	Applies To
	Product:	AutoPIPE
	First Affected Version:	4
	Found in Version:	09.06.00.04
	Fixed and Released in Version:	09.05.01.02
	Area:	Modeling
	Severity:	Critical
	Backlog Issue Number:	138778 (10751)

Problem Description

Program not reporting max stress from -ve and +ve faces of soil and kink points

Reason

If the axial forces are different between the minus (-) or upstream side of the point and plus (+) or downstream side of the point, only the stress results from the plus (+) side of the point are reported. Consequently, if the minus (-) side axial force is greater than the plus (+) side axial force the calculated stresses may be un-conservative.

Certain stresses include the effects of axial force. In some cases these stresses are required by piping code. Additionally, there are two result model options, “Include axial force” and “Include Axial Pcase in Sus”, that may be used to include the effects of axial force when calculating stresses in the piping system.

Solution:

To illustrate this problem the following scenario can be considered:

Step 1:

Consider a simple B31.3 model, with a pipe segment running in Global X direction with three points (A00, A01, and A02)

Step 2:

Anchor both end points (A00 and A02). Place a line stop support in Global X direction at point A01 with a certain stiffness value

Step 3:

Insert an imposed support displacement (Load case S1) with a translation value of 0.1” in X direction at point A02

Step 4:

Insert soil over the entire model.

Step 5:

Copy/paste the model with an offset of 3 feet in the Z-direction and reverse the new segment B (Edit > Segment > Reverse).

Step 6:

Analyze the model (Static and SAM Analysis for SAM case 1).

Step 7:

Create the output report for Local Forces & Moments and the Code Compliance:

In summary, we have two identical segments, A and B, except that the point order is reversed on segment B. A01 and B01 should show identical results, but they do not. Instead, the program will only display one set of local forces & moments and stress results for point A01 and B01 from the plus (+) side. And the occasional stress “Sus + S1” is calculated using the plus (+) side SAM axial force, which is un-conservative at point B01, since the SAM axial force on B01 minus (-) is higher (as is displayed for A01 above in the local forces & moments).

This error is limited to models that have soil points and/or kinks (i.e. a change in pipe direction without a bend). This error applies to all piping codes except JSME, BS 7159, and ISO 14692.

The following considerations are provided below to assist in your evaluation of the potential impact of this defect on the results.

1. Evaluate whether this defect has affected any existing models by considering the criteria below.

a) Was there soil or a kink inserted in the model?

b) Was the selected piping code other than JSME, BS 7159, or ISO 14692?

c) If the piping code was MITI 501 - Class 3, was the Result Model Option “Include axial force” checked?

d) If the piping code was B31.1, was a seismic + thermal or building settlement category defined, or were the Result Model Options “Include axial force” or “Include Axial Pcase in Sus” checked?

e) Was the stresses for minus and plus faces of the point not reported separately in the code compliance or stress summary report?

A ‘No’ to one or more of the above criteria means that this defect does not affect the model’s results. No further consideration for this model is necessary. Otherwise, some possible mitigating conditions described below should be considered.

2. Evaluate possible mitigating conditions.

a. If the local axial forces on the plus (+) face of a point are higher than the local axial forces on the minus (-) face of the point, the calculated stresses on the plus (+) face of a point would be conservative.

b. Increasing the number of soil points between piping points can reduce the difference in stress between the plus (+) and minus (-) faces of the soil points.

c. When the kink or angle change between the 2 straight pipes is small, the difference in stress between the plus (+) and minus (-) faces will be small.

Avoidance:

Reverse the pipe segment so that the higher local axial forces are on the plus (+) face of the piping point.

Insert a piping point a small distance upstream, e.g. 0.1”, of the minus (-) face of any nodes which are affected and evaluate the stress given by the inserted piping point instead of the minus (-) face of the original point.

Also See:

Critical and High issues released in AutoPIPE V8i v.09.05..

AutoPIPE known issue - defect 138778 (10751)

Reason

Solution:

Avoidance:

Also See: