Effect of trichloroisocyanuric acid on the corrosion ...

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Effect of trichloroisocyanuric acid on the corrosion resistance of
residential water pipes

R. LEIVA-GARCÍA, M.J. MUÑOZ-PORTERO, J. GARCÍA-ANTON*
Ingeniería Electroquímica y Corrosión (IEC), Departamento de Ingeniería Química y Nuclear

Universidad Politécnica de Valencia
Camino de Vera s/n, 46022 Valencia, tel: +34963877632, Fax: +34963877639

SPAIN
*[email protected] http://www.upv.es

Abstract: The aim of the present study is to assess the effect of one emergency disinfectant
(trichloroisocyanuric acid) on the corrosion resistance of different materials used in residential distribution
pipes (copper, lead, and galvanised iron). Corrosion in residential distribution systems may cause several
problems, such as pipe breaks or water quality deterioration. Therefore, it is interesting to study the effect of
disinfectants used in drinking water on the corrosion of metallic pipes. Potentiodynamic curves were carried out
for copper, lead, and zinc in trichloroisocyanuric acid solutions at different concentrations at 25 ºC. According
to the results, the presence of this disinfectant increases the corrosion rate of metallic pipes.
Key-Words: - disinfectants; drinking water; copper; lead; zinc; residential water pipes; corrosion

1 Introduction

Corrosion in distribution systems for drinking water can cause considerable problems. The consequences of
internal corrosion are pipe breaks, overflows, clogging of pipes with corrosion products and, the greatest effect
for consumers, which is water quality deterioration [1]. Corrosion products detected at the consumers’ taps
produce colour, bad taste and odour, they could even produce health problems, depending on the pipe materials.

Corrosion processes consist of a series of electrochemical reactions occurring at the metal surface in contact
with water and its constituents [2, 3]. Corrosivity of particular water depends on its chemical properties and
physical characteristics, as well as the nature of the pipe material [4]. Different materials can be used in the
residential distribution pipes. Lead piping was popular in plumbing systems until before the 1970, due to its
corrosion resistance; therefore, some old houses have lead pipes. Galvanised iron is another material employed
in old residential distribution systems. Nowadays, copper is widely used for tubing and piping in the
distribution systems of drinking water throughout the world due to its excellent corrosion resistance and ease of
installation.

The effects of free chlorine on the corrosion of pipes in drinking water have been studied more thoroughly,
since chlorine is a very common disinfectant used in drinking water distribution systems [5-7].
Trichloroisocyanuric acid can be used as a disinfectant agent in emergency cases according to the
SCO/1915/2009 order [8]. This substance has a 90 % of active chloride and it can maintain a constant level of
chlorine in the water due to its low solubility [9]. On the other hand, the trichloroisocyanuric acid is oxidant
and corrosive; then, it could produce corrosion problems in metallic pipes. Therefore, the aim of this work is to
study the corrosion effects of trichloroisocyanuric acid on the corrosion resistance of different materials in
residential pipes (copper, lead, and galvanised iron).

2 Experimental Procedure

2.1 Materials
Working electrodes were made of copper, lead, and zinc (galvanised iron) in order to simulate materials
commonly met in the residential pipes. They were cylindrically shaped and covered with Teflon. In this way,

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only an area of 0.5 cm2 was exposed to the electrolyte. Prior to the electrochemical tests, the samples were wet
abraded from 220 SiC (Silicon Carbide) grit to a 4000 SiC grit finish, and finally rinsed with distilled water and
dried with hot air.

2.2 Polarization potentiodynamic curves
Polarization potentiodynamic curves were carried out in aqueous trichloroisocyanuric acid solutions with
different concentrations (from 0 to 10 ppm). Solutions were prepared from well water without previous water
treatment processes. In all cases, tests were repeated at least three times. The scans presented in this paper are
one of the most representative curves. The cell used was a glass vertical cell with various inlets and a
thermostatic shirt, which maintains constant the temperature at 25 ºC. The potential was measured against an
Ag/AgCl with KCl 3M reference electrode. The counter electrode was made of platinum.

Polarization curves were carried out in aerated solutions. Before each polarization experiment, the open
circuit potential (OCP) was recorded for one hour; the OCP value reported here was the arithmetic mean of the
last five minutes recorded values. After the OCP test, the specimen potential was reduced progressively to –
1000 mVAg/AgCl (-1500 mVAg/AgCl in the zinc tests); this potential was maintained constant for 300 s in order to
create reproducible initial conditions. Then, the working electrode potential was scanned from – 1000 mVAg/AgCl
(-1500 mVAg/AgCl in the zinc tests) to 1000 mVAg/AgCl, using a scan rate of 0.1667 mV/s [10], which is slow
enough to appreciate the changes that occur due to the corrosion process. Therefore, polarization curves were
recorded from the cathodic to the anodic direction. Corrosion potential (Ecorr) and corrosion current density
(icorr) were estimated from these curves and information about the general electrochemical behaviour of the
materials was also obtained.

3 Results and discussion

Fig 1 shows the OCP values of copper, lead, and zinc in the different trichloroisocyanuric acid solutions at 25
ºC. OCP values of every tested material remain constant with the increase of the concentratrion, then, there is
not influence of the disinfectant in the open circuit potential. With regard to the electrochemical behaviour of
pipe materials, zinc shows the lowest OCP value, lead presents intermediate values, and copper shows the most
noble OCP values. Therefore, zinc has higher trend to corrosion than the rest of materials and copper presents
the lowest susceptibility to corrosion. This is the main reason, to choose copper as pipe material.

0.2
0.0

OCP (VAg/AgCl) -0.2
-0.4
-0.6

-0.8

-1.0 2 4 6 8 10 12
0 Concentration of trichloroisocyanuric acid (ppm)

copper lead zinc

Fig. 1. Open Circuit potential values of copper, lead, and zinc in the different trichloroisocyanuric acid
solutions at 25 ºC.

Fig 2 shows the potentiodynamic curves of copper, lead, and zinc in the different trichloroisocyanuric acid
solutions at 25 ºC.

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-1 -1
-2 -2

-3 -3

-4 -4
log |i| (A/cm2)

log |i| (A/cm2)
-5 -5

-6 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 -6 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
-7 Potential (VAg/AgCl) 10 ppm -7 0 ppm Potential (VAg/AgCl) 10 ppm
-8 -8
-9 -9 2 ppm 4 ppm 6 ppm 8 ppm
-10 -10
b) lead
-1.0 -1.0

0 ppm 2 ppm 4 ppm 6 ppm 8 ppm

a) copper

-1

-2

-3

log |i| (A/cm2) -4

-5

-6

-7

-8

-9

-10
-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Potential (VAg/AgCl)

0 ppm 2 ppm 4 ppm 6 ppm 8 ppm 10 ppm

c) zinc
Fig 2. Potentiodynamic curves for copper, lead, and zinc in the different trichloroisocyanuric acid solutions at
25 ºC.

From the polarisation potentiodynamic curves corrosion potential (Ecorr) and corrosion current density
(icorr),were obtained for the different materials and concentrations of trichloroisocyanuric acid. Fig. 3 and 4
show the corrosion potential values and corrosion current density values of copper, lead, and zinc in the

different trichloroisocyanuric acid solutions, respectively.

In the case of copper and lead, a slight effect of the disinfectant concentration on the corrosion potential can

be observed. The corrosion potential of copper increases and the corrosion potential of lead decreases with the

trichloroisocyanuric acid concentration. The corrosion potential of zinc remains constant in the presence of

trichloroisocyanuric acid.

On the other hand, zinc presents the lowest corrosion potential and copper has the most noble corrosion

potential. Copper and zinc have the best and the worst behaviour against the corrosion, respectively.

Corrosion current density, values are low for all the materials tested without disinfectant, the lowest
corrosion current density is obtained for copper (0.39 µA/cm2 for copper, 2.47 µA/cm2 for lead, and 3.48
µA/cm2 for zinc). When the trichloroisocyanuric acid is added, an increase of corrosion current density is

observed for all the tested materials, this increase is greater in the zinc. In the case of zinc, the corrosion current
density values remain without variation with the increase of disinfectant concentration (around 15 µA/cm2).

With regard to lead behaviour, corrosion current density is greater as the disinfectant concentration increases,
reaching the value 7.02 µA/cm2 for the concentration of 10 ppm. On the other hand, in the case of copper the

increase in the corrosion current density with the presence of disinfectant is low, the highest value being 0.7
µA/cm2 for the concentration of 10 ppm. Therefore, the trichloroisocyanuric acid has a harmful effect on the

corrosion resistance of metallic pipes; this effect is greater in the case of zinc that has a strong increase in its

corrosion current density with the presence of disinfectant. These results is in agreement with observations

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obtained by others researchers about the negative effect of other disinfectants, such as monochloramine or free
chlorine, used in water treatment on the corrosion of metal pipes [6, 11-17].

Corrosion Potential (VAg/AgCl) 0.0

-0.2

-0.4

-0.6

-0.8

-1.0 2 4 6 8 10 12
0 Concentration of trichloroisocyanuric acid (ppm)

copper lead zinc

Fig. 3. Corrosion potential values of copper, lead, and zinc in the different trichloroisocyanuric acid solutions at
25 ºC.

20Corrosion current density (µA/cm2)
18
16
14
12
10

8
6
4
2
0

0 2 4 6 8 10 12
Concentration of trichloroisocyanuric acid (ppm)
copper lead zinc

Fig. 4. Corrosion current density values of copper, lead, and zinc in the different trichloroisocyanuric acid
solutions at 25 ºC.

Corrosion current density is directly related with corrosion rate. Equation 1 expresses the corrosion rate in

mm/year.

Corrosion rate (mm/year) = k × A × icorr (1)
n×D

where:

A is the atomic weight,

n is the number of interchange electrons,
D is the density of the material (g/cm3),

k is the relation between depth and time (0.00327),
icorr is the corrosion current density (A/cm2).

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Table 1 summarises the results of the corrosion rate expressed in mm/year for copper, lead, and zinc in the
different trichloroisocyanuric acid solutions.

Table 1. Corrosion rates values of copper, lead, and zinc in the different trichloroisocyanuric acid solutions at

25 ºC.

Corrosion rate (mm/year)

Concentration (ppm) copper lead zinc

0 0.045 0.074 0.040

2 0.053 0.178 0.215

4 0.054 0.185 0.230

6 0.057 0.228 0.235

8 0.059 0.232 0.230

10 0.081 0.240 0.232

According to the values showed in Table 1, the effect of the disinfectant on the thickness loss of copper
pipes is low and its necessary 10 ppm to produce a noticeable increase in the thickness loss. In the case of lead,
there is an important increase in the material loss when the trichloroisocyanuric acid is added; this loss
increases with the disinfectant concentration. The corrosion rate of zinc grows in the presence of
trichloroisocyanuric acid; the concentration to have a high corrosion rate is 2 ppm. When the zinc film is lost in
the galvanised iron pipes, the corrosion of iron takes place, leading to the presence of iron ions in water that can
colour water reducing its quality.

Therefore, copper pipes present the best corrosion resistance in the presence of the trichloroisocyanuric acid
and zinc has the worst corrosion behaviour. Furthermore, due to the role of emergency disinfectant that the
trichloroisocyanuric acid has, the use is limited to 50 days [8]. Then, the main problems during this period will
be in the oldest pipes made of lead and zinc (galvanised iron) that have less corrosion resistance than copper in
presence of the disinfectant.

4 Conclusions

The main conclusions of this work can be summarised as follows:
- Copper presents the lowest trend to corrosion of the three tested materials. On the other hand, zinc
shows the highest trend to corrosion and lead has an intermediate behaviour.
- The addition of the trichloroisocyanuric acid, produce an increase in the corrosion potential of copper
and a decrease in the corrosion potential of lead, remaining constant for zinc.
- Copper has the lowest corrosion rate of the three tested materials in the presence of the disinfectant;
furthermore the effect of the trichloroisocyanuric acid increase is low, being necessary 10 ppm to
produce a noticeable effect.
- In the case of lead and zinc, the addition of the trichloroisocyanuric acid produce an increase in the
corrosion rate of both metals. Therefore, when the trichloroisocyanuric acid has to be used, it is
convenient to reduce the period of use, as far as possible, in areas with old residential distribution
systems.

Acknowledgements
We wish to express our gratitude to FEDER and to Dr. Asunción Jaime for her translation assistance.

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