Bolt material

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  • #1
brewnog
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Main Question or Discussion Point

Bolts.

I have an application where I need some more clamping force (currently got 12.9 capscrews), can't find any 10.9's, but have a load of B16's lying around.

Any idea what B16 is, in terms of bolts? I'm pretty sure it's some kind of metallurgical standard, definitely not a size or thread pitch or anything like that.

Would I be able to compare B16 to, say, 12.9 or 10.9, or would that be apples and oranges?

Help!
 

Answers and Replies

  • #2
FredGarvin
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Are there any markings on the heads or are they SHCS?

EDIT: B16 is an alloy steel designation spec. I'm seeing if I can find it anywhere. BRB.
 
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  • #3
FredGarvin
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Well, I have searched high and low. I think I may be at a disadvantage here. I did find one reference to it on this site:

http://www.hevilifts.co.uk/products/studs_bolts [Broken]

Maybe you can give them a call and talk to one of their applications engineers for the spec title or something you can search on.
 
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  • #4
Q_Goest
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Hi Brewnog. As Fred says, the B16 is an alloy designation. It's actually the grade of the material per ASTM A 193. These bolts are often used in ASME related piping or pressure vessel systems.

B16 is a ferritic steel with alloying elements that include chromium, molybdenum & vanadium in addition to the more common ones such as carbon. Both the ASTM spec and ASME B31.3 lists the yield strength at 105 ksi, ultimate 125 ksi and in metric units it lists as 725 MPa yield, 860 MPa ultimate.

Looks like you're stuck with your grade 12.9 which is significantly stronger.
 
  • #5
brewnog
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Cheers chaps.

Q_Goest said:
Looks like you're stuck with your grade 12.9 which is significantly stronger.
I was actually trying to find a weaker bolt, to stretch it more and get more of a clamping force between my two things to be fastened. We'll see...!

I'll chase up those links, thanks guys.
 
  • #6
FredGarvin
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Q, did you have any kind of cross reference on that ASTM spec or is that from experience? I couldn't find any ANSI or ASTM specs that listed the B16.
 
  • #7
Q_Goest
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I was actually trying to find a weaker bolt, to stretch it more and get more of a clamping force between my two things to be fastened.
Hi Brewnog. The clamping force is of course a direct function of the bolt load or tensile stress in the bolt. Force is stress times area, so for any given bolt area, the higher the stress, the higher the force.

As for how much it stretches, that's only dependant on the modulus of elasticity. The stretch of a bolt is per Hook's law - strain times the modulus equals stress. A grade B16 bolt will have the same modulus as the higher strength bolt, so you'll actually get more strain (stretch) from the higher strength one because you can increase the tensile stress of the stronger bolt.

The conclusion then is that the stronger bolt will stretch more and end up with a higher clamping load.
did you have any kind of cross reference on that ASTM spec or is that from experience? I couldn't find any ANSI or ASTM specs that listed the B16
Hi Fred. I know from experience that B16 is a common bolting material for piping systems. In all the piping codes (B31.1, B31.3, etc) there is a materials section giving you the allowable stresses which is an outstanding reference I might add. In the material section of the piping codes is a bolting material section which covers the various grades of bolts. ASTM A 193 has various grades in it including (from memory) B1, B5, B7, B8 and B16. Why they skip around like that I don't know. But the ASTM spec is what gives you the chemical composition and material properties. The piping codes only gives you stress allowables, yield and ultimate stress.
 
  • #8
FredGarvin
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I have B31.3 sitting on my desk, but I don't use it enough to know it that well. I will have to look through the materials section. Thanks for the tip. Ya learn something new every day.

I looked at ASTM A193 and sure enough, there it is. I was hoping there was a way to cross reference the specs some how, but nothing comes up in our spec system. Oh well.
 
