Efficient Plant April 2018 - 48

column | seeking reliability

Reliability's
Sexy Side:
Threaded
Fasteners
Drew D. Troyer CRE, CMRP
Contributing Editor

Stretch the threads
too far and your
bolts lose their
holding power.

+

This column explores, from a management perspective, the Five Pillars of
Knowledge, as defined by the Society for
Maintenance and Reliability Professionals
(SMRP), Atlanta (smrp.org). Expanded,
more technical, takes on topics covered
here will appear in Efficient Plant's
monthly "Reliability Solutions" e-newsletters. To receive them, visit efficientplantmag.com and select Subscribe
under the Magazine menu item.

48

| EFFICIENTPLANTMAG.COM

S

O THE TITLE is misleading. Threaded fasteners aren't
very sexy. But I wanted to
quickly draw your attention to what
is one of the most important, albeit
often overlooked, aspects of machine
reliability. Threaded fasteners are,
literally, the nuts and bolts of putting
reliability on the plant floor. They hold
things together and hold them down.
When they're managed correctly,
looseness-related vibration, which
leads to mechanical wear, leaks, and
poor electrical connections, is kept to a
minimum. When approached casually
and with a lack of precision, threaded
fasteners are a primary root cause of
mechanical and electrical failure.
Effective fastening is achieved by
applying the proper amount of clamping
force between two fastened components. Clamping force is achieved
by stretching the threaded
fastener, which acts like a spring
to create the tension required
to secure the connection. The
amount of tension applied is very
important. The threads on bolts are
elastic, which enables them to stretch-
the greater the stretch, the greater the
tension, up to a point.
Hooke's Law defines the elastic limit
of fastener materials. Much like a spring,
if a bolt is stretched to a point within the
elastic region for the material, the metal
returns to its pre-tension state undamaged and can be used again. If, however, the threads are stretched beyond
the elastic limit, the material fatigues,
is permanently distorted, and can't
maintain the tension required to achieve
the desired clamping force. The trick is
to tension the fastener to a reasonable

level within the material's elastic limit to
achieve the desired tension without exceeding what is called the yield, or plastic
deformation point. Doing so destroys
the threads, which brings us to tension
versus torque.
Torque simply measures the twisting
force applied to a fastener, which is a
combination of tension resistance, which
creates the desired elastic stretch on the
bolt, and friction, which is a wild card.
Studies on test stands suggest that 50%
or more of the resistance measured on
a torque wrench is due to friction. Thus,
it's imperative to lubricate fasteners prior
to tightening. Machine oil is good, but
a purpose-formulated fastener oil or
grease works better and minimizes the
friction-related error between torquewrench readings and actual achieved
tension.
Remember, when it comes to fasteners, an ounce of prevention is worth a
ton of cure. With a little investment of
time and money, diligence in fastener
practices pays big dividends in increased plant reliability and reduced
maintenance costs. For more details on
managing these critical components,
see my Efficient Plant May e-newsletter
article "Threaded Fastener Best Practices" at efficientplantmag.com/bolts. In the
meantime, read about some real-world
fastening mysteries in this month's
feature article, "What's Wrong with My
Bolts?" on p. 10. EP

Based in Tulsa, OK, industry veteran
Drew Troyer is principal with Sigma
Reliability Solutions. Email
Drew.Troyer@sigma-reliability.com.

APRIL 2018


http://www.efficientplantmag.com/bolts http://www.smrp.org http://www.efficientplantmag.com http://www.EFFICIENTPLANTMAG.COM

Table of Contents for the Digital Edition of Efficient Plant April 2018

Editorial
Implementations
What's Wrong With My Bolts?
Understand Vertical Motor Bearings
Bourbon Boom Drives Distillery Expansion
Lubricant Myths That Can Cost You
IIoT
SAP: When To Update SAP Master Data
Give Your Chain A 'Hand'
Why Do Hackers Hack?
Why Compressor Size Matters
Equipment-Rental Considerations
On The Floor
Microgrids Are On The Rise
Solution Focus
Products
Index
Showcase
Seeking Reliability
Efficient Plant April 2018 - Cover1
Efficient Plant April 2018 - Cover2
Efficient Plant April 2018 - 1
Efficient Plant April 2018 - 2
Efficient Plant April 2018 - 3
Efficient Plant April 2018 - 4
Efficient Plant April 2018 - 5
Efficient Plant April 2018 - Editorial
Efficient Plant April 2018 - 7
Efficient Plant April 2018 - Implementations
Efficient Plant April 2018 - 9
Efficient Plant April 2018 - What's Wrong With My Bolts?
Efficient Plant April 2018 - 11
Efficient Plant April 2018 - 12
Efficient Plant April 2018 - 13
Efficient Plant April 2018 - 14
Efficient Plant April 2018 - 15
Efficient Plant April 2018 - Understand Vertical Motor Bearings
Efficient Plant April 2018 - 19
Efficient Plant April 2018 - 20
Efficient Plant April 2018 - Bourbon Boom Drives Distillery Expansion
Efficient Plant April 2018 - 22
Efficient Plant April 2018 - 17
Efficient Plant April 2018 - 18
Efficient Plant April 2018 - 19
Efficient Plant April 2018 - 20
Efficient Plant April 2018 - Bourbon Boom Drives Distillery Expansion
Efficient Plant April 2018 - 22
Efficient Plant April 2018 - 23
Efficient Plant April 2018 - 24
Efficient Plant April 2018 - Lubricant Myths That Can Cost You
Efficient Plant April 2018 - 26
Efficient Plant April 2018 - 27
Efficient Plant April 2018 - 28
Efficient Plant April 2018 - IIoT
Efficient Plant April 2018 - SAP: When To Update SAP Master Data
Efficient Plant April 2018 - Give Your Chain A 'Hand'
Efficient Plant April 2018 - Why Do Hackers Hack?
Efficient Plant April 2018 - Why Compressor Size Matters
Efficient Plant April 2018 - Equipment-Rental Considerations
Efficient Plant April 2018 - On The Floor
Efficient Plant April 2018 - 36
Efficient Plant April 2018 - Solution Focus
Efficient Plant April 2018 - 38
Efficient Plant April 2018 - 39
Efficient Plant April 2018 - 40
Efficient Plant April 2018 - Products
Efficient Plant April 2018 - 42
Efficient Plant April 2018 - 43
Efficient Plant April 2018 - 44
Efficient Plant April 2018 - 45
Efficient Plant April 2018 - Index
Efficient Plant April 2018 - Showcase
Efficient Plant April 2018 - Seeking Reliability
Efficient Plant April 2018 - Cover3
Efficient Plant April 2018 - Cover4
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