Joule value for Impact test

[mechanical2014]

Hi All,

I am just wondering, how the "Joule" values has been arrived by ASME for the impact test

 

[weldstan]

Do you mean the minimum absorbed energy requirements in Joules or ft-lbs?

 

[mechanical2014]

Yes, the criteria for arriving at the minimum absorbed energy for impact test

 

[metengr]

The minimum CVN impact energy selected by the committee is to ensure risk against brittle fracture based on minimum service temperature and thickness.

 

[mechanical2014]

Thanks Metengr, i was just curious to know "How" the value has been chosen by the committee. Is there any relation between the energy value and any other parameter.

 

[weldstan]

Materials with increased tensile strength require increased absorbed energy to prevent brittle fracture. The values required in Code provide some assurance that adequate ductility is maintained at the test temperature under the design conditions. It does not provide such assurance when materials are quite thick.

 

[metengr]

The how is simply by consensus vote among voting committee members.

 

[mechanical2014]

Point taken but still some link is missing. We know that that thickness and impact test temperature are related. In the same fashion minimum absorbed energy for impact test should vary too (High joule value for thicker piece and vice versa)

 

[mechanical2014]

Correction: Less joule value for thicker piece and vice versa

 

[SJones]

The values have been derived after extensive studies of correlation between Charpy testing and fracture toughness testing - essentially starting from the work of Pellini (should you wish to Google).

In the same fashion, minimum absorbed energy for impact test should vary too

Or, the test temperature is altered whilst maintaining the same minimum Charpy energy criterion.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[weldstan]

On gas processing plants designed in the mid '70s to early '90s for locations in the USA, Canada and Britain on which I was directly involved, Joules-Thompson cooling was fully taken into account in selection of the MDMT for piping as well as vessels, initially at Owner direction.

 

[weldstan]

Another Senior moment. Previous post was meant for another question.

mechanical2014,
Greater absorbed energy values are required for very thick materials.

 

[mechanical2014]

Thanks everyone for the insight. I will accept, as it is mentioned in ASME ( Our Bible!!)

 

[Duwe6]

gotta keep in mind that large portions of Sect VIII Div-1 are "good, well-proven rules-of-thumb". Thus no precise calc's to support them, just a LOT of experience with good outcomes. 20-ftlbs has worked fine; no impetus to use a different [higher or lower] value.