Reusing Grade 8 Bolts 2

[Mowoki]

I am hearing and reading that ASTM A490 bolts and galvanized ASTM A325 bolts shall not be reused. I am also reading that although ASTM A490 bolts and SAE J429 grade 8 bolts are very similar in size and strength, but the head, thread length, and application are different.

It was strange to hear that ASTM A490 bolts cannot be reused as I thought going over yield is not desireable as it puts the hardware in danger of fatigue failure. Now, my question is if the SAE J429 grade 8 bolts also follow this rule. If we use the recommended torque range, my expectation is that the hardware will not be damaged, and thus may be reused. Am I missing anything?

 

[dvd]

 

[drawoh]

Mowoki,

It may depend on how you worked out and applied torque to your bolt. A very common pre-load is 90% of proof stress. When you apply your torque plus/minus the accuracy of your torque wrench, you have to assume that your bolt may have been plastically deformed. This is harmless and even safer on the first use of the bolt. It could be risky on the second use.

If you are determined to re-use bolts, you could calculate your own torque based on 70% or 50% of proof stress. Will that be a reliable pre-load?

--
JHG

 

[dvd]

Here are a couple of good and short articles. Read them. Consider buying a Skidmore Wilhelm Torque Tension Tester


You cannot tension all bolts

Lessons from the field-lesson 1

 

[desertfox]

Hi Mowoki

At my place of work all fasteners pre-loaded below and equal to 70% of the maximum preload for the grade of bolt can be re-used.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[drawoh]

dvd,

Torque is the amount of energy it takes to spin the nut up along the threads of a bolt. Force x Distance that is...

Is it really? Torque may appear to have the same units as energy, but it is not energy. Bolt torque times the number of turns would be a measure of energy.

--
JHG

 

[dvd]

drawoh - I think the article is a good article. I am not going to get drawn into an argument on the semantics of a single sentence.

 

[chez311]

As long as your fastener is kept within its elastic range, in most applications you should be fine reusing fasteners. If its a torque to yield application, then certainly reuse of the bolts would be a bad idea.

That being said, it really depends on the application. You have to weight the cost of replacing a fastener during service vs. the cost of potential failure (including human cost - risk of injury or loss of life). Even if a fastener is torqued within its elastic range, all kinds of things happen at a smaller scale which make it difficult to ensure that the design preload can be reached with the specified torque. The immense force/pressure resulting from a preloaded bolt can create all kinds of changes in the surface topography of the threads. Use of a thread lubricant can mitigate this to an extent, if acceptable for your application and will require modification of your specified torque (see ARP for some information on this

https://arp-bolts.com/p/arpultratorque.php

).

This of course ignores anything the bolt/joint may have experienced in the field such as corrosion, service loads, vibration, etc.. which (with the exception of corrosion) may be difficult or impossible to quantify by just looking at the fastener.

The articles below are good sources for the topic at hand.

http://www.boltscience.com/pages/the-re-use-of-threaded-fasteners.pdf

https://www.fastenal.com/en/77/reuse-of-fasteners

 

[CWB1]

The only rule of thumb that applies to engineering is that others' rules of thumb should not be applied.

 

[IRstuff]

Bolts don't error log, so you have zero idea where they've been or what they've experienced. All this to save a few bucks and run the risk of losing a thousand dollar main product itself seems a bit foolhardy.,

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[chicopee]

DRAWOH you got to finish what you started "...Bolt torque times the number of turns with units in radian would be a measure of energy."

 

[IRstuff]

Since torque is analogous to linear force; then there must be an analogy to distance, e.g., angle, wherein the product of torque*angle is work, since force*distance is work.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Tmoose]

FWIW Mowoki ain't been back since the day of the OP, which in turn was just a couple of days after joining Eng-tips.

 

[drawoh]

DRAWOH you got to finish what you started "...Bolt torque times the number of turns with units in radian would be a measure of energy."

Bolt torque in ounce-cubits, times rotation in Chicos, is a measure of energy. Chicos are of course, a unit of rotation named after my cat. I have not yet worked out the conversion factor.

--
JHG

 

[CWB1]

Bolts don't error log, so you have zero idea where they've been or what they've experienced. All this to save a few bucks and run the risk of losing a thousand dollar main product itself seems a bit foolhardy.

Some customers like to reuse hardware and in non-critical applications I do too. As to error logging, I've got thousands of instrumented bolts that disagree.