JPH0479532B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a corrosion testing method for materials used in exhaust gas passages such as muffler members of automobile exhaust gas treatment equipment. [Conventional technology] For the purpose of environmental conservation, the exhaust gas flow path that discharges engine exhaust gas outside the vehicle body is designed to convert hydrocarbons, aldehydes, carbon monoxide, and nitrogen oxides that are harmful to the human body into harmless substances. A catalytic converter is installed. In addition, aluminum-plated steel plates were used for the members constituting the exhaust gas flow path in consideration of high-temperature oxidation caused by corrosion caused by exhaust gas condensation. However, as the exhaust gas temperature has become stricter in recent years, the use of three-way catalytic converters has increased, and moisture corrosion of the exhaust gas flow path, especially the muffler, made of aluminized steel sheets has become apparent. Stainless steel plates such as SUC 41OL have come to be used in severely corroded areas where aluminum plated steel plates cannot withstand wet corrosion. A study of actual vehicle mufflers revealed that stainless steel is almost completely resistant to corrosion caused by exhaust gas condensation. However, considering the average lifespan of automobiles, stainless steel is of excessive quality, and from the standpoint of resource conservation and cost reduction, there is a desire to develop a low-cost material that has corrosion resistance commensurate with the durability of automobiles. In the corrosion resistance tests of muffler parts that have been published so far, the corrosion resistance of car muffler parts is currently becoming a problem, as the corrosion conditions are significantly different from the composition of condensed water in the muffler of current automobile exhaust gas treatment equipment. cannot be evaluated appropriately. [Problems to be solved by the invention] The present invention relates to a member constituting an automobile exhaust gas flow path,
In particular, when selecting muffler components, it aims to solve the problem that there is no corrosion test method that can evaluate the corrosion resistance of materials in order to find materials suitable for corrosive work environments where exhaust gas condenses and produces condensed water. . The present inventors studied the exhaust gas composition downstream of the catalytic converter, the composition of its condensed water, the composition during the evaporation process of the condensed water, PH changes, and muffler temperature changes, which are the causes of corrosion in the muffler of automobile exhaust gas treatment equipment. After careful consideration, we found the following: The condensed water from the exhaust gas from the three-way catalytic converter contains CO ^2- ₃ , SO ^2- ₄ , Cl ^- , etc. as shadow ions.
In addition, it is alkaline because it contains a large amount of NH ⁺ ₄ as a cation, but ammonium carbonate decomposes and evaporates during the evaporation process as the temperature of the muffler increases, ammonium evaporates from ammonium sulfate and ammonium chloride, and the PH of the condensed water gradually decreases. As it becomes acidic, SO ^2- ₄ and Cl ^- ions become concentrated, increasing the corrosivity of the condensate. On the other hand, when the engine is cold-started, incomplete combustion causes a significant amount of soot to be generated, and a large amount of soot adheres to the exhaust gas flow path. Automobile mufflers undergo repeated cycles of cold start, exhaust gas condensation, evaporation, and high-temperature oxidation, but aluminum- _plated steel sheets emit ^SO2-4 during the evaporation process.
