Caustic Soda tank

I want to build a degreasing tank using Caustic Soda (aka Sodium Hydroxide or Lye) as the active agent. I am already aware of the necessary safety
precautions and EPA considerations. My questions are: what material for the tank and how strong a solution? Thanks.
Roger in Vegas
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Roger Hull wrote:

I suggest using an old drum. If it's too tall, cut it off. Easy to make a sheet metal lid for. Here's the deal, though. Try to get one that has no paint and no rust on it. Sometimes drum companies strip their drums and repaint them, and if they do, you can buy them stripped.
One pound lye per 3-5 gallons of water is a pretty strong solution.
Any lye solution will be more aggressive heated. Advantage of a metal tank is you can put it on an outdoor propane turkey-fryer-type burner directly.
GWE
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NOT aluminum. Or Magnesium or Titanium. If I rememebr my high school chemistry correctly (and I admit, it's been quite a few years...) all three will die tragic deaths soon after contact with a strong lye solution. As for "how strong?", well... That's almost certainly going to depend on the "grunge" level of each piece you want to tank - Nastier pieces will probably need a stronger solution, "light crud"/finish cleaning probably won't need anywhere near the strength.
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or
the
Regular or stainless steel should be fine.. I'd suggest a 2% solution.. Not strong enough to do any serious damage to your skin on short term exposure, but strong enough to remove the worst parts..
If you want it more effective you could heat the solution to 60-70 C..
/peter
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If you use it hot be careful of stainless as some sodium hydroxide contains chloride.
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contains
I work for a rather large dairy company.. The preferred cleaning process for tanks, pipes etc. is a short rinse with water followed by 2% sodium hydroxide @ 80C, short rinse w. water, 1% nitric acid @ 60C followed by a rinse with fresh water.. The cleaning fluids are recycled and stored in large stainless steel tanks ( 316L )..
Some of the tanks cleaned with this system are used to store brine for the cheese ( 20% sodium chloride ), so contamination of the cleaning fluids is a frequent issue ( The returnline for the cleaning fluid is routed between lye and acid tanks and the sewer, but the conductivity sensor cant tell the difference )..
The stainless steel tends to turn brittle and nearly impossible to weld cracks on, but we have only seen this happen on really old equipment..
/peter
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Is there an issue with stainless and chlorides? - GWE
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Chloride SCC
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David Deuchar wrote:

Long on words, aren't you, David? OK, let's try again! What do you mean by "Chloride SCC"? Thanks - GWE
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Chemical question, shouldn't the protective chromium oxide on stainless be attacked by lye to form sodium chromate? Why not?
Tim
-- "California is the breakfast state: fruits, nuts and flakes." Website: http://webpages.charter.net/dawill/tmoranwms
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Roger Hull writes:

Cheap version is a Rubbermaid Brute trash can, if you watch the heat.
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or
the
I worked as an engineer in the food industry for more years than I care to remember. We traditionally used mild steel tanks for the storage of our caustic cleaning solutions and never had corrosion problems. The usual strength of the solution was about 2-3%. Back when beer bottles were washed and reused. the bottle washers were mild steel and had caustic solutions of up to 7% and 75 Degrees C.for quick removal of labels. Again, corrosion was never a problem.
Tom
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wrote:

I don't know if I can find another racing fuel barrel , plastic out? If its SS its mine. So, do you want me to find ya another? I've seen plastic ones for IIRC $5-$10 in the paper. Let me know, I can spot the metal ones a mile away if I need one.
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On Tue, 8 Mar 2005 15:38:10 -0800, Sunworshipper wrote

If you can come up with another metal drum that would be super. Thanks.
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wrote:

In the works. You know I saw one just last week, where the hell was that???
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On Tue, 08 Mar 2005 18:46:52 -0800, Sunworshipper

