Corrosion-active Nonmetallic Inclusions Research Articles

Influence of corrosion-active non-metallic inclusions on the accelerated destruction of the internal surface of the Oplot-M tank barrel

The metallographic features of operational damage to the inner surface of the barrel of the Oplot-M tank were analyzed. It was established that with the movement from the chamber to the cut of the barrel, the number and size of damage decreases, which is related to the distribution of pressures of working gases, temperature and aggressiveness of the environment. It is shown that the damage is placed on the inner surface chaotically and the nature of their destruction is corrosive and corrosive-mechanical in origin. Local analysis of their chemical composition revealed a high oxygen content, which indicates the formation of oxide-hydroxide compounds. The surface layers of the barrel were studied and it was established that a "white" layer with a thickness of ~50 μm and a microhardness of 930 kg/mm2 is formed on the surface, the structure of the inner layer of the steel of the barrel is troostite (HW 225 kg/mm2). 
 The effect of corrosion-active non-metallic inclusions (KANV) on the destruction of the surface of a barrel made of steel 38KHN3MFA was studied. It is shown that more sensitive to changes in the technical state of steel due to degradation are studies of corrosion resistance, microelectrochemical heterogeneity and impact toughness of steel. It was established that the presence of KANV in the steel structure leads to an increase in corrosion currents by 4 times and microelectrochemical heterogeneity, in particular, non-periodic potential peaks of 50-70 and 200-230 mV. Due to the influence of tap water on the surface of the steel, corrosion ulcers of a rounded shape and a size of 50-80 μm were recorded, which contribute to the local corrosion of the steel. The analysis of steel fractures revealed that inclusions of a round shape with a size of 3-5 μm contain impurities of harmful elements Al, Mg, F, which accelerate local corrosion on the surface of the steel of the tank barrel. It is shown that the study of fractures, and not of samples, provides an opportunity to estimate not only the size and density of inclusions, but also their chemical composition.

Corrosion-Active Non-Metallic Inclusions in Deposited Metal from Powder-Coated 30Kh20MN Wire Under AN-26 Flux

Corrosion-Active Non-Metallic Inclusions in Deposited Metal from Powder-Coated 30Kh20MN Wire Under AN-26 Flux

Role of Nonmetallic Inclusions in Premature Stress-Corrosion Fractures of Drill Pipes

We analyze the causes of the in-service loss of integrity of drill pipes made of G105 steel connected with their premature stress-corrosion fractures. In this case, the mechanical characteristics of steel are satisfactory, except a somewhat lowered elongation. At the same time, both in the structure and on the fracture surfaces of impact test specimens, we reveal a large number of corrosion-active nonmetallic inclusions of the calcium-aluminate type, which may increase the rate of local corrosion by an order of magnitude, promote the formation of deep pits on the inner surface of the pipe, and play the role of sites of initiation of corrosion-fatigue cracks. This is why we assume that the stage of crack initiation, which mainly determines the total durability of drill pipes after premature failures is controlled by the presence of corrosion-active nonmetallic inclusions and their density in the structure of steel.

New Type of Corrosion-Active Nonmetallic Inclusions and their Influence on the Corrosion of 38KHN3МFА Steel

We study the influence of corrosion-active nonmetallic inclusions on the corrosion of 38KhN3MFA steel. A new type of fluorine-containing inclusions of this kind with a size 2–30 μm is discovered. These inclusions are responsible for anomalously rapid damage of drill pipes made of the indicated type of steel. It is difficult to identify them with the help of metallographic analysis. They do not affect the general chemical composition of steel, the characteristics of strength and impact toughness at room and lowered (– 50°С) temperatures. We propose a new approach to the detection of corrosion-active nonmetallic inclusions in steels reduced to the investigation of the fracture surfaces of specimens instead of their microsections. Unlike the existing methods, this approach enables one to determine the chemical composition and correctly reproduces the shape of inclusions.

