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paresh_career001
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Location: Gujarat, India
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Differences in Allowable Stress for Materials

05/03/2009 9:33 AM

I have made study of two material (SA 387 Gr.11 cl2 & SA 542 Gr D cl 4a) regarding allowable stress for ASME VIII-2 ed. 2004 and ed. 2007.

I found that both code have different factor of safety i.e 3 and 2.4 respectively.

then why there is much difference in allowable stress and allowable stress basis......

if only factor of safety is changed then both material graph should be parallel like in second figure.

why this ?

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XMech
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#1

Re: Difference in allowable stress for material

05/03/2009 5:33 PM

Please consider ALL the criteria for allowable stress (yield, tensile, room/elevated, temperature, & creep)

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Jerry New Hampshire
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#2

Re: Differences in Allowable Stress for Materials

05/05/2009 7:56 PM

It has been some years since I have worked in ASME Boiler Code, but my first thought would be fatigue life syndrome. Some materials resist repeated load cycles better than others. As an example, aluminum when stressed, regardless of the level of stress, remembers that it has been stressed. Stress it enough times at any level and it will fail. Most steels on the other hand, if stressed to 33% or less, will never fail.

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