RU2552794C2 - Oil schedule cold-resistant pipe - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to structural cold-resistant steels used to manufacture oil schedule pipes, in particular for oil and gas production, that can be operated both under general conditions, and under macroclimatic cold at temperature decreased to minus 60°C. The pipe is made from hardened and tempered steel containing carbon, silicon, manganese, aluminium, sulphur, phosphorus, chrome, nickel, copper, nitrogen, iron and inevitable admixtures at the following ratio, wt %: C 0.28-0.34, Si 0.15-0.37, Mn 0.90-1.20, Al 0.02-0.05, S max. 0.010, P max. 0.015, Cr max. 0.25, Ni max. 0.25, Cu max. 0.25, N max. 0.012, Fe and inevitable admixtures, including V, Mo and Ti - rest.

EFFECT: pipe has ultimate strength 900 MPa or below, yield strength 830 MPa or below, impact strength at 0°C at least 41 J and impact toughness at -60°C at least 70 J/cm².

2 dwg, 3 tbl

Description

The invention relates to the field of metallurgy, in particular to structural steels used in the manufacture of pipes for oil and gas production, for example, tubing, which can be operated both under ordinary conditions and in conditions of macroclimatic cold when the temperature drops to minus 60 ° C.

Known low-carbon manganese steels in cold-resistant performance with the following compositions (wt.%): Carbon 0.09-0.12; silicon 0.20-0.35; Manganese 0.90-1.35; molybdenum 0.01-0.10; nickel 1.5-2.0; aluminum 0.020-0.045; cerium 0.005-0.010; zirconium 0.005-0.010; sulfur 0.001-0.008; phosphorus 0.001-0.008 [US Pat. RF №2233348, publ. 07/27/2004] and carbon 0.08-0.12; silicon 0.40-0.80; Manganese 0.90-1.20; chromium 0.01-0.50; molybdenum 0.20-0.35; nickel 0.30-0.90; cerium 0.01-0.02; calcium 0.005-0.050; sulfur no more than 0,020; phosphorus no more than 0,020 [US Pat. RF 2340698, publ. 12/10/2008].

The disadvantage of these compositions is the low level of strength properties (tensile strength (σ _in ) not more than 600 MPa and yield strength (σ _t ) not more than 480 MPa) after quenching with tempering, which does not allow them to be used for oil assortment pipes subjected to significant tensile loads throughout the entire life cycle.

Closest to the claimed invention is manganese steel according to GOST 4543-71, having the following ratio of components (wt.%):

carbon 0.26-0.39;

silicon 0.17-0.37;

manganese 1.40-1.80;

sulfur no more than 0,035;

phosphorus no more than 0,035;

chrome no more than 0.30;

nickel not more than 0.30;

copper no more than 0.30;

iron the rest.

It is known the use of manganese steel according to GOST 4543-71 as a material for the manufacture of pipes of oil assortment of strength group E according to GOST 633-80, GOST 632-80 according to the quenching scheme with tempering [Ferrous metallurgy. Bull. NTI No. 16. 1985 p. 11-28; Application for invention No. 2007103426 dated 08/10/2008, Bull. No. 22].

The disadvantage of this composition is that the cold resistance, estimated by the value of impact strength at a test temperature of minus 60 ° C (KCV ^-60 ), in high strength condition (σ _at least 690 MPa and σ _t at least 552 MPa) after quenching with tempering is not Meets the requirements of the international standard API 5CT.

In addition, manganese in an amount of more than 1.20% has a negative effect on the uniformity of the microstructure over the cross section due to its tendency to dendritic segregation in the cast metal, which leads to chemical heterogeneity of the initial austenite and during heat treatment (quenching with tempering) to form pronounced ferrites carbide bandedness. Sections of the microstructure enriched in the carbide phase have a low energy intensity and increase the rate of metal destruction, especially in the high-strength state and when exposed to low temperatures.

The technical problem to which the invention is directed is the creation of manganese cold-resistant steel with high structural strength at low temperatures (from 0 ° C to minus 60 ° C).

The technical result provided by the implementation of the claimed invention is expressed in the fact that when reaching the maximum strength of 900 MPa and yield strength of 830 MPa, the metal resistance to impact loads meets the requirements of the international standard API 5CT at a low temperature of 0 ° C (impact work of at least 41 J ) and the requirements of cold-resistant design (impact strength of at least 70 J / cm ² when the temperature drops to minus 60 ° C).

The specified result is achieved by the fact that in the known composition of manganese steel containing carbon, silicon, manganese, iron and inevitable impurities, the content of manganese (below the critical value of segregation) and harmful impurities of non-metals is reduced in the following ratio of components (wt.%):

carbon 0.28-0.34;

silicon 0.15-0.37;

Manganese 0.90-1.20;

aluminum 0.02-0.05;

sulfur not more than 0.010;

phosphorus no more than 0.015;

chrome no more than 0.25;

nickel no more than 0.25;

copper no more than 0.25;

nitrogen not more than 0.012;

residual impurities (V, Mo, Ti) and iron rest.

