Chlorine Corrosion Research Articles

Failure analysis of liquefied chlorine condenser

There was a serious blast of liquefied chlorine condenser last year in southwestern China and a few people were killed during the blast. To look for the reason of the explosion, the failed condenser was sampled and investigated through Industrial Computed Tomography (ICT), Scanning Electron Microscopy (SEM) and electrochemical methods. The tube sheet was made of 16MnR, and the tube was made of 10# seamless steel, while the welding material was J507 welding rod. ICT results showed corrosion in the inner of the tube sheet. Based on the SEM results, it was shown that there was obvious erosion near the inlet of chlorine gas and corrosion at the joint area of tube sheet, tube and welding material was much more serious than that of the other parts. Moreover, the electrochemical tests indicated that the corrosion potential of the tube sheet in 6wt.% FeCl3 solution was a little more negative than that of the other two parts while in 29.9wt.% CaCl2 solution the potential of the welding material was more negative than that of the tube. It could be inferred that there existed electrochemical corrosion. At the beginning, local corrosion of tube sheet, tube and welding material of condenser as well as the erosion of the tube interior surface took place. Then the corrosion was speeded up and led to the final failure of the condenser in a very short period after the condenser contacted the mixture of chlorine gas and the CaCl2 solution contained ammonia, which reacted with chlorine gas to form the explosive NCl3.

Preventing the chlorine-induced high temperature corrosion in power boilers without loss of electrical efficiency in steam cycles

The installation of combustion plants for waste and biomass with a connected boiler and steam cycle brought forth the problem of high temperature corrosion in the steam generators. This phenomenon originates from the composition of these fuels and in particular from the molar ratio of sulphur to chlorine, which is in the range of 2 and lower. Therefore, it is necessary to observe several demands on the construction and design of steam generators in order to prevent this sort of corrosion. All of these requirements arise from the limitation of the heating surface wall temperature as a function of the corresponding flue gas temperature and the gas velocity at the heat exchanger tube. It is, therefore, paramount to place the heating surfaces in the appropriate boiler areas to meet the temperature limits. The demands on steam generators to prevent high temperature chlorine corrosion are presented in this present work. Furthermore, one possible process design is presented, which in turn offers the possibility to operate a steam cycle at high pressure levels without the risk of high temperature corrosion or exceeding the limit for the final wetness at the steam turbine exit. This comparison points out that the new steam cycle gains the highest electrical efficiency when compared with two conventional cycles that meet the same goals.

Indirect Amperometry of Free Corrosion as a Method for Its Laboratory Investigation

A formerly developed electrochemical cell able to continuously measure the oxygen corrosion rate of a metal through the absorbed oxygen quantity is described. By the example of various metals and alloys, the cell is shown to be applicable to clarifying the effect of various factors on their corrosion rate in acidic aqueous solutions. The rate constants are also determined for a series of homogeneous chemical reactions consuming oxygen. Peculiarities of hydrogenation and dehydrogenation processes under cathodic polarization conditions with access for air are investigated. It is shown that substituting chlorine for oxygen enables one to investigate chlorination of rubbers and chlorine corrosion of a great many metals and alloys.

The effect of deposits on waterwall corrosion in fossil fueled boilers

Corrosion of water walls in fossil fueled boilers and gasifiers has traditionally been considered the result of gaseous corrodants, such as H2S and HC1, reacting with the heat exchanger tube surfaces. Under reducing conditions these corrodants prevent the formation of a protective oxide scale, leading to increased metal loss. Recent field experience in boilers, using staged combustion systems, has shown much greater corrosion rates than predicted by simple gas/solid corrosion processes. The presence of large quantities of unoxidized iron sulfide in deposits in areas where high corrosion rates were found, suggests that deposits play a role as well. Subsequent laboratory corrosion studies found that the presence of FeS can indeed lead to very high corrosion rates, but only under oxidizing conditions. Since FeS usually deposits only where reducing conditions are present, the accelerated corrosion observed requires alternating reducing and oxidizing conditions. These are usually found in load following boilers. It is also shown that chlorine corrosion may be caused or at least accelerated by chloride containing deposits in fossil fueled boilers, similar to waste incinerators, where the role of chloride rich deposits has been well established. Due to the relatively high sulfur content of fossil fuels, chloride deposits most likely form under reducing conditions only. However, once formed they can be highly corrosive under oxidizing conditions.

Electrochemical Process for Reducing Chlorine Dissolved in Hydrochloric Acid

A problem often associated with the manufacture of hydrochloric acid by combustion processes is that the hydrochloric acid is contaminated by dissolved chlorine. Conventional practice is to remove the free chlorine from the hydrochloric acid by adding reducing agents. As an alternative, an electrochemical chlorine reduction process has been developed and investigated both on a laboratory and pilot-plant scale. The advantages of this method are that it obviates the need to add chemicals and effectively prevents chlorine corrosion.

