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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.


Hydraulic 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!

NDT 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 torque wrench.

Why doesn't all the testing work?

Credit John 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 different bolts
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.

7.   SureBolt. How does SureBolt differ from any  other ultrasonic bolt gauge? Why are other ultrasonic bolt gages harder to use and less reliable? Why did NASA choose SureBolt?

8.   Engineer. Some mechanical engineers use a strain gauge to measure bolt tension because they know a torque wrench is not directly measuring tension. Why?

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 tension errors?

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" bolts.


See main SureBolt page. 


Watch animation below.


"Echo Time".  Animation below of how to ultrasonically measure the change in bolt tension using echo time.
This animation requires FLASH (version 4 or higher).


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


The links below are organized according to your possible background and application.

Mechanical Engineer New Technology Structural Engineer Bridge Design Civil Engineer Stress Analysis Flange Designers NDT, NDE, Ultrasonics ASME, ASTM, ASSE, ASCE Bolt Nut Specs New Invention

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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