preventing corrosion inside water jacket vessel

[Cheetos]

I have a fabricated enclosed water jacket vessel (internal dimensions (~25" ID, 25.5" OD and 30" length)). The water jacket skin all around is about 0.38" thick and it has to withstand ~ 3 bars of water pressure. Customer wants to use regular tap water without additives. The water jacket has to be water tight and also acts as a structural component. To manufacture it, I first weld the water jacket and then after I seal it, I weld the mechanical supports on the outside of the water jacket.

The problem is the corrosion inside the water jacket. The water jacket is made up of carbon steel. Some of the options I thought about:
1) I try to paint the inside of the water jacket before I seal it, but once I start welding the outside supports, the heat from the weld will destroy the paint inside.
2) After I finish all the weld, if I try to flood the inside of the water jacket with paint and drain it, it's hard to ensure an uniform paint thickness inside.
3) I thought about metal plating also, but I think I need to find someone with big enough tank to dunk the entire structure after the welding.
4) I may be able to weld the outside supports first and make the water jacket seal weld the last weld to minimize the heat input. I still have to weld at the end, so the heat input is still damaging to the paint inside. (maybe a little less damaging because I minimize the heat input.)
5) The last resort is of course to make it out of stainless steel, which is a major price adder.

Looking for suggestions on how to best deal with the corrosion problem.

 

[EdStainless]

The answer is water treatment. This is how it is generally done.
Even in Stainless steel units there is water treatment for suppression of biological activity.
No way around this that I know of.

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P.E. Metallurgy, Plymouth Tube

 

[Cheetos]

ya, I think so too, but customer is not willing to do that. sigh..

 

[weldstan]

If the customer is not willing to do the correct treatment, then he accepts the corrosion and likely repairs required to maintain the equipment. I have seen some repairs where improper or no water treatments were used and they were mighty expensive.

 

[LittleInch]

Eh? You have a jacket that is 0.38" thick??

Can you provide a sketch or drawing?

This water - Is it a fixed stable quantity or flowing through or what?
If we can understand it's use,, mode of operation and some idea of what it looks like we might be able to offer some ideas.

Also what sort of temperatures are we talking about here?

If the water doesn't flow, then corrosion will be minimal once all available oxygen is used up.

If the tap water is flowing through then you'll get corrosion - what does the customer think is going to happen - the laws of chemistry don't apply to him?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[btrueblood]

You could put sacrificial (zinc) anodes in the wetted space, like on commercial water heaters. This doesn't prevent corrosion, but will slow it quite a bit.

 

[Cheetos]

LittleInch,

Ya, it's thick because it has to carry the load. Usually we don't size it this thick. It's basically a thick cylinder with inside hollow out. Inside, I do weld ribs to form a serpentine type of pattern for the water to go back and forth. The customer wants a flowing tap water. The water temperature is probably between 25 and 35C. I hear you guys. I wish they would listen.

I was wondering about water heater tank construction. Was wondering if you guys know how they make it. I know, in addition to paint on the inside, they also use a cathode and anode device as a sacrificial piece. I guess water heater tank will still corrode over time. I'm just curious how they make it. They have to paint the inside first before sealing up the unit. Maybe because the wall is fairly thin, so the heat from the weld cools off quickly.

 

[PEDARRIN2]

Water heater shells typically have a glass lining to protect the metal interior.

 

[EdStainless]

If they are actually using city water (that is chlorine treated) and this flows all of the time then all they have to worry about is general corrosion and scale formation.

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P.E. Metallurgy, Plymouth Tube

 

[MikeHalloran]

If the inner pipe is not fairly thick or internally pressurized, 3 bar applied to the jacket will collapse the inner pipe.

It makes a hell of a bang.



Mike Halloran
Pembroke Pines, FL, USA