That Pesky O₂ Molecule – How Oxygen Finds Its Way Back Into a Steam Boiler

RayWohlfarth · January 16

In this weeks video, I talk about that pesky oxygen molecule and how, despite your best efforts, keeps finding its way back into the boiler water. The video goes over the damage it does and how to minimize the damage.

https://www.youtube.com/watch?v=lpcO3Qb_k-Q

ethicalpaul · January 16

An observation about where oxygen does its real damage:

You are right that oxygen enters cold water and we do of course see returns (usually at the boiler) rot out pretty quick.

However, where do the boilers always fail? At the top of the section, every single time. How is that possible? There's no water up there, there's only air and steam, right?

You also said in your video correctly that the oxygen is forced out of the water as the water is heated. But I would ask "where does that oxygen go?" It is released into the steam chest, or the upper part of each section, where it is free to attack the cast iron. This is why I think it doesn't matter when you heat the water you add to the boiler—regardless that oxygen is going to be freed to attack the boiler.

So in my mind, the best way to keep your boiler from seeing premature rotting death is to use makeup water that was recently boiled, and to use a product such as 8-Way that has oxygen scavenging capability as well as the known corrosion-reducing pH booster chemicals.

Thank you for your video!

hot_rod · January 16

Oxygen in hydronic systems gets consumed in the oxidation process. Within days or weeks you should end up with "dead" oxygen starved water. Air left over will be mostly nitrogen.

So if no additional water is added, or O2 is not being pulled in somewhere corrossion should stop.

Does that translate to steam systems? How much water should a typical system take on continually.

The pressure on the water has some to do with air solubility, but that is not an option in steam systems.

Steam specific manufacturers refer to mechanical deareation ad chemicals with sodium sulfite O2 scavengers, and ph control. So as @ethicalpaul suggests treating the steam boiler is just as important, maybe more so, as treating a hydronic boiler.

Some info from the Rhomar manual

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Day_Tripper · January 22

@ethicalpaul @hot_rod

This is one of my main concerns with my steam boiler. My water make up is from the cold water supply. We've only been in our house 2 seasons so I was only able to insulate some of the mains and condensate returns that were accessible in the basement. Another problem is I don't think I have an easily accessible port to add chemicals. The only vertical piping is the PTR valve and it's soldered in place.

Where would you recommend I add my treatment chemicals?
Do you recommend placing an inexpensive small tankless hot water unit & O2 separator inline with my water make up? I would prefer not to pipe off the hot water heater.

Thanks!

ethicalpaul · January 22

you have it very easy. Your Utica has these side outlets to which you can attach an elbow and a nipple sloped toward the boiler with an optional reducer and ball valve

With this setup you can add treatment or even all your makeup water (I add only heated distilled water because I’m a fanatic)

I don’t recommend a separate water heater setup because it’s too easy to just pour it in yourself every few weeks (minimizing leaks is the first priority)

PS I see from your contractor’s sticker you are in Michigan. Hello from a native Michigander

STEAM DOCTOR · January 22

Just cut out the soldered pipe, connected to the relief valve. Reinstall with threaded or compression fittings and piping

RayWohlfarth · January 22

Thanks @hot_rod Always there to offer expertise.

@ethicalpaul good point

wcs5050 · January 22

IMG_0712.jpeg

Could we consider rot above the water line as a victim of O2?

What are folks view on a small carbon block filter on the feed water to remove chlorine and light solids… not worth the bother, no point?

ethicalpaul · January 22

Could we consider rot above the water line as a victim of O2?

Absolutely

What are folks view on a small carbon block filter on the feed water to remove chlorine and light solids… not worth the bother, no point?

Ezzy and Clammy do it. I exclusively use pre-heated distilled water for makeup water, so I'm not one to judge

Day_Tripper · January 22

@ethicalpaul hello from MI! Thank you both for the info. I am manually adding make up water around every 7 to 10 days when I hit low water cut off and the house gets cold, so I don't think your suggestion is the correct solution for me. I do appreciate your dedication 🫡. I have looked at every single pipe and wall in my house and I would swear on my life there are no leaks. In terms of ease and function, I think @STEAM DOCTOR's suggestion is the one I feel most comfortable with completing myself.

Is your main concern with an external heater/bubbler that the potential for leaks increases with more connections?

STEAM DOCTOR · January 22

I don't know physics or water chemistry or metal chemistry or anything like that. I have long assumed that there is not much corrosion below the water level, because that metal is totally submerged in water. The metal above the water line, tends to have water and moisture on it, without being submerged. Would assume that is more likely to corrode. And the more oxygen in that water, the higher the corrosion likelihood is. Can't remember ever seeing a boiler rust out at the actual water level itself.

ethicalpaul · January 22

Yes I have noticed the same thing from a distance of this forum @STEAM DOCTOR that all holes seem to always be at the top of the sections.

And yet the other major rot point always seems to be where the wet return hits the boiler, so something interesting happens there as well.

