de-scaling steel boilers

Advert

New Replies

Report Bug

Help/FAQs

de-scaling steel boilers

This topic has 28 replies, 13 voices, and was last updated 27 February 2015 at 00:37 by Chris Pattison 1.

Viewing 25 posts - 1 through 25 (of 29 total)

1 2 →

Author

Posts
26 November 2011 at 17:47 #2726
Ompa Ompa
Participant
@ompaompa11814
Advert

26 November 2011 at 17:47 #78625
Ompa Ompa
Participant
@ompaompa11814
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.
26 November 2011 at 17:57 #78628
Richard Parsons
Participant
@richardparsons61721
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
27 November 2011 at 09:20 #78678
Hugh Gilhespie
Participant
@hughgilhespie56163
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
27 November 2011 at 11:13 #78685
Sub Mandrel
Participant
@submandrel
What about citric acids, as used for descaling coffe machines/kettles etc?

Works well, if a little slower, and fewer safety issues.

Neil
27 November 2011 at 12:25 #78691
JasonB
Moderator
@jasonb
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
27 November 2011 at 12:48 #78693
Ompa Ompa
Participant
@ompaompa11814
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.
27 November 2011 at 14:30 #78712
Hugh Gilhespie
Participant
@hughgilhespie56163
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
27 November 2011 at 15:05 #78715
JasonB
Moderator
@jasonb
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
27 November 2011 at 17:24 #78728
Hugh Gilhespie
Participant
@hughgilhespie56163
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
27 November 2011 at 17:44 #78730
Steambuff
Participant
@steambuff
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
27 November 2011 at 20:12 #78749
Hugh Gilhespie
Participant
@hughgilhespie56163
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
27 November 2011 at 21:05 #78759
Sub Mandrel
Participant
@submandrel
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
28 November 2011 at 00:37 #78772
Anthony Knights
Participant
@anthonyknights16741
water

H2O = H+ (OH)-

all acids contain H+ ions

Edited By Anthony Knights on 28/11/2011 00:38:56
28 November 2011 at 08:53 #78783
Kerrin Galvin
Participant
@kerringalvin72662
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
28 November 2011 at 10:27 #78795
Ompa Ompa
Participant
@ompaompa11814
Isn’t it amazing how these seemingly straightforward ‘threads’ quickly become overshadowed by more technical and sciebtific debates!!
28 November 2011 at 18:28 #78806
JasonB
Moderator
@jasonb
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
28 November 2011 at 21:15 #78822
Sub Mandrel
Participant
@submandrel
> 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
28 November 2011 at 21:26 #78823
Hugh Gilhespie
Participant
@hughgilhespie56163
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
28 November 2011 at 21:40 #78826
Hugh Gilhespie
Participant
@hughgilhespie56163
A quick ps

DON’T use ammonia in copper boilers. Good for steel boilers only.

Regards, Hugh
5 December 2011 at 14:10 #79256
Kerrin Galvin
Participant
@kerringalvin72662
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
5 December 2011 at 20:44 #79278
Hugh Gilhespie
Participant
@hughgilhespie56163
Hi Kerrin,

I am also one of the guys who has done boiler cleans. I was chief chemist and bottlewasher for 3 out of the top 4 boiler cleaning companies in the UK over the last 30 years. It is a funny industry, the names change but by and large the people stay the same. I worked for Atlas Products and Services, Redland Industrial Services, Costain Industrial Services, Brambles Industrial Services…. I have worked almost all of the old CEGB stations in the UK as well as many of the newer combined cycle stations. When we were Costain Industrial Services we pioneered the use of HF for in-service chemical cleaning in the UK. However, with the break-up of the CEGB, in-service cleans became much rarer and most of our work was pre-commission cleaning all around the globe.

Nice to hear from someone else who knows about boiler cleaning.

Regards, Hugh
6 December 2011 at 10:26 #79303
Kerrin Galvin
Participant
@kerringalvin72662
Hi Hugh,

Nice to see that somebody else counted minerals in water!

Yes we used HF, what an improvement over the other acids, not something to play with if you are not sure what you are doing.

Sounds like CEGB along with lots of other out fits with boilers a either reducing the frequency or conviencing themseleves that they dont need to do cleans… a favourite say around here……”The high cost of saving money will come to bite”

Currently I’m not involved in boiler cleans, we use hot oil instead of steam……not as much fun.

Cheers Kerrin
18 February 2015 at 02:39 #180158
Chris Pattison 1
Participant
@chrispattison1
Here in New Zealand, in order to reduce the humidity in our house, we use a dehumidifier. The water that is removed from the air drops into a tank and we use it for our iron, as it would clearly have no dissolved minerals in it. I don't think that it would be classified as deionised. Furthermore, it is free. Any reason not to use it in a boiler?
18 February 2015 at 09:49 #180186
Neil Wyatt
Moderator
@neilwyatt
HI Chris,

Water from a dehumidifier is effectively 'distilled' not deionised, so it should be as good as rainwater

Neil.
Author

Posts