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Nondestructive
Testing (NDT) and Nondestructive Evaluation (NDE) Engineers Have Been
Using Bolt Gages For Years. Why aren't they popular? |
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So What
Is So Different About SureBolt?
Reliability (avoids peak-jumping),
ease of use, and its all built into a high-powered laptop PC (Panasonic
Toughbook).
NDT
Update says:
" SureBolt outperformed the one-point bolt gauges
on every bolt and every test in reliability and accuracy." |
And the #1 reason for improper bolt pre-load? Relying on torque, not tension.
A torque wrench only measures bolt torque (friction) not bolt tension. This
friction varies so much, bolt to bolt, that the final error
is +/- 20% and not uncommon to have 50% error. Lubricants, calculations,
training, ASTM procedures, ... cannot help but so much.
Each nondestructive method (NDT, NDE, EMAT transducers, ultrasonic pulses, time
of flight - TOF, ...)
tries to measure bolt tension more reliably than a simple torque wrench. But,
each method requires so much training and experience. But now you can ...
Verify your design.
Engineers can use SureBolt to verify that their bolted joint has enough "over design"
to be safe.
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
torque wrench.
Why doesn't all the testing work?
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)
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X-axis = bolt position. 16
different bolts
Y-axis = bolt stretch (tension).
Large tension variations are typical with torque control. Notice
the > 250% variations.
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Useful Information and links to more details:
1. Bolt failures. What do NDT engineers say the number one reason for bolt
failures is? Lack of proper pre-load tension. What are some of the factors that cause pre-load
tension errors? This affects an engineer's bolted joint design.
2. Bolt tension, not bolt torque.
Mechanical tension not mechanical torque. You want to put a known amount of tension
into your nut and bolt combination, not just a known amount of torque. Your
mechanical joint analysis often relies on proper pre-load tension.
3. Measure Tension errors. How can a
NDE engineer measure torque wrench tension errors?
Do these bolt tension errors matter? These errors often
affect an engineer's structural analysis.
4. Bolt gage. What is an ultrasonic bolt gage? See an animated demonstration of
an ultrasonic echo inside of a bolt. NDT labs
rarely have enough resources to let each engineer learn about ultrasonic bolt
gages.
5. Friction. NDE engineers know
that bolt head and bolt thread 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?
6. Stress, strain & yield. A stress strain curve can be plotted using SureBolt. Stress strain
and yield. SureBolt can help a NDT engineer verify
his customer's bolted joint
design. Did their 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. Engineers. Some NDE engineers use a strain gauge to measure bolt tension because
they know a torque wrench is not directly measuring tension.
11. NDT & NDE resource. This site is a
nondestructive evaluation 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.
See animation.
12. 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.
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SureBolt's Whole Echo
patented technology greatly increases reliability by using the
patented whole echo method, instead of just one point. All other bolt gages use just "One
Point" (one zero crossing), that leaves you susceptible to peak
jumping (20% error or much more). Surebolt is a more reliable bolt gage due to
a this new DSP technology. See comparison table.
Bolt gages have been around for over 20
years. Their "Peak Jumping"
problems and difficult 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.
Example, 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"
bolts.
For more information, see the main
SureBolt
navigation screen.
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[SureBolt] [ Video ]
