Reverse Osmosis (RO) Water

When you are not running RO water in the equipment, what are you running, and for how many hours between flushes. I can't see much harm if once every week you flush it. Most of the data you will find will be for continuous exposure, so interpolate.

Better yet, get some carbon steel shims of the same material as your parts and run some exposure tests. Surely you have a micrometer? Measure some samples, stick them in some RO at 220 and measure them after 24/48/72 hours. Then do the math.

Be sure to keep fresh RO water flowing around the sample, to get an accurate etch rate.

I was going to write more, but I forgot. I think.

220degF is above the normal boiling temperature of the water, so the test samples above will need to be kept under pressure.

Keep the pH in the 8.5 region and corrosion will not be an issue.

Go to www.uswaterservices.com. They specialize in RO units and corrosion inhibitors. I am sure that they may have something on their website that might help you out or have contact information for someone that could.

Corrosion rates in 'RO water' can be either very low, or very high--depending on the level of dissolved solids, minerals,etc remaining in the RO water, the amount of dissolved oxygen, the surface 'contamination' on the steel before cleaning,etc. LOTS of variables to consider.

IF you allow air/oxygen to enter the vessel after it has been 'flushed', any damp, clean steel will develop 'flash rust' in minutes/seconds. How much? it depends on oxygen amount.

High purity (mega-ohm) water is a very aggressive solvent.

Hi AKsrey,

What are the etching salts you are cleaning off?

If you can rinse the items you are 'flushing' in normal H2O at around boiling point, before submersion in the RO it would keep the RO cleaner for longer with less suspended solid and so make it more effective. This may not be possible. But after the TDS build up over time and or use, the RO, if used specifically to 'clean', becomes obviously less effective and needs a filter and or scrubber to keep it at optimum. Your tanks may have this anyway but I have to mention it.

I see you also mention your flushing using a RO at 10 ℉ above boiling point. This may be to be certain a constant boiling temp' is maintained?

Are you using the water and or resultant steam as well as the 'cleanness' of the RO? If you allow TDS (Total Dissolved Solids) to build in the RO if you are flushing after acid treatment for instance, the RO will gradually become acidic, and RO at higher than BP will be corrosive under pressure. I had in mind the temp' at 220 ℉, which usually means under pressure).

If you are heating RO to a higher than BP to allow you to use the steam to flush then depending on what previous processes were used on the flushed items, the steam should be OK to flush with. But depending entirely on the TDS type, this could combine with your steam and be an aggressive wash rather than a steam clean. Just a thought. And some sites below will pick up on this.

See below for more details of corrosion Data, in the first site. And other what may be useful Date and other detail in the subsequent sites listed just as further possible information for you.

RO and corrosion Data.

I suggest you read from [1.2.1] and after on the site above first.

The site directly below this is the best RO and other filtration of all kinds site ! There is so much info'.

Water quality- different water filtration methods- Reverse Osmosis ...Home of APEC Ultra Reverse Osmosis Water Filter Systems ... Organics such as herbicides and pesticides, with boiling points lower than 100 °C cannot be ...www.freedrinkingwater.com/water.../quality-water-filtration-method.htm - Cached - Similar -

• Bibliography of Technical Papers - Corrosion Abstract: Persistent corrosion of carbon steel cooling water heat exchangers in a .... Various corrective measures are provided along with support data. ... of non-chemical pretreatment systems, e.g., desalination and reverse osmosis. ...
  www.cti.org/tech_papers/corrosion.shtml - Cached - Similar -
• [PDF]
• Corrosion of Candidate Materials in Lake Rotokawa Geothermal Exposure
• File Format: PDF/Adobe Acrobat - View as HTML
• by JC Estill - 1995 - Related articles - All 6 versions
• Corrosion rates were determined for CDA 613, CDA 715, A-36 carbon steel, 1020 carbon steel, and Alloy 825 flat coupons ... In an effort to gather corrosion data from an environment that is rooted in natural sources of water and rock, samples of some of the proposed container materials were exposed to a ..... ro ...
• www.osti.gov/bridge/servlets/purl/88595-EtAUgX/.../88595.pdf -
• Corrosion engineering - Corrosion rate of carbon & stainless steel ...
• 10 posts - 3 authors - Last post: 10 JulWe are currently battling stainless steel corrosion and stress cracking on our extrusion cooling systems. The RO water source was ...
• www.eng-tips.com/viewthread.cfm?qid=26273&page=84 - Cached -
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  by WK McGrane - Cited by 5 - Related articles - All 6 versions
  reverse osmosis system with ozone treatment for cooling tower water. ... instrumentation (corrosion meters) were installed. Copper and carbon steel were ... steel and reduced corrosion in copper. These data also are shown in Table I. ...
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  sensors for hydrogen in steels, reverse osmosis and water pollution and beneficiation of ores. ... 6.7 Published Corrosion Data. References. Bibliography. ... 7.22 Corrosion of a Carbon Steel Tank in a Phosphatizing Process. ...
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I hope this is of use to you.

