B31 Coefficient y for Pipe Thickness Calculation 1

[Ben4piping]

Hi, B31.1 was changed in the 2005 version to show coefficient y=0 for cast iron and non-ferrous materials. The previous version had y=0.4.

Will B31.3 have a similar change?

B31.3 shows only cast iron having y=0. I assume the non-ferrous materials fall in the "other ductile metals" category.

 

[stel8]

I am also interested in Y value for ferritic cast iron pipe according to B31.1 and B31.3, latest version.
Anyone, please with an answer!

 

[bvi]

It remains 0.4 for other ductile metals in B31.3. This is based on the stress distribution through the thickness of the pipe, and basically calculates the hoop stress at the ID for internal pressure. The factors goes up in the creep range, when it is defined as it is for some metals, because redistribution of stress due to creep reduces the maximum stress at the ID. Y is defined as 0, I believe, simply to be conservative, for cast iron. This results in the simple Barlow formula based on pipe OD.

 

[Ben4piping]

Example calculation per B31.1 for required thickness of titanium NPS 4, with P= 740 psig, SE = 12.1 psi, A = 0 :
when y = 0.0, tm = 0.1376
when y = 0.4, tm = 0.1343

So, I see there is little difference, and y = 0 is more conservative. Non-ferrous metals (aluminum, nickel alloys, copper, and titanium) have y = 0 in B31.1 and y = 0.4 in B31.3.

Thanks,
Ben Nottingham