Soils corrosivity evaluation

V. Nielsen, Evaluation of Soil Corrosivity Design of an Electrochemical Soil Probe, technical report, Department of Manufacturing Engineering, Corrosion and Surface Technology, The Technical University ofDenmark, 1996. 

F. Kajiyama, K. Okamura. Evaluating cathodic protection reliability on steel pipes in microbially active soils. Corrosion, Vol. 55, No. 1, pp. 74—80, 1999. 

Due to the wide range of condition for corrosion occurring, there are many tests to evaluate corrosion. These tests include the study of atmospheric corrosion, corrosion during episodic wet/dry conditions, corrosion under fully immersed conditions, corrosion in soil, corrosion in aqueous solutions and corrosion in non-aqueous solutions and in molten salts. Moreover, it is important to consider the in-service environment and the objectives of the tests being performed. 

Escalante, E Measuring the Corrosion of Metals in Soil, Corrosion Testing and Evaluation, R. Baboian and S. W. Dean, Ed., ASTM International, West Conshohocken, PA, 1990. 

Kajiyama F, Okamura K (1999) Evaluating cathodic protecHon reHahiHty on steel pipes in microbially acHve soils. CORROSION 55(1) 74—80... 

The final plant layout combines the various engineering considerations for soil conditions drainage railroad, truck and services access raw materials receiving waste materials removal climate effect on outdoor versus indoor operations and on types of structures prevailing wind direction for vent as well as climiatic moisture corrosion plant expansion and growth access to public, and many other general evaluation points. From these broad considerations the details are developed to suit the particular plant process and the combined effects of the location. 

Combination electrical methods Tomashov and Mikhailovsky describe a method developed in the Soviet Union. This test is essentially a combination of resistivity measurement and polarisation rates on iron electrodes in soil in situ. The usefulness and value of this procedure has not as yet been determined by practical application by corrosion engineers. The development of this combination test does, however, represent an attempt to integrate some of the complex factors controlling corrosion rates in soil. Much more research on these factors and methods of measurement should in the future enable the corrosion engineer to evaluate soil properties with respect to application of corrosion-alleviating operations. 

The study of the chemical composition of precipitation is of interest for the evaluation of many scientific and practical problems. Thus, a knowledge of the chemical composition makes it possible to evaluate the degree of air pollution, the sink terms in the atmospheric cycle of aerosol particles and water soluble gases, the corrosiveness of atmospheric waters and the effect of precipitation on the material balance of soils, waters and vegetation. For these reasons, many precipitation analyses have been done, mostly in the last three decades. In this book only those works are mentioned in which an extensive network were (or are) operated, as in the American, Swedish and Soviet programs. 

A further example, which confirms the necessity of evaluating the resistivity of the medium very carefully, concerns the corrosion of rebars in reinforced concrete. In this caae the intensity of the current flowing between the anodic and cathodic zones of a macrocell depends on the resistivity of the concrete and the extent of the region involved. To determine the concrete resistivity various methods have been developed, which can be applied in the laboratory [14] as well as in the field [15]. It should be noted, however, that in the latter case most researchers have pursued the approach suggested by Wenner [16] for the evaluation of the resistivity of soils. The contribution of the ohmic drop to the electrode overvoltage cannot be neglected when the values of the corrosion rate of the rebars are appreciable, even if the current intensity is small within a given polarization potential interval, because under such conditions the interpretation of experimental results could be completely distorted. 

Underground Corrosion of Water Pipes in Cities A total of 17 pipe failures and soil samples were studied by metallurgical and analytical evaluation and the conclusions are in almost all the failures, including the failure of the service saddle on an asbestos-cement 10-in. water pipe, corrosion from the soil side was to a great extent responsible for the failures. 