Deposit Formation in a 150 MWe Utility PF-Boiler during Co-combustion of Coal and Straw

A conventional pc-fired boiler at the Danish energy company I/S Midtkraft has been converted to coal−straw co-combustion, and a 2 year demonstration program was initiated in January 1996, addressing several aspects of coal−straw co-combustion. Deposition trials were performed as part of the demonstration program. A maximum straw share of approximately 20% (energy base) was used in the experiments. For the deposit samples collected, a visual analysis procedure was developed and each sample evaluated according to this. In addition, a number of samples were analyzed by scanning electron microscopy (SEM) combined with energy dispersive X-ray analyses (SEM-EDX) and bulk chemical analyses. In the visual analysis, a significant increase in the amount and tenacity of the upstream deposits was observed as a function of increased straw share, exposure time, and boiler load. The chemical analyses of the deposits show increased amounts of K and S during co-combustion, and the Fe-dominated upstream deposits formed during coal combustion are shifted toward more Ca- and Si-rich deposits during coal−straw co-combustion. However, the major part of K is observed to form K−Al silicates, which do not form problematic deposits. Co-firing straw also caused a change in the structure of the upstream deposits. During coal combustion an ordered, “finger” structure of the larger particles with small particles between was observed, whereas during co-combustion a more random deposition of the larger particles among the small ones was observed. No chlorine species was observed in the deposits collected, and selective chlorine corrosion is therefore not expected to constitute a problem in co-combustion of coal and straw up to 20% straw share, for the coal types utilized in the tests. However, deposition problems could arise when burning other coals, particularly coals with a high S or alkali metal content or a low content of ash. The behavior of K, Ca, S, and Cl was evaluated by use of thermodynamic calculations. The thermodynamically stable species agree with the observed behavior in the experiments, i.e. formation of stable K−Al silicate species as well as K2SO4 is predicted. The calculations also emphasize that the mixing between the coal and straw species is essential for the deposition behavior, primarily by affecting the split between K−Al silicates and K2SO4.

Lab-Scale Investigations of High-Temperature Corrosion Phenomena in Straw-Fired Boilers

The corrosion of superheater tube material in straw-fired boilers was investigated in the laboratory. Metal test elements of boiler tube steel (X20CRMV121 and AISI 347FG) were covered with synthetic (KCl and/or K2SO4) and real deposits, and exposed to a synthetic flue gas (6 vol % O2, 12 vol % CO2, 400 ppmv HCl, 60 ppmv SO2, balance N2) in 550 °C electrically heated ovens. Exposure times from 1 week to 5 months were used. The corrosion of the metal test elements was, in general, quite uniform, and the corrosion products consisted mainly of oxides of iron and chromium. All test elements covered with KCl suffered from minor internal attack, and some elements had severe pits with chlorine found in the pit. A dense layer of potassium sulfate and iron oxide was found adjacent to the metal oxide layers on all the metal test elements covered with a deposit containing KCl. The layer had a characteristic structure, with iron oxide threads in a dense potassium sulfate matrix. A mechanism for chlorine corrosion is s...

97/02085 Chlorine corrosion at steam generators. Thermodynamic calculations explain observations in the practice. Results from the VGB research projects 145 and 153

97/02085 Chlorine corrosion at steam generators. Thermodynamic calculations explain observations in the practice. Results from the VGB research projects 145 and 153

High-temperature chlorine corrosion of technical carbons Part II. Anodic corrosion in chloride melt

Medium (200 to 400°C) to high (600 to 800°C) temperature corrosion of technical carbons (Acheson graphites) have been investigated in alkali chloride melts at chlorine evolving anodes. At low temperature in chloride melts containing free Lewis acid (AlCl3) no chlorine is evolved — even at high current densities — because chlorine, together with aluminium chloride, instantaneously form intercalation compounds with graphite and, as a consequence, the carbon desintegrates very rapidly. At 200°C carbon is consumed anodically in a C/Cl of molar ratio ≈ 70/1. With increasing temperature Scheson graphites become more stable so that at 700°C short term destruction cannot be observed in melts which contain free Lewis acid. Chlorine corrosion of carbon electrodes in purified basic alkali chloride melts, which are free of oxygen carriers and, in particular, free of water at temperatures between 600 and 800°C in basic chloride melts, is an electrochemical reaction proceeding at low current densities slower than anticipated from thermodynamic data for carbon chlorination equilibria. The anodic carbon corrosion reaction has an activation energy of only 50 kJ mol−1 and its rate increases with increasing anode potential, or anodic current densities (rate: α exp (i)). At a technical current density of 0.4 A cm−2 at 700°C the corrosion rate is estimated to be of the order of centimeters per year, rendering carbon anodes dimensionally unstable. Most important is to note that apart from CCl4, chlorinated carbon compounds (olefins and arenes) are generated as side-products which are noxious and ecologically dangerous and must not be released from processes which use carbon anodes for chlorine evolution from salt melts.

