Microbiologically Induced Corrosion (MIC) mitigation for wet layup

[mfeldmann]

I am subcontracted to a company that is looking to do a wet layup of a stainless steel condenser at shutdown. It has been suggested to provide a wet lay-up with inhibited water containing 0.01 M sodium hydroxide (pH=12) after each shutdown, with a down time not to exceed one year.

Condensate from the last campaign indicated a maximum chloride concentration of 0.3 ppm, a maximum fluoride concentration of 0.2 ppm and a pH>9. The elevated process condensate pH has been attributed the the presence of ammonia. The shell side temp is 50 C at a pressure of 60 torr (vacuum). On the tube side, the max inlet temp is 21 C and max outlet temp is 32 C. The raw water use for cooling on the tube side is expected to have a chloride concentration of <25ppm.

At the current chloride levels, temperature, and pH, the SS condenser is expected to exhibit excellent corrosion resistance, leaving the concern of MIC. Will a wet layup with 0.01 M NaOH prevent MIC? Is this type of a wet layup a standard industry practice for controlling/mitigating MIC?

Your help is appreciated,
mfeldmann

 

[Metalguy]

Dunno what practice is standard, but bacteria don't seem to like a pH much over 9 or 10. Some of them can live quite well in weak battery acid solutions, but not alkaline.

I think you'll be OK if you can avoid evap. which will concentrate the Cl. You also might consider a non-Cl biocide to sterilize things. If so, make sure the manuf. know your intended pH!

What's the tubing-304?