Volume 23 Preprint 16
Polyphosphate performance for inhibiting corrosion of heat exchanger materials
Arini Nikitasari, Sundjono, Gadang Priyotomo, Ahmad Royani
Keywords: Polyphosphate, A192, C1015, Heat Exchanger, Ammonia Plant
The inhibitive performance of polyphosphate on the corrosion of heat exchanger materials i.e carbon steel A192 and C1015 in ammonia plant was explored. Corrosion rate measurement without and with polyphosphate addition were performed to investigate the inhibition of polyphosphate. There were three kinds of polyphosphate concentration and temperature used in this experiment : 75 ppm, 100 ppm, 150 ppm, and 32oC, 37oC, 50oC, respectively. The result revealed the effectiveness of polyphosphate for inhibiting corrosion of heat exchanger materials. The efficiency of polyphosphate boosts with concentration and diminishes with temperature.
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Polyphosphate performance for inhibiting corrosion of heat
Arini Nikitasari1, Sundjono1, Gadang Priyotomo1, Ahmad Royani1
Research Center for Metallurgy and Material-LIPI, Puspiptek, 15313, South Tangerang,
The inhibitive performance of polyphosphate on the corrosion of heat exchanger materials
i.e carbon steel A192 and C1015 in ammonia plant was explored. Corrosion rate
measurement without and with polyphosphate addition were performed to investigate the
inhibition of polyphosphate. There were three kinds of polyphosphate concentration and
temperature used in this experiment : 75 ppm, 100 ppm, 150 ppm, and 32oC, 37oC, 50oC,
respectively. The result revealed the effectiveness of polyphosphate for inhibiting corrosion
of heat exchanger materials. The efficiency of polyphosphate boosts with concentration and
diminishes with temperature.
Keywords: Polyphosphate, A192, C1015, Heat Exchanger, Ammonia Plant.
Heat exchanger is vital equipment for heat transfering and gas cooling in ammonia plant.
However, corrosion in heat exchanger equipment is an important issue particularly in
ammonia plant. During operation, corrosion products are usually formed on the surfaces of
heat exchanger. These deposits reduce the heat transfer efficiency and endanger the
lifespan of heat exchanger .
Corrosion occurs in the heat exchanger of ammonia plant as a result of an electrochemical
reaction between metal and the moisture present in the atmosphere . Moreover,
inorganic scaling and fouling deposit on the heat exchanger surface induce under deposit
corrosion attack and eventually causes failure of heat exchanger material –. In order to
protect heat exchanger material against corrosion, corrosion inhibitor is the best solution
due to low cost and ease in injecting.
Corrosion inhibitor is organic or inorganic compound that suppresses corrosion, regardless
of which electrochemical reaction it affects . Polyphosphate is one of corrosion inhibitor
that capable of slowing the rate of cathodic reaction . Polyphosphates consist of
phosphorus atom that linked to its neighbors through two oxygen atoms. Thanks to higher
phosphate content and also high chelate building potential with multivalentmetal cations,
the polyphosphates perform better inhibitive performance compared to other inhibitors.
Furthermore, it has been found that polyphosphates have sufficient water solubility to
supply corrosion inhibition , . Therefore, polyphosphate was chosen as corrosion
inhibitor of heat exchanger materials in this experiment.
Many research studies have been performed in recent years, in relation with the use of
polyphosphate for corrosion inhibition. Nevertheless, deep researches about polyphosphate
for inhibiting corrosion of heat exchanger materials have been seldom discussed. The aim
of the present work is to study the performance of polyphosphate for inhibiting corrosion
of metal A192 and C1015 (heat exchanger materials). Concentration and temperature also
varied to observe their effect to corrosion rate.
Materials used for test were carbon steel A192 and C1015 whose chemical compositions
were shown in Table 1. According to heat exchanger environment in Kujang Ammonia
Plant, the shell side medium of heat-exchanger was feed water (corrosion medium) and its
contents were displayed in Table 2.
Corrosion inhibitor was prepared using polyphosphate (p.a Merck). Concentration of
polyphosphate in this experiment were 75 ppm, 100 ppm, and 150 ppm. Polyphosphate
was measured using analytical scale and dissolved with feed water in volumetric flask
Table 1. Chemical composition of heat exchanger materials
Chemical Composition (%)
Table 2. Chemical analysis of feed water
Total Iron, Fe
The exposure test were carried out using carbon steel A192 and C1015 coupon (7 cm x
4 cm) in corrosion chamber which installed on heat exchanger of Kujang Ammonia Plant.
Position of corrosion chamber showed in Fig.1. Fig.2 displayed the installation of corrosion
chamber in Kujang Ammonia Plant. There were 5 duration of exposure test : 28 days, 56
days, 84 days, 112 days, and 140 days. All samples for 28 and 56 days of exposure located
at the bottom of corrosion chamber while samples for 84, 112, and 140 days lied on the
top of corrosion chamber.
Prior to the test, the surface of samples were degreased with acetone and rinsed with
absolute ethanol, weighted using a precision of 0.0001 g. Subsequent to the test,
specimens were descaled, rinsed with water and absolute alcohol, dried in nature state and
weighted again . The corrosion rate (v) was calculated according to Eq. (1)
ν = [(weight loss (mg))/(area (cm2) × time (sec))]
Figure 1. Position of corrosion chamber
Figure 2. Installation of corrosion chamber
Gamry instruments (Serial no. G750) was used to perform the electrochemical test. Carbon
steel A192 and C1015 were cut into size (1 cm x 1 cm) as sample of electrochemical test. In
this corrosion measurement system, sample were utilized as working electrode, saturated
calomel electrode (SCE) as reference electrode, and Pt electrodes as counter electrode. Feed
water used as solution in this test. Temperature of the solution was varied at 32oC, 37oC,
and 50oC. The electrochemical test permormed twice, in feed water solution without
polyphosphate inhibitor and with addition of polyphosphate inhibitor.
