International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 04, April 2019, pp. 180–190, Article ID: IJMET_10_04_020
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=4
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
CORROSION FAILURE ANALYSIS OF COPPER
HEAT EXCHANGER BY USING A
NON-DESTRUCTIVE TECHNIQUE
M.J. Suriani
School of Ocean Engineering, Universiti Malaysia Terengganu,
21030 Kuala Terengganu, Terengganu, Malaysia
K.H. Ghazali
Faculty of Electrical and Electronics Engineering
Universiti Malaysia Pahang, 26600 Pekan, Pahang
F. Zulkifli and H. Farhana
School of Ocean Engineering, Universiti Malaysia Terengganu,
21030 Kuala Terengganu, Terengganu, Malaysia
ABSTRACT
Heat exchanger is a device that operate in a higher and lower temperature. In this
study, a shell and tube heat exchanger has been observed and identified the period of
operational to analyze its failure under corrosion. Temperature is the corrosion
factors that give influences in many parameter such as pH and concentration of metal.
The heat exchanger tubes used were made of copper. NDT method namely; Infrared
(IR) thermal imaging, Atomic absorption spectroscopy (AAS) and pH verification
were used in this study to determine the corroded surface area that occur on the
copper tube and shell heat exchanger. Infrared (IR) thermal imaging detect the
corroded or defected surface area by provides rapid visual thermal appearance of
difference temperature results. IR thermography provides colorful images of samples
where local changes in surface temperature indicate subsurface defects. Atomic
Absorption Spectroscopy (AAS) determined the copper concentration in the water
samples that flow internal and external of copper tube. AAS is suitable and accurate
method to measure the metal concentration in fresh water or analyte. pH of water
samples were verified to relate the relationship between temperature and pH in
corrosion process. Temperature is directly proportional to the pH because of copper
oxide layer formed as semi-protective layer to protect the metal surface from corrode
and decrease the corrosion rate. With higher of temperature, the copper concentration
increase. This is because of extreme environment which is in very high or very low pH
will break down the protective layer and effect the concentration of water samples. As
a conclusion, the NDT methods used have significantly determine the corrosion failure
analyses.
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Corrosion Failure Analysis of Copper Heat Exchanger by Using a Non-Destructive Technique
Key words: Copper tube, Corrosion, Heat exchanger, Failure analyses and Nondestructive technique
Cite this Article: M.J. Suriani, K.H. Ghazali, F. Zulkifli and H. Farhana, Corrosion
Failure Analysis of Copper Heat Exchanger by Using a Non-Destructive Technique,
International Journal of Mechanical Engineering and Technology 10(4), 2019, pp.
180–190.
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1. INTRODUCTION
Corrosion is the process that happens in any equipment or structure which converts from
refined metal to the destruction or loss the originality by chemical reaction process [1].
Corrosion is also applied to the degradation of plastics, concrete and wood but general and
mostly refers to metals. The chemical process takes place when metal contact or exposed to
the environment which will acts as catalyst to the corrosion process. Any equipment that
made up from metal is vulnerable to the corrosion [2]. Same as like heat exchanger, corrosion
has been detected in heat exchanger tube when it is conducted under a long time of operation.
The environment factors that can cause the corrosion event are physical state (solid, liquid,
and gas), chemical composition (concentration) and temperature [3]. Corrosion behavior is
dangerous in major industrial plant such as electrical power plant. Shutdown of plant
operation will be the result of the corrosion event. Generally, corrosion is caused by low pH
value of water which is acidic. Acid has higher concentration of H+ ions which react electron
at cathode.
The corrosion factors are pH, oxygen content, temperatures, and chemical in the water,
dissimilar metals, velocity and pressure [4]. This factors are common and usually occurred in
the heat exchanger tube. Heat exchanger is a device to transfer the enthalpy between one or
more fluid. Heat exchanger is susceptible to degradation which can caused leakages [5]. In
raised of temperature in the heat exchanger (close system), corrosion rate increase because of
oxygen which cannot escape in the system. This phenomenon will give acidic pH of water
that through the system that caused by reaction of oxygen with absorbed atomic hydrogen.
