The Role of Nonmetallic Inclusions in Accelerating the Local Corrosion of Metal Products Made of Plain-Carbon and Low-Alloy Steels

Corrosive damage to oil and gas pipe is determined by the composition and hydrodynamics of the corro sive media, the presence of corrosion currents, and the composition, structure, and properties of the steel in the pipe. It is generally assumed that the greatest risk is local pitting corrosion in media containing dissolved CO 2 , H 2 S, and Cl, as in many Western Siberian fields.Two approaches are taken to increasing the corro sion resistance of carbon and low alloy pipe steel. The first is to limit the content of manganese, to form gran ular carbides, to minimize banding, and to monitor the nonmetallic inclusions. This approach was devel oped at OOO VNIITneft', under the direction of T.V. Tetyueva. The required steel structure is produced by quenching and tempering. Pipe produced by this technology at the Sinarsk, Seversk, Volga, and Tagan rog plants went into operation in the Samotlorsk field between 1996 and 2001. According to data from OAO NizhnevartovskNIPIneft', these measures reduced the frequency of pipeline failure in the oil and gas collection system by a factor of 2.0-2.5 over a period of eight years, in comparison with hot rolled steel 20 general purpose oil and gas line pipe with no heat treatment (State Standards GOST 8731-74 and GOST 8732-78).The second approach, developed at Bardin Central Research Institute of Ferrous Metallurgy and at OAO NIFKhI im. L.Ya. Karpova, is to impose strict con straints on a special type of nonmetallic inclusions, sometimes known as corrosive nonmetallic inclusions. In this approach, corrosive nonmetallic inclusions consisting solely of calcium aluminate or Ca 3 Al 2 O 6 surrounded by a CaS shell, are regarded as the source of pitting corrosion. The content of these inclusions in pipe steel is minimized by optimizing the ladle treat ment with Ca bearing materials. According to litera ture data, corrosion tests of steel 20 with no corrosive nonmetallic inclusions at OAO Surgutneftegaz indi cate reduction in the overall corrosion rate by half and reduction in the local corrosion rate by a factor of 1.3 relative to09ГСФ samples.OAO Severskii Trubnyi Zavod, which is one of the leaders in the Russian pipe industry, has successfully introduced the production of corrosion resistant steel 20 pipe. Current market requirements call for increase in the corrosion resistance of low alloy pipe steel-in particular, the elimination of corrosive nonmetallic inclusions.In collaboration with specialists at Ural Federal University, the development of the structure and prop erties of 13ХФА steel on quenching from the single phase austenitic region and the intercritical tempera ture range has been studied in detail [1]. The heat treatment conditions that produce ferritic-martensi tic structure have been established. Thermokinetic diagrams have been plotted for the decomposition of supercooled austenite in 13ХФА steel on cooling from the single phase austenitic region and the intercritical temperature range.In the present work, we analyze the nonmetallic inclusions in industrial batches of ...

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“…Thus, the corrosive nonmetallic inclusions identi fied in the steel differ fundamentally in composition from the inclusions described in [2,3].…”

Section: Resultsmentioning

confidence: 92%

“…It is widely thought that type 1 inclusions are based on calcium aluminate, sometimes with additions of magnesium or silicon oxides, while type 2 inclusions consist of a core of calcium aluminate (with different ratios of CaO and Al 2 O 3 ), magnesium sulfide, or another compound, surrounded by a calcium sulfide shell [2,3].…”

Section: Resultsmentioning

confidence: 99%

Nonmetallic inclusions in 13XΦA steel for reliable oil-line pipe

Stepanov¹,

Ashikhmina²,

Беликов

et al. 2014

Steel Transl.

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“…Recent research has established that particular types of inclusions may accelerate the corrosive failure of industrial pipe [1][2][3][4][5]. These are known as corrosive nonmetallic inclusions.…”

mentioning

confidence: 99%

“…The change in volume ΔV of the corrosive nonme tallic inclusion as a result of hydration is or (2) where V in and V f are the initial and final volumes of the corrosive nonmetallic inclusion.…”

mentioning

confidence: 99%

“…Estimate of the stress at some point in cast annealed metal as a function of its distance from the center of the corrosive nonmetallic inclusion: (1) calculation from the data of[10];(2) calculation from the hydration model (α = 0.1); (3) calculation from the hydration model (α = 1); σ y is the yield point; τ is the stress required for the onset of shear deformation.Chemical composition of technically pure iron used in the experiments,…”

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confidence: 99%

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