Why would the copper plumbing in a 30-year-old house develop small leaks all within an inch or 2 of a soldered fitting?

Answer 1

alot of times if the fittings are close together the solder takes but doesen't get full penetration. over time the pressure of the water will push through the solder joint. the best thing to do is drain down the system and replace the leaky joints.

Answer

More than likely the plumber used too much flux or the pipes are undersized and the velocity of the water is causing erosion of the pipe.

Copper pipe corrosion can be caused by many things and many people have had the electric power company, every electrician, water treatment company and plumber they could find try to solve their problem with no luck. It is not caused by defective pipes. The fact that you indicate that you indicate that you are using your home every few weeks may actually be aggravating the problem by not having a regular flushing of the pipes.

The known causes are: 1.) Water condition - PH, mineral content or lack of, dissolved gases, microrganisms etc. 2.) Excessive flux used in the soldering of the pipes. 3.) Water velocity in the pipes - Copper gets a thin green coating this actually inhibits further corrosion. 4.) Undersized pipes for the velocity of the water - the green coating may be eroded causing further corrosion. 5.) Electrolysis - you are correct in assuming that the stray millivolts may have something to do with your problem. Stray voltages may be from improper grounding, of electrical, cable tv, phone. Or, leakages of current from water heaters, circulator pumps, well water pumps, boilers etc. 5.) Dissimilar metals used on the piping or in contact with piping can also be a problem we all have seen where a lazy hack has used steel strap to hang a copper pipe or used a black iron nipple because he was to lazy to head for the supply house when he was 1 short for the job.

Treaments out there include: Sacraficial Anodes for underground copper pipes. Epoxy coatings inside the pipe (I'm a sceptic on that one). Finding the right water treatment for your water (Do have it tested). Finding something electrically to cure your problem Repiping the house with a pipe such as Pex tubing.

If your house has well water with a chlorinator for the presence of iron, sulphur or bacteria, the chlorine over time can thin the walls of copper pipe and cause leaks as well.

Good Luck and I hope you don't have to open the wallet too far on this one!