ASTM A489 Carbon Steel Eyebolts - Why 275°F upper temp limit ? 2

[A8yssUK]

Hi all, long time since I posted on here

I have an application that uses a hook to hold a load in a tensioning spring system.
The weight of the load is max 10kg but the tensioning system and the service could add a maximum 100kg.
It will see cyclic loading with maximum swings of perhaps 30-100 kg roughly 500000 times over 10 years.
Application is at 150-180°C (300-350°F)in an air environment. Corrosion seen before has been medium to normal, not excessive.

A 5/16" thick carbon steel bent wire hook bolt (cold rolled A1008) is more than strong enough for this, on paper. (yield 40k psi - 5/16" ~12000lbs / 5500+ kg)
Fatigue shouldn't be an issue as we don't approach anywhere near even 10% of the yield strength in the cycle...
Instron tests have the hook being able to hold 300+ kg before a bending open of the hook starts. 3x possible max loads.
However we had a failure (1 out of roughly 500 installed) after just a few years of service.
The hook snapped... straight snapped under the hooked section of the bolt with no necking at all... looks like a brittle failure, and the hook section was not bent out of shape at all so loads below 300kg caused the break...surface corrosion was visible but not excessive.

How could this occur, some sort of temperature aging ?? or embrittlement ? I thought aging at these temps wouldn't really occur and would require decades to lower the yield only slightly...even so why didn't the hook bend open before yielding?

We are looking to "upgrade" the bent wire hook bolt to an ASTM A489 carbon steel eye bolt, but the ASTM states it has a 275°F (135°C) temp limit.
Does anybody know why ? and could this be related to the previous failure ?

Thank you!

 

[SWComposites]

hmmm "bent wire hook bolt" - not really sure what you mean by this - can you post a picture and description. but the hook forming process may induce local yielding and/or residual stresses which then lead to fatigue failure. there may also have been a local flaw in the one hook that failed. can you also post a close up photo of the hook fracture surface?

also, have you done a stress analysis of the hook to obtain the local peak stress under load?

 

[A8yssUK]

Basically this...

 

[A8yssUK]

To answer your other questions, yes we did (afterwards) perform FEA and it shows the point of max stress not at the break point...local peak was ~300MPa @100kg so one of the reasons we want to swap to the full eye bolt as bending could occur.
I dont have a pic of the fracture surface on me (home office) but will post one asap.

 

[mrfailure]

Did you have a metallographic fractographic examination performed to determine whether the failure mode was ductile overload, brittle overload, fatigue, or creep?

 

[A8yssUK]

@mrfailure
As we have only had the 1 in 500+ fail. We have not yet.. this was a few months ago now and nothing else has shown up but if we start seeing any more I am sure we will.
I am currently in the what could have happend mode... not the what did happen mode

 

[SWComposites]

look like there are some significant stress concentrations from forming/bending just to the left of the "break here" line.

are these hooks from a pedigreed steel source? or some low cost supplier? (the picture looks like something I would get at Home Depot).

 

[btrueblood]

Pretty sure that bolt is NOT made per the ASTM standard, unless you can show me the standard allows for zinc plating.

 

[EdStainless]

My money is on either internal defect or surface defect.
These bent hooks are rated for zero load, unless you found someone who will engineer and QA them.
Go to forged eye bolts.
They will cost 10x as much but they will be reliable.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

I agree with EdStainless ...

These bent hooks are rated for zero load, unless you found someone who will engineer and QA them.
Go to forged eye bolts... They will cost 10x as much but they will be reliable.

(not sure that I agree with the 10X .... but if properly designed and selected hardware can keep you out of a lawsuit .... well worth it !!!) ... Even newly minted MBAs would agree with that !!!

Forged, certified eye bolts will acomplish the same function ... abandon your cheap Wal_mart TRASH !!!


Shouldered or not shouldered WELDED eye bolts, (combined with a properly sized, certified and inspected clevis) will do the trick

Read pages 20-23 of this fine guideline

https://www.energy.gov/sites/prod/files/2014/01/f6/HoistingRigging_Fundamentals.pdf

Note the use of the "eye bolt/hook" and "eye bolt/clevis" combination suggested in this fine Canadian Publication

https://www.ccohs.ca/oshanswers/safety_haz/materials_handling/eye_bolts.pdf

Your ball ...

MJCronin
Sr. Process Engineer

 

[A8yssUK]

Thanks everybody, the above hook was just a stock image to explain what it was... it is not what we used. Sorry I should have stated that.

We are moving to forged eye bolts... but they are also carbon steel, and the ASTM A489 states only upto 275°F. The application temp is above this... however the load requirements we have are minimal so I am wondering why such a hard stop at such a low temperature.....and could it be related to the failure already seen with the open hook. FEA on the eye bolt, with fatigue analysis at the higher temps calculates no issues... but why the limit ??

Also as promised a look at the fracture, don't get too excited Warning its from a dusty environment and not cleaned up, the grey bits are cement dust.
It is actually a bit more along the bend of the hook than I remembered...

 

[MJCronin]

Is that fracture also a "stock image" .... ??

.......Ummmmm....and you say that it is not "cleaned up" ... ?? ..., Why did you post it ???

Hmmmmm, ...... IMHO .... it looks a lot like something from "DUNE" ????

Explain why you CANNOT use stainless steel eye bolts .... They are good above 275F

https://www.chicagohardware.com/catalog/18_22_eyebolts.pdf

MJCronin
Sr. Process Engineer

 

[A8yssUK]

No this is an actual image of the failed open hook (just cropped), not an image of Shai-Hulud. I do see the resemblance!

Of course we can use stainless eyebolts... just have to express to the customer that they have to spend 5x more for some reason.
Sadly because the ASTM says no, will not be enough. I'd like to let them know why they can't use carbon steel eyebolts above 275F. Almost all the other steel work (which we have no control over) in the system are not stainless...including the tensioning system which this hook would connect too... so not only do I need a decent argument for the extra costs but more importantly if the 275F has good reasoning. I'd need to let them know that the tensioning systems are also at risk of similar failures.

I am leaning to a local flaw in this one hook, with its chances of repeated failure being very slim. Moving to the forged more controlled ASTM A489 eye bolts should reduce this risk even more...but I do not like not knowing *why* there is this 275°F limit.

 

[LittleInch]

There is some reference to this limit ins ASME B 18.15. Maybe get a copy or look to see what it says and why. Sometimes this is hidden in the history or scope section. Also might give you C Stl alternative for higher temperatures.

I would certainly get that broken end cleaned up a bit and examined under a microscope.

Was the load always vertically down?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mrfailure]

The fracture looks interesting and 3-dimensional even under the cement dust. I would still get the cement cleaned off to view fracture morphology, then use visual and if necessary SEM evaluation to identify the failure mode. You might need to know that to select an alternate material.

 

[A8yssUK]

Firstly sorry no cleaned up picture, our technician disposed of these pieces after taking photos and we haven't had any more failures (yet).

We ended up finding a reasonable stateside supply of DIN 580 galvanized CS forged eyebolts... more corrosion resistance and standard says good for up to 200°C.
When the units are swapped out they will get the new connections.
The issue should now be designed out.

However, I still don't know why the ASTM A489 CS eyebolts have such a low elevated temperature limit... so as I am not good at letting things go I emailed the ASTM F16 Committee about it, if I get a response I shall update this thread.