HDPE 4

[Frank1344]

Hello,

Does any body have any experience with Sodium Hypochlorite?
We have a system for removing H2S from the Basal Water, the line carrying the Sodium Hypochlorite is made of Titanium and we want to inject it to a HDPE line carrying the basal water.
I heard that the HDPE and Sodium Hypochlorite will react chemically and there will be a failure in the system.

Is that right?

If yes, what is a suitable material for the injecting spot of the main line to avoid the reaction?

Is lined carbon steel an option?

Any feedback is appreciated.

Frank

 

[patprimmer]

Sodium hypochlorite is a strong oxidising agent. Strng oxidising agents do attack HDPE to some extent.

PVC may be better but you need to do your own homework and look up chemical resistance tables. The major reputable raw material suppliers can provide these.

Regards
Pat
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[Frank1344]

Pat,

Thanks a lot.

What do you think of FRP?

Regards,
Frank

 

[Demon3]

I would avoid fiber reinforced plastics because the fibers can help wick the liquids inside the plastic, accelerating failure.

Here is a chemical resistance chart specifically listing sodium hypochlorite:

http://www.millerplastics.net/chemical_resistance_chart.html

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[btrueblood]

Frank,

Can you come back with what the concentration of hypochlorite will be near, and downstream of, the injection point? What is the concentration before injection?

Reason I ask, you can find a lot of information on-line about bulk storage tanks for concentrated hypochlorite, and what a bad idea that is. Failures occurring in heavy-wall tanks in 3-8 years, depending on the actual concentration in the tank over time (lower rates of failures in tanks that were refilled less frequently).

At the same time, weaker solutions (e.g. household bleach, roughly 3-6% concentration) are shipped all over the world today in very thin-wall, hdpe poly bottles (see link). I would say that depending on final concentration and temperature, the fully mixed hypo + water in the lines is probably ok, and thus all you may need to do is have a certain length of pipe near the injection point be of a more resistant material.

http://www.thefreelibrary.com/THE+C...+20+PERCENT+RECYCLED+BLEACH+BOTTLE-a011472222

 

[Frank1344]

Thanks Gentlemen,

According to our Process Engineering we are looking @ Bleach means 3 to 6 % concentration.

 

[btrueblood]

Frank, 3-6% before or after mixing with the water stream?

You should be able, knowing the concentration, to look up chemical resistance tables, possibly with the help of the hdpe pipe manufacturer, and/or find articles discussing the resistance of hdpe or pvc or whatever to hypo solutions, and have your question answered more completely.

 

[Frank1344]

Thanks again.
Unfortunately my references here are very limited.
Is there any online website for the "chemical resistance tables"?

Appreciate,
Frank

 

[Demon3]

I already posted a link to online chemical resistance tables for polymers including sodium hypochlorite. See above.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Chris

It does not list HDPE but it does list PP which has very similar chemical resistance.

5% at room temperature will not be a problem. 30% at 90 deg C might be a problem.

Regards
Pat
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[Demon3]

A Google search for "HDPE sodium hypochlorite" gives this as hit number three...

http://pt.rexnord.com/products/guards/orange_peel_guards/hdpechemresistpdf01feb.pdf

It says 30 days of 15% sodium hypochlorite gives no change in HDPE.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Frank1344]

Friends,

Process engineering confirmed that the concentration is 12.5%
Does this have a significant change in our discussions?
Thanks a lot.

 

[Demon3]

Given that I just wrote that HDPE is OK at 15% sodium hypochlorite and provided a link, I would say we can conclude that 12.5% would be fine at room temperature for at least 30 days. Under other conditions, you will have to test to make sure all is well.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[btrueblood]

I'd add some emphasis on what Chris writes - there are reports of HDPE tanks cracking after several years of exposure, so 30 days vs. 3000 days may make a difference.

Again, 12.5% is the injected concentration, or the fully mixed concentration after injection into the water stream? If it's the latter, I'd be looking for other materials than PE.

 

[Frank1344]

Dear Friends,

I never talked about any storage or static system, this is process piping and will operate 24/7 possibly 300 days per year.

Our mail line is a 16" Untreated Basal Water HDPE line with 370,000 kg/h mass flow rate, our injection line is a 3/4" Titanium which injects 500 kg/h of 12.5% Sodium Hypochlorite into the 16" main.

The NaOCl may never reach the HDPE pipe walls, but if it does it seems that these two will react and as a result FAILURE happens, when terms like "FAILURE" is showing up, we MUST do every thing that this is not going to happen and considered as Threat to Safety of Public and Environment.

Now the Parameters are Workability, Availability, Pricing, Safety,..etc.

Now at the end, I have to make the final call.

If I can not conclude any solution out of our discussions then I have to look at the Expensive Metals and or Alloys so I am not going to be Liable for the Potential Failure.

My gratitude to every one of you who is helping.

Have great weekend,
Frank

 

[IRstuff]

Both Clorox Cleaner with Bleach and Clorox Bleach, itself, are sold in HDPE containers.

Admittedly, nowhere near 15% or even 12.5%, both are way less than 10%. Nonetheless, the containers stay intact for years, assuming no egregious temperature extremes.

TTFN

FAQ731-376

 

[Demon3]

So you have about 0.015% sodium hypochlorite by the time the water has diluted it.

So, if as shown in the table provided, HDPE resists 15% sodium hypochlorite for over 30 days then we can be fairly confident that it can take 0.015% for many years.

Even if the water cuts off for some hours, the HDPE should survive because we know that it withstands at least 30 days of concentrated sodium hypochlorite.

One thing to mention is that sodium hypochlorite is an strong oxidizing agent so the resistance of the HDPE may well depend on what antioxidant package you use because they protect the pipe from oxidation which leads to cracks and failure.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Dear Friends,

I never talked about any storage or static system, this is process piping and will operate 24/7 possibly 300 days per year.

You also never sad anything to the contrary so forgive us for incorrectly filling in the blanks.

Sodium Hypochlorite is stored in HDPE drums for use as pool chlorine. I have not checked the concentration, but I expect it is somewhat higher than domestic bleach and quite probably 12.5%. The drums last for many years if protected from UV, extreme temperatures and stress. In the absence of data to the contrary, I am presuming normal ground temperatures and minimal stress.

0.015% is insignificant and will not damage HDPE pipe to any significant effect at temperatures and stress within the normal range that pool chlorine drums are exposed .

If the 12.5% concentrated form is left in prolonged contact at the injection point, and if the attachment method at the injection point creates stress, then that point may be at risk, but that seems highly unlikely.

Regards
Pat
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