The consequence of corrosion are many and the effects of these on the safe, reliable and
efficient operation of equipment are more serious than the loss of a mass of metal.
Performance of heat exchanger defines the system efficiency under operation during period of
time and optimization of operating costs, and it is also depends on the operating variables and
specification of heat exchanger [6]. When the heat exchanger is failure, the industrial will be
affected such as loss of time in availability of profile making production, costly in
maintenance of the equipment, hazard and injuries to the people and etc. NDT is the one of
inspection that have been used in many sectors in industries [7]. Therefore, to analyze the
corrosion failure in the copper tube shell heat exchanger, NDT method have been used in this
study. The NDT method used were Infrared (IR) thermal imaging, Atomic absorption
spectroscopy (AAS) and pH verification. Infrared (IR) thermal imaging is used to detect the
corroded or defected surface area by appearance of difference temperature result. The
abnormal spot of color indicate the defected surface area which is associated with problem of
corrosion. Next, the investigation of corrosion performances can be continue by Atomic
Absorption Spectroscopy (AAS) and verification of pH level. This method is related to
concentration of metal, pH level and temperature which is factors to the corrosion event in the
system. With all this, the precaution and maintenance can be take and this will reduce the
major cost of repair and maintenance for whole failure of the equipment. Initial inspection
must be done in any equipment to avoid the machine exposed to worse damage and give good
durability.
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2. EXPERIMENTAL SETUP
2.1. Preparation of samples
Copper tube and shell type heat exchanger has been selected to identify the specification and
its operation in the system. Figure 1 shows heat exchanger training model (HE 158C) has
been used in this study which the tube is made up by copper metal while shell is made up by
mild steel. Table 1 and Table 2 show the measurement of copper tube and mild steel shell
respectively.
Figure 1 Shows tube and shell heat exchanger used, model (HE 158C)
Table 1 The measurement of copper tube of heat exchanger
Copper Tube
Part
Internal diameter
Outer diameter
Length
Arrangement
Measurement
0.013 meter
0.016 meter
1.83 meter
Triangular
Table 2 The measurement of mild steel shell of heat exchanger
Mild Steel Shell
Part
Internal diameter
Outer diameter
Length
Measurement
0.1934 meter
0.2074meter
1.83 meter
2.2. Determination of defect surface by IR Thermal Imaging
The defected surface area on copper tube of heat exchanger is observed by using NonDestructive Technique (NDT). In this study, passive approach of IR thermal imaging method
was applied. Passive thermography means tested object is excited by natural temperature
which mean there was no external sources heating. Firstly the IR thermal imager or camera
(FLIR model) captured the tube and shell heat exchanger under room temperature of ambient
environment and at the same distance in every different temperature of heat exchanger
running the system.
2.3. Atomic Absorption Spectroscopy (AAS)
The water sample which running between shell and copper tube in heat exchanger under
operation has been taken and observed. The corrosion performances is analyzed and
concentration of metal in the heat exchanger water sample is one of the parameter that can be
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Corrosion Failure Analysis of Copper Heat Exchanger by Using a Non-Destructive Technique
study. The copper concentration of water sample is determined by using Atomic Absorption
Spectroscopy (AAS). AAS method provide accurate determination and suitable to measure
the concentration of metal in natural water. For this study, five standard solution has been
used to calibrate the concentration of copper. According to World Health Organization
(WHO), Copper in drinking water, standard range of copper concentration in natural water is
(≤0.005 > 30.0) mg/L [8].
2.4. pH Verification
pH of water sample has been verified by using pH meter. pH is the one of the factor
influenced of corrosion event. This was conducted to relate the relationship between pH and
temperature of water sample that influence the corrosion process. pH meter is chosen rather
than litmus paper because it has the ability to get the exact and accurate pH value of water
sample.
