RU2703767C1 - Pipe of oil grade from corrosion-resistant steel of martensitic class - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to the field of metallurgy, namely to production of pipes of oil range from corrosion-resistant steel of martensitic class, which can be used on oil and gas deposits with high concentration of carbon dioxide in the composition of extracted product, including in cold macro-climatic regions. Pipe is made from steel containing components at the following ratio, wt%: carbon 0.05–0.15, silicon 0.15–1.00, manganese 0.30–1.00, chromium 12.0–14.0, nickel 2.5–4.0, molybdenum 0.5–1.5, niobium 0.02–0.10, titanium not more than 0.05, vanadium 0.02–0.10, sulfur not more than 0.01, phosphorus not more, than 0.02, aluminum 0.02–0.05, copper not more than 0.25, nitrogen not more than 0.025, iron and unavoidable impurities – the rest. After quenching and tempering, the pipe has a yield point of not less than 758 MPa and impact viscosity at -60 °C (KCV) of not less than 70 J/cm.EFFECT: obtaining pipe with required strength characteristics, high cold resistance and minimum tendency to formation of cracks during hot deformation.1 cl, 3 tbl

Description

The invention relates to metallurgy, in particular to the production of oil-grade tubes from corrosion-resistant martensitic steel, which can be used in oil and gas fields, including in cold macroclimatic regions, with a high concentration of carbon dioxide in the composition of the produced product.

For oil and gas fields with a high concentration of carbon dioxide (CO ₂ ), the martensitic steel pipes are widely used as part of the extracted product, for example, pipes of the strength group L80 type 13Cr according to GOST R 53366-2009, containing (wt.%): Carbon 0, 15-0.22; manganese 0.25-1.00; chrome 12.0-14.0; nickel not more than 0.50; copper no more than 0.25; sulfur not more than 0.010; phosphorus no more than 0,020; silicon not more than 1.00.

Pipes meet the requirements for corrosion resistance, but have insufficiently high strength properties (yield strength not more than 655 MPa).

For the production of pipes of a higher strength group R95 according to GOST R 53366-2009 with a yield strength of 655 MPa to 758 MPa, including in a cold-resistant version for operation in cold macroclimatic regions, the use of martensitic steel is known (RF patent No. 2635205, C21D 9 / 08, С21D 8/10, С22С 38/18, published on November 9, 2017), additionally doped with nickel, containing (wt.%): Carbon 0.12-0.17; silicon 0.15-0.50; manganese 0.30-0.90; chrome 12.00-14.00; Nickel 1.80-2.20 and subjected to heat treatment with double hardening and tempering. The production of these pipes requires additional costs for the second heat treatment cycle, including re-quenching from the intercritical temperature range.

It is known (GOST R ISO 13680-2011) the production of corrosion-resistant oil-grade pipes of the P110 strength group with a yield strength of 758 MPa to 862 MPa from mild steel of the martensitic class with 13% chromium, additionally alloyed with 5% nickel and 2% molybdenum. The disadvantage of pipes made of this steel is the technical complexity of smelting high-chromium steel with a low carbon content (not more than 0.03 wt.%), As well as their high cost.

The closest solution, selected as a prototype, is a pipe made of steel of the martensitic class, containing (wt.%): Carbon 0.05-0.15; manganese not more than 5.0; chrome 7.5-15.0; nickel 2.0-3.0; copper no more than 0.5; sulfur not more than 0.03; phosphorus no more than 0.03; silicon not more than 1.5; molybdenum and tungsten in the amount of not more than 4; aluminum no more than 0.2; boron, selenium, magnesium, scandium, yttrium, lanthanum, beryllium, calcium, not more than 0.1 each; niobium not more than 0.02; cobalt no more than 10.0; antimony, tin, lead, oxygen, not more than 0.04 each; titanium 0.15-0.75; vanadium not more than 2.0; hafnium no more than 4.0; nitrogen is not more than 0.05, and subjected to hardening with tempering (patent US 6890393, C22C 38/50, C22C 38/44, C21D 8/10, publ. 10.05.2005).

The pipe has a high level of strength properties and satisfactory corrosion resistance in environments containing an aqueous solution of carbon dioxide. However, its disadvantages are:

- a significant likelihood of cracking during hot plastic deformation,

- low cold resistance (tendency to brittle fracture at low temperatures), associated with a high content of titanium and other strong carbide-forming elements and, as a result, an increased volume fraction of carbide phases in the steel structure.

