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New Corrosion Inhibitor for Evaporative Cooling Sys tems

- Corrsave ® 100 -

Matheis, J.; Stratmann, A.; Hater, W.; BK Giulini GmbH, Duesseldorf, Germany

Wolf, F.; Lunkenheimer, R.; BK Giulini GmbH, Ludwigshafen, Germany

Foret, C. ; ICL France SAS, Vaas, France

Summary

State of the art corrosion inhibitor programs for evaporative cooling systems are based on phosphate, phosphonates, zinc and combinations thereof. Although generally satisfying con-trol of corrosion can be achieved, all programs suffer more or less severe drawbacks, such as lack of biodegradability, content of heavy metals or necessity of pH control combined with acid dosage.

Consequently, there is a need for corrosion inhibitors having an improved environmental pro-file and/or improved performance. This contribution shows the results obtained with a newly developed corrosion inhibitor. The molecule is free of heavy metals and is characterized by an excellent environmental profile.

Corrosion tests have been carried out with metal specimen in dependence of inhibitor con-centration, water composition and water temperature. Electrochemical methods, e.g. volt-ammetry and polarization resistance, were applied as well as beaker tests and long term tests in cooling circuit simulating devices. Thereby, the efficiency of the new inhibitor as well as combinations with other organic inhibitors have been studied. Finally, the new inhibitor has been tested in a pilot cooling tower under practical conditions.

The results of the corrosion tests clearly show an excellent efficiency of the new corrosion inhibitor. Significant synergies could be identified between the new substance and other in-hibitors. The pilot plant studies of a formulation based on the new corrosion inhibitor show the same or better performance compared to commercially available corrosion inhibitors, but a marked reduction of the phosphorous entry into the waste water. The improved perfor-mance can be transferred directly into savings.

1 Introduction

The effluent from cooling water is the major part of the overall waste water amount and a significant portion is led without treatment directly into surface water. Therefore, all chemicals used for the treatment of cooling systems are subject of thorough governmental surveillance. The European Union has issued a reference document describing the best available tech-nology for cooling systems [1] and additionally some countries have issued explicit regula-tions concerning the effluent from cooling systems, e.g. Germany [2].

Corrosion of heat exchangers and installations in evaporative cooling systems is a serious problem of industry, as it may lead to increased maintenance effort, damages and plant shut-down, causing high cost. Furthermore, there may be a high environmental impact due to the discharge of blow-down water containing heavy metals or hazardous compounds, which may enter the water system via leakages.

Therefore, corrosion inhibitors are widely used to minimize corrosion and to enable proper plant operation. State of the art corrosion inhibitor programs for evaporative cooling systems

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are based on phosphate, phosphonates, zinc, polycarboxylates and combinations thereof. However, each one has a significant ecological drawback: zinc is a heavy metal and thus faces increased regulator attention; phosphate may contribute to the eutrophication of wa-ters, whereas phosphonates and polycarboxylates are poorly biodegradable.

New inhibitors have been subject of numerous studies: Polyaspartic acid has been one of the first biodegradable substances [3] being applied as antiscalant in special industrial applica-tions [4, 5], but also in cooling systems [6]. However, its good biodegradability led to degra-dation of the molecule already in the cooling system and thus to a limitation in its applicabil-ity. Oligocarbonic acids and natural fruit acids have been discussed as corrosion inhibitors [7, 8]. Although providing good efficiency as corrosion inhibitor economic constraints and a very rapid degradation prevented the application in practice.

Thus there is the need of efficient corrosion inhibitors with a balanced biodegradability. On the one hand the molecule should be degraded soon in the receiving water, but on the other hand without being degraded significantly already during the application.

Corrsave® 100 is a newly developed corrosion inhibitor molecule with an improved biodegra-dability, which is produced by a proprietary process via the reaction of a natural organic acid with inorganic phosphate. First studies obtained with the substance produced in lab scale showed very promising results [9, 10]. This paper now presents investigations with material, which was produced in a production facility.