Standards require that today s underground tanks must last thirty or more years without undue maintenance. To meet these criteria, they must be able to maintain structural integrity and resist the corrosive effects of soil and gasoline, including gasoline that has been contaminated by moisture and soil. The tank just mentioned that was removed in 1991 met these requirements, but two steel tanks unearthed from the same site at that time failed to meet them. One was dusted with white metal oxide and the other showed signs of corrosion at the weld line. Rust had weakened this joint so much that it could be scraped away with a pocketknife. Tests and evaluations were conducted on the RP tank that had been in the ground for 25 years tests were also conducted on similarly constructed tanks unearthed at 51 and 71 years that showed the RP tanks could more than meet the service requirements. Table 6.3 provides factual, useftil data from these tests. 

Can SRB Counts Affect Corrosion Rate One of the measures, or rather, rule of thumb, that is stiU in use in some industries is classification of the corrosivity of water environments based on the number of SRB cells, shown as cells per milliliter. According to this classification, if the SRB amount is 1000 cells/mL or less, the environment is considered as low corrosive. If the SRB amount is between 10 and 10 cells/mL, then the environment is considered as being mild corrosive. Therefore, if the SRB level is more than 10 ceUs/mL, the environment is labeled as highly corrosive. Likewise, there are also general criteria for evaluation of soil microbial corrosivity based on SRB counts alone. ... 

The process has been used for over 25 years and this section will document one of the older pipes that was evaluated after 20 years service. The service environment that the pipehnes experience are sewer water and corrosive soils. The process is used to restore corroded steel, cast iron and concrete pipes. Steel and cast iron pipe are susceptible to corrosion by sewer water through normal acid and salt attack, and by the galvanic... 

UNI 68.00.003.0 (1993). Evaluation of the Corrosivity of Soils for Low Alloyed and Unalloyed Metallic Materials (English translation by Di Biase), Italian Standards Organization, Milan, 25 pp. 

ASTM G 162 Standard Practice for Conducting and Evaluating Laboratory Corrosion Tests in Soils, Annual Book of Standards, Vol. 03.02, ASTM Intanational, West Conshohocken, PA, 1999. 

The oxidation-reduction behavior of a soil is not frequently measured, because it is difficult to obtain reliable data in the field. Extraction of soil samples for laboratory analysis is likely to introduce oxygen into the sample that will adversely affect the accuracy of the data. Accurate data can be obtained with the soil in situ, but special probes are required. The use of redox potentials in evaluating the corrosivity of soils is discussed in Refs 20 and 21. 

Normal probability and extreme value statistics have already been discussed as means of evaluating corrosion smd soil resistivity. Statistical methods have been applied to determine when steel tanks will fail [38]. Individual soil characteristics, such as resistivity, pH, and soluble ion content, are unsatisfactory methods of predicting the corrosion behavior of a structure in a particular soil. The statistical method is based on a regression analj is of all of the soil characteristics that affect corrosion as compared to actual corrosion of structures found in those soils. This method 5delds a mean time to corrosion failure (MTCF) as opposed to an actual corrosion rate. Its validity for structures other than steel tanks has not been demonstrated. 

Coupons are relatively small pieces of metal, the same composition as the structure being evaluated, that are buried in the soil next to the structure. They are intended to measure the corrosivity of the soil where the structure is buried or is intended to be placed. If the structure tdready exists, the coupon should be connected to the structure in order to expose it to galvanic and stray currents, as well as the soil. Coupons can be evaluated after a period of time using mass loss (ASTM G 112) or polarization as previously discussed. Coupons should be large enough for pitting to develop. All coupons should be evaluated visually after exposure. 

Case No. 1 Many of our infrastructures are built on soils containing aggressive chemical ions and moisture, supported on steel piles. There are no available data on the corrosion rate of such piles exposed to these types of soils, nor the long-term durability of such combinations, nor is there any standard test procedure for evaluating this over the structural life. It should be noted that one set of soldier piles supporting a 60-stoiy office building in a marine environment was recently inspected by basement sidewall excavation. The 27 in. web by 14 in. fiange by 75 ft deep piles had suffered more than 15 % web loss in less than three years service. 

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