Carbon steel and salt water

[Mosy7]

Hi there,

Can CS be used in vessel/pipes for water service (industrial) with +100,000 TDS salt water solution (mixed salt)? T around 50 C. Any code mandate?

Thank you

 

[EdStainless]

If it will be deeply submerged it will work, if exposed to air then you will have to account for possibly very high corrosion rates.
You could coat it, or use cathodic protection, in reality most applications do both.

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P.E. Metallurgy, Plymouth Tube

 

[Mosy7]

Thank you EdStainless!

Idea is to use C.steel for the pipes and the vessel carrying the salt water. The system is under deep vacuum, although the water may contain air already.

 

[zacharialamsyah]

The best material selection to facing sea water is Titanium. But it costly higher than carbon steel. the option is using Carbon steel with proper coating, ussually in splash zone area (by neoprene)

Titanium resists corrosion by seawater to temperatures as high as 500°F (260°C), even under high velocity conditions or in polluted water

Regards,
Zachari Alamsyah

 

[moltenmetal]

Every molecule of oxygen or any oxidant that is fed to that system will result in corrosion of the carbon steel. If the system is closed loop such that reintroduction of fresh oxygen doesn't happen, it might last a long time- assuming there is nothing else in the water which can act as an electron acceptor to further corrosion.

If the steel is thick enough, there are no galvanic joints in the system whatsoever and the solution doesn't mind being contaminated with the corrosion products (ie. Fe+2/Fe+3 in solution), then it might be OK. But if there is reintroduction of oxygen in the form of non-deoxygenated water or other feeds, it will not last long.

 

[EdStainless]

There are coating systems that work well, but you must clean and inspect them religiously, any coating failure can rapidly become a catastrophic piping failure if you don't watch.

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P.E. Metallurgy, Plymouth Tube

 

[rconner]

As to at least pipes, I believe what has proven to be one of the most durable linings is good quality, centrifuged cement (mortar).

 

[LittleInch]

Your "code mandate" is that in most design codes, you need to choose your materials to match the substance it is carrying at the pressure and temperature you have.

The key issue with C Stl and salt water is oxygen. If you have even quite low quantities of it, especially at 50C, and your carbon steel vessel and pipes won't last more than few months.

Actively de-aerate it using vacuum towers and oxygen scavenger and then you can use C Stl, the trick then being to make sure that the oxygen levels don't climb over time / in reality.

It's not clear what purpose you're using this for, is it a static volume or constant new liquid and what is the oxygen concentration in the fluid?? Only then can you say with any certainity whether C stl, without any coating is good for this service or not.

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

 

[Mateeng]

Oxygen main parameter in CS corrosion in water solution. Please find out Oxygen concentration.
CS in Salt Water without oxygen with any concentration of Cl slightly corrosion but fine. CS will be corroded in aerated water (High Oxygen) as much as the concentration of Cl is higher the severe is corrosion. Salt water with oxygen in closed loop is Okay since the oxygen will be consumed by oxidizing CS quickly and after that Cl has no effect on CS and will be safe and vise versa.
Temperature 50 C is high and can accelerate corrosion in aerated salt water. I can say CS depend on thickness but more than 6 months. Except proper inhibitor used or Cathodic Protection system.