Want To Verify Their Bolt Tensions Over 50 web pages on torque, tension,
& bolted joints.
design often relies on a
bolted joint's tension, which relies on bolt tension, not bolt torque. But the
bridge engineer has to specify bolt torque for the construction crew (not tension). Bolt
tension errors (20% to 50%) often become the limiting factor for these bridge designs. There is a
ultrasonic technology that allows bridge designers to more reliably measure actual bolt tension,
not just bolt torque.
Update says: " SureBolt outperformed the one-point bolt gauges
on every bolt and every test in reliability and accuracy."
A bridge construction engineer
may find the following information useful:
2. Bolt tension, not bolt torque.
Tension not torque. You want to put a known amount of tension
into your nut and bolt combination, not just a known amount of torque. Your
structural analysis often relies on proper pre-load tension.
Using only a torque wrench, on flange bolts, can
large tension errors.
Torque pass, after pass, after pass. But look what happens ---
Notice the variation in bolt tensions (stud stretch) on each of three passes with a
Credit Integra Technologies for this graph. They have taken data on 94
joints. They mislabeled the first pass (it should
show 100 Pound-Feet instead of 200 Pound-Feet)
X-axis = bolt position. 16
Y-axis = bolt stretch (tension).
Large tension variations are typical with
torque control. Notice the > 250% variations.
3. Measure Tension errors. How can a
bridge construction crew measure torque wrench errors?
Do these bolt tension errors matter? These errors often
affect an engineer's assumptions.
4. Verify using a bolt gage. Your joint's stress analysis
can be verified, bolt by bolt, using a bolt gage. What is an ultrasonic bolt gage? See an animated demonstration of
an ultrasonic echo inside of a bolt. Structural engineering labs
rarely have enough resources for each engineer to learn ultrasonics.
Are bolt gages reliable? Are they easy to use? New
patented technology has finally made ultrasonic bolt gages reliable and easy
to use. Verify your bolted joint design.
5. Friction. Bridge designers know
that bolt and nut friction consume over 80% of the torque measurement.
But, how does the actual tension vary bolt to bolt?
What if you use the same type of bolt? This may affect an engineer's structural analysis.
6. Stress, strain & yield. A stress strain curve can be plotted using SureBolt. Stress strain
and yield. SureBolt can help an engineer verify
his bolted joint
design. Did his bolt reach yield?
7. Flanges. 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?
8. SureBolt. How does SureBolt differ from any other ultrasonic bolt
gauge? What is the difference between a one-point bolt gage and SureBolt's
patented whole echo method? Are the prices similar? (Yes)
9. Bridge Engineers. Some engineers use a strain gauge to measure bolt tension because
they know a torque wrench is not directly measuring tension.
Yet their structural analysis software may assume a limited amount
of error (+- 25%) when calculating bolt tension from bolt torque.
Calculating Torque? If you think calculating
the correct torque is easy, just see either of these two web pages (no
affiliation with ARVC). Nut
factors or torque is
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.
10. Tension errors. What are some of the tension errors associated with using a torque
wrench? Does your stress analysis software let you enter the
tension error ranges?
11. Structural engineering. This site is a
structural engineering resource for torque versus
tension in bolted joints.
SureBolt is a nondestructive testing - NDT - method of measuring bolt tension.
Non destructive testing includes the use of ultrasonics.
SureBolt's Whole Echo
patented technology greatly increases reliability by using the whole echo
instead of just one point.
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
a new patented technology. See comparison table.
Bolt gages have been around for over 20
years. Their "Peak Jumping"
problems have kept them from being widely used. When your bolted joint
fails or flange leaks, then you find out your bolt gage may have
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
measurements because they are not reliable. When NASA used the
SureBolt prototype, no measurements had to be thrown away.
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". See animation below of how to ultrasonically
measure the change in bolt tension using echo time.
This animation requires FLASH
(version 4 or higher).
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No more guessing as to
which "one point" is the right point.
The FIRST whole
echo method (patented DSP Technique).
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September 27, 2011