Although 70Cu 30Ni is nobler than copper alone, they are very close each other in seawater galvanic series so, I don%E2%80™t think your corrosion mechanism was galvanic corrosion. You need to check if your welding filler metal was really 70Cu 30Ni. You should also investigate if the fluid service of your pipe was submitted of any kind of contamination, which induces corrosion on the stressed base metal heat affected zone. Best Regards Luis Marques

It seems that your copper pipe is being corroded by cold-water attack because of well water low velocity, low hardness and pH less than 8.5. You should have high oxygen and carbon dioxide content, maybe high sulfates, chlorides and dissolved solids, which are prone to copper. Copper ion deposition from copper pipe in the system causes pitting. If contaminants deposit onto the copper surface, differential aeration cells are set up, and pit the surface. Oxygen deposit corrosion causes tuberculation Regards Luis Marques