corrosion by stream, can we use 316L ?

[EMIP68]

I have a problem with a exchanger stream/air. It's rapidly corroded (changed all 4 years) by O2 or Cl-, I don't know.
Tubes are in carbon steel and I would like to know if we can use 316L to avoid corrosion, with this composition :
*Cl- = 10 to 15 mg/l
*pH = 8
*143°C
*3.5 bar

Help me please.

 

[mcguire]

Those conditions put you on the border between 316L and 317L in terms of immunity to pitting and other corrosion. The most cost effective may be to use 316 that has been bright annealed or electro-polished. Some tubing manufacturers ( it is a tube heat exchanger?) offer enhanced 316L chemistry and surface treatment.

 

[TBP]

Steam won't corrode carbon steel. There can be erosion, if water droplets are carried at steam velocities, but the problem is most likely due to condensate not being drained properly. If it's corrosion, and appears as as pitting, then that is likely from dissolved oxygen in condensate. Are there periods when the unit is out of service? If the condensate does not drain fully from the unit, then it will absorb oxygen from the air, and you'll suffer pitting at the water line. (Heating boilers shut down for the summer often suffer from this, if proper steps are not taken.) The solution could be as simple as adding a vacuum breaker, and ensuring that the condensate can drain by gravity to a receiver at atmospheric pressure. Unless there's some aspect to this that I'm not understanding, there should be no necessity for the use of stainless steel.

 

[mcguire]

AIR corrodes carbon steel. The Metals Handbook recommends that to control corrosion of carbon steel in steam systems
one:
a. use inhibitors
b. alloy with chrome/moly
c. remove oxygen
d. eliminate galvanic couples
This doesn't say that corrosion will be eliminated since even Florida air results in 0.003 to 0.030 inches per year of corrosion.

 

[TBP]

Fully 75% of the time, what appears on the surface to be a chemical/water treatment problem, in fact has a mechanical root cause. Design & install it right mechanically, and you've just eliminated 3/4 of the "chemical/corrosion" problems.

 

[JimMetalsCeramics]

316L is chlorine-resistant and readily available. Depending upon your budget, the structural forces impinging on the steel, and the temperature, you have additional options such as alloy tubing and specific platings on the tube.

In any event, high nickel content will address both problems.

 

[NickelMet]

Just one comment: Not enough information is given...

While all the answers above are good, there really isn't enough info given to properly address the situation. Which side is the steam on? the air? (Never assume you know from a description unless it explicitly states such...) Which side is the corrosion happening from? What type of attack is observed? pitting? general wastage? weld attack? (Without pictures, these are all valid questions...)

I don't wish to throw a damper on the discussion. I just wish for more information in order to make a better informed opinion.


~NiM

 

[EMIP68]

At first, thanks everybody for your help. I think I will try to put nitrogen in exchanger when stream will stop.

Stream and corrosion are in tubes. The type of attack is not like pitting. If you want I can send you a picture of this corrosion.

 

[ijaz]

Let me share my experience of Carbon Steel Fin Fan unit. The Unit was on Steam Turbine Condensing application. The client had corrosion problem within 16" from the outlet tube end.
We installed 20" long thin wall SS316 material sleeves to take care of the problem based on the knowledge that SS316 stand very well against steam/steam condensate and oxidation. But the sleeves failed within three months of orepation.
We took out the failed tube and had that analysed. We found out that the client was over dosing chemicals where Chloride was major content in that. When steam becomes wet, the chloride becomes most corrosive to Carbon steel as well to SS316. So we had those sleeves pulled out and replaced with AL6XN at no additional cost to the client.

May be you are facing the same problem. Please let me know the exact location of the attack. Only then one can decide what material should be selected to take care of the problem. Or if you want, we can give you I cost effective solution by installing thin wall sleeves made from higher grade material yet galvanically compatible to you parent tube material, instead of retubing.

send me an email if interested at following mailing address:
ijazch_isd@hotmail.com

 

[aberta]

EMIP68,
Your chlorides levels in steam appear to be fine. We have condenser for low-pressure steam, 100 kPag and we use admiralty brass. Our chloride levels are around 5-10 mg/L and at times they have been very high, 50-100 mg/L. At high levels, we were lucky not to get too much chloride stress corrosion cracking at our turbines. Our problem was condensate removal from stem drum mist eliminators. If you have high chloride levels, you will definitely see them as blockages in small diameter piping.
Major problem with steam is water carry over. This causes erosion of piping and failure of tubes. We always inspect our steam baffles, and tube supports for distortion. We also use a good steam trap in piping before the HX. Hope this helps.

 

[PVRV]

EMIP68,

I would appreciate it if you can email the pictures
to the following address,

aadsani@kockw.com

Regards