Corrosive atmosphere from leaking hypochlorite tank? 1

[Coprinus]

I recently took a volunteer position at my community's small UF WTP (850gpm total) where all equipment is in one large room. The facility is only 10 years old. Hypochlorite is generated from a small skid on site, at 0.8%. The solution is stored in a vertical tank which chronically leaks hypo solution all over the floor, likely from a cracked tank outlet bulkhead. There is a strong chlorine odour (which I understand to be the odour of hypochlorous acid vapour).

Every piece of electrical equipment not in a gasketed enclosure shows signs of extensive corrosion. Even the keys hanging from storage cupboard locks look very corroded. I am worried about mass failure of electronic and mechanical equipment such as local control panels and valve actuators having been exposed to what appears to be a very corrosive atmosphere.

My question is whether hypo leaks and spills are known to cause a corrosive atmosphere which can result in this level of equipment corrosion? Apparently during commissioning 10 years ago there was an HCl leak as well, which may have contributed to the situation.

 

[EdStainless]

Yes.
You have reason to be concerned.
The fact that there haven't been significant failures yet is actually surprising.
The hypo should be isolated from the rest of the system.
And you should have a plan to start working through all of the equipment.
You may have equipment that isn't working correctly now, it just hasn't completely failed yet.

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[IRstuff]

not to mention that the atmosphere is not particularly safe for humans as well.

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[QualityTime]

HCL off gassing will cause immediate corrosion. This would have caused severe corrosion. Sodium hypochlorite leaks and off gassing will corrode equipment metallic surfaces over time when the atmosphere is moist. You will see white powder on galvanized conduit, and blue green powder on copper piping

 

[hydrae]

This is a case where the designer look at a chemical, in this case NaOCl and see that if the concentration is less than 1% it is not hazardous according to NFPA, which is why salt generators run that low of concentration. True all sorts of rules fall by the wayside, (containment, placarding, storage volume limits, reporting requirements) but still pounds of chlorine are being produced per day and off gassing in the tank, leaks, and spills release the chemical.

Solution
Move the equipment to a separate room or build a separate room with separate ventilation. Even constructing a stick frame walls with wall board and an exhaust fan will slow down the corrosion in the rest of the room.
As an interim measure, build a scaffold frame around the skid, and cover with a plastic tarp, and add a bathroom exhaust fan pumping that air outside.

 

[EdStainless]

You don't use exhaust fans for Cl environments, they don't last very long.
You make a vent and blow clean air in.

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[nackra]

chemical supplier should provide SDS for hypochlorite

https://olinchloralkali.com/wp-content/uploads/2019/06/Sodium-Hypochlorite-5-17_US_EN.pdf

hypochlorite will definitely corrode metals. The hypochlorite concentration/strength will affect the amount of corrosion.

 

[hydrae]

Ed
There I beg to differ
I prefer to replace a cheap plastic fan when it fails in 5 to 10 years
which pulls a suction on the room and vents it outside (put the fan in an easy to replace location)
Than to pressurize the room with the corrosive agent which will leak out any penetration
be it door, pipe penetration, or worse electrical conduit, or any other imperfection
in the rooms construction. True, most of the bad air will go out the vent but some of it
goes elsewhere, when the room is under positive pressure and not negative pressure.
Also I recommend that the volume of air movement be slow, as rapid air exchange
will evaporate more of the vapor as the equilibrium between the liquid chemical and
the air in the room adjusts with high air turnover.

The fan that I have specified is the Fantech DBF110 which connects to 4 inch 3034 pipe
the only metal in the fan is the motor which is completely hidden inside

Now if you wanted to get fancy, use a fan to power a venturi eductor as the exhaust unit.

Hydrae

 

[EdStainless]

I have seen fan motors in Cl environments fail in days, not years.
Maybe if you use a bilge vent fan, or corrosive service vent hood vent fan, or a fan intended for continuous wet location service you can get some decent life out of it.
But if you can see the guts of the motor it stands no chance.
I would rather see a small shed built outside the main building to improve isolation.

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[bimr]

You don't mention the tank materials of construction, but the tank is likely past it's useful lifetime. See the comments here:

Tank Recommendations

The tank should be vented outdoors. The tank should have 100% secondary containment. You should have a safety shower.

 

[pierreick]

Hi,
To add to the discussion a memo about bleach.
Pierre