Model Engine Maker

Engines => Restoration of Model Engines => Topic started by: RonGinger on August 08, 2019, 09:14:22 PM

Title: Boiler cleaning
Post by: RonGinger on August 08, 2019, 09:14:22 PM
I have a large model tug boat, about 5 feet long. Its boiler is a horizontal tube about 6" dia and 12" long. I do not know the exact tube configuration, but the main fire tube is 1 1/2 dia. The boiler has two fittings on the bottom, connected to valves and a blow down manifold. I have removed the tubes for these bottom fittings and find they are plugged solid.

I put a cleaning solution for lime, scale and rust in and have let it soak for over a day. It has not loosened anything.

I cannot identify exactly what is on the bottom of the boiler, but it must be solid. What can I put in the boiler that might clean it? As far as I know it always contained normal tap water.
Title: Re: Boiler cleaning
Post by: rspringer on August 08, 2019, 10:58:53 PM
 I am assuming a copper boiler and that the boiler its self is plugged up.  Remove all plugs.  Use a piece of wire to see how bad the blockage is.  It could just be around those plugs.  Gently use a small drill or rod to open up the blockage if possible.  If you can remove a bit of the offending material,  put it in a plastic container and try different solutions.  You will find most of the commercial cleaning agents clean not dissolve.  I had a large boiler that was so stopped up that it held 120 psig with the washout plugs removed.  I ended up cutting the mud ring off and using a hammer and chisel to dislodge the crud.  Once a product that dissolves the crud is discovered you are home free.  Most of the off the shelve solutions work better if warmed and agitated.  It will be a slow process.  It did not collect in one day so it wont go away in a day.  I used muriatic acid on that steel boiler.  Even that only removed a small amount at a time.  I would suggest in the future to use a boiler treatment.  LSB 8000 is what we use in our steel boilers with copper tubes.  It helps to keep the solids in suspension until blow down.  You might want to contact them to see what they recommend for copper boilers.  I talked to one of their folks a couple of years ago and he said they were working on something for copper boilers.
Title: Re: Boiler cleaning
Post by: Zephyrin on August 09, 2019, 09:24:50 AM
limestone deposits normally dissolve with an acid solution, if not, there is probably a good layer of oil in the boiler, which happens when the boiler cools with the cap closed, and sucks the oil as being under vacuum. I suggest a good rinsing with acetone, followed by a descaling, as for the domestic coffee maker.
Title: Re: Boiler cleaning
Post by: rspringer on August 09, 2019, 09:40:50 AM
If it is the connecting tubes it may be better just to replace them.
Title: Re: Boiler cleaning
Post by: RonGinger on August 09, 2019, 12:20:29 PM
Thanks for the replies.

The boiler is all copper, with no handholds or cleanout plugs. It was built by a friend and in the 70's and used then but not much since then, and not at all since 1995. He does not remember a lot of the details of its use.

I had not thought of the oil possibility, but that is possible. The descaling product I am using is a commercial one, it has only a trade name no real indication of its composition.

I am in the US, and we don't descale a lot of tea pots here. What would be a good chemical name for a descaler? I know I can get muriatic acid and maybe some battery acid. I assume the copper would not be to bothered by either of these?
Title: Re: Boiler cleaning
Post by: MJM460 on August 09, 2019, 12:35:44 PM
Hi RonGinger, that is a nice size model and boiler. 

The salts contained in normal tap water are usually mostly sodium and calcium salts.  The sodium ones, eg sodium chloride, or common table salt are highly soluble in water and cause little problem (unless your boiler is stainless steel).

When your boiler steams, the water evaporates but leaves most of the salt behind in a solution which is much more concentrated than the original feed water.  Hence the need to blow down the boiler to empty it, preferably while still hot at the end of a run. 

Normal blowdown is pretty effective for the sodium salts but if your tap water has any ground water origin, it will contain calcium salts, calcium carbonate or limestone for example.  This is a totally different beast from the sodium salts.  It is hardly soluble at all.  Water can seep through limestone for thousands of years and create little more than a cave which we enjoy exploring for the stalactites and stalactites if we are thin enough to squeeze through.  And when the water emerges, usually warm and great for swimming, it deposits the calcium carbonate on everything it splashes on, or makes a floating mass as it cools.  Normal blowdown routines do not lower the concentration of the remaining water below the solubility limit, so the limestone is deposited in your boiler despite a careful blowdown practice, even from normal drinkable tap-water.

To remove this you need something that will dissolve the limestone and replace it with a soluble calcium salt.  Limestone is alkaline. The usual acid reaction is acid plus base gives salt plus water.  In the case of a carbonate you get hydrogen carbonate which continues to react to give CO2 plus water, but the Calcium remains.  So with hydrochloric acid you get calcium chloride, or sulphuric acid calcium sulphate.  Similarly with other acids. 