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  • #9
brewnog
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Q_Goest said:
As for how much it stretches, that's only dependant on the modulus of elasticity. The stretch of a bolt is per Hook's law - strain times the modulus equals stress. A grade B16 bolt will have the same modulus as the higher strength bolt, so you'll actually get more strain (stretch) from the higher strength one because you can increase the tensile stress of the stronger bolt.
The conclusion then is that the stronger bolt will stretch more and end up with a higher clamping load.
Ah, I was under the impression that the weaker bolt would also be less stiff, and therefore capable of pulling tighter on the threads at the end of the bolt. Thanks for that. The additional problem is that we're having trouble with the capscrews because of access, and are snapping Allen keys all over the place so wanted to try something with a hex head (and something which we wouldn't have to go out and buy!). We thought about durloks too, but figured that they would only help stop the bolts coming loose, rather than allowing more of a clamping force to be used.

Cheers.
 
  • #10
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Hi,

Does anyone know the torque capability of a 5/8 in. allen socket for a 3/4 in. socket head B18.3 capscrew. The comment about allens snapping off made me wonder if this is published information.

Thanks
 
  • #11
Q_Goest
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You need to provide thread diameter and pitch, and tensile strength. I believe B18.3 only specifies dimensions.

Also, it makes a big difference what the coefficient of friction is, so it's dependant on materials and any lubrication as well.
 
  • #12
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3/4-10 ANSI B18.3 x 2-1/2 NON STD MATRL A-193 GR B7 105 ksi min Sy, 35 ksi Sm
7/8 in. hole
Assume torque range 268-387 ftlb
Assume 5/8 in. hex socket
 
  • #13
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Also assume non lubricated K=.2
 
  • #14
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One more thing, I have already looked at bearing stress, just was wondering about the allen socket itself after I heard they were "breaking" - just curious what torque caused them to break and what size allen socket was used?
 
  • #15
Q_Goest
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The comment about allens snapping off made me wonder if this is published information.
Sounds like you're referring to a specific incident or incidents. I've heard of 'Chinese bolts' or other fasteners not being made to spec, but those stories aren't about a specific size bolt, they're very general in nature.
 
  • #16
FredGarvin
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When you say "break" do you mean that the shank itself failed or the threads failed?
 
  • #17
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Q Goest

Brewnog said:
"The additional problem is that we're having trouble with the capscrews because of access, and are snapping Allen keys all over the place so wanted to try something with a hex head "

My concern is how are Allen keys rated so that you might know their torque capability prior to getting into what brewnog describes...
 
  • #18
Q_Goest
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My concern is how are Allen keys rated so that you might know their torque capability prior to getting into what brewnog describes...
Allen keys aren't rated unfortunately. If you look at the size of the key compared to the size of the cap screw (for standard sized cap screws)*, you'll find the key has a dimension across the flats roughly equal to, or very slightly smaller than, the minor diameter of the thread. The key however, is generally of very high strength steel, even higher than a bolt, so in generally the key is strong enough to torque a cap screw right the way up to the point of breaking. At this point, depending on the strength of the cap screw, the Allen key may also be very close to breaking, so which one breaks will depend on material strength among other factors.

There are other factors however. The head of the screw creates friction with the parts being bolted such that the screw head can resist some torque without transfering that torque to the threaded portion of the cap screw.

In general, Allen keys should hold up to the torque requirements of the cap screw. Given the example provided, (a 3/4-10 UNC cap screw torqued to 387 ft lb) the shear stress in either part is unusually high. I could see either part shearing.

Before such bolts shear however, I've generally found the Allen key gets rounded off, or the cap screw socket deforms. If you're experiencing failed Allen keys or rounded off parts, it may be because the torque specified is too high.

*Note: Although standard sized cap screws should be ok, many of the low head cap screws have minor diameters much larger than the Allen key, such that the Allen key is much more likely to fail in shear. You may want to clarify if standard or low head cap screws are being used.
 
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Q_Goest,

Thank you!
 

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