Steam condensate corrosion 2

[kevlar49]

We have a carbon steel line that is experiencing steam condensate corrosion. We are primarily seeing it at socket welded connections. Any idea why? This condensate is the return from steam tracing used to keep Coker instrument gages from plugging up.

Also, if I were to upgrade, would upgrading to type 405S stainless pipe be a good alterntative to Type 304. I am trying to avoid chloride SCC.

many thanks

 

[EdStainless]

What is the pH of the condensate? Fairly acid from disolved gases?
Moving to a steel grade with jsut a bit of Cr may be all that you need.

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Rust never sleeps
Neither should your protection

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

 

[metengr]

What is the material on the other side of the socket welded connection?

 

[kevlar49]

Socket weld connection is carbon steel on both sides. I am in the process of determining the condensate pH, however before I started the determination was that the corrosion was due to carbonic acid.

 

[TBP]

Why not just deal with the water treatment issue?

 

[0707]

Carbon dioxide (CO2) corrosion results when CO2 dissolves in water to form carbonic acid (H2CO3). The acid may lower the pH and sufficient quantities may promote general corrosion and/or pitting corrosion of carbon steel.

The partial pressure of CO2, pH and temperature are critical factors.

Increasing partial pressures of CO2 result in lower pH condensate and higher rates of corrosion.

Corrosion occurs in the liquid phase, often at locations where CO2 condenses from the vapor phase.

luis

 

[kenvlach]

Commonly, condensate lines are protected from corrosion by adding a chemical such as cyclohexylamine to the boiler feedwater. The cyclohexylamine volatilizes along with the steam and then condensates in the cooler condensate system, where it
1) neutralizes acidity (from CO[sub]2[/sub] in air from vacuum breakers & vents), and
2) forms a protective film on the ferrous metals.

I recall cyclohexylamine may attack copper and copper alloys, but there are other chemicals available, depending on your steam system:

http://www.google.com/search?source...1,GGLG:en&q=boiler+treatment+condensate+lines