So far I have not been faced with the problem, though recently we went through places where the water contained enough calcium to leave grit in the bottom of the coffee cup.  It makes truly horrible tea.  And only a few jug fulls has left the kettle in serious need of a clean.  So I will have to face it soon. 

I tried a search for ďcalcium salt solubilityĒ, to see what comes up.   From the list I found, I suggest the following.

Calcium chloride is quite soluble in water so hydrochloric acid is a likely candidate, calcium sulphate is not soluble, so sulphuric acid will not work, citric acid less likely unless you find information to the contrary.   Vinegar is acetic acid, may work, as calcium acetate is another which is quite soluble in water.  Also nitric acid, as calcium nitrate is soluble, but nitric acid is nasty and better avoided.  Always the solubility of the resulting salt is the best clue to which acid will be worth trying.  All assuming of course that you have a copper boiler, which will not be harmed by these good pickling acids.  In the end, if you can chip out a bit and test it is the best as already mentioned, but sometimes a bit of relevant theory can save time and also save the cost of fluids unlikely to do the job. 

They will attack a steel boiler so more care is needed if your boiler is steel.  And you donít want chlorides anywhere near a stainless steel boiler.  Because the deposit is not very soluble, it may take quite a while if your acid is not strong enough.  But if too strong, the reaction may develop a lot of heat.  So start with relatively weak acid, and slowly increase the strength by making up progressively stronger solutions.  Always add acid to water not the other way around as this also creates a lot of heat and can spit acid if there is not enough water in the mixture.  Chemical resistant gloves, goggles long sleeves etc.  look after yourself first.

And if the water is from ground water it will have other compounds as well though in smaller amounts which may or may not be soluble in water, but the majority is probably calcium carbonate.

So worth a try with some vinegar first, then hydrochloric acid, but not sulphuric acid nor oxalic acid (in some rust treatments).

I have had minimal success with CLR and similar cleaning products, and I suspect the commercial coffee machine cleaners are more useful when you have it nearly clean.

Hopefully that will get you a good start, but with a well crudded up boiler it will probably be a slow process.


Three posts while I typed, so some repetition of what others have said.  Sorry about that.

Muriatic acid is hydrochloric acid, used in this country quite strong for brick cleaning.  Battery acid is sulphuric acid and will not work as explained above.
Title: Re: Boiler cleaning
Post by: steam guy willy on August 09, 2019, 02:54:55 PM
Hi MJM. My step brother was an ERA in the navy and he said they used Ferric Cloride in the steam ships still in use then ...this was about 1968 if i remember correctly ??  !!this came up because when i was an electronics engineer in the Army i was using FeCl3 to make name plates and printed Cct boards ..PS....would it be worthwhile when making a boiler to have at the bottom a large screw in plug that can be periodically removed to keep an eye on the deposits ??

Title: Re: Boiler cleaning
Post by: Stuart on August 09, 2019, 03:11:00 PM
If and when you have it cleaned be careful for the first few streamingís it will prime like crazy to the extent of hen the safeties lift it will chuck out the water as well , often happens with a brand new boiler as well

Citric acid will do the job , as you donít have tea pots use coffee machine descaled 😂

Citric acid is the choice for decaying injector cones but donít leave them in to long hour is ok

Title: Re: Boiler cleaning
Post by: Admiral_dk on August 09, 2019, 08:06:53 PM
As most acids WILL destroy the copper and therefore the boiler - I will say they are not options ....

Vinegar is a nice descaler that usually don't do anything to metal and I use it from time to time as such - mind you I only have about 1 mm. to remove and this will be done in less than 12 hours.

I would also consider citric acid as sugested, since it is very mild. Another option is the stuff sold for descaling coffee machines.
Title: Re: Boiler cleaning
Post by: rspringer on August 09, 2019, 09:18:10 PM
If any kind of acid is used don't forget to wash the boiler well with baking soda to neutralize the acid. Use it even on the commercial stuff  boilers have lots of little hiding places for the acid to keep working away.

Strange some of the things that work in boilers.  I have seen potato peels used,  they help keep crud in suspension.  When I said it would be a slow process I did not mean leave it sitting in acid long.  The acid will do its thing pretty quick and then start eating the harder and desirable  substances.
 Also remove any brass fittings.  Brass and copper react differently to solvents and cleaners. 
Title: Re: Boiler cleaning
Post by: cnr6400 on August 09, 2019, 10:49:44 PM
Can you apply any harsh vibration to the scale by putting something against the outer shell? A blunt point tip in an air chisel comes to mind, or a blunt tip in a hammer drill maybe? Good luck.
Title: Re: Boiler cleaning
Post by: crueby on August 09, 2019, 10:57:54 PM
Can you apply any harsh vibration to the scale by putting something against the outer shell? A blunt point tip in an air chisel comes to mind, or a blunt tip in a hammer drill maybe? Good luck.
Wouldn't that dent up the copper something fierce?
Title: Re: Boiler cleaning
Post by: cnr6400 on August 10, 2019, 01:57:27 AM
Hi Chris, well yes it would, unless the appropriate gentle approach with such potentially harmful treatment were used.....

