The Effect of Elemental and Mercury Compound Presence in Solution on Corrosion Phenomena of Aluminum and Low Carbon Steel


Bambang Widyanto1,4, Iryanni Dewi Tanto2, Secta Ariardi Aviananto3

1,2,3 Materials Engineering Department, Faculty of Mechanical and Aerospace

Engineering, Bandung Institute of Technology

4Indonesian Corrosion Association (INDOCOR)

bambwid@cbn.net.id

 

 

Abstract

Several studies have shown that the presence of small amount of elemental and mercury compound in raw oil or LNG caused a corrosion failure in oil and gas industrial equipment.This research was undertaken to observe the effect of the presence of elemental mercury inside the solution and dissolved mercury compound (HgCl2) on the corrosion phenomena occurred on aluminum and low carbon steel.

The immersion test used in this research was based on ASTM G 31-72 with some variation on HgCl2 concentration and immersion time. In order to observe the effect of elemental mercury, a solution with pH between 3 and 9 and variation on immersion time were employed.  Sample characterization was carried out by using an optical microscope, Scanning Electron Microscopy, X-Ray Diffraction and FTIR.

The experimental results revealed that the presence of elemental and mercury compound accelerate corrosion rate. The higher the HgCl2 content in the solution increased corrosion product significantly. The corrosion rate of aluminum was found 8.76 times higher than on low carbon steel. On aluminum uniform corrosion and also a small scale of exfoliation were observed. On low carbon steel pitting corrosion was observed. The corrosion products were aluminum hydroxide (Al(OH)3) and iron oxide (Fe2O3) respectively. The presence of elemental mercury in acidic and basic solution increased the aluminum corrosion rate by 1.47 and 7.25 times respectively. Whereas on low carbon steel, the corrosion rate in an acidic solution increased 1.4 times and 1.25 times in basic solution. In general, uniform corrosion was observed with a tendency of pitting at the contact edge of elemental mercury and the specimen surface. In a basic environment a corrosion product of Al(OH)3 was formed.

Keywords: elemental mercury, mercury (II) chloride, amalgam corrosion.


  1. INTRODUCTION

 

Corrosion is a degradation of metals due to its interaction with the environment. The previous study shows that some amount of elemental mercury (>25 ppb) at crude oil and liquid natural gas[1], cause a corrosion problem at oil and gas processing plant. The first mercury corrosion case found at 1973 in Algeria[2]. It creates a catastrophic  failure especially at aluminum heat exchanger at an LNG production plant. An investigation reveals that a concentration of elemental mercury during cooling sequence attack aluminum heat exchanger. In Indonesia this problem occur in certain LNG Plant in Natuna island.

Beside the problem of the mercury elemental presence, another form of mercury in hydro carbon which is organomercury or dimetyl-mercury (Hg(CH3)2) as an impurity in crude and natural gas, could attack metals severely[3].

 

  1. EXPERIMENTAL METHODS

 

Aluminum and low carbon steel plate samples in dimension 30 mm x 25 mm x 3 mm were used, followed by surface grinding and cleaning. The experiment  is comply to ASTM G31-72 immersion test procedure, and every sample was weighed and measured before the test. Some test condition are used. The first test use a deposition of  elemental mercury at the surface at acidic (acetic acid) and basic (NaOH) solution, and the second test use a HgCl2–methanol solution in concentration 1ppm, 10ppm, 25ppm, 50ppm and 100ppm. The test duration vary from 1, 2, 3, 4, and 5 days in room temperature. After test, the test samples were weighed again to determine the weight change and calculate the corrosion rate. The next evaluation was done using SEM, XRD and FTIR.

 

  1. EXPERIMENTAL RESULTS

 

3.1. Corrosion test with elemental mercury in solution

 

Principally the influence of the mercury presence is the major interest of this study, but the result will be compared with the corrosion test results without mercury. The corrosion test used some condition, which are acidic and basic solutions, with and without the presence of elemental mercury, and using two metal samples which are aluminum and steel. The deposition of elemental mercury in every sample surface was done as a droplet in the same quantity.

The result use weight change/weight loss measures because the corrosion attack will be concentrated only around the mercury droplet.

 

 

3.1.1. Aluminum

 

Figure 3.1 and 3.2 show the weight change/weight loss of aluminum in acetic acid solution with and without  the presence of elemental mercury in the solution. The difference weight loss of aluminum exposed in basic and acidic solution is very high, where in basic solution the corrosion attack aluminum more severe than in acid solution. Figure 3.3. shows the difference weight loss in basic and acidic solution with the presence of mercury.

