Black Pipe Scaling
So when i working with a mechanic the other week i asked him what causes such heavy scale build up in the black iron nipples n 90s on the chilled and condensor water loop. He really didnt have a 100% answer for me so he gave it to as a homework assignment to find out. after looking through numerous books and google searches i still haven't found anything. So im hoping that someone on here could give me an answer that would explain what kind of chemical reaction takes place that makes scale adhere to the inside of black pipe.
Water has oxygen, which reacts with iron to form rust.
Also, pure water is VERY expensive, so water used in boilers and condensers is often full of minerals and salt which oxidize, react and due to the roughness of the pipe, eventually builds up molecule by molecule until its visible.
I would say that is a pretty good explanation given by syndicated.
With what he said about "pure water", though, I would think that theoretically, pure water could make the problems worse, or perhaps cause other problems. Since pure water would be completely void of minerals, it would try to absorb minerals from it's surrounding. Also, "pure water" rapidly absorbs carbon dioxide as soon as it is exposed to atmosphere, turning it acidic.
It is good to have a chemical guy that understands this stuff to test the water and recommend a course of treatment to keep the piping in good shape.
I had the luck of taking over a large property that had many closed loops, all of which had been neglected big time for eons.
One particular steam to water heat exchanger was basically ruined do to total lack of blowdown....and with blow down air separators right beside it.
Several important important things came out of fixing all the former " Lack " of workmanship.
Some chemical treatment of closed loops is definitely needed. If they are very dirty, you need multiple blow down points, and isolation valves galore never hurt...ESP when dealing with fancoil units. You may find yourself in some ceiling at a far point from the pump and things are like mud, and you have no flow through your fancoils. From that point you have to start cleaning the loop up.
Aside from inhibitors and other things your chemical guy should know about, you may have to add a caustic cleaning agent to help you get a bad loop flowing again. Air eliminators at the right places are invaluable also if you have to take these systems down and then get them to pump again. If they are not there, get a welder in and tell him where they are to going to be put. Weld on female NPT fittings to which you can then put a nipple, ball valve and air eliminator. Gauges at specific points will tell you whats happening in the loop and also give you and indicator you can look at for what is normal for that system. Too many old systems are neglected in the area of readout devices. You are flying blind without guage readings etc.
One absolutely brilliant device I found to aid the process is an air and dirt eliminator made by Spirotherm. If you are lucky the local rep has a table top demo made of clear lucite, which will show you how the canister drops dirt out of moving water. They work.
Once the loop is clean and hopefully fairly leak free, the inhibitor is set to do the job. Like anything chemical treatment has to be monitored regular for it to work. If you are not keeping the concentration, then you have leaks and are making up water.
Working wye strainers, valves, and reducing stations are all part of the equation. You need about 12 PSIG of static water at the highest point of your building loop for it to work and flow. The better the design, the quicker it is to get it back up if you have to take a quantity of water out for repairs of any kind. There is a valuable tool we used to keep called a " Jet Sweat " another brand is " Water Gate " which allow you to sweat or thread fit a live water line. Very useful and timesaving in some instances.