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Nondestructive Testing (NDT) and Nondestructive Evaluation (NDE) Engineers Have Been Using Bolt Gages For Years. Why aren't they popular?

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)

X-axis = bolt position. 16 different bolts
Y-axis = bolt stretch (tension). 
Large tension variations are typical with torque control. Notice the > 250% variations.



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. 



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 SureBoltTM navigation screen.



If you have made it this far, read on ....

SureBolt FLASH Video Why NASA Used Video Download Animated Demo Tutorial On-Line Torque Errors Technical Info Torque Wrench Specifications+ Prices & Compare Services News    

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"Echo 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).




Let us know how we can help you.

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 No more guessing as to which "one point" is the right point.


The FIRST whole echo method (patented DSP Technique).

SureBolt picture

Built into a 
Panasonic Toughbook

Weather proof keyboard.

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Last Modified: September 27, 2011