 

 

 

 

 

The microscopic observation results at the sample surface are presented in figures 3.4, figures 3.5 present cross section of corroded samples and figures 3.6 present SEM observation results.

 

 

3.1.2.  Low Carbon Steel

 

The corrosion test experimental results of  low carbon steel are presented in figures as follows. Figure 3.7, 3.8 and 3.9 show weight loss of steel samples exposed on acidic and basic environment in the  presence and without the presence of mercury droplets. Figure 3.10, 3.11 and 3.12 show the microscopic observation result to the surface and cross section of the samples after corrosion test. In this case, low carbon steel was attacked more severe in acid solution comparing with the corrosion on basic solution.

 

 

 

 

 

 

3.2. Corrosion test of aluminum and low carbon steel on HgCl2 solution

 

Beside corrosion test using elemental mercury in the solution in droplet form, the test is continued with using mercury compound (HgCl2) in methanol as electrolyte. The test results are presented in figure 3.13 and 3.14 as follows and the microscopic observation results using metallurgical microscope and SEM are presented in figure 3.15, 3.16 and 3.17.

 

 

 

 

 

 

 

 

To have a complete information of the corrosion product XRD and FTIR examination were used to characterize the corrosion product formed in the surface of the samples. The results are shown in figure 3.16, 3.17 and 3.18 as follows.

 

 

 

 

4. DISCUSSION

 

The problem of  oil and gas production facilities in some places like in South East Asia offshore platforms, as well as in Africa and at the other places, is the presence of mercury that was mixed with oil and gas were reported [[1][2][7][8]. This product will be transported through the pipeline and finally arrive to the production facilities. During this transportation, mercury will corrode the facilities material especially aluminum that was attacked more severe than steel. Mercury can attack in elemental or in compound form, and the previous studies revealed that the corrosion rate in the presence of bio mercury or dimethyl mercury (DMM) in the mixture with HCl cause the corrosion rate increase up to 400 times than corrosion rate due to the presence of DMM only and 70 times than corrosion rate in acid.

Based on this study, it will be very interesting to understand the influence of many variation of the mercury condition in solution to the corrosion of aluminum and steel. The influence of elemental mercury will be studied more and the presence of mercury compound in HgCl2 will be observed in this study.

The weight loss of aluminum is not significant when aluminum is immersed in basic solution as well as in acid solution as presented in figure 1 and 2. But in the presence of mercury, in general the condition changes where the increase of corrosion attack, become very important in corrosion test at basic solution comparing to acid solution.

 

After the reaction described above, the corrosion will continue in acid solution with the reaction as follows[5]:

 

Hg + Al à (Hg)Al                                                                              (1)

 

(Hg)Al + 2H+ à Al3+ + Hg + H2 + e                                                  (2)

 

2H+ + e- à H2                                                                                   (3)

 

In this condition (acidic), the corrosion is lower and the microscopic observation shows that the corrosion attack aluminum lightly in local corrosion model as presented by figure 5.

 

 

In basic condition the reaction is described as follows:

 

 

Al2O3 + 2NaOH + 3H2O à 2Na+ + 2[Al(OH)4]-                                       (4)

 

 

The corrosion rate in basic solution containing mercury much more higher due to the destruction of passive film of aluminum by Na(OH). Na(OH) destroy Al2O3  in a severe manner as presented by figure 5 clearly. Without the presence of aluminum oxide in the surface, the galvanic action by mercury to aluminum become higher and multiply the aggressivity[2][4], cause a very severe corrosion that attains more than 10 times comparing to the condition of the solution when mercury was absent, but hundreds times more severe than corrosion in acid solution (figure 1 and 2). These results are confirmed by microscopic observation as presented by figure 4, 5 and 6. Some pits are observed at corrosion test in acidic solution but still indicate a light corrosion.

 

 

In basic condition the amalgam reaction will be[6]:

 

 

2Al(Hg) + 6H2O + 2OH- à 2[Al(OH)4]-+ 3H2 + 2Hg                          (5)

 

 

As the corrosion happened in aluminum, the corrosion attack in low carbon steel have a similar tendency which higher with the presence of mercury, but much lower than what happen in aluminum.

