	Applies To
	Product(s):	AutoPIPE
	Version(s):	V8i
	Area:	Calculations
	Original Author:	Bentley Technical Support Group
	Date Logged & Current Version	Oct. 2015 09.06.02.06

Problem:

It has been stated that the minimum Sy is used by Autopipe to calculate the stress ratchet allowable (temperature range) for each load pair. Is this Sy the minimum from each load pair considered or the lowest Sy from the whole set of load cases analysed?For calculation of y' in NB-3653.7 what is calculated if x<0.3 or x>0.8? Are values extrapolated linearly / curve fitted / or 0.3 and 0.8 are used as the minimum or maximum value to be used

Solution:

The procedure for determining a more accurate Ratchet Range was included in the nuclear training material. There is more information there than in the Program help.

In short all the load pairs are considered and the most conservative value of Sy is used associated with the largest Average Temp for the pair, thus leading to the lowest DT1 range.

As for x and y’ you can develop an expression that links x to y’. It looks like this.\

AutoPIPE limits the calculation of y’ to between x values 0.001 and 1.0.

Note: Again, the program works to a range on x values from 0.001 to 1. It follows the expressions your y' and linearly extrapolates all intermediate values.

The online help has been updated with the following image and will appear in future versions of the program:

Note: There was a change in the handling of Ratchet Stress check in 1995.

Prior to 1995 the check tested only failing pairs as per code requirement.

After 1995 the check tests all pairs where the fail or not for Ratchet.

Conclusion:

The ratchet allowable Sy applied by Autopipe Nuclear is very conservative. It is especially conservative if there are a few high temperature transient ranges as opposed to numerous small temperature range transients. The program does not take an average of the worst range. It takes the maximum temperature from all the ranges.

For further information on this topic see the notes at the following AutoPIPE help section:

Help > Contents> Contents Tab> Reference Information> Code Compliance Calculations> ASME BPV-III-1-NB, NC, or ND > Level A and B service Limits> NB - Primary Plus Secondary Stress Intensity Range (Equation 10)

Q. When calculating ratchet allowable, is Sy the minimum from each load pair considered or the lowes

Problem:

Solution:

Conclusion:

See Also