Investigation of the Conditions of Formation of Aluminum-Magnesium Spinel Inclusions in Low-Carbon Automotive Sheet Steels of 08Yu type and Ultralow-Carbon Automotive Sheet Steels of the if and IF-HS Types

We study the regularities of reduction of MgO from the lining and surface slag accompanied by the formation of adverse corrosion-active nonmetallic inclusions (CANI) based on aluminum-magnesium spinel in the course of treatment of the melts of 08Yu-type low-carbon steel and ultralow-carbon steels of the IF and IF-HS types with ten different compositions. It is shown that the amount of formed CANI regularly increases with the aluminum content of steel up to 0.05–0.06 wt.% and the MgO content of slag, especially over 12–14 wt.%. We proposed some efficient techniques aimed at guaranteeing the required purity of steel (from the viewpoint of these inclusions). For the first time, it is shown that the deposition of titanium sulfide and carbosulfide on the surfaces of aluminum-magnesium spinel inclusions increases their corrosive activity.

Modification of Non-Metallic Inclusions in Oil-Pipeline Steels by Ca-Treatment

Corrosion rate in different steel grades (including oilfield pipeline steels) is determined by the presence of non-metallic inclusions (NMI) in steels. Specifically, the effect of different inclusions on the quality of steels depends on their characteristics such as size, number, morphology, composition, and physical properties, as well as their location in the steel matrix. Therefore, the optimization and control of NMI in steels are very important today to obtain an improvement of the material properties of the final steel products. It is well known that a Ca-treatment of liquid steels in ladle before casting is an effective method for modification of non-metallic inclusions for improvement of the steel properties. Therefore, the NMI characteristics were evaluated in industrial steel samples of low carbon Ca-treated steel used for production of oil-pipelines. An electrolytic extraction technique was used for extraction of NMI from the steel samples followed by three-dimensional investigations of different inclusions and clusters by using SEM in combination with EDS. Moreover, the number and compositions of corrosion active non-metallic inclusions were estimated in hot rolled steel samples from two different heats. Finally, the corrosion resistance of these steels can be discussed depending on the characteristics of non-metallic inclusions present in the steel.

Characterization of non-metallic inclusions in corrosion -resistance nickel - based EP718 and 718 alloys by using electrolytic extraction method

It is known that non-metallic inclusions (NMI) that are formed during steel production and heat treatment can significantly affect the properties of final steel products. Therefore, it is very important to be able to determine the content of harmful NMI in steels. Nickel-based alloys are widely used in the oil and gas recovery industry, due to a good combination of strength and corrosion properties. Earlier studies have shown that the corrosion properties in immersion test and electrochemical tests for Ni-based EP718 alloys are slightly lower than that for 718 alloys. The focus in this study was the influence of different NMI on the corrosion resistance of these alloys. The characteristics of inclusions (such as size, morphology, and chemical composition) were analysed by using the electrolytic extraction method followed by three-dimensional investigations using SEM in combination with EDS. It was found that some non-metallic inclusions in EP718 alloys significantly reduce its corrosion resistance. It was also shown that a primary dissolution of the metal matrix occurs around certain inclusions during electrolytic extraction. Based on obtained results, the corrosion active non-metallic inclusions can be determined in these Nickel-base alloys and some recommendations for optimization of their production technology can be formulated.

Prediction of Nonmetallic Inclusion Composition and Amount During Low-Alloy Pipe Steel Production

Thermodynamic modeling is provided for nonmetallic inclusion formation during extra-furnace treatment and solidification of low-alloy low-carbon steels intended for use in corrosion-active media. Relationships are established for the effect on inclusion composition of alloying element additives, a periclase lining, calcium-containing materials, and presence of sulfur within a melt. Conditions are determined for a reduction in the amount of corrosion-active nonmetallic inclusions.

Low-Alloy Steel Corrosion Resistance in Natural Gas Preparation Production Solutions

Corrosion resistance of low-alloy steels 20-KSKh, 07GBK, 06GBF, 13FKhA, 09GSF, and 20 with different overall contents of corrosion-active nonmetallic inclusions (CANI) in process media for preparation and drying moist casing-head gas is studied. A study in a model medium simulating seam water of the Khar’yagin deposit, and in a moist hydrogen sulfide atmosphere for ten days shows that a reduction in CANI reduces the corrosion rate of low-alloy steels in a model medium compared with steel St20 by about a factor of two. In a moist hydrogen sulfide atmosphere after testing a steel 20 surface is coated with a uniform layer of corrosion products; in low-alloy steels, corrosion damage occupies 1–7% of the overall area. The results obtained agree with the role of CANI determined previously in developing overall and local corrosion.

