×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Bolts

Bolts

(OP)
what is the difference between torquing and tensioning in relation to bolts. Is there a particular size or material which needs one in preference to the other.

RE: Bolts

Both are referring to the same thing, achieving preload on a fastener. Torquing refers to turning the nut or head of the bolt to achieve a predetermined bolt stress. Tensioning refers to stretching the bolt by some means to achieve a set amount of stretch in order to achieve the same bolt stress. Tensioning usually refers to a stud and nut combination where you have some stud exposed to grip.

RE: Bolts

Another consideration in choosing between torquing or tensioning is the required accuracy of the preload.  Torque is a very inacurate means of developing precise bolt preload, as the exact amount of friction is often unknown.  Bolt tensioning, on the other hand, is very accurate as it relies upon known mechanical principles, and is completely independent of friction.  Using the equation d=FL/AE the bolt stretch (d) is determined knowing the active bolt length (L), the desired preload (F), the modulus of elasticity of the bolt (E) and the tensile stress area of the bolt (A).  One caveat though.  Measuring bolt extension in the field requires skilled craftsmen and proper measuring equipment.  Ultrasonic tension indicators are a bit easier to use but are temperature sensitive.

RE: Bolts

tothepoint,
           You may wish to note that bolt tensioning can only provide +/- 30% accuracy of the target bolt load which is not very accurate in the scheme of things.

RE: Bolts

DSB123- I think you are confusing torque accuracy with strain measurement accuracy.  Torque, at best, is about +/-30% because of a variety of factors (lubrication, calibration, speed of tightening, etc.), measurement of bolt strain is +/-5% accuracy.  In applications where bolt preload is critical, bolt strain is the measure used to insure preload.

RE: Bolts

Method Accuracy Relative Costs
Feel +/-35% 1
Torque wrench +/-25% 1-1/2
Turn-of-the-nut +/-15% 3
PLI washers +/-10% 7
Bolt elongation +/-3-5% 15
Strain gages +/-1% 20

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources