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de-scaling steel boilers

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Ompa Ompa	26/11/2011 17:47:10
43 forum posts 1 photos	In case I have missed some previous chat on this subject, is there anybody out there that has used a successful de-scaling treatment on a steel boiler recently. I know about the process used for a copper boiler but with the steel versions I wonder if there is anything different that should be used. Obviously after care is important as well as the need to prevent foaming and priming if possible. Thanks.
Richard Parsons	26/11/2011 17:57:28
645 forum posts 33 photos	Hi Heronsgate In a word- 'Fernox' (usual disclaimer). These folk make all sorts of plumber’s products. The tackle I used contains Phosphoric Acid. I used to buy it at a plumber’s merchant. Drgs Dick
Hugh Gilhespie	27/11/2011 09:20:56
130 forum posts 45 photos	Hi Heronsgate, The choice of 'best' descaling treatment for a steel boiler depends on what the scale is. Unless the boiler has been run on deionised (distilled) water it is likely that a lot of the scale will be hard water salts, calcium carbonates and sulphates typically. This is actually more difficult to remove than iron oxide (magnetite) scale and I wouldn't use phosphoric acid based products because it will form a layer of calcium phospate which is very insoluble and stop any futher action of the acid. The same will apply to using sulphuric acid which forms calcium sulphate. If it is a hard water scale - easy to tell as the scale will be a greyish colour I would recommend dilute, say 5% hydrochloric acid, fairly warm 40 - 60 C and with agitation. DON'T seal the boiler as there will probable be some CO2 released and DON'T leave it in any longer than needed. Hydrochloric acid will attack the steel. It is possible to inhibit the attack on the underlying metal with special chemicals but these are not easy to come by. So, fill, agitate for say 10 minutes, pour out and have a look. If the scale is still there put the acid back in and repeat until the scale has gone. Usual warnings about using acids, good PPE including very good goggles, wash off any splashes immediately. If the scale is a nice dark brown or black then it is probably nearly all iron oxide and hopefully mostly magnetite. This will dissolve easily in most acids so use the safest acid. Personally I would use citric acid at about 6% and 50 C. Will take a couple of hours to dissolve the scale and you may get some copper plating - not a serious problem. Again DON'T leave it in any longer than you need - you are losing precious metal thickness! Hope this helps, Regards, Hugh
Stub Mandrel	27/11/2011 11:13:52
4318 forum posts 291 photos 1 articles	What about citric acids, as used for descaling coffe machines/kettles etc? Works well, if a little slower, and fewer safety issues. Neil
JasonB	27/11/2011 12:25:38
25215 forum posts 3105 photos 1 articles	Deionised and distilled water are two different things, The deionised is not good for steel boilers (or silver solder if copper)as it tries to get the missing ions back from the steel. If its not massive then as Stub says kettle descaler works OK just rinse out well afterwards and then use treatment to help prevent the scale reforming. If its a bit bigger then worth investing in a proper descaler like this J Edited By JasonB on 27/11/2011 12:28:39
Ompa Ompa	27/11/2011 12:48:53
43 forum posts 1 photos	Hi to all that have answered my original question. The variety of descalers/water treatment on the market will always cause some concern, as this question poses. I/we will sift through the different ideas and advice an try whatever we decide. Thanks again for the input, all worthwhile and imformative.
Hugh Gilhespie	27/11/2011 14:30:47
130 forum posts 45 photos	Hi Jason, 'Deionised and distilled water are two different things' Are you really, really sure ? Because if you are I would guess you are up for a Nobel prize Regards, Hugh
JasonB	27/11/2011 15:05:51
25215 forum posts 3105 photos 1 articles	Two different processes. One basically by condensing steam the other done by passing the water through special resins. I have read it on a number of occasions when suitable water for our boiler uses were being discussed that deionised water was not suitable, amoung those saying it were club boiler inspectors and authors on model steam subjects. "De ionised water rips the silver solder to bits in a copper boiler. It can weaken the soldered joint to the point of failure in a matter of months. How do i know this? I used it in a small boiler when I was a lot younger." "De-ionised water is particularly nasty stuff and not good for boilers" "Don't use de-ionised water it's not the same as distilled water and can be very corrosive." I don't know the science maybe some one can comment? J Edited By JasonB on 27/11/2011 15:22:37 Edited By JasonB on 27/11/2011 15:43:04
Hugh Gilhespie	27/11/2011 17:24:51
130 forum posts 45 photos	The idea that deionised and distilled water have different properties is a myth. Different processes certainly. End result is exactly the same though - pure water with the same properties regardless of the way it was obtained . Distillation is very energy intensive and very difficult to get very pure water due mainly to entrained droplets in the steam. Ion exchange is cheaper and with good quality resins gives very pure water. I don't know owt about small boilers but on an industrial scale all high pressure boilers run on deionised water. Usually a minimum of three treatment stages for raw water, anion, cation and finally mixed bed polishing. After all that the water is treated with steam to remove dissolved gases, particularly oxygen, before going to the feed water pumps. The recirculating condensate is sometimes put through a mixed bed unit to clean it up before being reused. Water treatment quality is probably the single most important factor in the time the boiler will operate between outages. Regards, Hugh
Steambuff	27/11/2011 17:44:40
544 forum posts 8 photos	I disagree ... Deionized water is exactly that - water that has essentially been stripped of all of its ions. Water likes to be balanced in its natural state, however, and this means that it adds ions to itself to achieve that goal. Therefore, DI water grabs ions from everything it touches that can be dissolved or absorbed. It is about a close as you can get to a Universal Solvent. In our case, it will extract metals from all of the brass fittings you have, and will also pull carbon dioxide from the air. Dave
Hugh Gilhespie	27/11/2011 20:12:44
130 forum posts 45 photos	Dave, Lovely thought but water makes it own ions, hydrogen ions (plus) and hydroxyl ions (negative). These can't be removed from the water. What can be removed are impurities such as calcium ions, magnesium ions, sulphate ions, chloride ions, bicarbonate ions - the list is endless. The way that deionising resins work is by swapping nasty impurity ions with nice hydrogen or hydroxyl ions so the water is ionically balanced but without any impurities. Regards, Hugh
Stub Mandrel	27/11/2011 21:05:20
4318 forum posts 291 photos 1 articles	Wikipedia isn't very helpful although it does say: "Deionized water, however, is inherently acidic and contaminants (such as copper, dust, stainless and carbon steel, and many other common materials) rapidly supply ions, thus re-ionizing the water." But it doesn't explain why it is slightly acidic. Neil
Anthony Knights	28/11/2011 00:37:33
681 forum posts 260 photos	water H2O = H+ (OH)- all acids contain H+ ions Edited By Anthony Knights on 28/11/2011 00:38:56
Kerrin Galvin	28/11/2011 08:53:40
44 forum posts 9 photos	Hi guys, As posted by Hugh, deionised water is just that, all dissolved minerals are removed, usually in a 3 stage process, as per Hugh. The end product contains no dissolved minerals, well for most practable purposes, the reason for the reduced pH is the dissolved carbon dioxide, which forms carbonic acid. Distiller water is condensed steam, which as was noted by Hugh will most likely still contain some minerals, multiply distilling will reduce this, deionisation is quicker. Have played this game in a couple of jobs, 1 in the power industry where we used a " zero solid " dosing regime...using hydrazine to give pH control.......you won't find this in your local chemist, well not any more! The other in the petrochemical industry where we used 2 forms of phosphate, 1 which gave us a pH reducing mix, the other a pH increasing mix, blend to get the desired boiler pH. In both cases these where high pressure boilers, 100 bar. The 2nd also had 2 boilers at 24 bar. In all cases we ran a deairator up stream. Oh cold water contains 10 ppm dissolved oxygen, which you most defiantly don't want in a HP boiler. For steel boilers, or cooper there are off the shelf chemicals for dosing. Cheers Kerrin
Ompa Ompa	28/11/2011 10:27:20
43 forum posts 1 photos	Isn't it amazing how these seemingly straightforward 'threads' quickly become overshadowed by more technical and sciebtific debates!!
