Boiler water high pH, condensate low pH

DrewBoatright

Hi,

I am having some issues figuring out what is going on with out steam system. I am new to this chemical job and may not have all the terminology down, but I will try my best. Our set up is a single boiler which cycles at 100 psig. We use sodium hydroxide, cyclohexylamine, hexametaphosphate, and diethyl aminoethanol for treatment. We have a DA tank for condensate recovery along with a water softener.

The issue we are having is our boiler water blowout is testing at 11.31 pH using a laboratory grade pH meter and our deaerator tank is testing at 6.7 pH surface sample. I have collected water samples from steam traps, condensate drip legs, and steam drip legs and each sample is within 5.7 pH to 6.95 pH. We changed a steam trap and I noticed some pitting in the pipe interior surface, and upon doing research I was wondering if CO2 / O2 could be causing the pitting picture attached. After seeing the pitting I started collecting water samples to evaluate the pH, and of course it was acidic which makes me think that CO2 is being dissolved in the condensate, but we are not using any carbonate or bicarbonate chemicals in our treatment program so I am not sure where the CO2 is coming from CO2 may not even be the culprit. I am fairly confident in my pH probe, despite the samples being very low in conductivity.

My questions are, is a pH of 11.31 with the boiler water too high?
Is a pH of 6.95 too low? The pH of 6.95 came from an IB trap drain plug
Could the volatile amine that is suppose to keep an alkaline pH downstream of the boiler be not volatilizing, or could carbonic acid be overcoming the alkalizing effects of the volatile amine?

In the samples I collected, most of them had a yellow tint, and most of them had a black sludge that reacted to a magnet. Most of the samples also had bubbles under the waterline in the sample jar. The bubbles formed on the glass and did not go away when the sample cooled.

I'm sure this is a mess of a post but any help whatso ever would be greatly appreciated.
Thank you

p.s. I have a background in chemistry and have access to a laboratory if any testing recommendations are given.

Jamie Hall

Not a bit of a mess. Nice to have someone with some chemistry background...

My own feeling is that the boiler pH is a bit high. However, if it isn't foaming I'd not worry about it. Leave it be.

On the low pH in the condensate, however... keep in mind that condensate, barring your volatile amine, is essentially distilled water -- and distilled water has no buffering capacity to speak of. In theory (right...) at standard conditions of temperature and pressure, the pH would be 7. However, even very short term exposure to normal air will drop that to the mid 6's or even lower, depending a good deal on temperature and the partial pressure of CO2 in the air. In principle there are various volatile amine treatments -- as you are obviously aware! -- and it is possible that you could use a more aggressive treatment with them.

However... don't take my word for it. Presumably you have the backing of a boiler water treatment company, and they should if they are any good at all have specialists in this kind of thing. Talk to them!

DrewBoatright

@Jamie Hall Thank you so very much for that response. You have saved me many hours of looking through forums for a similar post. I now know what to do next. Have a good one