High-temperature chlorine corrosion of metals and alloys

High-temperature (> 200° C) corrosion of metals and alloys in atmospheres containing Cl2 and/or HCl, which are widely encountered in many industrial environments, is reviewed. Topics include high-temperature corrosion mechanism and kinetics, thermodynamic considerations, and effects of gaseous components in the atmosphere (oxygen, air, water vapour, sulphur dioxide, and nitrogen) on the corrosion.

Chlorine corrosion of graphites and technical carbons – I. Reaction with gaseous chlorine at elevated temperatures

AbstractGraphite and graphitized technical carbons are used for the construction of chemical apparatus and equipment, which handle chlorine at higher temperatures. Technical carbons are attacked at temperatures above 500°C by chlorine with seizable rate so that they cannot be assumed to be stable at elevated temperatures although thermodynamically carbon in chlorine atmosphere becomes more stable as the temperature increases. The erosive/corrosive degradation of a number of technical carbons, including glassy carbons, by chlorine has been investigated in the temperature range 600 to 800°C. Chlorine corrosion has been compared with the corrosive action of oxygen, mixtures of oxygen and chlorine, carbon dioxide and mixtures of CO2 and chlorine. Chlorine corrosion is the slowest degradation process of all. Between 600 and 800°C the weight loss of these carbons in chlorine atmosphere is much slower than mass transfer limited and is kinetically controlled and its rate increases up to 0.5 mm/year at the highest temperature (800°C). Combustion in oxygen atmosphere is by five orders of magnitude faster than chlorine attack on carbon.Chlorine in presence of oxygen decelerates the combustion rate a lot, but chlorine has almost no influence on the rate of CO2‐attack on technical carbons. The detailed structure of different technical carbons bears only little on chlorine corrosion rates whereas it has an influence on the combustion rate with oxygen. A number of chlorinated aromatic olefines and compounds like octachlorostyrene and hexachlorobenzene are formed as byproducts of the chlorine attack on carbons. The main products are CCl4 and C2Cl4. A second paper will deal with anodic corrosion of Cl2‐evolving carbon anodes.

Plessites and associated structures in the Cape York iron meteorite revealed by chlorine corrosion

The selective attack of meteoritic minerals by chlorine has been used to reveal structures, formed during prolonged extra-terrestrial cooling, in certain iron meteorites. Several minerals, including low-nickel metal (kamacite), iron sulphide (troilite) and chromite (Reichenbach lamellae), are preferentially corroded by chlorine at 350°C, leaving other minerals suitably for examination by the scanning electron microscope and the electron microprobe. Information on elemental distribution in relation to topography has been obtained over the boundary of a plessite (a fine-grained intergrowth of kamacite and taenite) and also for kamacite with its associated schreibersite which enclosed Reichenbach lamallae.

Control of corrosion in coal liquefaction plant fractionation columns

Severe corrosion has been encountered in fractionation columns at the solvent refined coal (SRC) pilot plants in Fort Lewis, Washington, and Wilsonville, Alabama, as well as at the H-Coal Pilot plant in Catlettsburg, Kentucky, and the Exxon Donor Solvent Pilot Plant in Baytown, Texas. At the SRC plants, corrosion rates as high as 25 mm per year (one inch per year) on carbon steel and 6.4 mm per year (250 mils per year) on type 18-8 stainless steels have been measured in the portions of the columns operating at 220 to 260 °C (428 to 500 °F). Less severe corrosion is generally found at temperatures outside this range. The severity of this corrosion is related to the chlorine content of the coal. Studies of this corrosion problem by Oak Ridge National Laboratory (ORNL) personnel included exposure of corrosion coupons in the pilot plant columns, analyses of liquids collected at the pilot plants, and performance of laboratory experiments. As a result of this work, we can specify alloys with adequate corrosion resistance for construction of fractionation columns, identify the chlorine-bearing compounds, and propose chlorine transport and corrosion mechanisms. Identification of the corrodent and its mechanisms enables us to suggest process changes to remove the corrodent and thereby to control the corrosion.

Reaction between Chlorine Extreme Pressure Additives and Metal Surfaces at High Temperatures

The high temperature corrosion of iron was investigated in hydrocarbon oils containing chlorine type EP additives, using the hot wire method1).With regard to the corrosion rate, both the parabolic law and the cubic law were observed. The former law was demonstrated by the diffusion mechanism of corrosion. The cubic law was shown by the retarding action of a barrier film which was formed on the reacting surfaces, causing the decomposition of the chlorine compounds.The complexity of the chlorine corrosion mechanism was revealed by using X-ray analysis on the formed films. The oxidation reaction and hydrolysis of formed iron chloride had to be taken into consideration in conjunction with the chlorination reaction.In the correlation between chemical reactivity and load carrying capacity of oils containing chlorine compounds, it has been found that more active oils exhibit higher load carrying capacity.Sulfur compounds were observed to yield higher Mean Hertz Load values than chlorine compounds of the same chemical reactivity. Conceivably, the solid lubricant films formed by sulfur and oxygen possess higher load carrying capacity than those formed by chlorine.