Everything in degrees of course. I would just let the tool rattle on the copper at first to gently get the metal vibrating, hopefully at a different rate than the scale, shaking it loose. I would not push hard or apply heavy force.

Just pretend you are waking up shop elves with the tool, rather than causing them gross blunt trauma.  :naughty:

Of course vinegar / citric acid is probably the safest method to remove scale without harming the metal. It just takes time and many changes of chemicals.
Title: Re: Boiler cleaning
Post by: crueby on August 10, 2019, 03:33:24 AM
Title: Re: Boiler cleaning
Post by: Steamer5 on August 10, 2019, 08:08:22 AM
Hi guys,
 Depending on how much scale you have, the acid will react with the scale & in doing so will be neutralized!  SO you will most likely have to have a couple of goes, pour out the spent acid, & adding fresh acid, which ever you use, warm acid will speed up the reaction
IF you have silica based deposits thatís a whole other kettle of fish! The acid required arenít for the faint hearted, and likely unavailable to us.
Good luck & remember we are all rooting for a win, no pressure!

Cheers Kerrin
Title: Re: Boiler cleaning
Post by: RonGinger on August 10, 2019, 01:48:36 PM
Thanks, lots of good info here.

I have wondered about just leaving the acid sit there, seems like it might dissolve some top layer material then it will need to be flushed off. That suggests some kind of recirculating pump.

I like the idea of mechanical tapping. I may just try some light hammer taps, just short of denting the shell.

I got some muriatic acid, sold for cleaning bricks. I think I will try putting some in, shaking and rolling the boiler for a few minutes, then dumping it out and repeating a few times. The boiler is heavy, maybe 25 pounds, so it will be tough to do it to much. I will give it a final rinse with some baking soda.
Title: Re: Boiler cleaning
Post by: derekwarner on August 10, 2019, 11:12:38 PM
Spent some in in South Australia with family......ironed a white [Funeral] shirt and the conventional Sunbeam type steam iron spat out a few brown steam stains.......thankfully these were on the back of the shirt & it was winter so my jacket would cover them

After the event, I poured CLR into the iron & left it for 2 hours........emptied the CLR out via the press pump on the handle to ensure the CLR had penetrated all internal steam tubes & orifaces

Poured clean tap water into the iron & turned the machine to high/cotton selection

Brownish ooze shot from all of the iron sole plate holes :stickpoke:................depleted the water via the clean function........refilled  & waited....

Brownish ooze shot from all of the iron sole plate holes :stickpoke:

This process was repeated again the next day :facepalm:

Went to a Department store, purchased a new electric iron and a 4 litre bottle of de-mineralised water

Title: Re: Boiler cleaning
Post by: MJM460 on August 10, 2019, 11:45:24 PM
I finally found some information on calcium citrate, hardly soluble at all, not worth trying in my view, you need to make a soluble salt.

Acetic acid definitely worth trying, as calcium acetate is quite soluble.  Vinegar is not very strong, so it will take a large quantity applied by many rinses.  Possibly gentle rocking the boiler for agitation.

Be careful when you handle that brick cleaning acid.  Check the strength on the label as it is sold here it is really concentrated and fumes when you open the lid.  Gloves, goggles, even a face mask, and definitely out doors, remember it dissolves concrete.

Then remember the chemistry, with the molecular weights of hydrochloric acid and calcium carbonate, it will take a lot of acid if you have a significant weight of scale, it does not just ďdisappearĒ with a quick rinse.  As the limestone is dissolved, the acid is neutralised and has to be replaced.  I am guessing many times to get it all.

So as not to dissolve the boiler, you need weak acid, add acid to the water to make only about 10% strength or less.  But it will always be a balance between time and copper loss.  Think of what you see when pickling for silver soldering.  Then it will take a lot of rinsing and emptying.  Scale is probably mostly in the bottom half and around the tubes.

As Willy says an iron chloride is used to dissolve the background for pcb manufacture.  I donít know the chemistry there, but you clearly donít want it that aggressive.  Perhaps the navy uses a very weak form to keep boilers clean.

Itís not a quick or easy process as Derek has found with his iron scale.  There are many reports of the problem, not so many reports of a solution in my observation.  We all want you to win, but if all else fails, look up Ramonís amazing Wide a Wake build log for his boiler restoration.