Besides data from efficiency tests using methods of different complexity, also studies on specific properties important for the application in cooling systems are shown. Finally, results of a full scale pilot cooling tower test are shown for a formulation based on the new corrosion inhibitor in comparison with two state of the art corrosion inhibition programs.

2 Experimental

The water qualities for the used test methods can be taken from Tab. 1.

Tab. 1: Survey of water qualities used for different test methods.

Hardness

Stabilisation Corrosion Tests

Unit Electrochem.

Measurements

Fast Beaker / Labor a-tory-Scale Circulation

Experiments

Pilot Cooling Circuits

Ca2+ [ppm] as CaCO3 540 120 440

[mol/m3] 5.4 1.2 4.4

Mg2+ [ppm] as CaCO3 180 30 100

[mol/m3] 1.8 0.3 1.0

HCO3-

[ppm] as CaCO3 1000 95 170

[mol/m3] 20 1.9 3.4

Cl - [ppm] 120 60 197

[mol/m3] 3.4 1.7 5.6

pH - 8.5 8.0 – 8.51) 8.21) 8.22)

T [°C] 80 25 30 25

[°F] 176 77 86 77

1)adjusted by 0.1 M NaOH or 0.1 M H2SO4; 2)adjusted by 10 % H2SO4

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2.1 Biodegradability

The biodegradability of Corrsave® 100 was determined according to the OECD-guideline 302b [11]. A mixture containing the test substance, mineral nutrients and a relatively large amount of activated sludge is agitated and aerated at 20 to 25 °C (62 to 77 °F). A control, containing activated sludge and mineral nutrients but no test substance runs in parallel. The biodegradation process is monitored by determination of DOC (dissolved organic car-bon).The ratio of eliminated DOC corrected for the blank, after each time interval, to the initial DOC value is expressed as the percentage biodegradation at the sampling time. The per-centage biodegradation is plotted against time to give the biodegradation curve [11].

2.2 Properties relevant for Application

Inhibitor programs applied in cooling water systems need to meet high demands. Since oxi-dising biocides, especially chlorine or bleach, are often used as a biocide, a corrosion inhibi-tor needs to have a high stability against them. Further, it should not react with calcium, even at high contents of calcium often present in water used for cooling.

2.2.1 Chlorine Stability

To determine the stability of Corrsave® 100 against oxidizing biocides, 2 L drinking water containing 1 ppm free Cl2 were prepared by addition of sodium hypochlorite solution. Addi-tionally, the pH was adjusted to 8.5 with NaOH and Corrsave® 100 was added. During the total test duration of 4 hours the amount of free chlorine was tested every 15 min (Aqua-merck Chlorine Test) and adjusted if necessary. The pH was adjusted as well.

At the beginning, the total- and ortho-phosphate amount was determined. Half-hourly, a sample was taken and total- and ortho-phosphate were analyzed. To destroy remaining chlo-rine in the sample, 1 mL of a 4 % urea solution was added. The relative chlorine stability was obtained from the measured organic phosphate concentration and division by the initial val-ue.

2.2.2 Calcium Tolerance

The evaluation of the calcium tolerance was done in a 500 ppm Ca2+ solution (as CaCO3). 250 mL aliquots were filled into flasks and Corrsave® 100 was added in different concentra-tions, varying from 1 to 40 ppm t-PO4. The pH was set in each flask to 9.0 with NaOH. Then, the flasks were put into a heating cabinet at 80 °C (176 °F).

After 24 h, the samples were cooled down, filtered through a 0.45 µm filter and the remaining total phosphate in solution was analyzed. The relative calcium tolerance is obtained from the remaining organic phosphate concentration and division by the initial value.

2.3 Hardness Stabilization Evaluation of dynamic calcium carbonate scale inhibition was conducted in a test apparatus shown in Fig. 1. A test water providing stressed conditions was used (see Tab.1) with a Langelier Scaling Index of approx. 2.9 at the outlet of the heat exchanger. Over a two hour period the test solution was pumped at a constant flow rate through a helical glass tube heated from outside by water of 80 °C (176 °F). The calcium carbonate precipitate formed inside the glass tube was removed with a defined quantity of hydrochloric acid and the calci-um level in the acidic solution was determined. Comparison against a blind sample provided the relative calcium carbonate inhibition of the tested compound.

