SMYS question 1

[LearnerN]

In regards to steel pipelines, what is the yield strength point referred to as being the SMYS of the pipe when looking at a stress-strain curve for steel? Is it the yield point on the stress-strain curve that accompanies the beginning of plastic strain? But I've also read about the difference (for materials) between "Upper Yield Strength" (where the sudden drop in stress happens...the point that accompanies the beginning of plastic strain) vs the "Lower Yield Strength" (the lower being the "plateau" yield strength after the initial yielding occurs). I was reading in the Lindeberg PE reference manual that LOWER yield strength is commonly reported as the yield strength.

So my question for steel pipelines: is SMYS (1) the point that accompanies the beginning of plastic strain, OR (2) the LOWER "plateau" yield strength?

 

[C2it]

Conservatism suggests that the lower yield point is recognised. That would also accord with the notional yield point assigned to stainless and some other metals, where 0.2% strain is addressed as the 'yield' point.

 

[TGS4]

C2it - not 0.2% strain, but using the 0.2% offset method. That should be described in the referenced ASTM specs.

 

[LittleInch]

WRT steel pipelines a good place to look is API 5L.

This defines two ways of testing for this.

For pipes > L 625 / X90 then it is the 0.2% offset method or Rp0.2

For all others it is the Rt0.5, i.e. the stress at which strain of 0.5% occurs.

See this for an explanation of what that means...

http://www.tiniusolsen.com/pdf/Pamphlet4.pdf

As TGS4 says - look in the spec for your particular definition for your material / specification.

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Also: There's usually a good reason why everyone does it that way