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Cast iron for steam a bad idea?

I’m fairly new to steam heat and I’m taking care of a boiler that has a terrible steam leak. The leak is so bad that the unit will rarely shut down from reaching pressure or satisfying the call for heat. The lwco will shut down the unit and the VLT will fill the boiler with cold water almost every call.
My concerns are 

1.  Thermal shock to the cast iron sections causing damage. Injecting cold water into a hot boiler with low water is a concern I have

2. Sustained flue gas condensation due to the boiler always having cold water injected into it. If the boiler  doesn’t fire often due to a secondary heat source could a cast iron boiler and the chimney flue be severely damaged by this condensation on start up.

3.  With so many gallons of make up water being added daily causing extreme oxidation from so much fresh oxygen being added couldn’t this damage a cast iron boiler quickly. 

4. With so much make up water and oxidation the clogging of wet returns is very likely isn’t there a potential for overheating the boiler? 

Are these concerns legitimate and is cast iron really a good  boiler for steam giving these potentials? 

Comments

  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    Yes cast iron is good for steam. Your boiler is already trashed. If you replace it, the new one won't be leaking and you won't have these concerns.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
    EdTheHeaterManSTEAM DOCTOR
  • mattmia2
    mattmia2 Member Posts: 9,631
    Are you sure there is a steam leak in the boiler? if there is a lot of fresh water entering the boiler the oxygen and minerals in it will trash the boiler.

    you do need to confirm it is leaking steam above the water line and not a leaking buried wet return or a leak somewhere else or condensate getting stuck somewhere in the system before you condemn the boiler. if you do end up replacing the boiler you have to make sure you fix any leaks in the system or that will destroy the new boiler.
    Long Beach EdNeild5
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,829
    edited March 11
    I might say that Cast Iron is the BEST boiler for steam. Second best may be a steel fire tube boiler.
    is this a residential system?
    Can you locate the leak?
    Has it been leaking for long?
    If not leaking for long, then you may be able to save the boiler. Get someone there it assess the situation before you MUST replace the boiler.

    If the boiler is the location of the leak, then I agree with @ethicalpaul time to get some prices.

    And be sure the contractor has experience with steam. You don't want to end up coming back here with all the problems associates with inexperienced boiler installers
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Hyrdonic_Nut88
    Hyrdonic_Nut88 Member Posts: 11
    edited March 11
    I found the leak it’s in the steam line the pipe is rotted it probably a 100 years old. I filled the boiler for 20 min pulled burners and looked for leaks found known saw known the bottom of the boiler where the burner tubes are is severely rusted but I think that is due to sustained flue gas condensation not a steam leak. I can only imagine what the chimney looks like at this point. 

    The leak I found is dumping out of the main steam supply line. However I’m going to assume this is not the only leak as in how fast the Lwco comes on 

    the wet returns I cleaned as best I could they were plugged when I open the drain at the low point on the Hartford I got pretty good flow not great which makes me think one of the other returns are plugged somewhere. I plan to use a thermal imager to try and find something. 

    It’s also leaking at the sight glass pretty badly so I ordered a new one and just valved it off which I hate to do but I feel there was no better option


  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    Seems like someone would have noticed all that steam pouring into the basement!
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
    mattmia2
  • Hyrdonic_Nut88
    Hyrdonic_Nut88 Member Posts: 11
    The vlt shows 800 gallons used it’s 16 years old I feel the leak is probably 1-3 years old.  But it fills every call for heat. No matter how much I skim it I can’t get clean water back it’s wild. 
  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    Fresh water intrusion causes more corrosion, as was probably said above. Leaks must be addressed in timely fashion to minimize it.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Steamhead
    Steamhead Member Posts: 16,832
    @Hyrdonic_Nut88 , where are you located? We might know someone who can help you............
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,829
    edited March 11
    This sounds like the same boiler in your other discussion Vxt@25 fills 3-4 times a day
    You may want to merge them in order to keep this from getting confusing.

    You may also want to look at this video to get more information about Steam Boilers and how they operate. https://www.youtube.com/watch?v=U07Mp5DeFX4&t=8905s
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • mattmia2
    mattmia2 Member Posts: 9,631
    Sustained condensation is nearly impossible in a steam boiler, it needs to be far above the condensation temp to produce steam. I suppose if there were a hot water loop off of the boiler that could cause sustained condensation if it were really poorly designed.
  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    edited March 11
    Can you elaborate on that @mattmia2 ? I'm don't think I'm following. What needs to be far above the condensation temp to produce steam? Surely not the water.

    Edit: Oh you mean condensing in the exhaust gases must be
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • mattmia2
    mattmia2 Member Posts: 9,631

    Can you elaborate on that @mattmia2 ? I'm don't think I'm following. What needs to be far above the condensation temp to produce steam? Surely not the water.

    Edit: Oh you mean condensing in the exhaust gases must be

    I suppose you could get condensation in the vent somewhere but the boiler has to be at 212 f or higher to make steam and condensation happens below 140 f or so.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,517
    edited March 11
    @Hyrdonic_Nut88

    If you want to fix this you need to find and fix every leak and get the water MU under control. It may be too late to save the boiler. But you need to flush, fill and skim after you get all the leaks fixed. And flush and clean any suspect piping and clean the low water cut off and pressure control and pigtail.

    You can't blame the boiler for system problems.
    ethicalpaul
  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    mattmia2 said:


    I suppose you could get condensation in the vent somewhere but the boiler has to be at 212 f or higher to make steam and condensation happens below 140 f or so.

    Yeah, when you said condensation, it wasn't clear to me that you meant in the flue and I thought you were talking about steam condensation in the system
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el