Using a torque wrench with a more reliable ultrasonic
bolt gage can help you prevent bolt failures and flange leaks. Over 50 web pages on torque,
tension, & bolted joints.
torque wrench, dial torque wrench, digital torque wrench, ... they all have
tension errors. A torque specification from a tension calculation has errors. Verify
your bolted joint design.
Note: New ultrasonic method cannot be fooled by
friction (torque) variations. Critical information about torque wrenches:
1. Friction. Bolt and nut friction consume over 80% of the torque measurement.
How does the actual tension vary bolt to bolt?
What if you use the same type of bolt? A monkey wrench,
electric impact wrench, gear wrench, multi tool wrench, strap wrench, hydraulic
wrench, crescent wrench, socket wrench, spud wrench, ratchet wrench, hex wrench,
moment wrench, air wrench, adjustable wrench, ..., ALL RELY ON TORQUE, not
tension. A torque tool only gives torque values. Torque specs,
tension measurement, torque gauge, tension calculations, tension measurement,
torque tester, torque calibration, bolt torque chart, torque conversion table,
torque transducers, stress equations, ... are
related, but have large errors due to friction variations. You want tension, not torque!
Update says: " SureBolt outperformed the one-point bolt gauges
on every bolt and every test in reliability and accuracy."
2. Bolt Tension Gage. What is an ultrasonic bolt gage? See an animated demonstration of
an ultrasonic echo inside of a bolt. An ultrasonic bolt gage can help you measure the actual tension in
your bolt. This can help avoid
flange leaks. Each bolt's tension error can cause your flange
seal to leak.
3. Tension error. How can your torque wrench's tension
error be measured?
Do these tension errors matter? No matter what type of torque wrench (hydraulic
torque wrench, dial torque wrench, digital torque wrench, deflecting beam torque
wrench, ..., etc.) or method is used (turn of the nut method, angle method, etc.), the user is only
accurately controlling bolt torque, not bolt tension.
4. Torque wrench on flange bolts. Flange
joints sometimes leak. Why does the tension in a flange bolt
vary so much, bolt to bolt? How can you tighten each flange bolt to closer tolerances?
How can you use SureBolt on a flange?
Bolted joint analysis is improved if you can measure the actual bolt tension,
not just bolt torque. Why are these tension errors greater in flange joints?
Because when the torque wrench tightens one flange bolt, it loosens the adjacent
flange bolts. A flange seal can leak due to these uneven bolt tensions.
Test, test, and test some more. But look what happens ---
Notice the variation in bolt tensions (stud stretch) on each of three passes with a
Why doesn't all the testing work?
Bickford for this graph. He mislabeled the first pass (it should
show 100 Pound-Feet instead of 200 Pound-Feet). This is corrected in his
new edition. Mr. Bickford is probably the world's expert on bolted joints.
X-axis = bolt position. 16
Y-axis = bolt stretch (tension).
Large tension variations are typical with
torque control. Notice the > 250% variations.
5. Torque wrench or "tension" wrench? You want bolt tension, not
just bolt torque. You want to put a known amount of tension
into your nut and bolt combination, not just a known amount of bolt torque.
Mechanical engineering departments teach a mechanical engineer how to do bolted
joint analysis. The mechanical engineer learns that pre-load tension, or joint
compression, is one of their most critical measurements. Mechanical engineers
want bolt tension, not just bolt torque. Verify your bolted joint design.
6. Stress strain
and yield. A stress strain curve can be plotted using SureBolt.
SureBolt can help you verify your bolted joint
design. Did your bolt reach yield?
Bolted joint analysis relies on bolt tension, not just bolt torque. See your
mechanical engineering texts on stress analysis under structural analysis.
8. Engineer. Some mechanical engineers use a strain gauge to measure bolt tension because
they know a torque wrench is not directly measuring tension.
9. Bolt failure. What is the number one reason, stated by bolting experts, for bolt
failures? Lack of proper pre-load tension. What are some of the factors that cause pre-load
10. Engineering Resource. This site is an
engineering resource for torque versus
tension in bolted joint analysis.
SureBolt is a nondestructive testing - NDT - method of measuring bolt tension.
Non destructive testing includes the use of ultrasonics.
See how NASA used SureBolt's Whole Echo
patented technology to greatly increase reliability, accuracy, and
ease of use.
All other bolt gages use just "One
Point" (one zero crossing), that leaves you susceptible to peak
jumping (20% or more error). Surebolt is a more reliable bolt gage due to
this new patented technology. See comparison table.
Bolt gages have been around for over 20
years. Their "Peak Jumping"
problems and long learning curves, have kept them from being widely used. When your bolted joint
fails or flange leaks, then you find out your one-point bolt gage may have
jumped peaks. And you still cannot be sure, because you only
record "one-point", not the whole echo.
With a lot of training and laboratory testing, NASA has used bolt
gages for years. NASA physically takes Polaroid pictures of the echoes
before and after tensioning. Then they use their trained human
experience to determine if the echo has distorted
"too-much". Even after all
this, they have to throw away approximately one third of the ET
(External Tank umbilical bolts) measurements because they are not reliable. When NASA used the
SureBolt prototype, no measurements had to be thrown away.
If you think calculating the correct torque is easy, just see
either of these two web pages (no affiliation with ARVC or any bolt
gage manufacturer), nut
factors or torque
is not easy. With SureBolt, instead of calculating the torque to get
you the correct tension, you just measure the tension directly. You
can even use SureBolt to determine the torque.
SureBolt gives you a 13.3" TFT, portable PC
(Panasonic Toughbook Model 72). The ultrasonic pulser and digitizer are built into the CD ROM
and PCMCIA slots. Click here to see
the actual SureBolt screens. See the animated DEMO page
to see how an ultrasonic bolt gage can measure tension. SureBolt has been used
on special high strength titanium bolts to standard "off the shelf"
Time". Animation below of how to ultrasonically measure the change in bolt tension using echo time.
This animation requires FLASH
(version 4 or higher).
The links below are organized according to your possible
background and application.
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No more guessing as to
which "one point" is the right point.
The FIRST whole
echo method (patented DSP Technique).
Built into a
Visitors Since 1-22-02
September 27, 2011