Dissimilar-metals and electrolysis corrosion

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Dissimilar-metals and electrolysis corrosion

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RomanP

I haven't had any issues in closed loop systems, but it is disaasterous in open systems. Fresh water is a booster for galvanic corrosion. With that being said, I found a black steel riser clamp on a copper riser, in the building that is about 30-40 yo. Riser clamp fell apart with me just breathing next to it. Steel always loses the battle

Jaberstein

Find it funny that most HVAC Specifications require dielectrics union or nipples, yet the manufactured equipment that we install totally disregards that requirement, Prime example, steel coil header brazed to copper branches.

LarryK

I'm not a HVAC contractor, but this is a real issue in metal boats. In a galvanic cell you have two dissimilar metals connected electrically and also connected by a common electrically conductive fluid. The less noble of the two metals in the galvanic series will corrode and the other metal will be unaffected. So a brass valve in a steel pipe will not corrode. If there is a lot more steel than brass the steel will corrode very slowly. Fresh water with dissolved oxygen conducts electricity much better than water in a closed system that has given up its oxygen so it causes faster corrosion as we all know from Dan's books about boiler care. When I first moved to Brooklyn 30 years ago there were a lot of houses with brass water pipe and someone would put in a repair with a galvanized elbow. It didn't take long for that elbow to crack in two! Where I work we etch metal plates by immersing them in salt water and inducing a current with a DC welder.

hot_rod

The thermal conductivity of the fluid has a lot to do with corrosion and electrolysis.

Jeff Persons has presented some water quality seminars, this was part of an RPA presentation a few years back. Adding more minerals, or salt would increase the conductivity, for example. That is one of the concerns with using softened water in boilers, you have a high conductivity due to the ion exchange process of the softener.

A TDS meter will give you a more accurate number in PPM.

warno

@Jaberstein

We do that exact thing at work. Not real often but a 4- 6" carbon steel nipple soldered to a copper connection is not to uncommon in our shop. And it almost always seems to be a threaded carbon stub sweat on.