Complex Nonmetallic Inclusions Formed in Billets Heated for Rolling and Characteristics of Structural Steels

Complex bimetallic inclusions formed in billets from steels 09G2S and K52 during heating for rolling are studied by methods of electron microscopy and local x-ray spectrum analysis. To check the established evolution of oxide inclusions based on aluminomagnesium spinel and other oxide compositions, individual inclusions of manganese sulfide and complex oxide-sulfide inclusions, a method developed by the Severstal’Company and the Karpov NIFKhI for determining the content of corrosion-active nonmetallic inclusions (CANI) as a function of the heating mode is applied to the steels studied. It is recommended to increase the temperature and duration of heating of billets for hot rolling in order to lower the content of CANI and to raise the resistance of the steels to local corrosion.

Developing a Technological Means of Obtaining Superior Properties and Quality for Quenched and Forged Structural Steels

In order to establish the scientific principles of a technology for the production and ladle treatment of new steels that can be quenched at forming, steels which were made in factory and laboratory heats and had different carbon contents were analyzed to explore the key factors and processes that determine both their total content of nonmetallic inclusions (NIs) and their content of certain types of NIs – particularly the types that are harmful. It was found that the most important factors in producing steel which is clean based on its content of all types of inclusions (which has an NI rating no higher than 1.5 in the government standard GOST 1778) are the slag regime and the ratio of the weights of the lime and aluminum added to the steel-pouring ladle during tapping. The optimum ranges of values for these parameters are determined. The existing requirements on the slag-regime parameters are observed to ensure a low content of harmful corrosion-active nonmetallic inclusions (CANIs) in the steel. However, it is essential to maintain a low (at or below the lower limit of 0.02% specified for the grade of steel) aluminum content for the duration of the ladle treatment. Aluminum content can be increased during the final stages, if necessary. A study was made of the effect of the MgO content of the covering slag on the possibility and rate of formation of CANIs based on alumomagnesian spinel. it was found that the steel’s content of such inclusions rises sharply when the concentration of MgO in the covering slag is greater than 14.1%. An MgO content of up to 8% guarantees that the steel will be clean based on its content of all types of inclusions. The results obtained for the metal of two trial heats confirmed the adequacy of the key parameters that were identified and the ranges of values for those parameters which were determined to be optimum for obtaining a low CANI content and high resistance to local corrosion.

THE MODEL OF DISTRIBUTION OF TENSILE AND COMPRESSIVE STRESSES IN METAL AROUND CALCIUM-CONTAINING NON-METALLIC INCLUSIONS IN WATER MEDIA

The mechanism of interaction between corrosion-active non-metallic inclusions (CANI) and metal in water media was developed. This mechanism consists in CANI volume increase, as a result of hydration, and tension and compression areas formation. On the basis of this mechanism the model of distribution of mechanical stresses around hydrating inclusions was developed.

Laws governing the transformation of undesirable types of nonmetallic inclusions during the treatment of steel 20-Kt in the solid state

A study is made of the effect of the regimes used for heating, hot-rolling, and heat-treating seamless pipes of steel 20-KT on their content of corrosion-active nonmetallic inclusions (CANIs). Technological measures are developed to ensure that the low CANI content which is required is obtained and that the steel thus has high indices for resistance to local corrosion in aqueous chlorine-bearing media.

Effect of a pipe-steel killing technology on the composition and number of nonmetallic inclusions

Pipes made from steels 19G, 17GS, 17G1S, 10G2FBYu, 13G1S-U, and 20KT of various manufacturers and technologies are studied. Electron microprobe and fractional gas analyses are used to determine the main types and number of nonmetallic inclusions (NIs). The effect of a modification procedure on the oxidic cleanness of steel 20KT (produced at JSC “Volzhskii Pipe Works”) is studied. The use of a silicocalcium-filled wire is shown to increase the total contamination of the steel by nonmetallic, in particular, calcium aluminate and magnesium spinel inclusions, which are conditionally related to corrosion-active nonmetallic inclusions (CANIs). Fractional gas analysis is shown to allow the number of oxide inclusions of various types to be accurately determined in pipe steels. No correlation is found between the volume fraction of oxide inclusions determined by fractional gas analysis and the number of CANIs determined by a metallo-graphic method.