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Fig. 1: Setup for hardness stabilization experiment (1: test water; 2: hose pump; 3: thermostat; 4: heat exchanger; 5: measuring cylinder).

2.4 Corrosion Tests

2.4.1 Electrochemical Measurements

Electrochemical measurements were carried out using an Autolab Metrohm frequency re-sponse analyser with an electrochemical interface. The polarization curves were determined potentiostatically with ohmic drop compensation. They were plotted point by point to ensure quasi steady-state conditions. The anodic and the cathodic parts were obtained independent-ly from the corrosion potential after 2 h of immersion. The electrolytic resistance (Re) is de-termined from the high-frequency limit of the electrochemical impedance measurements.

The impedance diagrams were plotted at the corrosion potential after 2 h of immersion in a frequency range of 65 kHz to a few mHz with eight points per decade. The electrochemical results were obtained from at least five experiments to ensure reproducibility.

The corrosive medium is a 200 ppm NaCl solution (reagent grade) in contact with air main-tained at 25 °C (77 °F) for the experiments. The pH of each tested solution was adjusted between 8.0 and 8.5 by addition of NaOH or H2SO4.

The material selected for the study is an XC 35 carbon steel and has the following composi-tion in percentage by weight: C=0.35, Mn=0.65, Si=0.25, P=0.035, S=0.035 and Fe to 100. For all the experiments, the carbon steel samples are polished with SiC paper down to grade 4000, cleaned in water in an ultrasonic bath, and then dried in warm air.

The working electrode was a rotating disc consisting of a rod of carbon steel of a 1 cm2 cross-sectional area to ensure a uniform thickness of the diffusion layer at the electrode sur-face, and a heat-shrinkable sheath leaving only the tip of the cylinder in contact with the solu-tion. All experiments were carried out at a rotation rate of 500 rpm. A saturated calomel elec-trode (SCE) was used as reference and the auxiliary electrode was a platinum grid.

The carbon steel/solution interface was mathematically described in terms of an electric equivalent circuit consisting of a resistance electrolyte in series with a parallel constant phase element (CPE)/resistor combination. The semicircular shape of the impedance dia-grams led us to choose this equivalent circuit to obtain the characteristic parameters: Rp, polarization resistance and C, double layer capacitance. The CPE is generally attributed to the roughness of the surface or to a nonuniform distribution of the current density on the electrode undergoing corrosion [12[13].

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2.4.2 Fast Beaker Experiments

The corrosion inhibition efficiency of Corrsave® 100 was assessed by stirring steel- (UNS G10100) and brass coupons (C44300) at 100 rpm in the described test water containing a defined concentration of the substance to be tested. A water bath was used for temperature control. After 24 h, the metal concentration in the solution was measured by atomic absorp-tion spectroscopy. By normalization of the metal content in the test solution (cMe(Inh)) against the blank value (no inhibitor) (cMe(blank)), the relative corrosion inhibition (CI) [%] was pro-vided according to equation 1:

( )( )

−= 100*100[%]

blankc

InhcCI

Me

Me (1)

To evaluate the behavior of the inhibitor more in detail, further tests were carried out varying temperature, pH as well as the calcium and chlorine concentration. The influence of the cal-cium concentration on the corrosion inhibition was studied in the range from 0 to 10 mol/m3 (0 to 1000 ppm CaCO3) by adding Ca(NO3)2 to the test water. The impact of the chloride concentration was studied between 0 to 500 ppm by adding NaCl, respectively. A blank was determined for each calcium and chlorine concentration as well. Fig. 2 shows a picture of the experimental setup.

Fig. 2: Fast beaker screening experiment for corrosion inhibition testing.

