Reduced impact test temperature

[kwaliteitshenk]

We have tested a piece of SA350 LF2 with specimen thickness of 3 mm at -40°. Now Both ASME VIII-1 and B31.3 say that our minimum design temperature should be 22.2°C higher.(-40°-22.2°= -17.8°C). In other words for a min. design temperature of -40° we should have been testing at -62.2° (-40°C minus 22.2°C).What is the reason for this reduction. It seem to me that a test specimen of 3 mm absorbs less energie than a test specimen of 10 mm at the same temperature. So when a the smaller specimen has acceptable value's a thicker also will be acceptable.

Please advise

 

[SJones]

It doesn't quite work like that. The thinner the test piece as compared to the actual material, the more benign (less conservative)the test because triaxiality is reduced. Therefore, some compensation in the test parameters has to be made. Some codes reduce the test temperature; some codes increase the relative energy requirements.

Steve Jones
Materials & Corrosion Engineer

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

 

[stanweld]

You must reread the Code requirements. The temperature reduction is required when the test coupon is less than 80% of the thickness of material welded.