CP for steel pipe in Steel casing

[BRIS]

We have a 72in diameter buried CS welded steel pipe with CP protection. Specification called for road crossings by thrust boring with an 80 inch ID concrete casing. Steel line pipe was to pass through casing with annulus between the pipe and casing grouted with cement grout. Contractor has instead provided steel casing. Question is what impact does this have on the pipeline CP protection ?

Are there standard solutions for CP protected pipe passing through a steel sleeve or casing ?

 

[brimmer]

As far as CP, none or very little. The CP would not have reached the pipe (or very little current would have made it through the concrete). No current will reach the pipe or the steel casing if the casing is electrically isolated, and remains electrically isolated. If the end seals fail (which usually they eventually do), the casing can become continuous with the CP system, which usually is not too much of an isuue with most CP systems as there is enough current. The part I would be concerned about, is the potential for the steel casing to eventually fill up with soil and water when the seals fail, or a casing vent gets damaged etc. creating a corrosive condition in the casing. The casing will shield CP from getting to the pipe. This is why we now generally avoid the use of casings all together, but use a combination of increased wall thickness and burial depth under crossings, as opposed to casings. With the concrete motar fill you would not have had to worry about this.
If you are concerned with this, you could fill your steel casing with a high dielectric material (such as wax, or other products specifically designed for this) from the start. I only use a steel casing where the local code would require it.