2.4.3 Laboratory-Scale Circulation Experiments

Corrsave® 100 was subjected to additional tests in a laboratory-scale circulation device equipped with a coupon rack according to ASTM D 2688 [14] resembling the flow conditions encountered in actual cooling circuits. The testing time was 14 days at a temperature of 30 °C (66 °F) and the flow was adjusted to 450 L/h (119 gal/h) corresponding to a water flow of 0.23 m/s (0.77 ft/s) in the coupon rack. During the test period, the pH was daily re-adjusted to 8.2. The determination of the corrosion rate was done by determination of mass loss of the coupons. Fig. 3 shows the experimental setup for the laboratory-scale circulation experi-ments.

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Fig. 3: Setup for the laboratory-scale circulation experiments (1: coupon test rack; 2: flow meter; 3:

water basin; 4: circuit pump; 5: heat exchanger; 6: thermostat).

2.4.4 Corrosion Inhibition in Pilot Cooling Circuits

The pilot cooling tower closely emulates all relevant features of an evaporative cooling sys-tem. The total water volume of the system was 1m3

(35.3 ft3). The temperature difference in the tube heat exchanger operated with steam amounts to 6 °C (11 °F). The maximum water temperature in the system was 25 °C (46 °F). The make-up water replacing the losses could be taken from different water qualities mixed at any ratio of tap water and de-ionised water. System blow-down was controlled by conductivity measurements and was kept at a variable preset level. A typical holding time index of approximately two days was adjusted. The cycle of concentration was 2.0. The water flow through the heat exchanger had a water velocity of about 1.0 m/s (3.3 ft/s). The water composition was similar to corrosive water from a coal fired power plant.

Corrosion inhibition was determined with mild steel coupons (UNS G10100). During the trial, all important water parameter were analyzed routinely. Upon trial conclusion (typically 14-21 days), coupon surfaces were visually evaluated and the corrosion rate was determined via mass loss.

Fig. 4: Scheme (left) and photo (right) of pilot plant cooling tower. 1: valves; 2: dosing pumps; 3 circu-lating pump.

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3 Results and Discussion

3.1 Biodegradability

State of the art corrosion inhibitors generally are classified as poorly biodegradable, leading to a pollution of the environment. Compared to other well-known inhibitors, Corrsave® 100 has an improved environmental profile. According to the results of the Zahn-Wellens test, Corrsave® 100 is degraded to 70 % within 28 days and thus is classified as inherent biode-gradable.

3.2 Properties Relevant for Application

3.2.1 Chlorine Stability and Calcium Tolerance

To define the frame conditions for an application of Corrsave® 100 in cooling water treatment, two important properties were determined. Fig. 5 illustrates the result for calcium tolerance and chlorine stability for Corrsave® 100 compared to three well-known phosphonic acids widely used in water treatment: Aminotrismethylenphosphonic acid (ATMP), Hydroxiethandi-phosphonic acid (HEDP) and Hydroxiphosphonoacetic acid (HPA). Concerning calcium tol-erance and chlorine stability, Corrsave® 100 is significantly better than HEDP, ATMP and HPA. Especially the chlorine resistance is remarkable; after 4 h with 1 ppm Cl2/L, the loss is only 21 % for Corrsave® 100.

Fig. 5: Calcium tolerance (20 ppm t-PO4, 24 h, 80°C, 176°F) and chlorine stability (4 h, 1 ppm Cl2) of Corrsave® 100 compared to standard phosphonic acids.

3.3 Hardness Stabilization

The anti-scaling efficiency of Corrsave® 100 is shown in Fig. 6 in comparison to the perfor-mance of well-known polycarboxylates. Corrsave® 100 shows an excellent inhibition of calci-um carbonate scaling similar to polyacrylic acid but clearly outperforming the biodegradable polyaspartic acid. In contrast to the polycarboxylic acids Corrsave® 100 shows additionally a good corrosion inhibition (see Fig. 8).

Clearly, Corrsave® 100 can be the backbone of a complete treatment program for cooling systems due to its very good corrosion inhibition and anti-scaling efficiency.

