Flame Cutting A490 Bolts 8

[stscwi]

Greetings all!

I searched quite a bit looking for information on this and cannot seem to find anything concrete. The situation is such: 1"x5" A490TC bolts were used to bolt double clip angles to the web of a beam. The threads extending beyond the face of the nut after the spline was severed using the TC gun were long enough that they would interfere with the connection on the other leg of the angle. Instead of replacing the bolts with shorter ones, the bolts were cut 1/4" above the nut using the oxy/acetylene process.

I know that A490 bolts are heat treated, therefore any thermal cycle, especially uncontrolled such as oxy-fuel cutting, can alter the heat treating properties of the material. I am of the opinion that this is clearly not acceptable but I cannot find anything concrete that directly addresses this issue. ASTM A490, RSCS, AISC, etc seem to have nothing written (that I can find) regarding the acceptability or not of this practice.

Any insight, especially anything code/standard related would be greatly appreciated.

Thanks in advance for your time and help!

 

[MintJulep]

It wouldn't be a good idea to soak the bolt in hydrofluoric acid, drill out half the diameter and fill it with peanut butter before installing it either, but you're not going to find a code that says not to do that.

It's impossible for code and standard writers to anticipate every stupid thing that someone might do and write "don't do this..." in the code.

 

[DRWeig]

Good on ya, MintJulep!

stscwi, if the installer wants to argue with you, you should have the right to demand a statement from the manufacturer of the bolt/nut that it's OK.

My thoughts anyway...

Goober Dave

 

[MiketheEngineer]

Guess you will never have to worry about the nut backing off...

 

[Duwe6]

By definition, a Quenched & Tempered item cannot be heated above it's tempering temp without altering its properties. Thus: IF the bolt mfr would allow it in writing, and
If the Engr-of-record would deem these softened, weaker bolts acceptable, then the installation would be conditional;y acceptable.

The chances of either happening is about 1Billion : 1
Thus the chances of both happening is about 10exp81 : 1. Not gonna happen in the remaining life of the universe.

 

[Ron]

A490 bolts and nuts are not even allowed to be hot-dip galvanized because of the heat effects. Flame cutting a high strength, hardened steel bolt is by no means a good idea and not allowed. Reference:

"Specification for Structural Joints Using ASTM A325 or A490 Bolts", Research Council on Structural Connections (RCSC)

 

[dik]

I thought the galvanising restriction was due to hydrogen embrittlement caused by some pickling processes... I didn't think it was a temperature issue...

Dik

 

[CoryPad]

dik,

It is both.

 

[dik]

thanks... and, Ron, I stand corrected...

Dik

 

[Duwe6]

Molten zinc is about 600-deg F. Tempers & softens hardened steels.

 

[Guest102023]

Sounds like you are dealing with a fitter who has an 'I'll make it fit' mentality whose first choice of weapons is the acetylene torch. Without reference to any codes or standards, it is sufficient to state that thermal cutting on a hardened steel part should not be permitted, at least not without clearance from the Engineer.

(A thin abrasive disk should do the job, and with a whole lot less mess.)

 

[connectegr]

At the last RCSC Specification Committee meeting I asked a similar question. "Why does RCSC not specifically address welding or cutting of structural bolts in the spec."

The response from nearly all of the bolt manufacturers on the committee was simply that none of them would warrant their products or guarantee their performance if the user welded or torch cut the tempered material.

Your best resource for your argument may be to contract the bolt manufacturer for comment.

http://www.FerrellEngineering.com

 

[stanweld]

Galvanizing bath temperatures are normally in the range of 830F to 850F; even greater tempering effect.

 

[dik]

From Portland Bolt, "Effect of Heat on Quenched and Tempered Fasteners

The second issue of concern when considering hot-dip galvanizing high strength fasteners is potentially reducing the mechanical strengths due to the introduction of heat during the hot-dip galvanizing process. Portland Bolt operates its hot-dip galvanizing tank at 840° Fahrenheit. Is this enough heat to potentially alter the strength of a quenched and tempered fastener? In theory, the amount of heat that a high strength fastener is exposed to during the hot-dip galvanizing process should not alter its mechanical properties.

It is obvious that the application of heat to a bolt that develops its strength through a heat treating process could adversely affect the strength of the fastener. The question is, how much heat is necessary to potentially change the mechanical properties? On page 4-4 of the Ninth Edition of the AISC Manual (American Institute of Steel Construction), the following statement occurs:

“Anchor bolt material that is quenched and tempered (heat treated) should not be welded or heated.”

