impedance of a pipe, skin effect

["\"Tesla list\" <tesla-at-pupman-dot-com>Terry Fritz" <teslalist-at-twfpowerelectronics-dot-com>]

Original poster: =?iso-8859-1?Q?=C1lvaro?= Aballe <aaballe-at-eupecespana-dot-com> 

Dear tesla experts,

First of all, I should say that I am a chemist (no familiar with what you 
may normally talk here). However, I think you can help me a lot.

I would like to know what is the impedance of a pipeline (about 10-mile 
long buried pipe (0.375 inches thick) made of steel (ferromagnetic) 
carrying natural gas or oil).
There is a rectifier having one of these leads connected to the pipe, and 
the other lead connected to a grounding system: so a 120Hz rectified 
current is going through the ground into different points of the pipe (with 
damaged coating) and coming back to the rectifier through the pipe.

I understand that I should not considered the system as a transmission line 
because is too short (10 miles or so) compared to the current frequency 
(120Hz).

Is the impedance for a pipeline the same as for a cylindrical conductor (no 
hollow)? That is; is the Z= (1+j)/(s·d); s=conductance, d=skin depth, 
valid?. Can I apply this equation even for low frequencies such as 120Hz?

 From Z= (1+j)/(s·d), I can obtain the internal inductance and the surface 
resistance..Are there any other factors to consider (external inductance, 
coupled inductance)?

Thanks a lot.

Alvaro Aballe