Here is how I do this type of piping (Lofting) in Blender.

Select your mesh and in edit mode (edges) select an edgeloop where you want the piping to go.

Press Shift+D followed by enter to duplicate the edgeloop then immediately press "P" and choose selection.  This separates the edgeloop from the original mesh without moving its position.

Select your original mesh and press "H" to hide it, you should now be left with the duplicated edgeloop.

In Object mode select your duplicated edgeloop.  Press Alt+C and choose Curve from Mesh/Text.  This converts your edgeloop mesh to a curve.

In general 3D terms you now have a "path" that you can loft a "profile curve" along.

Now add a bezier circle to your scene.

Select your path curve and in the Properties panel select the Curve tab.

Click on the Bevel Object field (in Geometry) and select the Bezier Circle that is listed.

You will now see the profile curve lofted along the path curve.  You will probably find that the lofted shape is way to big.  To fix this select your profile curve (Bezier Circle) and scale it down.  You may have realised at this point that what ever shape your profile curve is that is what gets lofted along your path.  If you select your profile curve and change to edit mode and move the points around you will see the changes in the lofted mesh.

If you unhide your original mesh you will now see that the lofted mesh follows the original edgeloop.

A couple of tips at this stage. 

If you still needed to subdivided your original mesh you will want to avoid creating a heavily dense mesh in your lofted mesh.

To adress this select your profile curve.

In the curve properties panel look for the "Preview U" box (in Resolution).

Reduce the default number to around 2-4.  If you zoom in on your lofted mesh, then change the "Preview U" number you will see the effect this has on the loft.  By reducing the resolution of the loft it will reduce the density of the mesh when it gets subdivided later.

Once your happy with the result select the lofted mesh and press Alt+C and change the selection to "Mesh from Curve".  Now you can delete the profiel curve as it is no longer needed unless you have other lofts to do that you want the same profile.

At this stage the original mesh and your lofted mesh will have the same number of rings.  So if you need to make the two meshes one continuous mesh you can delete any unwanted faces on the lofted mesh and then "Bridge Edgeloops" to join them.

Now you can subdivide and smooth as required. 

 

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