Corrodes due to the action of and Cl ^- . Here, we found that soot adhering to the inner wall of the muffler is an important factor in corrosion, and that the adhesion of soot significantly accelerates the corrosion of aluminum-plated steel plates, and elucidated the corrosion mechanism of exhaust gas flow path members. was completed. ^[ Means for Solving the Problems] _The present invention was made based on the results of ^this _research . ) ₂ Corrosion of automobile muffler parts by repeating the process of immersion and drying or heating at high temperature using a test solution containing an appropriate amount of activated carbon in suspension in a solution containing SO ₄ and NH ₄ Cl. Solved by test method. [Structure of the Invention] According to the present invention, (NH ₄ ) ₂ SO ^2- ₄ as SO ₄
Immersion and drying in a gas phase using a test solution in which 5g/~100g/activated carbon was added to a suspension in a solution containing NH ₄ Cl as a main component of 500ppm or more and 50ppm or more as Cl-. A corrosion testing method for a muffler member of an automobile exhaust gas treatment device is provided, which comprises repeating the following steps. According to the invention, (NH ₄ ) ₂ SO ^2- ₄ is further converted into SO ₄
500ppm or more as NH ₄ Cl - 50ppm as Cl ^-
5g/~100 in a solution containing the above as the main component
Using a test solution containing 1.5 g/g of activated carbon in suspension, immersion, drying in a gas phase and
A corrosion testing method for a member for a muffler of an automobile exhaust gas treatment device is provided, which comprises repeated heating at a temperature of 500°C or lower and 200°C or higher. Today, muffler parts for automobile exhaust gas treatment are usually made of aluminum-plated steel sheets, stainless steel sheets, and aluminium-plated stainless steel sheets are also used. Therefore, the test method of the present invention targets these materials. In the method of the present invention, the shape and size of the sample are arbitrary. Heating after drying is carried out at a temperature of 500°C or lower and 200°C or higher. The effect of temperature on corrosion becomes noticeable from around 200℃,
This is because the temperature of the muffler section rarely exceeds 500°C. The actual condensate is (NH ₄ ) ₂ CO ₃ , (NH ₄ )HCO ₃
However, since they easily decompose and evaporate and have little effect on corrosion, they do not need to be added to the test method. [Specific Description of the Invention] The present invention will be described in detail below. There is almost always a large amount of soot attached to the exhaust gas flow path of automobiles, and we believe that it has some effect on the corrosion of the aluminum-plated steel plate that is the constituent material, so we installed a 15 mm x 30 mm A test piece was prepared by inserting an aluminized steel plate cut into a short fence shape and SUS 41OL into the muffler and covered with soot by driving in an actual vehicle for 7 days, and its electrochemical properties were investigated. Figure 1 shows 7.6g of NH ₄ Cl and (NH ₄ ) ₂ SO ₄
This figure shows a cathode polarization curve measured in an aqueous solution containing 6.95 g/dissolved at 50°C and open to the atmosphere. As a result, it was found that the cathode current increases significantly when soot adheres in both acidic and alkaline conditions. An increase in cathode current causes a commensurate increase in anode current,
In other words, this suggests acceleration of corrosion. It can be seen that the presence of activated carbon causes the aluminized steel plate to corrode, and the greater the amount of activated carbon, the more accelerated the corrosion. Next, the following test was conducted to confirm the effect of this soot. As shown in Fig. 2, a 25 mm diameter part of the center part 7 of a disk 1 with a diameter of 60 mm was
An overhang is added to form a recess for storing the corrosive liquid, and holes 9 for attaching a hanging line are provided at both ends of the orthogonal diameter.
(See Figure 3). A tank 2 equipped with a liquid supply pipe 6, a liquid drain pipe 5, and a liquid sending pump 4 is filled with a liquid close to the actual condensate (NH ₄ ) ₂ CO ₃ CO ^2- ₃ of 2000ppm (NH ₄ )HCO ₃ HCO ^- ₃ of 2000ppm. (NH ₄ ) ₂ SO ₃ SO ^2- 500ppm as (NH ₄ )Cl Cl ^- 50ppm HCHO 12ppm solution 3 was immersed in _the suspended sample at 50℃ for 3 minutes and dried at 80℃ for 17 minutes (during this period). (The stored liquid evaporates) This cycle was repeated 72 times. The amount of activated carbon powder added and the corrosion state of the aluminized steel sheet in that case were as follows. No corrosion occurs at 0g/. At 20 g/kg, activated carbon lightly adhered to the surface, the plating layer was eluted, and corrosion of the base was also observed. At 100 g/kg, activated carbon was deposited thickly, the plating layer was almost dissolved, and the underlying steel was corroded. Next, in order to investigate the corrosive effects of SO ^2- ₄ and Cl ^- ions, Cl ^- and SO ^2- ₄ were added to the simulated condensed water with the standard composition described above.
