	Applies To
	Product(s):	AutoPIPE,
	Version(s):	2004, XM, & V8i
	Area:	Modeling
	Original Author:	Bentley Technical Support Group

Problem:

How do i model the boundary or contour conditions at the endpoints of the scope of project, when the line continues outside of our scope?

Another words, the piping inside of an AutoPIPE model continues beyond what has been model. How to account for extra piping with out actually modeling it?

Solution:

Due to liability law suits, Bentley cannot be expect to dictate what percentage of a large piping system is needed in an AutoPIPE model to validate the analysis. The individual assumes that responsibility. As a suggestion, the best place to start and stop modeling a piping system is at an anchor location or what can be considered an anchor. Also, another good starting and stopping point is at equipment connections. One last suggestion, a virtual anchor location (i.e. point of zero relative pipe-soil strain).

However, if your scope of work / modeling is only concerned about a small fraction of piping in a large system that contains no anchor or equipment nearby then refer to any project documentation or company standards. Some company's have a standard of modeling beyond the "Scope of work" piping by 3 additional supports and a minimum of 2-3 pipe directional changes. Another words, model extra system piping that extends past the "Scope of work" are by 3 piping supports and the piping must change directions a minimum of 2-3 times before the modeling can be terminated or assume to be insignificant to the "Scope of work" piping. The best location to end a model will always be a rigid anchor point.

Some companies choose to stop their piping model at the scope-of-work boundary, such as a flange face, isolation valve, line number change, or another selected node point. To represent the effect of the piping that exists beyond this boundary, engineers typically apply three translational stiffness values (X, Y, Z) and three rotational stiffness values (RX, RY, RZ) at the termination point. These stiffness values simulate the forces, moments, and restraint provided by the piping that is not included in the model. Suggest taking the time to validate this workflow using both Linear Analysis and Non-linear Analysis in AutoPIPE. Recall Linear Analysis is often useful because it ignores support gaps, friction, and soil effects settings defined in the model. and Applies all loads simultaneously. Results with Linear analysis workflow should show some consistencies. HOWEVER, Non-linear Analysis is more complex because the system stiffness can change during the analysis. Support gaps may open or close, supports may lift off /apply friction forces, and soil restraints may respond according to their egagement. In addition, loads are applied in a defined sequence rather than all at once. Because of these changing conditions, it is very difficult to accurately predict the true system stiffness and response in a non-linear analysis when modeling a scope-of-work boundary using equivalent stiffness values. Therefore, careful sensitivity studies and comparison with Linear Analysis results are recommended to understand the impact of the boundary assumptions.

Which workflow to choose is entirely up to the user.

Note, extending the modeling to rigid anchor(s) will always be one of the best workflows.

06a. Modeling approach to account for piping beyond modeled piping

Problem:

Solution:

See Also