SS Selection for Hot Water Storage w/ Well Water 1

[JustAnotherChemE]

Hi, I'm trying to decide if my company needs to step up to 316 grade stainless from 304 for our future direct gas fired heating system.

The system will be operating at 170-190 deg F with city water that has a variable 100-150 ppm chloride content (lake/stream versus well water seasonally)

I understand that 304 would be stable with this chloride count below 140 deg F, but some tank manufacturers have been warning us that we'll need to use 316 to avoid nasty things like stress corrosion cracking etc.

I'm mostly concerned about the 20,000 gallon storage tank we'll be using to store waste heat from other process equipment... during the day the water will be fairly stagnant which will affect the corrosion kinetics / diffusion, correct?

Any help would be appreciated. I'm the only engineer here so it's fallen upon me to nitpick details like this plus I'm fairly ignorant when it comes to corrosion, but I'm picking it up!
Thanks.

 

[EdStainless]

Moving to 316 would improve the pitting resistance, but it will not help prevent chloride stress corrosion cracking.
I would suggest that you look at other alloys.

439 is one option. It is a ferritic alloy that has about the same pitting resistance (slightly better) as 304. It is immune to chloride SCC. This has been used for hot water tanks for years.

The other option would be the lean duplex LDX2101 or AL2003. The LDX2101 is slightly better than 304 and the AL2003 is better than 316. Both alloys are highly resistant to CSCC. Both alloys are also significantly stronger than 304 or 316 and would allow you to use thinner walls for the tank. This could result in saving money on the project.

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Rust never sleeps
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[JustAnotherChemE]

Reliability on this project is paramount. This system must operate every night for sanitation of food process equipment, so plant management basically want it over sized and redundant.

I'll take your suggestion on the AL2003 and research into it alittle more before contacting my suppliers...

Do you think we could get away with using 316 in the heaters where the flow is somewhat higher? (or is that only for crevice corrorsion?)

Thanks alot.

 

[EdStainless]

Actually the risk of CSCC is worse in the hotter sections, so be extra careful there.
What is the heat source?

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Rust never sleeps
Neither should your protection

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[mcguire]

If this is a critical piece of equipment you can't take a chance on SCC. Use the 2101 or 2003, and not 316. 316 does not avoid SCC. It has a long history of succumbimg to it.
439 will not SCC, but may pit. Before 2003 and 2101, the alloy of choice was 442. This is essentially 439 plus 2% Mo.It's very hard to find. If you cannot find 2003 or 2101 use 2205.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[JustAnotherChemE]

It's a direct gas fired system. Basically a packed tower with natural gas exhaust flowing up through stamped stainless steel rings with cool city water introduced from the top. Much better than the current boiler=>condenser system.

Now the supports for the packing directly above the incoming hot gas will have the highest heat flux. Actual water temperature will be in the 190 deg F range once the system has achieved steady state.

The tank will run with a recycle through the burners to keep it at >70% capacity and above 185 deg F.

Should we be considering a synthetic tank? I know there are some pretty slick polymers out there... but this needs to last 15-20 years in an external environment, although aluminum sheeting over the insulation might eliminate UV problems.

 

[EdStainless]

Many high heat flux direct fired water heaters use Ni alloys for the hottest section with 825 being a good option.
I would suggest staying with duplex stainless for the rest of the tank.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[rolledalloy]

There are numerous manufacturers in Europe using duplex for their water heaters varying from LDX 2101 to 2205. AL 2003 would also fit in between the two in performance. Data sheets on all three alloys are available at

http://www.rolledalloys.com.

We have seen some SCC in commercial water heaters in the form of external SCC from the insulation side of the tank as well.

Here are a couple that are using duplex currently.
Albion - UK
Andrews/SOLARFlo - UK
TriangleTube/PhaseIII