We investigated test methods that do not contain chlorine and those that vary its concentration. The results are shown in Table 1. The amount of activated carbon added as soot was 10g/. An aluminized steel plate and a base steel (rimmed steel) for the aluminized steel plate were used as test materials. Other conditions and test equipment were the same as above. From Table 1, Cl ^- ions promote corrosion of the aluminum plating layer, but their corrosivity to the underlying steel is relatively small. On the other hand, SO ^2- ₄ ions suppress corrosion of the aluminum plating layer, but significantly accelerate corrosion of the underlying steel. From this, it is thought that corrosion of the aluminized steel plate that constitutes _the exhaust gas flow path occurs when the plating layer is first dissolved by Cl ^- ions, and then the underlying steel is eroded by SO ^2-4 . [Example] This example simulates the corrosion of members constituting an exhaust gas flow path in a corrosive environment where exhaust gas condenses to produce condensed water.The condensation-evaporation cycle is captured by immersion-drying. ing. Therefore, two cycles of the method of the present invention may correspond to one day's driving of a commuter car. Therefore, a comparison was made between the corrosion of the afler of an actual vehicle and the corrosion of an aluminized steel plate tested using the method of the present invention. The standard solutions listed in Table 1 were used as the simulated condensed water. Figure 4 shows the results. In the figure, the test is a immersion-drying test conducted under the cycle conditions described above for the test to confirm the effect of soot. This is a test that includes Actual running vehicles are commuter cars (domestic production, engine capacity) with 0.3 years and 1.5 years running.
A 1500 c.c. vehicle equipped with a three-way catalyst was selected, and after the test, the muffler was removed and the corrosion status of the aluminized steel plate was investigated. In the figure, the distance between the sample symbol and the base line (vertical dashed line with an arrow) indicates the thickness reduction. In comparing the reduction in plate thickness due to corrosion of aluminum-plated steel plates, the test was slightly more severe than the test, and good agreement was observed with the reduction in plate thickness of the muffler of an actual vehicle. In addition, when we investigated the corrosion products, we found that they were similar to those found in the muffler of an actual vehicle. As is clear from the above examples, the present invention has been proven to be a corrosion test method that can accurately evaluate the corrosivity of materials in an environment of condensed water caused by condensation of exhaust gas.

【table】

[Table] 〓 Severe corrosion compared to standard solution 〓 Lighter compared to corrosion using standard solution
1) Activated carbon 10g/contains in the above composition [Effect of the invention] According to the present invention, in a corrosive environment where automobile exhaust gas condenses and produces condensed water, the exhaust gas flow path,
In particular, it is possible to accurately evaluate the corrosion resistance of members constituting an automobile muffler. Therefore, a member having the corrosion resistance and economy (reasonable cost) required as a material for an automobile muffler can be easily found in a short period of time.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of cathode polarization measurement, FIG. 2 is an example of the specimen shape used in the test method of the present invention, and FIG. 3 is a conceptual diagram showing an example of the test device. FIG. 4 is a graph showing the results of a comparison between the corrosion of an aluminized steel plate according to the corrosion evaluation test of the present invention and that of a muffler of an actual vehicle in terms of plate thickness reduction and pit depth. 1... Test piece, 2... Water tank, 3... Simulated condensed water, 4... Pump, 5... Suction pipe, 6... Discharge pipe, 7... Corrosion liquid reservoir, 8... Hanging tool, 9... ...Hanging string fixing hole, 10... Hanging string.

Claims (1)

[Claims] 1 (NH ₄ ) ₂ SO ₄ as S ^2-4 of 500 _ppm or more,
Repeat immersion and drying in the gas phase using a test solution in which 5g/~100g/of activated carbon is added to a suspension in a solution containing 50ppm or more of _NH4Cl as ^Cl- as a main component. Corrosion test method for muffler parts for automobile exhaust gas treatment equipment. 2 (NH ₄ ) ₂ SO ₄ as S ^2-4 _, 500 ppm or more,
^Dipping _,
A corrosion test method for muffler parts for automobile exhaust gas treatment equipment, which consists of repeated drying in a gas phase and heating at temperatures below 500°C.