ASME VIII-2 5.5.3: Which Yield and Tensile Strength Values Apply for Sps Calculations?

[HPVDE]

Hi,

I have a question regarding the value of Sps to be used when performing a fatigue assessment in accordance with 5.5.3 of ASME Section VIII, Division 2. The value of Sps is defined in 5.5.6.1 (d). Now my doubt is what values of yield and tensile strength is the code referring to in (d)(2). The designer is supposed to calculate the ratio of Sy/Su and check if it is greater than 0.7: “except that the value from (1) shall be used when the ratio of the minimum specified yield strength to ultimate tensile strength exceeds 0.70 or the value of S is governed by time-dependent properties as indicated in Annex 3-A.”

Are Sy and Su the values at RT, operating temperature, design, average for the cycle?

I have checked API 579-1 Ed. 2021 paragraph 14.4.3.5.1 to see if that clarified the matter, as the procedure described in API 579-1 paragraph 14.4.3.2 is analogous to ASME VIII-2 5.5.3, but this condition based on the yield to tensile ratio is not there.

thanks

 

[GD2]

OP,
Its simple. To determine, Sps, you need to find out the S and Sy of the material of construction. Applicable allowable materials are given in Annex 3-A.
You can find S value from ASME Sec II Part D Subpart 1:
For Carbon and Low Alloy vessels:
For class 1, use Table 2A
For Class 2, use Table 5A

Sy values are found in ASME Sec II Part D Subpart 1 Table Y1.

 

[HPVDE]

Thank you. But this doesn't really answer my question.
I know where to find the values and which table applies to which class. My question is whether the values used to calculate the ratio Sy/Su are values at room temperature or operating temperature.

 

[IdanPV]

See 5.13 Nomenclature:

 

[TGS4]

@HPVDE - to answer your specific question regarding the Sy/Su ratio - I would calculate the ratio based on the average values of Sy and Su over the cycle of investigation.

Note that this terminology will go away in the 2025 Edition, reverting only to Sps being equal to Sy_cold+Sy_hot - per this paper.

The ratio of Sy/Su<0.7 will go away, but remains important since certain materials cyclically-soften, and so the cyclically-softened values of Sy_cold and Sy_hot need to be used.

 

[HPVDE]

Thank you, this is very helpful. I am a regular user of Div. 3 and rarely use linearisation or elastic analysis these days. I attended the PVP in Seattle so I will have a look at the paper you mentioned. I wonder if the SGHPV has noticed this change in Div 2. Maybe we need to open an item to update Div 3 as well.