The technical problem solved by the invention is to obtain a high-strength oil-grade pipe with the required technological properties, intended also for deposits located in cold macroclimatic regions.

The technical result consists in providing a yield strength of at least 758 MPa, a minimum tendency to crack during hot deformation and high cold resistance, estimated by the value of impact strength at a test temperature of minus 60 ° C (KCV _{-60 ° C} ) of at least 70 J / cm ² .

The problem is solved due to the fact that in the pipe of the oil gauge, made of corrosion-resistant martensitic steel, hardened and tempered, according to the invention, it is made of steel containing the following ratio of components, wt. %:

carbon 0.05-0.15;

silicon 0.15-1.00;

Manganese 0.30-1.00;

chrome 12.0-14.0;

nickel 2.5-4.0;

molybdenum 0.5-1.5;

niobium 0.02-0.10;

titanium not more than 0.05;

vanadium 0.02-0.10;

sulfur not more than 0.01;

phosphorus not more than 0.02;

aluminum 0.02-0.05;

copper no more than 0.25;

nitrogen no more than 0,025;

iron and unavoidable impurities - the rest,

while the content of chemical elements meets the conditions:

where [Ti], [Nb], [V], [C], [N], [Mn] and [Ni] are the contents in the steel of titanium, niobium, vanadium, carbon, nitrogen, manganese and nickel, respectively, wt. %

To ensure the high-strength state of the pipe with the declared technical characteristics, made of steel of the martensitic class and subjected to hardening and tempering, the carbon content should be at least 0.05 wt. % The carbon content in an amount not exceeding 0.15 wt. %, it is necessary to minimize the content of the carbide phase in the microstructure of steel, an excessive amount of which reduces the cold resistance and corrosion resistance of the steel, and to exclude the content of residual austenite, which reduces the yield strength.

Manganese is an austenite-forming element, so its content in steel should not exceed 1.00 wt. % due to the appearance in the microstructure of residual austenite, which reduces the yield strength of steel. The introduction of manganese in an amount of more than 1.00 wt. % can cause chemical segregation and lower cold resistance of steel.

Silicon and aluminum within the specified limits provide the required degree of deoxidation of steel. With their lower content, complete deoxidation of the steel is not ensured, the oxygen concentration in the steel increases, which leads to an increase in the number of non-metallic inclusions of the oxide type. When the silicon and aluminum contents are in excess of the upper limit of each element, non-metallic inclusions of the silicate type are formed, as well as large aluminum nitrides and carbonitrides, which adversely affect the toughness and corrosion resistance of steel.

Alloying steel with chromium in an amount of from 12.0 to 14.0 wt. % provides corrosion resistance of the pipe in environments containing carbon dioxide due to the formation on the metal surface of a dense oxide film enriched in chromium and promoting self-passivation of the metal. Excessively high chromium content (more than 14.0 wt.%), Which is a ferrite-forming element, can cause the formation of brittle delta-ferrite (δ-ferrite) in the microstructure of steel, which reduces the ductility during hot pipe deformation and cold resistance. In this case, the introduction of nickel, which is an austenite-forming element, in an amount of 2.5-4.0 wt. % has an overwhelming effect on the formation of δ-ferrite in the microstructure of steel. In addition, the nickel content in the specified range provides high cold resistance by increasing the mobility of dislocations in the crystal lattice of steel. When the Nickel content is less than 2.5 wt. % element does not have a significant positive effect on the toughness of steel. In addition, the content of Nickel - austenitic element - above 4.0 wt. % leads to an increase in the proportion of residual austenite in the structure of hardened steel and, thereby, to a decrease in the yield strength.

For martensitic steel, it has been experimentally established that the ratio of the content of austenite-forming elements: carbon, nitrogen, manganese and nickel must meet the following condition:

If this ratio of elements is less than 5.50, δ-ferrite appears in the microstructure of the steel, which reduces the process ductility and cold resistance, and when the ratio of the elements is more than 7.00, residual austenite is formed in the structure, which significantly reduces the yield strength.