LOL , ahhh Reefer ok? Got to pick it up between 7-9 am tomorrow !
Fast eh? :o) Color not optional.
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What 20 hours.
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Roger Hull wrote:

old style potato peelers and peach peelers in the food industry used strong lye solutions in carbon steel tanks. The lye tends to protect the metal and I've never seen one actually rust or corrode out. The carbon steel metal conveyor belting we ut in them lasted for years.
Don't paint it though....for some reason people liked to paint these tanks (outside) during shut-down cycles while they were painting the rest of the equipment that needed it. Paint lasts about a minute.
Koz
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Probably the most researched corrosion issue in the world. Simple slightly inaccurate explanation. Take an austenitic stainless steel, (the type that is non magnetic), add stress eg welding or cold work, put in hot salty water. Result:- cracks in the steel. The steel will look OK unless you have a hand lens to look for the cracks but it will leak. To avoid:- use duplex stainless steel.
http://www.hghouston.com/cl_scc.html
http://www.mcnallyinstitute.com/CDweb/c-html/c036.htm
http://www.safeclimbing.org/education/deepbluesea.htm
http://www.firth-metals.com/english/firth/documents/artikelHeselmans-vanDuijnStainlessBuilding07-06-04.pdf
http://www.npl.co.uk/ncs/docs/stress.pdf
http://www.corrosionsource.com/technicallibrary/nidi/literature/pdf/14050.pdf
The classic case is the Swiss swimming pool roof collapse, mainly used because it is a long time ago, there are tens of thousands of more recent cases. Stress corrosion cracking A material failure may be accelerated by the combined effect of corrosion and mechanical stress. The most common type is transgranular stress-corrosion cracking, SCC, that may develop in concentrated chloride-containing environments. Previously, it was generally considered that an elevated temperature was necessary for SCC to occur. In recent years, however, SCC has been experienced at ambient temperature on standard grade steels like 304(L) or 316(L) that were exposed to high tensile stresses. In these cases the steel surface was contaminated with solid salt deposits and the humidity of the atmosphere was rather high. These two factors resulted in a thin liquid film saturated with chloride. Other contaminants, such as H2S, may increase the risk of SCC in chloride containing environments. Other environments that may give rise to SCC, particularly on low alloy steels, include very alkaline solutions at high temperatures. A typically SCC attack takes the form of thin, branched cracks.
Stress Corrosion Cracking (SCC) Under the combined effects of stress and certain corrosive environments stainless steels can be subject to this very rapid and severe form of corrosion. The stresses must be tensile and can result from loads applied in service, or stresses set up by the type of assembly e.g. interference fits of pins in holes, or from residual stresses resulting from the method of fabrication such as cold working. The most damaging environment is a solution of chlorides in water such as sea water, particularly at elevated temperatures. As a consequence stainless steels are limited in their application for holding hot waters (above about 50C) containing even trace amounts of chlorides (more than a few parts per million). This form of corrosion is only applicable to the austenitic group of steels and is related to the nickel content. Grade 316 is not significantly more resistant to SCC than is 304. The duplex stainless steels are much more resistant to SCC than are the austenitic grades, with grade 2205 being virtually immune at temperatures up to about 150C, and the super duplex grades are more resistant again. The ferritic grades do not generally suffer from this problem at all.
In some instances it has been found possible to improve resistance to SCC by applying a compressive stress to the component at risk; this can be done by shot peening the surface for instance. Another alternative is to ensure the product is free of tensile stresses by annealing as a final operation. These solutions to the problem have been successful in some cases, but need to be very carefully evaluated, as it may be very difficult to guarantee the absence of residual or applied tensile stresses.
From a practical standpoint, Grade 304 may be adequate under certain conditions. For instance, Grade 304 is being used in water containing 100 - 300 parts per million (ppm) chlorides at moderate temperatures. Trying to establish limits can be risky because wet/dry conditions can concentrate chlorides and increase the probability of stress corrosion cracking. The chloride content of seawater is about 2% (20,000 ppm). Seawater above 50C is encountered in applications such as heat exchangers for coastal power stations.
Recently there have been a small number of instances of chloride stress corrosion failures at lower temperatures than previously thought possible. These have occurred in the warm, moist atmosphere above indoor chlorinated swimming pools where stainless steel (generally Grade 316) fixtures are often used to suspend items such as ventilation ducting. Temperatures as low as 30 to 40C have been involved. There have also been failures due to stress corrosion at higher temperatures with chloride levels as low as 10 ppm. This very serious problem is not yet fully understood.
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On Thu, 10 Mar 2005 11:57:15 -0800, David Deuchar wrote
<Major snip>

<major snip>
    "Caustic Embrittlement" is/was a common term to steam boiler operators back when I was one; slightly over ten years ago. We used Caustic Soda to treat the boiler water for Ph, along with a bunch of other chemicals to remove dissolved Oxygen, Carbon Dioxide, minerals, control foaming, ect. You cannot feed boilers tap water (for long).
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