B31.3 Chapter IX, Allow. Stress 2

[Irpin]

I am currently working on a wellhead system, to API 6A and B31.3 Chapter IX High Pressure Piping, my question is to calculate the thickness of an inline 2’’ NB Blind, I was using Para K304.5.3 Blanks(B31.3), which stipulates Allowable Stress from Table K-1. However the Material is Alloy 625 UNS N06625 which is not represented in Table K-1. Would I be correct in referring to Table A-1 where the Material is available.

Thanks in advance

 

[XL83NL]

No, you wont be corrected. The basis for chapter IX is different, review K302.3.2.

 

[Irpin]

Hi XL83NL,
Thanks, having read K302.3.2, the equation(31) I believe would establish the allowable stress for my material, but I am having trouble defining Ry, I just don't understand the wording of the definition "Ry is the ratio of the average temperature dependant trend curve value of yield strength to the room temperature yield strength". I have noticed there are a few threads on the same topic but I don't think its been explained yet. Help would be appreciated.

 

[metengr]

Ry refers to the knock down ratio of yield strength reduction at temperature normalized to the yield strength at room temperature. So, if the YS at room temperature is 3 and the yield strength at elevated temperature was determined using a trend curve is 1, the Ry would be 1/3.

 

[XL83NL]

metengr, could you elaborate on those trend curves? where are they taken from - where can you find em? what is it exactly?

regards

 

[metengr]

Hi XL83NL
First, Happy New Year. One of these days I am going to take my bucket list vacation to Australia and New Zealand. The YS trend curves are established by submitters of code cases, as part of a technical data package. Also, you can develop your own basic trend curves by picking off the yield strength values listed for the applicable materials in ASME B&PV Code, Section II, Part D, Table Y-1.

 

[Irpin]

Thanks Metengr,
I will look at BPV Code and try and develop a trend curve as you suggested. Can you explain why Table K-1 does noy simply cover the same materials as Table A-1 ?