@Day_Tripper that is a lot more water than I like to see being added. Look for leaks of steam or water, especially the vents. There is also the possibility that your boiler has a hole in it as seen in the above picture (but probably smaller). I want to see less than 1" of drop in the gauge glass every month or so during the heating season. Using as much water as you are using will reduce the lifespan of your boiler. Of course if it already has a hole in it that concern is in the past.

Is your main concern with an external heater/bubbler that the potential for leaks increases with more connections?

No, just that it's a lot of hassle for minimal benefit

Day_Tripper · January 22

@ethicalpaul I agree that the make up water cadence is too short. I have looked at every vent and wall and joist and pipe and I do not see any obvious leaks. I will say this: my radiators will occasionally hiss for an extended period. I have looked at the vents while this is happening but I don't see an obvious 'drip' of water, perhaps just steam escaping. How can I check my boiler for a hole?

ethicalpaul · January 22

if your vents are letting steam out, that could be the whole leak.

the easiest way to test the boiler is to overfill it to the header and see if water starts raining down to the floor under the boiler

Day_Tripper · January 22

@ethicalpaul I will try and preform the overfill test today but my guess is it's the vents. Here's the long and the short of it. 2 story house with thermostat on 2nd floor. 1st floor only has half the rooms with radiators because the previous owners were morons and removed them from the kitchen and dining room at some point. Because of this, the 2nd floor reaches temp with ease while the 1st floor never gets a chance to 'catch up'. My wife then bumps up the heat from the nighttime program of 68 deg to 73 deg in the morning when we get up so the living room will be ~67 deg. This is when the hissing is most pronounced. The boiler is working to take the house (with missing radiators on half the first floor) from 68 to 73, so the living room where we spend a lot of time in is remotely comfortable.

ethicalpaul · January 22

You are in a difficult situation with that removed radiation.

But you are exacerbating it with that 5 degree setback at night. I recommend stop doing that and see if the downstairs is able to stay comfortable.

If the upstairs gets too hot for your comfort at night, try covering one or more radiators with blankets until you are comfortable, but keep in mind doing so is similar to removing radiation and may make your system cycle more.

Cycling more isn't a big deal for gas, but could be more problematic for oil.

Megawboiler · January 22

Hmmm… my experienced HVAC man advises weekly blowdowns of the rust separator on my single pipe low pressure system. Circa early 1900's, massive cast iron. This obviously means that I'm adding water from the city main 40-50 times a year. Any advice on this? Is there such a thing as an inline oxygen eliminator?

Day_Tripper · January 22

@ethicalpaul Thanks again. I'm going to put that thermostat on a permanent 72 deg hold. We have radiator covers with top hinges that I can close or prop open a bit with plywood to increase/decrease air convection. I'll keep the upstairs covers down and the 1st floor open. Thanks again.

ethicalpaul · January 22

https://forum.heatinghelp.com/discussion/comment/1883530#Comment_1883530

Can you send a photo of this "rust separator"? You might be referring to a float-style low-water cutoff device

RayWohlfarth · 11:16AM

As water is heated, the o2 molecules are driven from the water. They bounce around the steam side of the boiler until they end up in the steam and out into the system.

Captain Who · 12:34PM

Do you think that Rectorseal 8-way can protect steam mains at all? They say it does but I'm skeptical unless there is a lot of carryover. Otherwise it should be distilled water I believe. Here's what 100 years of corrosion inside a steam main that is not pitched correctly looks like. This is the downstream end of a 16 ft. section that went into a Tee for the riser to an upstairs radiator and what it looked like after I cut through it and chiseled it out. Kept it as a souvenir. Even if it is basically distilled water I would think that it would absorb CO2 from the air in the main and create some carbonic acid. But it is obviously very hot and would limit absorption. In the off season I had cool distilled water pooled up in there and saturated with air containing CO2. Would be interesting to know what the pH was. Anyway, you can see that this main rotted out at and below the waterline and there is lots of meat still on the pipe in the upper areas.

ethicalpaul · 2:27PM

No, I don’t think 8-way protects the mains. I have thought about carryover helping but given that even a sagging, rusting main lasts 100 years, it hardly seems worth it to consider.

Captain Who · 3:15PM

For comparison, here is the upstream end of that 16 ft. main that did have a small amount of downward pitch (unlike being level at the other end), and 1/2 in. higher elevation. Much less corrosion and presumably no standing water situation.

Captain Who · 4:01PM

These pictures show corrosion on upstream end better. I'd estimate 1/2 way through penetration at the worst spots. Uneven corrosion must be due to localized differences in alloy composition, and once the pitting corrosion starts a self perpetuating small pool of water exists. Definitely a different situation from boiler corrosion with treated water and mostly de-aerated water and "maybe" some protective effect from scale buildup.

That Pesky O₂ Molecule – How Oxygen Finds Its Way Back Into a Steam Boiler

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