0

20

40

60

80

100

Chlorine Stability [%] Calcium Tolerance [%]

Sta

bilit

y [%

]

Corrsave 100 ATMP HEDP HPA

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Fig. 6: Hardness stabilisation of Corrsave® 100 in comparison to standard polycarboxylic acids.

3.4 Corrosion Inhibition

3.4.1 Electrochemical Measurements

A series of experiments had been done to establish the mode of action of Corrsave® 100, i.e. if it acts as an anodic, cathodic or mixed inhibitor. Thus, steady-state current–voltage curves and impedance diagrams were obtained in the presence of our compound and compared with the curve obtained in the inhibitor-free solution after 2 hours of immersion.

Fig. 7 shows the current-voltage curves and the impedance diagram. Initially, the corrosion potential (Ecorr) of the carbon steel (without inhibitor) measured in our experimental conditions is about -0.4 V/SCE (left diagram). In the cathodic range, the current densities are lowered in the presence of the tested inhibitor solution compared to the result obtained without inhibitor. In contrast, the solution containing Corrsave® 100 does not modify the anodic current densi-ty. Therefore, Corrsave® 100 acts predominantly as a cathodic inhibitor.

Fig. 7: Left: Polarization curve obtained after 2 hours of immersion at Ecorr for Corrsave® 100 (c = 100 ppm); (-) blank solution without inhibitor; (- -) Corrsave® 100

Right: Electrochemical impedance diagram obtained after 2 hours of immersion at Ecorr for Corrsave® 100 (c = 100 ppm).

(- -) Corrsave 100 (-) blank

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The impedance diagram obtained for Corrsave® 100 is characterized by a single capacitive loop. The polarization resistance values (Rp) obtained from the diagrams can be related to the charge transfer resistance of iron dissolution in the pores of the inhibitive layer [15[16]. Assuming that electrochemical processes are taking place only at the pores, the change of the polarization resistance value gives direct information on the quality of the protective layer [17[18]. In fact, the higher the Rp value is, the better is the anticorrosion efficiency.

The Rp values for the tested inhibitor dosed from 0 to 100 ppm are reported in Tab. 2. It can be noted, that the Rp values for Corrsave® 100 are significantly higher than that obtained for the blank solution without inhibitor and they increase with increasing concentration in a non-linear way. It clearly shows that the inhibitor brings a protective effect on the carbon steel against corrosion mechanisms. From the curve of the impedance spectra (single loop) it can be derived that new corrosion inhibitor does not have distinct film forming properties.

Tab. 2: Polarization resistance for carbon steel immersed in NaCl solution containing the tested in-hibitor in concentration from 0 to 100 ppm.

c [ppm] R P [Ω cm²]

0 (Blank) 819

10 1460

25 1890

50 2270

100 2870

3.4.2 Fast Beaker Experiments

a) Survey of Corrosion Inhibitors

A series of different experiments have been carried out to establish the effect of the new in-hibitor. First, a comparison with different corrosion inhibitors was conducted, which is illus-trated in Fig. 8. Clearly, Corrsave® 100 shows a very good efficiency compared to well-known inhibitors. Zinc, phosphate and polyacrylic acid were chosen to represent state of the art poorly biodegradable inhibitors, whereas polyaspartic acid is an example of green inhibitors.

Corrsave® 100, containing phosphorous, indicates a slightly better performance than Zinc. A corrosion inhibition of 92 % was achieved. Clearly these results indicate a high potential of the newly developed corrosion inhibitor. Polyaspartic acid and polyacrylic acid are both well known for their anti-scaling efficiency, but as expected show very little corrosion inhibition abilities.

To evaluate the behavior of the new inhibitor concerning corrosion inhibition more in detail, further tests were carried out varying inhibitor concentration, pH and water composition, i.e. water hardness and water temperature, reflecting the typical range of conditions in an evapo-rative cooling system.