Take care and good luck.

Hello, That was a very good answer, There is really not much else to say that you have not already said. I give you my GA vote for the answer it was very informative.

We have a RO water treatment facility at the mill that I work at that purifies water that feeds 3 large boilers. The mill had a new storage tank made from 304 stainless steel because the water was very corrosive to carbon steel. When it was first put on line the RO water was to cold and it caused allot of problems with the boiler systems DA tanks and heaters so we also had to install a heat exchanger system to heat the water before feeding it to the boilers. We had all of the RO water treatment system piping, valves and other materials made from 304 stainless steel because of the corrosion problems.

Hi pipewelder,

I hope all your problems are fine now?

The stainless system as you have fitted now is kind of what I was 'hinting' at, but for some, the cost has to be borne in mind. Though of course if a system needs changing you can hardly get round that by short cuts?

It was not really made clear, well, to me anyway, what exactly the OP is having problems with and what 'type' of total RO system he has. So until I get a post from him or her I hope my post helps them. I had to make the scope broad because I just did not know the details the OP was talking of.

I thank you for your GA my friend. Unexpected it was for sure, as others had more or less answered the question. But as I got into it, it kind of 'muddied the waters' and I realised the OP had not really given enough detail. Though at first glance it said he was flushing in RO, why have the water higher than boiling point. And if it is higher than boiling point does that mean they are using the steam and not the liquid as first reading suggest?

Take care and thank you once again.

The hot RO water is used to flush a polymer gel from equipment surfaces. This occurs about once per week and lasts four hours. The temperature is >212 F because there is a slight back pressure due to the vent pipe.

The RO water has a pH of 5.7. Specific conductance of < 3 micromhos. Total hardness of 0.06 ppm of CaCO3. Other ions available upon request.

Hi AKsrey,

I appreciate your reply post, thank you.

Just a couple of queries. You first mentioned the Temp was 220, now you say 212, which is waters BP. I just thought I had to point out what may happen if and when you kept the cleaning at 220, thats all.

I think you must have some kind of scrubber or filter, otherwise I would expect the ppm to be much higher.

I hope my post #5 was or will be of some use?

My research was aimed at the 'tank' as a 'cleaner', rather than what may have been an alternative problem you were getting with say a water heating system or similar?

Knowing it is specifically a kind of cleaning tank and you flush using the water rather than the steam, means there should be no problems with any circulatory pipework, except perhaps any drainage.

What was your worry with carbon steel, was it what you are cleaning or part of the tank the RO is in? If this is a real worry and is part of the tank then perhaps a new tank may be the way to go? If the carbon steel if part of, or the part you are cleaning you may have to either use another way of cleaning, or treat the corroding parts asap after you remove them with a light oil, or perhaps a lacquer?

Is it possible to maybe dip the carbon steel in zinc or similar to help prevent the corrosion?

These are just thoughts ruminating in my head. If you want more help after perhaps some tests and or research of your own, please do not hesitate to ask anything else.

Good luck.

One of the pieces of equipment being flushed is a polymer cutting machine. Some of the knives in that machine appear to have increased corossion and pitting on their surfaces. This is a qualitative and not a quantitative observation. One of the differences over this time period is the flush occassionally uses the RO water whereas before it used steam condensate. Economically we would prefer to use the RO water. Originally we thought that the time period of exposure 200 hrs per year maximum was short enough that there would be no issue.

Hi AKsrey,

Thanks for getting back to me.

I used to run several machines with hardened carbon steel cutters. I could remove the cutters though. Are you able to remove them before flushing the rest of the machine you need to clean? If not, and if they still cut OK with no rough edges or waste left on the plastic you cut, perhaps you can replace them every 4 years or so? That is only if the knives are to difficult to remove before flushing?

RO and 'water' in general are good dissolver's of carbon steel. Is there any other steel the cutters can be made from, like perhaps Titanium? Or maybe a crome olly? I have not looked into this so do not know if Titanium would actually be better for you or not?

Is there any chance you can send a pic of the cutting part of your machine and the part you usually flush?

There may be different ways of cutting, like water? But not knowing your exact situation I cannot give that kind of advice. I pic would help though.

I wish you luck

hey,

look for different possible ways of corrosion may happen in RO water, including dissolved CO2,O2 corrosion, LSI(Langelier saturation index), RI(Ryzner index), LR( Larson ratio) and so on which apply for RO water. in addition to that high temperature of the water basically increases te potential of corrosion as it increases the solubility of dissolving materials. you may refer to this site which contains good information : www.lenntech.com

increasing PH,Alkalinity may reduce the corrosion rate.you may also use some kind of anti corrosion materials.

good luck