3. RESULTS AND DISCUSSIONS
3.1. IR thermal imaging
FLIR camera with high resolution is used to capture thermographic image by measuring
amount of radiation received (radiosity) through lens from each point (horizontally). This
camera measured infrared energy and convert the data to corresponding image, where
differentiated with distinct color [9]. Copper has lower emissivity. Emissivity is the amount of
radiation emitted from an object compared to that perfect emitter or blackbody at same
wavelength temperature. With lower emissivity will give higher reflectivity. As illustrated in
Figure 2, Figure 3 and Figure 4 respectively. The thermographic image that captured on heat
exchanger during operation for three different temperature is passive thermograph which is at
room temperature of ambient environment. The blue color shown the cold region while red
color shown the hot region and green/yellow shown the warm region. Figure 2 was captured
when heat exchanger started to operate at 40ᵒC. The defected area was begin visible with
green/yellow. Figure 3 was captured when heat exchanger operate and achieve the
temperature at 40ᵒC. The defected area become bigger and visible. While Figure 4 was
captured when heat exchanger operate at higher temperature 70ᵒC The red color region was
abnormal hot spot which typically associated with problem such as corrosion or leakage due
to contact of metal with analyte, pressure or flow rate of fluid in copper tube during
operation[10].
Figure 2 Shows Heat exchanger started to operate at 32.5ᵒC
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Figure 3 Shows Heat exchanger started to operate at 39.8ᵒC
Figure 4 Shows Heat exchanger operate and achieve the temperature at 69.7ᵒC
3.2. Atomic Absorption Spectroscopy (AAS)
Atomic Absorption Spectroscopy (AAS) is a technique for measuring quantities of chemical
elements in environmental samples by measuring the absorbed radiation by chemical element
of interest. The concentration of element is calculated based on the Beer Lambert law which
is absorbance is directly proportional to the concentration of analyte absorbed for existing set
of conditions. The concentration is determined from a calibration curve which obtained using
standard solution concentration. Water which is flow through the copper tube (internal of
copper tube) and water which is flow between copper tube and mild steel shell (external of
copper tube) are taken for three water samples for each different temperatures (40°C, 50°C,
60°C and 70°C). The standard range of copper concentration in natural water according to
WHO, Copper in Drinking-water is (≤0.005 > 30.0) mg/L [8]. For this study, five standard
solutions have been prepared to get the calibration curve. Figure 5 shows the calibration curve
for copper concentration.
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Corrosion Failure Analysis of Copper Heat Exchanger by Using a Non-Destructive Technique
Figure 5 Shows Calibration curve for copper concentration
This calibration curve can be determine by using formula:
Equation (1)
*0.0044 – Concentration of analyte that would give an absorbance (1% absorption)
*Standard concentration = 0.0357mg/L
The concentration of copper is the important parameter considered in this study. Figure 6
and Figure 7 presented the water sample results by AAS analyses and Figure 8 shows the
concentration of copper in water sample increases with higher temperature either water flow
through the copper tube or flow between copper tube and mild steel shell. This results are
resembling the theory where higher temperature of water sample will cause lower of pH level.
Lower of pH level will increase the copper concentration affected by the flow of copper ion
and hydrogen ion in the copper tube.
