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HARVEY WATER SOFTENERSCORROSION REPORT

H a r v e y Wa t e r S o f t e n e r s L t d , H i p l e y S t r e e t • Te l e p h o n e : 0 1 4 8 3 7 5 3 4 0 0 • w w w. h a r v e y w a t e r s o f t e n e r s . c o . u k

http://www.harveywatersofteners.co.uk

http://www.harveywatersofteners.co.uk

Aluminium Heat Exchanger Corrosion

Introduction! 1

Boiler Manufacturer Comments! 1

BS 7593:1992! 2

BS 6798:2000! 4

CLG Building Regulations! 4

Current Boiler Manufacturer Opinion! 6

Tracing the Answer! 9

Findings! 12

USA Situation! 13

The Energy Saving Trust! 15

Current British Standards and Guidance Notes! 16

Conclusion! 16

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H a r v e y Wa t e r S o f t e n e r s! A l u m i n i u m H e a t E x c h a n g e r C o r r o s i o n

Aluminium Heat Exchanger CorrosionIntroduction

Since 1992, boiler manufacturers have been led to believe that softened water is corrosive. Some of them even put a warning label on the inside of the boiler cover stating that: “Artificially softened water should not be used in the system.” The below shows an example of such a label.

Boiler Manufacturer Comments

In 2004 we contacted the boiler manufacturers to ask them why they state this; we received the response:

“We have no particular evidence, but if you look up BS 7593:1992 you will find out that it says you cannot use softened water in a central heating system where you have an aluminium heat exchanger.”


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BS 7593:1992

The standard read as follows:

“Water supplied via a water softener should not be used in any central heating system unless a corrosion inhibitor specifically formulated for the purpose has been added. Base exchange softening tends to raise the pH of the system water, which is unacceptable where the system contains aluminium, and softened water should not under any circumstances be supplied to such a system.”

BSI Meeting

We attended the next BSI committee meeting and asked why that comment had been included in the previous standard. The reply was: “It seemed like the right thing to do!”

No evidence was submitted to support that statement.

Unfortunately, nobody from the water softener industry was present at that meeting. This is the first time ever that softened water had been accused of causing corrosion by a regulation.

The standard was updated in 2006 and BS 7593:2006 now reads as follows:

“Naturally soft waters of low alkalinity or those supplied via a base-exchange resin softener have an increased potential for corrosion and, if they are to be used in any central heating system, a corrosion inhibitor specifically formulated for the purpose should be added and properly maintained”

Asking around the industry to find out why the original standard had been written excluding softened water, we were told that it was because the inhibitor manufacturers didn't want to have to spend money formulating an inhibitor that would include softened water. It was seemingly more cost effective to leave it out.

Corrosion Inhibitors

Upon further examination, in particular a report published by Phil Munn of Fernox, there is evidence to suggest that inhibitors themselves can cause corrosion.

Page 1500 refers to corrosion being caused by the chelating agents which are part of the inhibitor formula.

Please see overleaf:


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Corrosion Inhibitors Can Cause Corrosion

It specifically states:

“The chelating agents may be able to interfere with the passivation process sufficient to cause active corrosion.”

The chemical inhibitor includes chelating agents, which look for calcium in the water. When it finds calcium it forms a complex, which prevents the calcium precipitating and forming scale on the heat exchanger.

When there is no calcium in softened water, it looks for the next least noble metal, which of course is aluminium. The chemical inhibitor itself can cause corrosion in softened water.

This explains why the chemical inhibitor manufacturers did not want softened water in central heating systems. It would mean that they would have to reformulate, which would cost them a lot more money. The simple way out for them was just to ban softened water and spread the rumour that it caused corrosion.

BS 6798:2000

Once BS7593:2006 had been amended (see page 2), we approached boiler manufacturers and informed them that they could now start using softened water based on the amended British Standard. However, they responded by stating that under BS6798: 2000 softened water cannot be used. It read as follows:

5.4.5.3 Water supplied by a water softener shall not be used in any central heating system unless a corrosion inhibitor specially formulated for the purpose has been added. Softened water shall not be supplied to any system that contains aluminium.

The misinformation from BS7593 had in fact spread across to BS6798. Our trade association - the UKWTA sat in on that committee meeting where it was then changed. The new BS6798:2009 now reads that you can use softened water, provided that you use the correct inhibitor:

6.2.1.3 Water supplied by a water softener shall not be used in any central heating system unless a corrosion inhibitor specially formulated for the purpose has been added.

CLG Building Regulations

We consulted with the boiler manufacturers again and informed them of the amended rules and that they can using softened water again. They then stated that the recently published building regulations guidance suggested not using softened water! According to the CLG Building Regulation Guidance:


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Where water is artificially softened, it is advisable to feed unsoftened water not only to the drinking water taps, but also to the boiler primary circuit.

The guidance stated that where water is artificially softened it is advisable to feed unsoftened water not only to the drinking water taps, but also to the boiler primary circuit.

The urban myth from the 1992 British Standard 7593 had spread again via the inhibitor manufacturers through their trade association - the Domestic Water Treatment Association (DWTA).

Our trade association again had meetings with the CLG - the Communities and Local Government and they agreed to change the wording so that it follows BS7593: to use the correct inhibitor.

After 6 years of hard work, all the regulatory documents in the UK now say the same thing: “When using softened water, use the correct inhibitor.“

However, there is a catch.

BuildCert product certification for chemical inhibitors does not yet have a scheme for approving an inhibitor formulated for softened water.

