| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | Modeling |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Nov. 2016 10.01.00.09 |
Problem:
We have modeled a reducer. Changing the cone angle from 0.01 to 45 deg ups the expansion stress ratio from 98% to ~ 145%
Solution:
Yes, this expansion stress should increase with cone angle.
Example:
The reducer distance from the model input grid, Point tab: A09 - A10 = 22mm
The cone angel has been user specified as 0.01 deg. Therefore, per the code calculation, SIF = 0.50, but the minimum must be at least SIF =1.0.
However, if you factor in the length of the reducer as shown in the Tools> model Listing Reducer Report:
R E D U C E R D A T A L I S T I N G
OD OD Thk Thk Cone
From To Length From To From To From Angle SIF
Point Point (mm) (mm) (mm) (mm) (mm) Material (deg)
----- ----------------- ----- ----- ----- -------- ----- ------
A09 A10 22.00 105.0 60.3 30.7 11.1 A105<.3C 0.0 1.00
To Material = A106-B
The cone angle would actually be calculated to approx = 45 deg.
Using a more precise cone angle of 45 deg on Reducer dialog would calculate a new SIF = 1.56. Thus increasing the stress by a factor of the new SIF value.
If one looked at the SIF code equation, the length of the reducer is of NO concern, only the diameter, wall thickness, and cone angle. So reducing the length between reducer points will have no affect, but changing the cone angle, small diameter,or small dia pipe wall thickness will have a change.
Please refer to the code SIF calculation.
Note:
a. ASME B31.1 has the ability to consider cone angle where in ASME B31.3 a reducer SIF = 1.0.
b. A user can enter any cone angle, but this may be an incorrect value as seen above, resulting in lower loads there were wrong. The user is responsible to enter the correct cone angle as the program does not automatically calculate it.
See Also
Reducer Piping Components - Modeling Approach