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Fig. 8: Comparison of different corrosion inhibitors (Concentration: commercial products: 40 ppm; zinc and phosphate: 5 ppm).

b) Concentration Series

The corrosion inhibition efficiency depending on the corrosion inhibitor concentration, ranging from 0 to 60 ppm for mild steel, is illustrated in Fig. 9. With 30 ppm, a high level of protection (> 80 %) can be achieved.

Furthermore, the corrosion inhibition ability of Corrsave® 100 for brass was determined. With 20 ppm an excellent protection (> 80 % corrosion inhibition) was achieved for zinc. However, the protection for copper was mediocre.

Fig. 9: Corrosion inhibition of Corrsave® 100 determined by fast-beaker experiments depending on

inhibitor concentration (left: steel, right: brass).

c) Ca2+ - and pH Variation

To assess the influence of calcium on the corrosion inhibition efficiency on steel, corrosion tests with different Ca2+ contents between 0 and 10 mol/m³ (0 and 1000 ppm CaCO3) were carried out. It is apparent from Fig. 10 (left) that Corrsave® 100 is able to protect the metal from corrosion even if no calcium is present. Furthermore, the corrosion inhibition of Corrsave® 100 is almost constant between 70 and 80 % up to a Ca2+ concentration of 10 mol/m³ (1000 ppm CaCO3).

Fig. 10 (right) shows the results of corrosion tests on steel as a function of the pH of the test water. The corrosion inhibition efficiency of Corrsave® 100 is independent from the pH within the usual range of cooling waters.

Steel Brass

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Fig. 10 : Corrosion inhibition on steel of Corrsave® 100 (30 ppm) determined by fast-beaker experi-ments depending on Ca2+ concentration (left) and pH (right) of test water.

d) Chloride - and temperature variation

The chloride concentration in cooling water ranges typically from 200 to 500 ppm. With in-creasing chloride concentration, the corrosion inhibition efficiency of Corrsave® 100 decreas-es. However, corrosion inhibition in the common chloride range is sufficient.

To estimate the influence of fluctuating cooling water temperature, tests at three different water temperatures were conducted: 25, 30 and 40 °C (77, 86 and 115 °F, respectively). The results show, that Corrsave® 100 has a very good performance nearly independent from the temperature.

3.4.3 Laboratory-Scale Circulation Experiments

Additional to the fast beaker experiments, Corrsave® 100 was tested in a laboratory-scale circulation experiment resembling the flow conditions encountered in actual cooling circuits. The corrosion rate and the relative corrosion inhibition can be seen in Fig. 11. The corrosion inhibition of Corrsave® 100 is in good accordance to the previous fast-beaker result (see Fig. 9).

Fig. 11: Corrosion rate on carbon steel (CR) and corrosion inhibition as function of Corrsave® 100 concentration in laboratory-scale circulation test. (1 mm/a = 40 mpy).

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3.4.4 Synergy Tests

In order to further enhance corrosion inhibition efficiency of Corrsave® 100, fast beaker tests were carried out to find synergistic co-inhibitors. The portion of Corrsave® 100 was varied between 0 and 100 %, whereas the total inhibitor concentration was kept constant at 20 ppm. Fig. 12 shows the result for a standard phosphonic acid providing a marked synergy with Corrsave® 100. The maximum corrosion inhibition of 61 % was obtained for a combination of 60% Corrsave® 100 and 40% standard phosphonic acid.

Fig. 12 : Synergy in corrosion inhibition on steel between Corrsave® 100 and a standard phosphonic acid; the total inhibitor concentration was 20 ppm.

3.5 Formulation based on Corrsave ® 100: Aktiphos ® 4170

Following the results from the synergy tests, a formulation based on Corrsave® 100 and a standard phosphonic acid was developed to leverage the improved corrosion inhibition. Fur-thermore, Aktiphos® 4170 contains a dispersant (sulphonated copolymer) and a nonferrous metal inhibitor (triazole).