As of December 2010 we are waiting for the HHIC to request this from BuildCert.H a r v e y Wa t e r S o f t e n e r s! A l u m i n i u m H e a t E x c h a n g e r C o r r o s i o n

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Current Boiler Manufacturer Opinion

Meanwhile, if you ask the boiler manufacturers whether they recommend softened water for their central heating installations, you get a mixed response.

These boiler manufacturers approve:


6

This boiler manufacturer is unsure:

This boiler manufacturer endorses using softened water:


7

This is Viessmann and they positively suggest that softening the water is the only treatment necessary.

They sent us a copy of their commissioning instructions for the heating system and throughout the document they mention that softening the water is all that is required when treating the water for a heating system.

One manufacturer says different things between their UK and USA guides! See the below images:

! ! UK Manual! ! ! ! ! USA Manual

This reflects the sheer level of confusion in the central heating marketplace with regard to the use of softened water and chemical inhibitors.


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Tracing the Answer

Going back to the beginning of the last century to 1903, the Permutit 'ion exchange' process was invented by a Dr. Robert Gans in Germany. Germans are often considered the best engineers in the world, with the added benefit that they like to follow the regulations and guidance from their institutes.

If you go to the Institute of German Engineers and look up their document ‘scale formation in drinking water and water heating systems’ you will find they explain very clearly what needs to be done with regard to softening and demineralisation. When you study the document you will see that they recommend the use of softened water as the best method for treating central heating water.


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They also go on to say that physical water treatment can only be used if its effectiveness can be demon-strated. At present there is no reproducible evidence so it is a catch 22. They do not recommend physical water conditioners because they do not work.

The same institute publishes part II, which is the ‘prevention of damage in water heating installations from water-side corrosion.’


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On numerous occasions throughout the document, they recommend softening as the preferred treatment and to avoid using chemical inhibitors wherever possible.

There is another DIN standard 14868, which is now a European norm so it is now also a British standard entitled ‘The Protection of Metallic Materials Against Corrosion.’

BS EN 14868:2005

The standard points out that the role of oxygen is the driving force for corrosion. If it can be prevented from getting into the central heating system, corrosion will be prevented under normal circumstances.

It mentions here that aluminium is different and that you will get no corrosion without further treatment i.e. “don’t use an inhibitor” it also goes on to explain that when alkaline products are added, i.e. corrosion inhibitors, for the protection of ferrous metals, then the pH can rise and cause problems with the aluminium.

So the best solution is to not put any inhibitor in at all or alternatively make sure you use one that has been correctly formulated.


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Again mentioning that the primary cause of corrosion is oxygen.

This is explaining that inhibitors can be used in a Case II condition, when you cannot prevent oxygen from getting in. This would be a large commercial installation over multiple storeys where it is impossible to keep air out of the system altogether.

In a Case I condition, which is standard domestic system with an expansion tank in the loft or preferably a sealed system with expansion vessel, then no oxygen can get in and so there is never a problem.

Findings

So there you have it. In Germany, where water softeners were invented, the Institute of Engineering and their DIN standard all say that you should not use chemical inhibitors and you should only use softened water and keep the oxygen out.

On the other hand, Fernox and Sentinel in England state that softened water cannot be used and that you should use a chemical inhibitor.

A further search of documents shows the European standard BS14743:205 the standards for water softeners, do not mention anywhere that softened water causes corrosion.


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The WRAS installation guidelines for water softeners do not mention corrosion at all.

USA Situation

In America, there are well over 10 million water softeners installed. If corrosion was a problem statisti-cally it would have shown up by now.

So Guy Franklin, the Managing Director of BuildCert Ltd, wrote to the National Sanitation Foundation, which carries out the standards work in America for water softeners and asked them the question.

The response came back that they’d never had a problem over there with corrosion caused by softened water.


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In 1949 when the British government published a long report on softened water there was no mention of corrosion anywhere.

If you go back even further to the 1920’s when Permutit was part of United Water Softeners they had the following to say:

A water which is naturally soft is more than likely to be corrosive, not because it is soft, but because it is probably acid owing to the ground through or over which it has passed; this is very different from a water which is soft because it has had the hardness forming salts removed in a water softening plant.

They go on to say that the idea that the boiler feed water can be rendered too soft is proved to be a relic of the days before the introduction of the scientific softening of hard water.

One thing we do know is that science does not change; the physics remains the same.

In 100 years we have been softening water and we have never had a problem with corrosion.


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The Energy Saving Trust

The Energy Saving Trust are insisting that they will not endorse a water softener until there is a chemical inhibitor available that has been approved.

The last meeting was in March 2010 and until we get a standard for a chemical inhibitor for softened water, we cannot get our endorsement from the Energy Saving Trust.


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We need an inhibitor that is approved.

Current British Standards and Guidance Notes

BS7593 – says use the correct type of inhibitor.



CLG – says use the correct type of inhibitor.

The Energy Saving Trust says they will approve your water softeners when we have a standard for a chemical inhibitor formulated for softened water.

Conclusion

If you have survived reading this long, well done!

It has been driving me potty for years but we have at last learned the lesson. You have to be a member of a trade association that attends these meetings and makes sure that our side of the story is heard and that we protect ourselves from people whose commercial interests are different to our own.

The moral is “if you are not at the table, you are on the menu!”

We are currently waiting for the HHIC to formally request BuildCert to provide a standard for an inhibitor for use with all types of water, including softened. Once we have that, we can then go back to the Energy Saving Trust and get our water softeners endorsed for their energy saving benefits.

There is more work to be done but we are turning the tide and beginning to make some progress. So your membership of the UKWTA is important. As a dealer, you owe it to yourselves and to the future of our industry to maintain your membership and to support us in our endeavours to get this situation resolved.

Thank you for your support.

Best regards,

Harvey


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