Table 3 Copper concentration in the three water samples through copper tube (internal of copper tube)
at three different temperatures
Temperature
(˚C)
40˚C
50˚C
60˚C
70˚C
Sample 1
0.0540
0.0693
0.0598
0.0714
Copper Concentration (mg/L)
Sample 2
Sample 3
0.0551
0.0653
0.0519
0.0657
0.0645
0.0638
0.0660
0.0668
Average
0.0581
0.0623
0.0627
0.0681
Cu Concent. (mg/L)
Copper Concentration Vs Temperature
0.08
0.06
0.0653
0.0551
0.054
0.0693
0.0657
0.0519
0.0645
0.0638
0.0598
40˚C
50˚C
60˚C
0.0714
0.0668
0.066
0.04
0.02
0
70˚C
Temperature (˚C)
Sample 1
Sample 2
Sample 2
Figure 6 Graph of copper concentration vs temperature in three water samples through the copper
tube (internal of copper tube) at three different temperatures
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As illustrate above, the result of the copper concentration in three water samples through
the copper tube (internal of copper tube) at three different temperatures. The copper
concentration for every each water samples at 40°C, 50°C and 70°C increase with increasing
of temperature. But at temperature 60°C, the copper concentration decreases for each three
water samples. The average of copper concentration in three water samples still increasing for
four different temperatures.
Table 4 Copper concentration in three water samples through the mild steel shell (external of copper
tube) at three different temperatures
Temperature
(˚C)
40˚C
50˚C
60˚C
70˚C
Copper Concentration (mg/L)
Sample 2
Sample 3
0.0026
0.0216
0.0125
0.0139
0.0241
0.0202
0.0262
0.0176
Sample 1
0.0037
0.0119
0.0163
0.0188
Average
0.0093
0.0128
0.0202
0.0208
Copper Concentration Vs Temperature
Cu Conc. (mg/L)
0.03
0.025
0.0216
0.02
0.0139
0.0125
0.0119
0.015
0.01
0.005
0.0241
0.0202
0.0163
0.0262
0.0188
0.0176
0.0037
0.0026
0
40˚C
50˚C
60˚C
70˚C
Temperature (˚C)
Sample 1
Sample 2
Sample 3
Figure 7 Graph of copper concentration vs temperature in three water samples through the mild steel
shell (external of copper tube) at three different temperatures
For copper concentration in three water samples through the mild steel shell (external of
copper tube) at 40°C, 50°C, 60°C and 70°C, water sample 3 has fluctuate of copper
concentration than water sample 1 and water sample 2. At 50°C, the copper concentration of
water sample 3 decrease. At 60°C the copper concentration increasing and back to decrease at
70°C. But the average of copper concentration for every each water samples increasing with
four different temperatures.
Table 5 Copper concentration of water samples through the copper tube (internal of Cu tube) and
through the mild steel shell (external of Cu tube)
Temperature
(˚C)
40˚C
50˚C
60˚C
70˚C
Copper Concentration (mg/L)
Internal of Cu tube
External of Cu tube
0.0581
0.0093
0.0623
0.0127
0.0627
0.0202
0.0681
0.0208
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Cu Conc. (mg/L)
Copper Concentration Vs Temperature
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0.0623
0.0581
0.0093
0.0127
40˚C
50˚C
0.0627
0.0681
0.0202
0.0208
60˚C
70˚C
Temperature (˚C)
Internal Cu tube
External Cu tube
Figure 8 Shows Graph of copper concentration vs temperature
For this analysis, the important parameter is the concentration of copper. The AAS
analysis on each water sample results shown in Figure 6 and Figure 7. Figure 8 shows that
the concentration of copper in water sample increases with higher temperature regardless of
the water flow either through the copper tube or between copper tube and mild steel shell. As
stated by previous researcher [9], lower of pH level will increase the concentration of copper
because of the flow of copper ion and hydrogen ion in the copper tube is increased. The
finding of this research revealed that there are corrosion activities occur in the copper tube of
heat exchanger due to the temperature fluctuation.
3.3. pH Verification
pH is another sources of indirect influence to the corrosion rate. Lower of pH will accelerate
the corrosion rate by providing supply of hydrogen ion. While higher of pH level means there
are free of hydrogen ions and will decrease the corrosive of the system because of fewer
hydrogen ion in solution. In neutral to alkaline water which pH range is 6-8 with reasonably
higher oxygen content, metal will initially produce an insoluble layer of metal oxide which
also known as protective layer. This protective layer will against the corrosion rate of metal.