JasonB	28/11/2011 18:28:43
25215 forum posts 3105 photos 1 articles	Thanks for the insight Kerrin. So would it be fair to say that with our small boilers with out the PH adjustments the di-ionized water would be acidic and this is what is no good for our boilers rather than it removing ions from the steel? J
Stub Mandrel	28/11/2011 21:15:16
4318 forum posts 291 photos 1 articles	> water > H2O = H+ (OH)- > all acids contain H+ ions pH is depends on the ratio of H+ to OH- so in pure water as the H+ are balanced by an equal amount of (basic) hydroxyl ions ... no net acidity and pH=7. Presumably in deionised water the remaining organic content locks up a sufficient proprtion of the hydroxyls to create a weak organic acids. (Hypothesis unsupported by any evidence). Neil
Hugh Gilhespie	28/11/2011 21:26:02
130 forum posts 45 photos	Hi Jason A couple of drops of household ammonia in the water will jack the pH up to a safe level and will be beneficial to the boiler. Somewhere around pH 10 would be ideal. I would avoid any non-volatile water treatments as without using a lot of blow-down you risk getting a lot of deposits building up. Ammonia won't cause any deposits and is perfectly safe to use, although a bit niffy when concentrated. The other advantage of using ammonia is that it makes draining and drying the boiler after use less important. You won't get any rusting when the water pH is 10 or over. Still some risk in the head space above the water level though so for long term storage draining is best. Regards, Hugh
Hugh Gilhespie	28/11/2011 21:40:26
130 forum posts 45 photos	A quick ps DON'T use ammonia in copper boilers. Good for steel boilers only. Regards, Hugh
Kerrin Galvin	05/12/2011 14:10:30
44 forum posts 9 photos	Hi Jason, Sorry for the slow reply. Yes you are correct, deionised water is acidic as produced. It would require something to raise the pH to prevent corrison. Neil, pH is the measure of the negative log of the hydrogen ion concentration... written as pH = - [log H+]. The scale runs 1 to 14, 7 being neutral, a decrease of 1 is 10 times more acidid, conversly an increase of 1 10 times less acidic. Ok back to the orginal topic, de-scaling boilers, here goes.... Helment on standing behind protective walls Industry uses some great acid to clean boilers, however they also have a lab & a bunch of guys to make sure the clean isnt over done. The concentration of acid is not high & is most likely inhibited to control the rate of clean. Monitoring of temperature, pH, iron, acid conc to name a few. It is unlikely that many if any, yours turely as well, will have access to the equipment to do this. Beside which you would be very unlikey to get this acid, which if you get it on you likes to go looking for bone!! So what can we use? I have asked a couple of guys who have done boiler cleans & they both say using citric acid for us is the way to go. As Hugh suggests warm it up, use say 5%, & keep it moving about in the boiler (easier said than done). IF you leave it in the boiler a bit long ( this is the hard bit) it wont eat the boiler before your eyes, as would be possible with sulphuric or hydrochloic acids. It may take a couple of washes, using new solution to remove the scale ( as was also pointed out hard or soft scale will take different times) Jason posted a link to a company that can supply a boiler de-scaler which looks like it might be worth a go..anybody tried it? It may be worth checking with your local council on what hardness water you have in your area, simple test does your soap form foam easily? Most of us dont blow our boilers down during a days running, except at the end of the day, as you top up on the run you are cycling up the minerals in the boiler. If you want to get into deionising your boiler feed then you only need to use a water softener, cation resin used in the sodium for, this will replace calcium & magnesium ions ( the predominant cations, plus a couple of others) with sodium. This produces a soft water with less likely hood of forming hard scale & then by adding something to raise the pH ( my suggestion would be trisodium phosphate, this can be used in both copper & steel, there are suppliers of boiler treatment for our size as well) make the upkeep of the boiler a lot easier. The cation resin is reuseable & is regenerated using common salt. Cheers Kerrin

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