3.5.1 Corrosion Inhibition in Pilot Cooling Circuits

The formulation described in 3.5 was studied in a pilot cooling system to determine the cor-rosion inhibition efficiency under realistic conditions. The formulation Aktiphos® 4170, con-taining Corrsave® 100, was compared to two other standard corrosion inhibitors: a formula-tion based on the high performance corrosion inhibitor hydroxiphosphonoacetic acid (HPA) and a low phosphorous containing product.

Fig. 13 shows the results after 25 days of operation, Fig. 14 the appearance of a representa-tive coupon for each treatment program. Aktiphos® 4170 showed an excellent corrosion inhi-bition with a corrosion rate of 0.04 mm/a (1.6 mpy), comparable to a high performance standard corrosion inhibitor. Remarkably, this result is obtained with a 60 % lower total-phosphate concentration. Furthermore, the new corrosion inhibitor provided clearly superior corrosion results compared to the low P-containing formulation with even slightly lower total-phosphate content.

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The coupon of the low-P program is characterised by pronounced pitting, whereas the cou-pon treated with Aktiphos® 4170 shows even less pitting than the coupon of the HPA based program. Additionally, cost of treatment for Aktiphos® 4170 is only approximately 50% of the two standard corrosion inhibition programs.

Fig. 13 : Comparison of corrosion rate on carbon steel (CR) and total-phosphate (t-PO4) concentration in the cooling water of Aktiphos® 4170 based on Corrsave® 100 with standard corrosion inhi-bition programs (1 mm/a = 40 mpy).

Fig. 14 : Steel coupons after etching treated different corrosion inhibitors (corrosion inhibition test in pilot plant).

CR = 0.04 mm/a (1.6 mpy)

Aktiphos® 4170 High Performance formulation

Low P Formulation

CR = 0.03 mm/a (1.2 mpy)

CR = 0.08 mm/a (3.2 mpy)

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4 Conclusion and Outlook

A new heavy metal free, low P-content corrosion inhibitor for evaporative cooling systems based on natural organic acids has been developed: Corrsave® 100 is a proprietary sub-stance produced from the reaction of a natural organic acid with inorganic phosphate. It has an improved biodegradability and is classified as inherent biodegradable. The corrosion inhi-bition efficiency as well as properties important for the application in cooling systems have been studied in beaker tests and pilot cooling systems as well as with electrochemical meth-ods.

Beaker tests under standardized conditions showed that the substance provides excellent corrosion inhibition of carbon steel. The efficiency is not depending on the temperature and pH within the range typical of cooling water. Corrsave® 100 showed an almost constant cor-rosion inhibition within a wide range of water hardness, even in very soft waters.

Voltammetric studies led to the conclusion that Corrsave® 100 is mainly a cathodic inhibitor. According to the electrochemical impedance spectra the substance does not show filming properties.

Further studies showed a pronounced synergy on corrosion inhibition with state of the art inhibitors.

Additionally to its performance as corrosion inhibitor, Corrsave® 100 is an excellent anti-scalant, clearly outperforming polyaspartic acid and at least meeting the efficiency of a mod-ern polycarboxylate.

Application oriented tests showed, that Corrsave® 100 has an excellent performance with regard to chlorine stability and calcium tolerance. Compared to some well-known phospho-nates it has a significant better application profile.

In a pilot cooling system, equipped with heat exchanger (heated with process steam), cooling tower and automatic blowdown control a formulation based upon Corrsave® 100 was tested versus two other corrosion inhibitor programs: a high performance inhibitor formulation using hydroxiphosphonoacetic acid and a low P-containing program. The new corrosion inhibitor provided superior corrosion protection compared to the low P-containing formulation with an even slightly lower P-content. Compared to the high performance inhibitor the same corro-sion inhibition was obtained, but with approximately one third of P-content. At the same time the cost of treatment could be reduced by approximately 50 %.

Due to the excellent results obtained with Corrsave® 100 a formulation based upon this new innovative technology – Aktiphos 4170, is already being applied in industrial cooling systems, replacing traditional all-organic corrosion inhibition programs.

5 Acknowledgement

The authors would like to thank Marlies Bodewig, Patrick Kraft and André Schirmer for the experimental work and scientific input.

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