When is a Charpy Test Required?

[zrck99]

I've attached a pdf of a substation structure that I designed and is currently being fabricated. The only specifics that I submitted to the fabricator were requiring that the W8x28 beams be ASTM A572 GR 50 or ASTM A992 GR 50. I believe that the fabricator added their own specs prior to sending to the mill for fabrications which required that the steel meet standard Charpy Test requirements. Since graduating from school, I haven't really thought about Charpy Tests much and haven't had any issues from steel members not meeting their requirements. I refreshed myself on their purpose and it looks like Charpy Tests are used to determine the brittleness/ductility of the steel. The structure will see light wind and seismic loading. I've never heard of people being concerned about fatigue loading on substation structures similar to this but wanted to make sure that I'm not missing something before having the mill go ahead with the steel that isn't passing the Charpy Tests.

Does it surprise anyone that the steel isn't meeting the Charpy Tests? Should this be cause for concern? I've tried to find the actual requirements for A572 and A992 testing to see if Charpy Tests are even required to meet these specs but haven't had luck tracking them down online. If anyone knows where I could find them to review, that would be welcome.

Thanks for any advice.

 

[EdStainless]

If you wrote those spec number dorn then you need to buy copies of hte specs from ASTM. The legal contractual term for the materials and you had better know the requirements. As I recall at least one of these specs has provision for a supplemental requirement of impact testing.
That said, what energy at what temperature was required? And what were the results?
While this may be common for outdoor structures in very cold climates most people don't worry (not that they shouldn't).

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P.E. Metallurgy, consulting work welcomed

 

[dauwerda]

What Charpy requirements are being proposed? That is, how much energy absorbed at what temperature?

ASCE 48 is the design standard for tapered tube structures used for transmission poles and often the H-Frame and/or A-Frame deadends inside substations. This standard requires that the plate steel used on these structures meet the requirements of 15ft-lbs absorbed energy at -20°F.

This requirement sometimes gets applied to all substation structures (both mistakenly and on purpose), though it is not typical and often does come at an extra cost as it is not a test that is typically done for the HSS and rolled steel sections typical in substations.

I know that AASHTO also has requirements for steel to pass specific energy absorption requirements at different temperatures for different climate zones (I don't know what they are off the top of my head).

In general, the requirement is there to ensure the steel won't be subject to brittle fracture at colder in service temperatures, as higher strength steels tend to become less ductile at colder temperatures. I know that A572 Grade 50 typically doesn't have any issues passing the requirements of ASCE 48.

Neither A992 or A572 have a specific requirement to have charpy testing done - it would have to be specified as a supplement if it was wanted.

 

[zrck99]

Dauwerda,

Thanks for the response. I got the spec from the steel supplier and the Charpy Test is specifically required by them. This is an A992 rolled W shape with plenty of capacity. The max utilization on the column under strength level loads is 40% so I'm not concerned the structure will have performance issues. I was more wanting to make sure I was still meeting the spec itself.

Thanks,
ZRC

 

[dik]

For northern projects, I normally spec G40.21 350 WT which is a low temperature Canadian steel and they have 5 different categories...for northern projects, I usually do a CAT3, unless there are special concerns. I don't recall ever using a CAT5.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kingnero]

In Europe, we have two major criteria for determining required charpie values: thickness and temperature. If interest, I can post an excerpt from the eurocodes...

 

[dold]

Charpy tests are required (or at least we require them) for certain seismic resisting elements. Moment frames, braced frames, baseplates for those, collectors, etc. This is what we spec:

Take that for what it's worth. Your requirements may be different. I've never designed a substation. And I don't do much design considering cold weather either, so I can't speak to that.

 

[HTURKAK]

If the steel subject to tensile forces and has insufficient toughness, the impurities tend to crack and the crack propagates rapidly, which is called ‘brittle fracture’, and is a concern because of the sudden failure. The toughness of the steel decreases as the temperature decreases and thickness increases..

The accepted norm to follow is, check for design temperature and thickness of the steel .

The following doc. gives valuable info. for material selection issues..