However, it does not address the amount of heat that should be avoided. Welding obviously applies a tremendous amount of heat to the components being welded, whereas hot-dip galvanizing is performed at significantly lower temperatures. Another reference that addresses the heating of high strength bolts (which occurs during hot-dip galvanizing) can be found in the ASTM F1554 specification. Section 6.4.3 of the ASTM F1554 specification states:

“Hot bending performed on heat-treated bar stock shall not have the temperature come within 100°F (56°C) of the tempering (stress relieve) temperature of the heat-treat process at any location during hot bending and shall be allowed to air cool after bending.”

Although this statement refers to hot bending, it implies that any process (including galvanizing) that applies heat approaching or exceeding the tempering temperature of a high strength bolt may potentially alter the mechanical properties of the fastener and should therefore be avoided. However, galvanized bolts only remain in the zinc tank for a few minutes and even though the surface temperature may approach 840°, it is unlikely that the entire fastener is heated to that temperature. The most relevant reference found in any ASTM specification addressing the possibility of the hot-dip galvanizing process altering the mechanical properties of a high strength fastener is found in section 7.2.1.2 of the new hot-dip galvanizing specification ASTM F2329 which states:

“Testing for mechanical properties is not necessary if the galvanizing process is carried out at a lower temperature than the stress relief or tempering temperature of the fasteners.”

This implies that the mechanical properties have the potential to be altered only if high strength bolts are tempered at temperatures at or below the 840° temperature that the bolts are subjected to during hot-dip galvanizing. As Table 2 indicates below, the minimum tempering temperature for both ASTM A193 grade B7 and ASTM F1554 grade 105 is 1100° Fahrenheit. Therefore, it is not possible for the galvanizing temperatures to exceed the tempering temperature for these specifications. Although in theory it is possible for the other specifications to be tempered below the galvanizing temperature, recent records indicate that the minimum tempering temperature used for any of these grades listed in Table 2 that Portland Bolt has manufactured is 950°. Therefore, hot-dip galvanizing performed by Portland Bolt on any of the high strength bolt specifications listed in Table 2 will not adversely affect the strength of these fasteners."

 

[CoryPad]

dik,

Different specifications allow different minimum tempering temperatures. ISO 898-1 allows various temperatures for high strength fasteners, from 340 [°]C (640 [°]F) for 10.9 property class, 380 [°]C (720 [°]F) for property class 12.9, and 425 [°]C for 8.8, 9.8 and 10.9 property classes. Thus, galvanizing of high strength fasteners can decrease strength.

Obviously the hydrogen embrittlement issue exists for all of these steels regardless of minimum tempering temperature.

 

[lindsaygreg]

Portland Bolt's website addresses welding of quenched and tempered fasteners in this FAQ:

http://www.portlandbolt.com/faqs/welding-high-strength-anchor-bolts.

The same issues occur when flame cutting as they do when welding....heating a high strength bolt in an uncontrolled environment. There is a reference to welding (flame cutting also) quenched and tempered anchor bolts (other configurations of bolts as well) in the AISC:

On page 4-4 of the Ninth Edition of the AISC Manual (American Institute of Steel Construction), the following statement occurs:

“Anchor bolt material that is quenched and tempered (heat treated) should not be welded or heated.”

Another reference is in the F1554 specification that Portland Bolt references in the above FAQ.

 

[Compositepro]

A lot of structural steel is flame cut.The heat affected zone does not extend far from the cut. These bolts were cut to remove excess length that is under zero stress. Although 1/4" from the nut seems much closer than necessary I think it highly unlikely that the bolt inside the nut got close to tempering temperature. There is no comparison between welding and flame cutting in terms of heat input to adjacent steel.

 

[RolMec]

Anything technical will one day or other come down to dimensions. So we need now a comparison of 1/4" versus the torch flame thickness. And job requ.ts as "Shakiness of hand grade one" of workers.
Under teperature & strain, all metals start to yield much faster than under normal conditions. And if... if it's just the bolt in that only joint of all where all the bolts should have been fully bearing and the torch touched the nut?
As for standards, I'd pull out the erection drawings, and if it isn't mentioned: "surplus iron maybe torched away", there you are. And then, erection contract surely says something like "Any rep. any alteration of orig. erection dwgs during assembly MUST be ok'ed IN ADVANCE by responsible engineer."

 

[Guest102023]

Compositepro,

Structural steel sections provide a far bigger heat sink than a fat stubby bolt. Subequent welding of these sections usually obliterates the effects of all but the messiest flame cutting. Strength-wise, A490 Q&T bolts have more to lose than structural steel.