Heavy Internal Corrosion on Cold Water Line.

You have not stated what kind of material the piping is Galvanized steel, galvanized wronght iron, Yalloy, brass (red) Brass (Yellow)
copper type K L or M or T.P. Copper or even lead piping like the piping off a city water main

So taking a guess it is galvanized steel the internal corrosion could be lime or other mineral deposits and the severity or the PH factor is also not known and not knowing if your using well water or city water makes it a very tough call also. You menthion inhibitors is this a rust inhibitor for the feed water to cast iron or steel boiler or to a cooling tower to prevent bacteria/ alga from growing?

You could also have errosion problems if your using copper tubing and if the velocity is exceeding the proper guidlines.
there can also be a turbulence problem if the piping was not properly reamed during installation

OR if self cleaning flux residue was not properly flushed out origionally.

Further clarification of my
07 April 2000 inquiry.
The line is copper and the
heavy deposit clusters are
copper oxide with some severe
underneath errosion. The water supply is city and the
inhibitor was added to counter this problem, so I am informed. Thanks, IJD

Try getting a water sample and contacting the copper Development association with these findings. If possible look for the manufacturers name on this tubing and the type (K,L,M) You should also try to get a pressure reading and the size (DIA) of this tubing. Unfortuntly although copper is a great material it is subject to failures under certain
water conditions AND excessive velocity (FPS)especially on hot water piping. Once you have the information the CDA can tell you exactly what caused this failure.

You may also want to check with any neighbors to see if they also have copper and if they also have this problem.
If they dont it could very well be you have a boot leg copper in your home OR the piping wasnt properly reamed and flushed out during installation and could also be undersized for the pressure you have. Good Luck