Chilled Water System Chemistry 1

[KenRad]

Not sure if this is the right forum, but here goes.

I have a chilled water system which uses an atmospheric storage tank, so I guess you'd call it &quot;open-loop,&quot; although the system hardly loses or makes up any water at all. I had a mild steel corrosion coupon in the system, which after a month, showed <.01 mil/year loss. The way I understand it, the water is non-corrosive, and our water treatment program is working well. Are there any conditions where I still could have active corrosion of the steel piping in the system, and it not show up on the coupon? System circulation is good, so all the metal is seeing the same water.

---KenRad

 

[EMKWR]

Coupons are great to measure uniform corrosion. Local corrosion is more difficult to observe (MIC, pitting, intergarnular corrosion etc. One has to observe the sample under dimmed light (see ASTM G4), and still there is a possibility that it happens elsewhere. Can you tell a bit more about the water quality ? Edwin Muller
KEMA Power Generation & Sustainables
Arnhem, The Netherlands
E-mail e.f.muller@kema.nl
Internet:

http://www.kema-water.nl

 

[Metalguy]

Any dissimilar metals in your system?

 

[kenvlach]

Like Edwin asked, what are your water parameters? I suggest a pH of 10.5-11.

Threaded connections are a likely spot and an easy place to check for corrosion.

I suggest hanging a piece of plastic sheeting inside your tank to act as a floating membrane to reduce CO₂ and O₂ absorption from the air.

 

[wiggs]

Corrosion coupons are a good indicator of system protection if:
Coupons are representative of the system. (This sounds like a no brainer but mistakes do happen.)

Coupons have been prepared properly. They must be kept clean and not handled before insertion. Body oils can provide a protective barrier from the solution.

 

[PVRV]

KenRad,

The corrosion growth seems to be negligable. At any rate,
we have two chiller plants. I cannot recall off hand the condition of the piping or where the access fittings are installed. However, I will post the operating conditions for you, any area of concern with regards to locations prone to corrosion growth and treatment measures. (dosing)


Cheers