Is Ductile Iron Pipe electrically continuous?

[linus2003]

Is DIP electrically continuous? I have to make a decision whether to install a tracer wire on a DIP water line. Any input will be appreciated.

 

[CarlB]

Only if it was installed with continuity straps (jumpers) at each joint. This is done if it was intended to be able to thaw a line using applied current, or possibly for cathodic protection purposes.

can you test the line for electrical continuity?

 

[bimr]

Ductile Iron pipe is manufactured in nominal 18- and 20-foot lengths and employs a rubber-gasketed jointing system. These rubber-gasketed joints offer electrical resistance that can vary from a fraction of an ohm to several ohms but nevertheless is sufficient for Ductile Iron pipelines to be considered electrically discontinuous. In effect, the rubber-gasketed joints normally segment the pipe, restricting its electrically continuous length.

Pipe joints have electrical discontinuity unless the joints are electrically bonded. DIPRA does not recommend the wholesale practice of joint bonding, but some engineers and owners call for joint bonding.

The electrical discontinuity (isolation) of the individual ductile iron pipeline sections (without cathodic protection is considered important by some for avoiding the creation of corrosion cells over extended distances, as well as for preventing stray current accumulations. Others recommend that joints be bonded to allow corrosion monitoring and interference mitigation. However, electrical isolation is not desirable when cathodic protection is used for the protection of a pipeline.

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc45225/nrcc45225.pdf

 

[rconner]

Ductile iron pipe is of course a metallic (and ferrous) pipe that may often also be locatable with magnetic or inductive methods and equipment that do not require the imposition of an electrical current on the pipeline (and regardless of joint resistance). See e.g. the information in Chapters 6 and 5 (inductive and magnetic methods) at

http://www.mytoolstore.com/schon/locating.pdf

. [I noticed e.g. a statement at this site concerning magnetic location, “…18-inch length of ¾ rebar which can be located at depths up to 7 feet”, and specifically it appears on page 44 also with regard to magnetic metal pipe locating, “Four-inch pipes can be located at depths up to 8 feet”.]
All methods and equipment for locating underground infrastructure likely have pluses and minuses and limitations, and it might not be a bad idea to consult with experienced folks in utilities and constructors etc. concerning preferred equipment and methods (as there is certainly a bewildering array out there!)
I guess it probably also could be mentioned that if extreme pipe depth is a problem with any instrument readings, comparative periodic instrument readings might also be taken as excavations proceed downward, perhaps then with more signal strength and dependability. While ductile iron pipes are known quite rugged, vacuum excavation, hand shovels and probe rods are probably best locating tools when very near all working pipelines.
There are however many different means of providing dependable electrical continuity (primarily as others have mentioned) for electrical thawing or cathodic protection purposes with ductile iron pipelines. Any new or existing joint can be “jumpered” even in the field, e.g. with insulated copper wires and thermite welds and/or field-tapped connections (with aluminum bronze bolts etc).

 

[rconner]

Oops, the kind of bolting I meant to say for thawing or CP etc. conductivity connections is "silicon bronze".