Result and Discussion
Visual and weight loss analysis
Visual observation was provided to assist in corrosion monitoring of exposure test. Fig. 3 –
Fig. 7 showed visual observation of metal A192 after exposure test during 28, 56, 84, 112,
and 140 days, respectively. While, visual observation result of metal C1015 presented in
Fig.8 – Fig. 12. Based on the visual observation, corrosion product increase with time of
exposure. Corrosion product on the C1015 surface greater than corrosion product on the
A192 surface according to visual observation result after exposure test.
Table.3 listed result of weight loss measurement. According to Table.3 weight loss increase
from 28 days to 56 days of exposure test, but from 84 days to 140 days,the weight loss
decrease. The decrease of weight loss after exposure test more than 56 days due to the
thickness of corrosion product. Corrosion product covers metal surface and prevents
contact between metal and environment as of corrosion rate reduce.
Figure 3. Corrosion coupon of A192 after exposure 28 days
Figure 4. Corrosion coupon of A192 after exposure 56 days
Figure 5. Corrosion coupon of A192 after exposure 84 days
Figure 6. Corrosion coupon of A192 after exposure 112 days
Figure 7. Corrosion coupon of A192 after exposure 140 days
Figure 8. Corrosion coupon of C1015 after exposure 28 days
Figure 9. Corrosion coupon of C1015 after exposure 56 days
Figure 10. Corrosion coupon of C1015 after exposure 84 days
Figure 11. Corrosion coupon of C1015 after exposure 112 days
Figure 12. Corrosion coupon of C1015 after exposure 140 days
Table 3. Weight loss measurement result
Weight Loss (mg)
Corrosion Rate (mpy)
Weight Loss (mg)
Influence temperature to corrosion rate of carbon steel A192 and C1015
The influence of temperature to corrosion rate of A192 and C1015 was observed with
electrochemical test. Electrochemical test result of A192 at temperature 32 oC, 35oC, and
50oC presented in Fig.13-15, respectively. Fig. 16-18 displayed curve of C1015
electrochemical test at temperature 32oC, 35oC, 50oC, respectively. From the curve of
electrochemical test, corrosion rate of A192 and C1015 at various temperature obtained
and listed on Table.4. Based on Table. 4, metal C1015 have higher corrosion rate than
A192 in all temperature. This result appropriate with visual and weight loss result.
Corrosion rate of A192 less than C1015 because chrome content of A192 more than
chrome content of C1015 according to Table.1.
Corrosion rate of A192 and C1015 increase with temperature. Temperature able to increase
the corrosion rate because reaction of corrosion is faster at high temperatures. Therefore,
the highest corrosion rate of A192 and C1015 is at temperature 50 oC.
Figure 13. Curve of A192 electrochemical test at temperature 32 oC
Figure 14. Curve of A192 electrochemical test at temperature 37oC
Figure 15. Curve of A192 electrochemical test at temperature 50oC
Figure 16. Curve of C1015 electrochemical test at temperature 32oC
Figure 17. Curve of C1015 electrochemical test at temperature 37oC
Figure 18. Curve of C1015 electrochemical test at temperature 50oC
Table 4. Corrosion rate based on electrochemical test
Corrosion Rate (mpy)
Polyphosphate inhibitor efficiency
Inhibitive performance of polyphosphate was analyzed using the difference of corrosion
rate (CR) between without and with polyphosphate addition. Polyphosphate was mixed in
various concentration with feed water to investigate the effect of concentration to corrosion
rate. Corrosion rate with polyphosphate addition also obtained using electrochemical test
as corrosion rate without polyphosphate addition. Fig. 19-20 depicted corrosion rate of
carbon steel A192 and C1015, respectively, with polyphosphate addition at various
concentration. Based on Fig. 19 and Fig. 20, corrosion rate increase with temperature and
decrease with increasing polyphosphate concentration.
Table. 5 presented the efficiency of polyphosphate inhibitor. The efficiency inhibitor
calculated according to Eq.2. Percentage of polyphosphate efficiency boosts with
concentration. This condition indicate that polyphosphate give ideal performance for
inhibiting corrosion of heat exchanger materials (carbon steel A192 and C1015).
Polyphosphate inhibit corrosion by dissolving into the water and adsorbing on the metal
surface, thereby reducing the access of hydrogen ions. The reduction of hydrogen ions
leading to metal surface will interfere the reaction of hydrogen evolution. Therefore,
polyphosphate is classified as cathodic inhibitors that interfere with the cathodic site of the
electrochemical corrosion cell formation.
Figure 19. Corrosion rate of A192 at various polyphosphate concentration
Figure 20. Corrosion rate of C1015 at various polyphosphate concentration
Corrosion rate of heat exchanger materials in ammonia plant was assessed through
exposure test and electrochemical test. Based on exposure test and electrochemical test,
the corrosion rate of carbon steel A192 was lower than carbon steel C1015. Carbon steel
A192 was found to be superior in corrosion resistance compared carbon steel C1015 due to
higher chromium content. Polyphosphate inhibitor has good performance for inhibiting
corrosion of carbon steel A192 and C1015. Polyphosphate able to reduce the corrosion rate
up to 40% with concentration 150 ppm at 32 oC. The efficiency of polyphosphate boosts
with concentration and diminishes with temperature.
The authors are grateful to Kujang Ammonia Plant for providing essential information and
technical guidance made this research possible at Kujang Ammonia Plant. In addition, they
would like to thank Research Center for Metallurgy and Material, Indonesian Institute of
Sciences for financial support.
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