Study of the effect of the parameters of an out-of-furnace treatment of tube steels on the degree of contamination of the steels by corrosion-active nonmetallic inclusions

Study of the effect of the parameters of an out-of-furnace treatment of tube steels on the degree of contamination of the steels by corrosion-active nonmetallic inclusions

Increasing the corrosion resistance of low-alloy and carbon steels for automobile construction by optimizing the metallurgical technology

It is shown that the corrosion resistance of automobile sheet can be improved by ensuring that steels of this type have a low content of corrosion-active nonmetallic inclusions (CANI). The main mechanisms responsible for the formation of CANI in automobile sheet have been established, and recommendations have been developed to reduce their concentration in this product

Determination of Regimes for Out-of-Furnace Treatment of Steel by Statistical Analysis of Production Control Data

Parameters of the process of out-of-furnace treatment of liquid steel in the ladle with participation of highly basic slag, which ensures the required level of purity with respect to corrosion-active nonmetallic inclusions, are determined with the help of methods of statistical analysis of production control data.

Evaluating Pipes from the Sinarskii Pipe Plant Based on their Content of Corrosion-Active Nonmetallic Inclusions

To refine existing standards on the content of corrosion-active nonmetallic inclusions (CANI) in semifinished products, the Sinarskii Pipe Plant has made a study of the change in the density and shape of CANI from the semifinished product to the finished pipe. The study was performed on three heats having a CANI density within the established norm (no more than 2 inclusions/mm2) and on six specimens with a CANI density greater than 2 inclusions/mm2. Researchers followed the change in inclusion density in relation to the degree of deformation of semifinished products of steel 20-PKS made by the Volga Pipe Plant. The semi-finished products were 120 and 156 mm in diameter and were used in pipe production. An analysis of the study results showed that CANI density in the finished pipe is no greater than 2 inclusions/mm2 if the CANI in the semifinished product are uniformly distributed, their average density is no greater than 2 inclusions/mm2, and their maximum density is no greater than 4 inclusions/mm2. It was determined that CANI density is not affected by the degree of deformation of the semifinished product.

Study of the Effect of Process Parameters in Steel Production on the Content of Corrosion-Active Nonmetallic Inclusions in Corrosion-Resistant Pipes

The main reason for the accelerated local corrosion of tubes is contamination of the steel by corrosion-active nonmetallic inclusions (CANI), which determine the metallurgical properties of tube steel in terms of their corrosion resistance. Studies have shown that there are two main types of corrosion-active nonmetallic inclusions: CANI1 — inclusions based on calcium aluminates; CANI2 — complex inclusions that contain calcium sulfide. In order to master to production of tubes of steel 20-PKS at the Volga Pipe Plant (VTZ), a study was made of the effect of the parameters of out-of-furnace treatments on the contamination of steel by CANI.

Analysis of the Processes Involved in Refining Steel at the Tagmet Combine to Remove Corrosion-Active Nonmetallic Inclusions

The processes involved in refining steel at the Tagmet combine to remove corrosion-active nonmetallic inclusions (CANI) were analyzed using the program GIBBS®. The analysis was performed with the assumption that CANI are a special case of the oxide and sulfide inclusions normally seen in steels. Thus, it was proposed that the total number of all endogenic primary inclusions be reduced to a minimum and that their composition be optimized (that the inclusions be converted to the liquid state) in order to remove them from steel. It was shown that from 6 to 20% of all primary inclusions in steel are CANI, the exact percentage depending on the amount of alumo-calcium used in the treatment of the steel. It was also noted that the secondary oxidation of steel increases its volume content of primary inclusions by an order of magnitude. It was determined that the infiltration of oxygen into the treatment unit even at a rate of 0.3 kg/ton makes it impossible to obtain liquid primary inclusions. Modeling of the deoxidation of steel on a ladle-furnace unit at Tagmet made it possible to determine the optimum range of alumo-calcium consumption: 0.7–1 kg/ton (depending on the consumption of aluminum wire rod used for preliminary deoxidation). The formation of liquid primary inclusions — which includes CANI — is minimal in this case.