In AutoPLANT you can switch Tracing on and off in Piping > Setup > Drawing Preferences. Tracing on/off is represented by the value 0 or 1 in the Tracing property of each piping component.
If you want the Tracing property to be available for OpenPlant Isometrics Manager, you need to map these properties in the schema.

Open the Schema:

Use the class editor to open the OpenPlant_3D.01.04.ecschema.xml from the project location: c:\ProgramData\Bentley\Plant V8i\Bentley Plant V8i Projects\<project>\Config\OpenPlant\schemas\OpenPlant_3D.01.04.ecschema.xml.

Steps to Accomplish:

1- In the Class Editor tree browser, expand “Classes” to:
Classes > Plant Base Object > Named Item > Device > Piping Component.

2- With Piping Component, click the “Properties” tab.

3- The TRACING property is not yet available, so we need to add it: click the “Add” button and select “Add New”

4- A new property is added in the property list.
You need to replace the name in the name field: replace “Property” with “TRACING”:

5- To define property mapping for TRACING, now select TRACING from the property list to make it active

6- Click “Custom Attributes” > “Add/Remove”

7- From the displayed list of custom attributes, find “AutoPLANT_PDW_Property_Map”

8- Use the down-arrow button to add AutoPLANT_PDW_Property_Map to “Applied custom attributes”

9- Click OK

10- The new property map is added to the TRACING property definition:

11- For “PropertyName” you can now specify TRACING, which is the AutoPLANT property to which you want to map TRACING.

12- Now save the schema changes and exit Class Editor

13- To make tracing visible on the iso, we are going to superimpose the tracing value (0 or 1) on the insulation thickness. OPIM draws a dashed line along the pipe line when insulation thickness > 0.
NOTE: The same dash-line symbology is used for insulation and tracing alike.

14- Supplement the OpenPlant_3d schema with OpenPlant_3D_Supplemental_Isometrics_Isoextractor.01.04.ecschema.xml

15- Browse to Classes > Plant Base Object and make sure the “Class” tab is the active tab.

16- On the class tab you will be able to find the category “Default Bill Of Material Labels”

17- Right-click “other attributes and select “Add Element”

18- On the new entry in the “other attributes” array, specify the Name: INSULATION_THICKNESS.
And for its value specify:
IM.GetValue("INSULATION_THICKNESS","0") + IM.GetValue("TRACING","0")/100

 
NOTE: by dividing tracing by 100, we are sure to not increase the insulation thickness value with any full millimeter. But if insulation thickness is empty, then it will make thickness to become larger than zero and so trigger the dashed line to be drawn in the iso.

19- Save the schemas and close the Class Editor.

If you now process isos from a 3D model with the TRACING property set to 1, you will see a dashed line along the pipe line in the iso.