HDG and dual cert A325/A490 bolts

[Dinosaur]

Folks,

We received certification paperwork for high-strength bolts to be used on our project. The fasteners have been dual certified to ASTM A325 and ASTM A490. The fasteners have been hot-dip galvanized. I understand there has been a long standing prohibition on galvanizing ASTM A490 bolts due to concerns of hydrogen embrittlement. We specifically state that ASTM A325 Type 1 bolts get HDG and that ASTM A490 bolts get painted, not HDG. Is there anyone that can discuss whether a dual certified bolt could be at risk for hydrogen embrittlement? Thanks.

 

[ajh1]

Given that the issue of hydrogen embrittlement is most related to bolt strength and hardness, it would seem that a dual certified bolt (never heard of such) would be required to meet the most stringent criteria of the various certifications, i.e., in this case the A490 and should therefore not be HDG.

 

[HgTX]

What ajh1 said. I've never heard of dual-certified A325/490 bolts, and if they're HDG, then they do NOT meet the A490 requirements, and thus the dual "certification" is completely bogus. Which to me means everything from that supplier is questionable.

A charitable explanation might be that they are actually not HDG, but instead coated in accordance with ASTM F 1136, which is water-based dip or spray Zn/Al coating. Does any of the paperwork actually say HDG, or are they just silver-looking?

But, really, I question the dual certification. What size bolts are these? For bolts up to 1", there is a tiny overlap in the required hardness in the two specs. For bolts over 1", there's no overlap at all, so no way they could even be dual-certified. Have you checked the test results against the spec requirement? (Has your supplier?)

Hg

Eng-Tips policies: faq731-376

 

[Dinosaur]

The bolts in question are 7/8 inch diameter. The reported properties do fall in the overlap. My inclination is to say these ASTM A490 bolts that were HDG do not meet our specs. However, I would like to hear what others think.

 

[unclesyd]

I agree with HgTx in that this supplier should go to the top of your list.

I just talked to my fastener distributor buddy and he stated that he has never heard or seen a dual certification of A325 and A490 bolts. He also stated that he has never seen or supplied A490 HDG. He also stated that he does get several requests a month about A325 HDG.
He also stated that the only fasteners he has seen dual certified is the occasional A193 B7 and L7 and even this is rare.
He said to be careful in the purchase of any structural bolting as there is some very questionable material coming from offshore. He said they are currently supplying several thousand A394 tower bolts to replace some that evidently were purchased on the gray market.

 

[25oak]

Just to reiterate what has already been said above; A325 and A490 structural bolts are VERY different both from a chemical and mechanical standpoint. It is improbable that there would ever be a situation that these bolts could be dual certified. The load requirements of a full size 7/8" A325 bolt is a minimum 55,450 lbf tensile. The same diameter A490 has a minimum tensile 69,300 lbf and max of 79,950 lbf. Hardness also becomes issue, because A325 has a maximum hardness that roughly equates minimum tensile of A490. Moreover, there are differences between these bolt's head marking and testing. Whether your design requires A325 or A490, neither product can be certified to the other.

In addition, no knowledgeable distributor or manufacturer would supply galvanized A490 and I would strongly recommend questioning anything from this supplier. ASTM covers the dangers of galvanizing A490s extensively (A143, F2329, A490 etc).

Adam

 

[HgTX]

Good point about the marking; I'd forgotten all about that. What do they say on them? And which kind was specified?

Hg

Eng-Tips policies: faq731-376

 

[25oak]

Each grade and manufacturers unique identifier must be marked on the top of head. Both specifications state that bolts which are not marked "shall be considered nonconforming and subject to rejection."

A325 Head Marking

A490 Head Marking