1000 Gregg St., PO Box 683 Carnegie, PA 15106
Tel: (412) 279 1149 Email: bolting@nord-lock.com
www.superbolt.com
EzFit expansion bolts replace
OEM fitted studs and hex nuts