Problem:

How does "Use corroded thickness in all analysis" on Edit Model options dialog different from "Use nominal thickness" on Results Model Options dialog?

Solution:

The Edit Model Option "Use corroded thickness in all analysis" setting is often confused with Results Model Option "Use Nominal Thickness" setting. These two are 2 complete different settings will that affect the analysis by:application in different ways. 

"Use corroded thickness in analysis"

One of the first analysis performed by AutoPIPE is in an area of the program referred to as the pre-processor. At this time the The program will break up the entire model into a number of stiffness equations that are all solved simultaneously by matrix or Stiffness Matrixwith matrices. On particular property This setting will control which wall thickness is used at th 

"In analysis" can be defined in a number of different ways. For AutoPIPE there are analyin Edit Options will affect when determining pipe stiffness matrix, like EA/Lsolving these matrices for calculating displacement, 3EI/L3forces, etcand moment.

Using  

Enabling this feature results in setting may lower forces and momentsBUT , however most piping codes insist on using nominal thickness for the flexibility analysis. After changing this setting, the model should be re-analyzed. 

"Use nominal thickness" in Result Options will " 

This setting does not affect Stress the calculations of moments. The input in this field determines which pipe wall thickness value is used in stress calculations in the Post processor. Once After the moments Force and Moments have been computed, the stress are calculatedas M/Znom or M/Zcor. Zcor will give higher stress. After changing this setting and re-analyze the system, notice that the moments have not change. 

When calculating the displacement, forces, and moment AutoPIPE will need to create a model stiffness matrix

The typical approach in most piping codes is to use nominal in analysis (Edit) and use corroded in stresses (Result) to give most conservative results.

The result option is confusing often as there are different stresses, like hoop, expansion, sustained, occasional and some codes require corroded for some but not others.For this reason we have a table in the online help to show what happens for each code for different stress types.

In v9.4 we will add a separate option for hoop stress. "Use nom thk for hoop".

See AutoPIPE help for complete details on these settings. 

See Also

Tools> Model Options> Edit settings

Bentley AutoPIPE