When is CVN Required

Date 01-30-2008 21:14

D1.1 - 2.26.2.1. i think this requirement comes more from the job specs, and/or municipality requirements based on seismic zone for the most part. my DOT requires charpys for anything 5/8" and over. this started on just plate, but has grown to include shapes.

By pax23

Date 01-30-2008 21:55

Short and direction answer - when the job specs/contract documents require them.

Longer answer - when expected load types (seismic), service temperatures (low, depends on steel), and design (redundancy of members) require a expected level of notch toughness to avoid failure. Anytime where you think service conditions may creep toward a steel's transition temperature. When such cases require it, it is the engineering firms job to make sure it gets specified on job specs/contract documents.

By eekpod

Date 01-31-2008 11:41

So it sounds like it would be a contract document requirement, other than a code requirement.

In other words , let's say pre-heat. I know if I use a certain grade and thickness material, that the approitate pre-heat chart would apply.
But unless the contract says there is Charpy v-notch requirments, I don't have to worry about it.
Thanks Chris

By swnorris (****)

Date 01-31-2008 14:57

That's correct. Furthermore, and this has nothing to do with D1.1, but since you mentioned jumbo shapes, if CVN testing is required, hot rolled shapes with flanges 1 ½" thick or thicker must have a minimum CVN toughness of 20 ft.-lb at 70 degrees F, tested in the alternate core location as described in ASTM A6 Supplementary Requirement S30, and plates 2" thick or thicker must have a minimum CVN toughness of 20 ft.-lb at 70 degrees F, measured in any location permitted by ASTM A673 (which establishes the procedure for longitudinal CVN of structural steel and contains two frequencies of testing). It's critical that this information is contained in the contract specs, and that your detailer is aware of them and follows them, because he/she must include this information on the advanced bill of material so that purchasing can specify this testing at the rolling mill. There are also specific requirements for clipping corners of continuity stiffeners that will keep welds away from the k area in the web. The same goes for web doubler plates. They're sized so that there are no welds in the k area. This is because there have been issues in the last few years with cracking in the k area. This is due to the final cold straightening process at the mill, which alters the steel properties in the k area. The result is very high yield stresses coupled with lowered elongation and single digit CVN toughness. That's the reason If for some reason welds welds on continuity stiffeners or web doubler plates occur within the k area, the area adjacent to the weld has to be inspected as required by the EOR.

By eekpod

Date 01-31-2008 15:55

Snorris, thanks for your reply. We did have a job a few years ago that the jumbo shapes needed to meet CVN requirements, and we had to take a sample from the piece and send it to the lab because this stuff was from Russia and they don't automatically do CVN testing over there.
Chris

By CHGuilford (****)

Date 01-31-2008 17:57

Actually, even in the USA. CVN testing by the producing mill is not automatic. Generally you have to specify CVN requirements in your purchase order to the mill to be sure it gets done. It's not all that unusual to have to arranage for CVN testing yourself, particularly if you only need small quantities of certain sizes.

Quite often a job will be specified as requiring CVN tested material for everything on the job. This is oftentimes the result of an engineer being too "busy" to review the actual need for CVN material in a structure. Rather that check out each application, it's easier to say that all material has to be tested.
What then happens, you find some materials are difficult/impossible to have tested (16 gauge sheets for shims for example). In the course of trying to get that resolved you may then find out the engineer wasn't sure so he/she wanted to "play it safe".
If every item on, say, a building project is called out as requiring CVN tests, you might want to ask a few polite questions. It is unusual for every piece of steel to actually need CVN testing. (Of course that should happen at bid time because otherwise you have agreed to it once it's in your contract)

By Noel Tan (**)

Date 02-01-2008 02:03

eekpod,

I agreed with CHGuilford,

I think not only Rassia and US do not normally perform CVN as part of the mill testing, but all the world's mill. Without knowing the project specified:
1) Testing temperature (normally based on minimum design temperature, some code/standards are more stingent... for example: DNV submarine pipeline system sets testing temperature to be minimum design temperature - 10degree C for thickness more than 20mm)
2) Minimum energy absorbed requirement.
3) Number and location of test. (CVN may be required at root and cap if the thickness is more than or equal to 45mm)

Best Regards,
Noel Tan