Galvanized Steel vs. Stainless Steel with epoxy anchors 2

[tdstructural]

I'm using galvanized A36 structural steel members in outdoor conditions. The weather is moderate with some rain but not extreme cold/hot and it isn't near the ocean. I need to anchor the columns and baseplates to existing concrete.

I'm using Hilti HIT-RE 500-SD epoxy anchor bolts. If I use the ASTM A193 Grade B and galvanize the steel will I still get the epoxy to steel adhesion? If I use the ASTM F 593 Stainless Steel will I have problems with the dissimilar metals (A36 galvanized baseplates and stainless steel bolts)?

This is a high seismic hazard region - I don't know if that is relevant in this situation.

 

[dik]

If mild condition, I'd use galvanised anchor rods... chemically compatible with galvanised steel... with stainless, you may have some galvanic activity.

Dik

 

[jtx]

I've used stainless fasteners to connect dissimilar metals before without any problems so you could use the stainless rods provided that you design the anchors properly.

As far as galvanizing the anchor rods and it's ability to bond to the epoxy...that may be a question for your local Hilti rep.

 

[tdstructural]

thanks for your response dik and jtx.

As an update to my original post:
I called Hilti - they said that there could be problems with using stainless steel bolts and galvanized A36. The also said there is NO problem with galvanizing bolts - the epoxy will have the same adhesion to the bolts with our without galvanizing.

 

[hokie66]

Whoever you want to believe...Hilti reps are not always experts in corrosion. Agree with jtx, and I think you can use either without problems.

 

[dik]

Hokie...

From a legal point, if there are any problems and it comes to light that it was recommended that you do one thing, and you decide to do another... it may be difficult to explain to the judge...

I'll see if I can locate some photos of galvanic corrosion of stainless anchor rods used with HDG steel... I've got them somewhere.

Dik

 

[hokie66]

My experience is that stainless bolts used with galvanized steel or aluminum are not an issue unless in a marine or other aggressive environment.

http://www.bssa.org.uk/topics.php?article=89

 

[tdstructural]

I called Hilti and I also e-mailed them with the same question. It took a few more hours to hear back with the text but I did end up getting answers from two different people at Hilti.

They both gave the same general response but the e-mail response did point out that they did NOT have an expert in their office to advise on the galvanic corrosion.

I agree with the post regarding my legal obligation. If Hilti tells me to use galvanized bolts instead of stainless steel I will do that. After all, I am using their product. Besides - the carbon steel galvanized bolts have a higher strength.

I plan on providing specs that ask for oversize tapping on the nuts to make room for the galvanizing. I know it is a very small increase in bolt size but I've read on this forum that some engineers have witnessed situations where the nuts shred the threads because they no longer fit right.

 

[Ron]

Here are your two questions:

I'm using Hilti HIT-RE 500-SD epoxy anchor bolts. If I use the ASTM A193 Grade B and galvanize the steel will I still get the epoxy to steel adhesion? If I use the ASTM F 593 Stainless Steel will I have problems with the dissimilar metals (A36 galvanized baseplates and stainless steel bolts)?

One at a time...

No. You will get epoxy to galvanizing adhesion. As long as the galvanizing stays, the epoxy will likely adhere to that. If you get a condition where the galvanizing layer has to do its job and become sacrificial, you will lose the epoxy bond.

Next....

Stainless steel to carbon steel is not enough of a dissimilar condition to be of concern.

As others have noted, I specify stainless steel fasteners (bolts, screws,rivets, etc.) where I have dissimilar metal conditions such as aluminum and steel applications.

I would use the stainless steel for your application.

 

[dik]

Ron:
Take a gander at the difference between galvanized steel and stainless and compare it to carbon steel.

Dik

 

[apsix]

It's generally OK to use stainless fasteners for galvanised structure due to the relatively low exposed surface area of stainless.

It is not OK in reverse as the galvanising will disappear prematurely.

 

[Ron]

dik...agree there's a difference, it's just that the area effect is greater than the electrical potential difference, so it works. (see apsix's post above)

Which corrosion series chart were your checking?

 

[jtx]

The link below, I think, definitively answers this question. As long as you are using 300 series stainless steel anchors, you should be fine in terms of corrosion by dissimilar metals.

http://www.galvanizeit.org/images/uploads/drGalv/HDG_stainless_steel.pdf

 

[dik]

I have the same *.pdf file in my Corrosion file and the use of austenitic stainless (316L) minimises the effect. For mild corrosion conditions, however as noted in my post, I would still use HDG anchor rods with HDG structural steel.

Dik