A325 vs. A193 Gr B7 2

[StructTaco]

I have a contractor that has substituted A193 Gr B7 for the specified A325. Both were galvanized. Any problems that anyone might see with that?

Thanks as always!

 

[unclesyd]

In or on what and what is the environment?

 

[StructTaco]

it is a structural application, on a pedestrian bridge tower that is exterior, inland and not exposed to a corrosive environment like salt air...

 

[unclesyd]

I'm going to defer to one of the more knowledgeable structural members for the answer.

Personally I would not allow the substitution without a written change order from EOR because of two words in your reply, "pedestrian and bridge". Normally B7 bolts aren't galvanized while A325's are. The 325's have a very definate product form with a specific length of threads to shank length, which isn't normally found in B7s'.

 

[metengr]

Yes, I do have a problem. The answer is NO you cannot substitute materials because you need the approval of the Engineer that is going to sign and seal the drawing and bill of materials. Do you realize the liability if something happens and the smoking gun is a material substitution???

 

[StructTaco]

I am the engineer of record, I'm asking the difference in the two types of bolts, both are galvanized, so corrosion resistance is the same. The tensile and yield strengths are greater than A325. Is there any other difference I should be aware of. I can make them take the bolts out if necessary, so the question is, is it necessary?

 

[CoryPad]

The differences between the two are chemical composition and thermomechanical processing. The A193 Grade B7 material is higher strength, and has a minimum tempering temperature that should avoid problems with 1) strength reduction due to hot dip galvanizing and 2) delayed fracture due to hydrogen embrittlement. You should be able to approve this, but there is a slight risk if the wrong procedures are used during manufacturing. You can read more here:

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

 

[unclesyd]

Here is a US manufacturer's (Portland Bolt) take on the subject. You are correct as far as physical properties go in that both fasteners are on the same page. The devil is in the details in the HDG process and how was the fastener treated to rid it of Hydrogen. The vast of majority of HDG fasteners are coming from off shore no verifiable pedigree. Things are being done with fasteners in spite of the NFA that will scare the hell out of you .
Again personally I would use a galvanized B7 fastener in any situation where I didn't have the history of said fastener from bar to box.

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

 

[StructTaco]

thanks all, much appreciated.

 

[unclesyd]

Correcting the last sentence my previous post:

Again, personally I would not use a galvanized B7 fastener in any situation where I didn't have the history of said fastener from bar to box.

 

[HgTX]

Pre-tensioned connections? Slip-critical? Just bearing?

Hg

Eng-Tips policies: faq731-376

 

[StructTaco]

just bearing connections

 

[crossframe]

Typically I say "No" to these types of requests, based mainly on the quality and inspection requirements.