01. Why does AutoPIPE apply the square root only “partially” when calculating SNiP 2.05.06-85 (1997)

Applies To
Environment: N/A
Area: Analysis
Original Author:Bentley Technical Support Group
Date Logged
& Current Version
Oct. 2015


SNiP 2.05.06-85 (1997) verify longitudinal stress:

Underground section, the longitudinal stress shall be lower than y2*R1 .

SNiP formula for y2 is the following:


AutoPipe applied formula for y2 is the following (from the program online Help):


Why does AutoPIPE apply the square root only “partially”? (verified by hand calculation that Autopipe really applies the declared formula) 

Note: the same holds true for y4


AutoPIPE calculates y1 through y4 keeping the last term outside of the square root. 

The equations used in the actual SNiP code are not consistent and do not seems to yield correct results for a possible range of values. So AutoPIPE implementation seems to be the more logical solution, which may not be exactly as the actual Russian code states.

If we use the exact formula from the Russian snip code, we would run in to undefined values when HoopStress/R2 crosses 0.866.

AutoPIPE's equation yields a better graph in which the ratio ó/R2 can range from 0.0 to 1.0:

AutoPIPE results are conservative when compared to using the actual Russian SNiP equation (in the range where SNiP equation would yields real numbers).

See Also

SNIP Piping Code Calculation Issues in AutoPIPE

Bentley AutoPIPE