corrosion failure analysis of copper heat ......key words: copper tube, corrosion, heat exchanger,...

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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://iaeme.com/Home/issue/IJMET?Volume=10&Issue=4 ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Indexed Scopus

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. N method namely Infrared DT ;

(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 temperatu indicate subsurface defects. Atomic re

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.

Corrosion Failure Analysis of Copper Heat Exchanger by Using a Non-Destructive Technique


Key words: Copper tube, Corrosion, Heat exchanger, Failure analyses and Non-destructive 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. –http://iaeme.com/Home/issue/IJMET?Volume=10&Issue=4

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.

M.J. Suriani, K.H. Ghazali F. Zulkifli and H. Farhana,

http://www.iaeme.com/IIMET/index.asp 182 [email protected]

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 Measurement

Internal diameter 0.013 meter Outer diameter 0.016 meter Length 1.83 meter Arrangement Triangular

Table 2 The measurement of mild steel shell of heat exchanger

Mild Steel Shell Part Measurement

Internal diameter 0.1934 meter Outer diameter 0.2074meter Length 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 Non-

Destructive 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



study. The copper concentration of water sample determined by using Atomic Absorption isSpectroscopy (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 32.5 ᵒC



Figure 3 Shows Heat exchanger started to operate at 39.8 ᵒC

Figure 4 Shows Heat exchanger operate and achieve the temperature at 69.7 ᵒC

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- study, five standard water is (≤0.005 > 30.0) mg/L [8]. For this solutions have been prepared to get the calibration curve. Figure 5 shows the calibration curve for copper concentration.



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 show the s 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)

Copper Concentration (mg/L) Sample 1 Sample 2 Sample 3 Average

40 ˚C 0.0540 0.0551 0.0653 0.0581 50 ˚C 0.0693 0.0519 0.0657 0.0623 60 ˚C 0.0598 0.0645 0.0638 0.0627 70 ˚C 0.0714 0.0660 0.0668 0.0681

Figure 6 Graph of copper concentration vs temperature in three water samples through the copper

tube (internal of copper tube) at three different temperatures

0.054

0.0693 0.0598

0.0714

0.0551 0.0519 0.0645 0.066 0.0653 0.0657 0.0638 0.0668

0

0.02

0.04

0.06

0.08

40C̊ 50C̊ 60C̊ 70C̊

Cu

Co

nce

nt.

(m

g/L)

Temperature (C̊)

Copper Concentra on Vs Temperature

Sample 1 Sample 2 Sample 2



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)

Copper Concentration (mg/L) Sample 1 Sample 2 Sample 3 Average

40 ˚C 0.0037 0.0026 0.0216 0.0093 50 ˚C 0.0119 0.0125 0.0139 0.0128 60 ˚C 0.0163 0.0241 0.0202 0.0202 70 ˚C 0.0188 0.0262 0.0176 0.0208

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)

Copper Concentration (mg/L) Internal of Cu tube External of Cu tube

40 ˚C 0.0581 0.0093 50 ˚C 0.0623 0.0127 60 ˚C 0.0627 0.0202 70 ˚C 0.0681 0.0208

0.0037

0.0119

0.0163 0.0188

0.0026

0.0125

0.0241 0.0262

0.0216

0.0139

0.0202 0.0176

0

0.005

0.01

0.015

0.02

0.025

0.03

40C̊ 50C̊ 60C̊ 70C̊

Cu

Co

nc.

(m

g/L)

Temperature (C̊)





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)

pH Sample 1 Sample 2 Sample 3 Average

40˚C 6.51 6.62 6.57 6.57 50˚C 6.67 6.67 6.74 6.69 60˚C 6.70 6.75 6.71 6.72 70˚C 6.91 6.92 6.99 6.94

0.0581 0.0623 0.0627

0.0681

0.0093 0.0127 0.0202 0.0208

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

40C̊ 50C̊ 60C̊ 70C̊

Cu

Co

nc.

(m

g/L)

Temperature (C̊)


Internal Cu tube External Cu tube



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)

pH Sample 1 Sample 2 Sample 3 Average

40˚C 5.44 5.74 5.69 5.62 50˚C 5.99 5.94 5.96 5.96 60˚C 6.16 6.18 6.07 6.14 70˚C 6.43 6.29 6.31 6.34

Figure 10 Graph of pH vs Temperature in three water samples through the mild steel shell (internal of copper tube) at four different temperatures

6.57

6.74 6.71

6.99

6.2

6.4

6.6

6.8

7

7.2

40C̊ 50C̊ 60C̊ 70C̊

pH

Temperature (C̊)

pH Vs Temperature (Internal Cu tube)


5.44

5.99 6.16

6.43

5.74

5.94

6.18 6.29

5.69

5.96 6.07

6.31

4.8

5

5.2

5.4

5.6

5.8

6

6.2

6.4

6.6

40C̊ 50C̊ 60C̊ 70C̊

pH

Temperature (C̊)

pH Vs Temperature (External of Cu tube)




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)

Copper Concentration (mg/L) Internal of Cu tube External of Cu tube

40 ˚C 6.57 5.62 50 ˚C 6.69 5.96 60 ˚C 6.72 6.14 70 ˚C 6.94 6.34

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.

6.57 6.69 6.72 6.94

5.62 5.96 6.14 6.34

0

2

4

6

8

40C̊ 50C̊ 60C̊ 70C̊

pH

Temperature (C̊)

pH Vs Temperature

External of Cu tube Internal of Cu tube



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[8] Fitzgerald, D. J. (1998). Safety guidelines for copper in water. The American journal of clinical nutrition, 67(5), 1098S-1102S.

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[11] Oliphant, R. J. (2003). (pp. 14-34). Causes of copper corrosion in plumbing systemsFoundation for Water Research.

corrosion failure analysis of copper heat ......key words: copper tube, corrosion, heat exchanger,...

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