New Exhaust Elbow - Cast Iron or Stainless?

[Cliffhanger]

I would avoid stainless steel for one simple reason, galvanic corrosion. Alumiuium and carbon steel are close to each other on the nobility chart but the stainless steel is far more noble. So, yes, it won't corrode but it will encourage the rest of the engine corrode instead.

https://www.jlconline.com/how-to/ext...vanic-metals_o

The exhaust elbow will be bolted to either a cast iron or aluminium exhaust header (often with heat exchanger housing). Then add in a nicely heated Hydrogen Chloride solution as a electrolyte (i.e. salt water) and you have created the perfect conditions for galvanic corrosion.

So, your exhaust elbow might still look shiny and new in 5 years time (on the outside at least) but so what if you have to replace the entire heat exchanger instead $$$$$$$$$$$$$$$$$$$$$$$

[Compass790]

Originally Posted by Cliffhanger

I would avoid stainless steel for one simple reason, galvanic corrosion. Alumiuium and carbon steel are close to each other on the nobility chart but the stainless steel is far more noble. So, yes, it won't corrode but it will encourage the rest of the engine corrode instead.

https://www.jlconline.com/how-to/ext...vanic-metals_o

The exhaust elbow will be bolted to either a cast iron or aluminium exhaust header (often with heat exchanger housing). Then add in a nicely heated Hydrogen Chloride solution as a electrolyte (i.e. salt water) and you have created the perfect conditions for galvanic corrosion.

So, your exhaust elbow might still look shiny and new in 5 years time (on the outside at least) but so what if you have to replace the entire heat exchanger instead $$$$$$$$$$$$$$$$$$$$$$$

In the OP's case he has a cast-iron ( mostly) raw water cooled engine with no heat exchanger so that warning doesnt apply. Have been running ss exhaust on our cast-iron ( mostly ) raw water cooled yanmar of a close era to OP's for about 6 years IIRC & no corrosion issues & no increase in anode consumption. Not looking for an argument as I'm no galvanic corrosion expert but just relaying experience.
I certainly would not ever use our style of Yanmar cast iron elbows even if I could afford one. Guess they'd be fine if you replaced every 4 years as recommended by Yanmar.

[ftamburrano]

Originally Posted by Cliffhanger

I would avoid stainless steel for one simple reason, galvanic corrosion. Alumiuium and carbon steel are close to each other on the nobility chart but the stainless steel is far more noble. So, yes, it won't corrode but it will encourage the rest of the engine corrode instead.

https://www.jlconline.com/how-to/ext...vanic-metals_o

The exhaust elbow will be bolted to either a cast iron or aluminium exhaust header (often with heat exchanger housing). Then add in a nicely heated Hydrogen Chloride solution as a electrolyte (i.e. salt water) and you have created the perfect conditions for galvanic corrosion.

So, your exhaust elbow might still look shiny and new in 5 years time (on the outside at least) but so what if you have to replace the entire heat exchanger instead $$$$$$$$$$$$$$$$$$$$$$$

I do not see any possibility for Hydrogen chloride (HCl) to be present. The heated solution contains Sodium Chloride (NaCl), not HCl ! It would be industrially nice to be able to produce HCl just heating a salt (NaCl) solution!