The technical result provided by the selected content of individual chemical elements in the steel is determined by the following factors.

Carbon (0.28-0.34) is introduced to achieve strength properties, the upper limit content of 0.34% is regulated in order to avoid the formation of quenching cracks during cooling in water.

Manganese (0.90-1.20) provides hardening of steel by increasing the stability of supercooled austenite, without reducing the viscoplastic properties, and gives the effect of deoxidation of steel. With a manganese content of more than 1.20%, manganese segregation and deterioration in cold resistance are pronounced.

Limitations of sulfur (not more than 0.010) and phosphorus (not more than 0.015) are strictly regulated to minimize their negative impact on the resistance of steel against brittle fracture due to the formation of segregation along the boundaries of austenite grains.

Chrome, nickel and copper (not more than 0.25 each) are unavoidable impurities in steel, especially as a result of using the scrap process in steel production. The content of chromium, nickel and copper in an amount of up to 0.25% each additionally strengthens the steel due to the fact that pearlite and bainitic transformations in the decomposition diagram of supercooled austenite are shifted to lower temperatures.

In the conditions of the Sinarsky Pipe Plant, pipes were made from the well-known accepted as a prototype and the steel proposed in the invention with an assessment of the microstructure, mechanical properties and cold resistance. The results are shown in tables: 1 - chemical composition options, 2 - mechanical properties, 3 - impact bending tests and in the figures: 1 - metal microstructure after quenching with tempering, 2 - fracture surface of samples after impact bending tests.

As a result of complex studies of pipes from the well-known, adopted for the prototype, and proposed in the invention of the steel after quenching with tempering established the following:

1) at one level of strength properties, poor cold resistance, estimated by the value of impact strength at a test temperature of minus 60 ° C (KCV ^{-60 of} at least 70 J / cm ² ), is accompanied by the presence of increased heterogeneity of the metal microstructure, which is a ferrite-carbide banding in the form light and dark etching bands (thin section etching to reveal the microstructure in a 2-4% solution of nitric acid in ethyl alcohol). Type of microstructure - vacation sorbitol;

2) formation of inhomogeneous microstructure due to metal chemical manganese content of inhomogeneity due to its propensity to dendritic segregation in the cast metal, so the ratio of manganese content in the light (Mn _{communication)} and temnotravyaschihsya (Mn _order) release strips sorbitol averages 1,38 (Mn _sv / Mn _tem = 1.25 ... 1.51) according to the X-ray microanalysis of the chemical composition, that is, the difference in manganese content in different parts of the metal volume is estimated up to 1.5 times on samples with poor cold resistance (KCV ^-60 not less than 70 J / cm ² );

3) the fracture surface of the samples after impact bending tests with poor cold resistance (KCV ^{-60 of} at least 70 J / cm ² ) was almost completely formed as a result of brittle fracture by the quasiscole mechanism. In the quasiscole zone, there are separate elements of viscous fracture — separation ridges having a dimple structure.

Thus, the achieved level of strength properties and cold resistance of the pipes of the proposed steel make it effective to use after quenching with tempering in accordance with international API Spec 5CT and other standards that contain requirements for the value of metal resistance to impact loads at temperatures of 0 ° C and lower, and also for operation in conditions of macroclimatic cold when the temperature drops to minus 60 ° C.

In addition, the advantage of the claimed invention is the lower cost of metal compared to the prototype by reducing the content of the main alloying element (manganese).

Table 1 Chemical Options Steel composition Mass fraction of elements,% C Si Mn Cr Cu Ni S P A1 N Steel pipe one 0.33 0.23 1.16 0.10 0.14 0.11 0.002 0.007 0.02 0.008 2 0.30 0.22 1.05 0.08 0.20 0.13 0.005 0.009 0.02 0.007 Steel pipe according to the prototype (GOST 4543-71) 0.34 0.25 1.45 0.16 0.18 0.15 0.011 0.019 - -

Claims (1)

An oil gauge pipe made of hardened and tempered steel containing carbon, silicon, manganese, aluminum, sulfur, phosphorus, chromium, nickel, copper, nitrogen, iron and inevitable impurities, characterized in that it is made of steel containing components in the following ratio, wt.%:
carbon 0.28-0.34 silicon 0.15-0.37 manganese 0.90-1.20 aluminum 0.02-0.05 sulfur no more than 0,010 phosphorus no more than 0.015 chromium no more than 0.25 nickel no more than 0.25 copper no more than 0.25 nitrogen no more than 0,012 iron and unavoidable impurities, including vanadium, molybdenum and titanium rest,
however, it has a tensile strength of 900 MPa or less, a yield strength of 830 MPa or less, impact resistance at 0 ° C of at least 41 J and impact strength at -60 ° C of at least 70 J / cm ² .

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