Dezincification attacking brass

Special_K · July 2010

First, please forgive the lenght of this posting. there are a lot of details involved.I have not posted in the past, this is my first time. I was reading through my copy of Modern Hydronic Heating looking for something on water quality and it’s effect on hot water heating system components. I have a system that is show signs of what I think is a water quality problem and am at a loss as how to approach correcting it. Your help would be greatly appreciated.

 

Let me give you some back round on the job. Approximately 3 years ago we replaced an old oil fired steel boiler in a home on the main line out side of Philadelphia. The boiler we removed was not the original based on how it was piped. I believe the original system was a gravity system. The home has the original cast iron radiators, a zone of staple up radiant installed in the mid to late 90’s, and a zone of radiant in wet bed in a bathroom installed some time after the staple up. The staple up tubing is what I have come to know as “ Onyx “, the black rubber flexible tubing attached to a brass manifold with small balancing valves.

 

We installed a Weil McLain Ultra gas fired boiler and an indirect tank for the domestic hot water. Flushed, filled and started the system. The system includes a primary loop on a panel with one full temp. zone for the cast iron radiation, 2 thermostatic mixing valves with there own circulators, one for each radiant zone. The zone circulators are Grundfos UPS15-58FC. The domestic tank is piped directly off the boiler per manufacture recommendations. The boiler is piped to the primary loop to closely spaced tees. The bladder expansion tank and pressure reducing fill valve are piped in at the air separator on the primary loop in such a way as we are pumping away. The system has been working well with no heating complaints.

 

The first sign of this problem we noticed was corrosion around the top of the air separator where the cap screws on over the float vent. Later we found a brass ball valve corroding through the body of the valve. We have a dry well thermometer on the outlet of the mixing valves. One of the brass wells corroded through and was leaking! The brass manifold for radiant heat staple up was corroding through. We replaced the leaking parts and brought them back to examine. The copper pipe connected to the brass manifolds look fine. The brass is what was being attacked! Also the water in the system is rusty red with red mud that settles out.

 

I started looking around on the internet researching what brass is composed of and what might attack it and found information on Dezincification of brass. The information indicated that one cause would be “ Chlorine Diffusion “ what ever that is. Did I mention I’m just a HVAC guy not a metallurgist or chemist? Anyway we had the system water tested. The results are as follows;

 

- pH - 8.5

- Alkalinity to pH=4.5 - 31 mg/1 as CaCO3

- Hardness – 142 mg/L

- Iron – 0.73 mg/L

- Langelier Index – 0.01

- Manganese – 0.03 mg/L

- pH of Saturation – 8.49

- Total Dissolved Solids (TDS) – 232

 

The pH and Hardness seemed high. We called our local Weil McLain rep. with this information and told him what was happening. His direction was to flush the system with a product called Sentinel X400 Sludge Remover for Central Heating Systems. The product can remain in the system for up to 2 weeks per the instructions. Then flush the system with fresh water to remove the X400 and any trash with it and add in Sentinel X100 Inhibitor for Central Heating Systems to treat the water. The X100 is recommended by Weil McLain for the cast aluminum heat exchangers in their boilers. A piece of the puzzle is that the water supply to the house is public water that could likely have chlorine added to it. Based on that information we have the water company come to the house and test the water from the tap. The results are as follows;

 

- Hardness – 242

- Iron – 0

- Copper – 0.73 mg/L

- Chloride – 92 mg/L

- Phosphate, Meta – 0.21 mg/L

- Phosphate, Ortho – 0.21 mg/L

- Phosphate, Total – 0.33 mg/l

- Zinc – 0.55 mg/L

- pH – 7.2

- Chlorine – 1.27 mg/L

 

We are unclear what conclusions or direction this information should take us. The description of Dezincification clearly looks like what we are experiencing however the path for correcting it is not as clear. It seems the high pH may be causing it but why the pH is high is the question. Your expertise and insight into this condition would be most welcome.

hot_rod · July 2010

consider

buying some DI or DM, de-ionized or de-mineralized water to fill and blend with. I buy it locally and they fill plastic barrels for me. Most chemical and glycol companies recommend you blend and fill with this filtered water.

DI water is not the same as softened water, or RO, or distilled water. It is water that is passed through a special resin bed to remove hardness, solids, etc. Google DI water to learn more about the differences between different water treatments.

Call the local water filtration companies to find this water. I buy mine from Rhomar Water in Springfield, MO. Culligan may be another source.

Soon there may be point of use DI equipment available that you can take to the jobsite, connect to a faucet and produce DI water to fill boilers with, on a small scale

It takes a LOT of water to properly clean, flush and fill a hydronic system. The cleaner, flush, and final fill water should all be done with DI water if the water in your area is in fact the problem. Adding an expensive cleaner to "bad" water is not the best use of the product and $$. Same with blending glycols with hard, or out of spec water.

As you are learning there is a lot to know and learn about water treatment in multi-metal systems.

hr

TonyS · July 2010

Small mixed beds

are available.

http://www.portablewaterdi.com/

Special_K · July 2010

Thanks

Hot Rod

Thanks for the input. I'll look into some local suppliers. Any other thoughts would be most welcome.

Dezincification attacking brass

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