Figure 8, Figure 9 and Figure 10 show the result of pH value on water samples through the
copper tube (internal of copper tube) at four different temperatures and water samples through
the mild steel shell (external of copper tube) at four different temperatures by using pH meter.
Table 6 pH in three water samples through the copper tube (internal of copper tube) at four different
temperatures
Temperature
(˚C)
40˚C
50˚C
60˚C
70˚C
pH
Sample 1
6.51
6.67
6.70
6.91
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Sample 2
6.62
6.67
6.75
6.92
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Sample 3
6.57
6.74
6.71
6.99
Average
6.57
6.69
6.72
6.94
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pH Vs Temperature (Internal Cu tube)
7.2
pH
7
6.99
6.8
6.6
6.74
6.71
6.57
6.4
6.2
40˚C
50˚C
60˚C
70˚C
Temperature (˚C)
Sample 1
Sample 2
Sample 3
Figure 9 Graph of pH vs Temperature in three water samples through the copper tube (internal of
copper tube) at four different temperatures
Table 7 pH in three water samples through the copper tube (internal of copper tube) at four different
temperatures
Temperature
(˚C)
40˚C
50˚C
60˚C
70˚C
pH
Sample 1
5.44
5.99
6.16
6.43
Sample 2
5.74
5.94
6.18
6.29
Sample 3
5.69
5.96
6.07
6.31
Average
5.62
5.96
6.14
6.34
pH
pH Vs Temperature (External of Cu tube)
6.6
6.4
6.2
6
5.8
5.6
5.4
5.2
5
4.8
6.18
6.16
6.07
5.99
5.96
5.94
6.43
6.31
6.29
5.74
5.69
5.44
40˚C
50˚C
60˚C
70˚C
Temperature (˚C)
Sample 1
Sample 2
Sample 3
Figure 10 Graph of pH vs Temperature in three water samples through the mild steel shell (internal of
copper tube) at four different temperatures
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Corrosion Failure Analysis of Copper Heat Exchanger by Using a Non-Destructive Technique
Table 8 pH of water samples through the copper tube (internal of copper tube) and through the mild
steel shell (external of copper tube)
Temperature
(˚C)
40˚C
50˚C
60˚C
70˚C
Copper Concentration (mg/L)
Internal of Cu tube
External of Cu tube
6.57
5.62
6.69
5.96
6.72
6.14
6.94
6.34
pH Vs Temperature
6.57
5.62
6.69
5.96
6.72
6.14
6.94
6.34
40˚C
50˚C
60˚C
70˚C
8
pH
6
4
2
0
Temperature (˚C)
External of Cu tube
Internal of Cu tube
Figure 11 Graph of pH vs temperature
4. CONCLUSIONS
Temperature will influence in many parameters, not only to the pH and concentration of metal
but also to solution viscosity, diffusion rates, enthalpies reaction, compound solubility and
oxidation rates. Heat exchanger transfer the heat to one or more fluid during the operation.
There must have corrosion event in the heat exchanger under operation. Corrosion event give
failure to the efficiency of the heat exchanger. The defected area have been detect by using
infrared (IR) thermal imaging method of non-destructive technique. The abnormal (red color
region) is defected area. Temperature is directly proportional to the pH because of copper
oxide layer formed as semi-protective layer to protect the metal surface from corrode and
decrease the corrosion rate. But with higher of temperature, the copper concentration increase.
This is because in extreme environment which is in very high or very low pH will break down
the protective layer. This research result is corresponding to the theory but it has been prove
by other researcher and make it reasonable. This shell and tube heat exchanger need take an
action with properly inspection to overcome the problem and to avoid costly maintenance.
ACKNOWLEDGEMENT
The authors would like to thanks all the staff at Maritime Technology Laboratory, Universiti
Malaysia Terengganu (UMT) for their supports through conducting and completing this
research study.
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