2 replies to this topic

We are operating our cooling tower with 300 ppm nitrates,200ppm chlorides,250 ppm sulphates the calcium hardness is 550 ppm and total hardness is 650ppm the alkalinity is 60 ppm.
our make up water alkalinity is 40 ppm even with 5coc our ct water alaklinity is not shooting beyond
60 ppm and no acid is used for reducing pH,
The pH is always being maintained at 7.0 to 7.5, the tretment followed is with oragno phospate and azoles
But the corrosion rates are observed high.

Any solution for this

[kumaqal.engr]

sir
please check out this site.
www.waterandwastewater.com

Thankyou.
with kind regards.

[wnovaes]

pbhavanam,

I think the quality of your cooling water is quite good. However, I thought calcium hardness high and I think may your cycle of concentration be high? I just can’t understand where nitrates came from.

A cooling water system has more tendencies for scaling than corrosion because in the most cases cooling water systems have an alkaline treatment.

One source may lead corrosions rates increasing is the chemicals used for biofouling control. So, what are the kind of the biofouling chemicals used in your system? For example, most cooling water systems use Cl2 for biofouling control because is cheaper. But, Cl2 dissociates: Cl2 + H2O --> HClO + HCl. Therefore, the free chlorine concentration can increase cooling water corrosion characteristics because HCl formation. The recommended free chlorine concentration for cooling water systems is maximum 1 ppm and this parameter is critical for high cycles of concentration systems. Once question is: where are the high corrosion rates observed on the test coupons or cooling system (piping and heat exchangers)? I asked because before I faced a problem seemed as yours. In our bigger cooling water system (13000 m3/h of recirculation flow) the corrosion rates based on test coupons were so higher than before used be. We observed this increase in the corrosion rates since the test column, where test coupons are fixed, was damaged and coupons were dived into cooling tower basin. After some moths problem still continued, a day we observed test coupons were dived close to chlorine dosing distributor and therefore a high acidity region. In a few days after, test column was placed on-line again and kept another test coupons close to chlorine distributor too. Who guess what’s happened? So, the point for cooling water sampling and test coupons installation are crucial for a good cooling systems diagnostics. The main return cooling water piping close to cooling tower is better point for cooling water quality control.

Another source for increase corrosion characteristics for cooling water systems is chloride and sulfate contents and mainly for stainless steal. For carbon steal, high chloride content is dangerous for fouled heat exchangers damage for pitting corrosion under fouling. The critical chloride amount is strongly dependent of kind of the chemicals used for cooling water treatment. For your system a think 200 ppm for chloride ions is quite good. For example, in our systems treatments program we have a maximum limit for chloride of 400 ppm and chloride plus sulfate contents less than 1000 ppm. Our cooling towers work with relative high cycles of concentration and treatment are based on scaling dispersant plus corrosion inhibitors.

For avoid corrosion problems is important keep pH neutral to slightly alkaline and chloride content as low as possible. Soluble iron analysis is good parameters for corrosion monitoring in cooling water systems and if it tends to increase the system may be facing corrosion problems.

Langelier and Ryznar Saturation Index can be used for monitoring cooling water corrosion and scaling tendencies.

Best Regards,
WSN.