There is the difference between corrosion at steel and aluminum at point of view acid-basic condition. Steel corrosion on acidic solution is higher than in basic solution. The result of corrosion attack in steel surface with the presence of mercury could be observed at figure 10. It shows clearly  the difference of scale behavior between aluminum oxide and iron oxide. Aluminum oxide in general is more stable than iron oxide, but if it is destroyed by the action of sodium hydroxide, the effect of direct contact of mercury with aluminum, produce a catastrophic attack to the aluminum surface. As corrosion in aluminum at acidic solution, some pits also appear in surface of steel surface during corrosion test as shown on figure 12.

 

Corrosion test results in mercury compound (HgCl2) solution give some different behavior than corrosion test results in solution containing elemental mercury. The similarity is shown on the different between aluminum and steel, where the corrosion of aluminum always higher than steel, but this difference is not so high than the test using elemental mercury. Corrosion rate of aluminum attain approximately 10 times than corrosion rate of steel. Morphologically, observation result on SEM shows the surface attack at aluminum sample is more severe  than the attack on steel sample with a small tendency of exfoliation on aluminum sample (figure 15, 16 and 17). The high concentration of  HgCl2  in general always increase corrosion rate of aluminum and steel. But, the corrosion rate after several days of exposure is always decrease in all cases and at all concentration of  HgCl2. The cause of this phenomena is formation of a more stable corrosion product that avoid an excessive attack of corrosion media to the surface. An increase of weight gain was reported in previous study[9].

 

The XRD and FTIR examination reveal that hydroxide of aluminum was formed on aluminum and iron oxide formed in steel surfaces exposed on to aggressive media.

 

5.  SUMMARY

 

The presence of mercury in the solution in general gives a strong influence to increase the aggresivity of the environment to promote corrosion attack to metals. Aluminum is corroded at higher value of corrosion rate than steel, and corrosion rate of aluminum in basic solution in the presence of elemental mercury is much higher than in acid solution.

Whereas corrosion behaviour in steel is somehow different, this is due to that corrosion attack in basic is less severe than in acid solution, because the corrosion attack at basic solution is less severe than in acid solution. But the difference of corrosion rate in steel in basic and acidic solution is not so high than the difference of corrosion rate of aluminum.

Mercury compound (HgCl2) increase the aggresivity with the increase of mercury compound content in solution for aluminum and steel, but similar with the presence of elemental mercury, aluminum is more corroded than steel.

Corrosion test in mercury compound containing solution shows a diminution in corrosion rate at the longer period of test. It seems that the process follow a general corrosion model, and if mercury presents in elemental form, the corrosion process become localized and produce more severe attack to metals.

 

REFERENCES

[1]       Widyanto B et al, LAPI ITB, The study of the influence of mercury content crude oil to Balikpapan Refinery Plant Facilities, Bandung, 2011.

[2]       Zerouali D., Derriche Z., dan Azri M. Y. Contribution To Comprehensive Study Of Aluminium Alloy Aa 5083 Corrosion Induced By Elemental Mercury In LNG Industries. Algeria : Nigerian Journal of Chemical Research, 2005.

[3]       Wongkasemjit S. dan Wasantakorn A. Laboratory Study of Corrosion Effect of Dimethyl –mercury on Natural Gas Processing Equipment. Thailand : The Journal of Corrosion Science and Engineering, 2000.

[4]       Wilhelm S. M. Risk Analysis for Operation of Aluminium Heat Exchangers Contaminated by Mercury. New Orleans, 2008.

[5]       Zerouali D., Derriche Z., dan Azri M. Y. Contribution To Comprehensive Study Of Aluminium Alloy Aa 5083 Corrosion Induced By Elemental Mercury In LNG Industries. Algeria : Nigerian Journal of Chemical Research, 2005.

[6]       Reaction of Aluminium with Water and Sodium Hydroxide (http://www2.uni-siegen.de/~pci/versuche/english/v44-10.html, diakses 4 September 2012)

[7]       Gangstad A, Berg S.Mercury in Crude Oil and Natural Gas, Stat Oil, 2006

[8]   EPA R&D, National Risk Management Reseach Laboratory, Mercury in Petroleum and Natural Gas: Estimation of emission from production, processing and combustion, 2001

[9]   Wilhelm M.S, Nelson M, Interaction of Elemental Mercury with Steel Surfaces, The Jourcal of Corrosion Science and Enginering, Vol 13, 23 September 2010



SHARE THIS :

Artikel Lainnya

Kontak Kami

Tertarik untuk kerja sama dengan Kami? hubungi sekarang juga.

Telepon

+62 8562 1828 53

Faximile

-

Alamat

Jln. Rereng Wulung No. 37 Bandung