The introduction of surface-active (horophilic) elements, the most effective of which is molybdenum, has a positive effect on the toughness of steel. The introduction of molybdenum in an amount of more than 0.5 wt. % reduces the free energy level of austenite grain boundaries and inhibits the formation of carbonitrides along grain boundaries, thereby ensuring a high level of toughness of steel. In addition, molybdenum provides increased resistance to local (pitting) corrosion in environments containing carbon dioxide, due to chemical passivation of the metal. Since molybdenum is a carbide-forming element, then with its content of more than 1.5 wt. % coarse coarse carbides are formed at the grain boundaries, which leads to grain boundary embrittlement and negatively affects the cold resistance of steel.

что устраняет блокировку дислокаций и уменьшает размер зерна стали, в результате снижается склонность стали к хрупкому разрушению и повышается хладостойкость. Эффект измельчения зерна стали и упрочнения стали наблюдается при введении ниобия и ванадия не менее 0,02 мас. % (каждого элемента), а при содержании каждого элемента более 0,10% не происходит дальнейшего повышения прочности, но заметно снижается хладостойкость стали.The alloying of steel with niobium and vanadium in the declared amounts (0.02-0.10 wt.% Each) is necessary for the binding of carbon to carbides such as NbC and

which eliminates the blocking of dislocations and reduces the grain size of steel, as a result, the tendency of steel to brittle fracture decreases and the cold resistance increases. The effect of grinding steel grains and hardening of steel is observed with the introduction of niobium and vanadium at least 0.02 wt. % (of each element), and when the content of each element is more than 0.10%, there is no further increase in strength, but the cold resistance of steel noticeably decreases.

Titanium forms thermally stable TiC carbides and Ti (C, N) carbonitrides of an unfavorable acute-angled shape. In the case of the manifestation of carbide inhomogeneity in the microstructure of steel, which cannot be eliminated by heating pipes for quenching, a significant drop in the impact strength of steel occurs. The technological properties are also deteriorating, which is manifested in the formation of cracks during hot deformation of pipes, so the titanium content should be no more than 0.05 wt. %

The proposed content of strong carbide and nitride forming elements (titanium, niobium and vanadium) in steel should meet the following condition:

If the indicated ratio of the elements is greater than 0.10, then the carbonitride phases formed in the microstructure of the steel have an embrittlement effect and reduce the cold resistance of the steel.

Sinarsky Pipe Plant PJSC (SinTZ PJSC) produced oil-grade tubes of 114.3 × 6.88 mm in size for use as tubing from martensitic steel with the proposed ratio of chemical elements (smelting No. 1-3 , table 1) and from steel prototype (heat No. 4, table 1).

In smelting No. 4 (prototype steel), the ratio of austenite-forming elements (2) is less than 5.50, and the ratio of carbide and nitride-forming elements (1) is more than 0.10, which leads to the formation of δ-ferrite and large particles of titanium carbonitrides in the microstructure of steel , reducing technological plasticity and provoking the appearance of cracks during hot deformation (table 2).

To confirm the high operational reliability of pipes made of steel of the proposed chemical composition and subjected to hardening and tempering, mechanical tests of pipes of the proposed steel and steel of the prototype were carried out for compliance with the requirements of strength group P110 according to GOST R 53366-2009 and additional requirements for cold resistance (table 3).

As can be seen from table 3, tubing made of steel of the proposed chemical composition (smelting No. 1-3) have mechanical properties corresponding to the strength group P110 according to GOST R 53366-2009: temporary tensile strength (σ _in ) - from 952 to 970 MPa, yield strength (σ _t ) - from 769 to 840 MPa, elongation up to 20%. In addition, the impact strength at a test temperature of minus 60 ° C (KCV _{-60 ° C} ) is from 110 to 162 J / cm ² , which indicates the required level of cold resistance and meets the requirements of consumers for pipes intended for operation - in fields in cold macroclimatic areas (not less than 70 J / cm ² ).

Pipes made of prototype steel (smelting No. 4) and heat-treated for strength group P110 do not meet the specified cold resistance requirements (actual KCV _{-60 ° C} less than 70 J / cm ² ).

Thus, the proposed oil-grade tubes made of corrosion-resistant martensitic steel and hardened and tempered have increased operational reliability:

- mechanical properties correspond to strength group P110 according to GOST R 53366-2009 (requirements for yield strength from 758 to 965 MPa);

- provided satisfactory technological plasticity, consisting in the absence of metal cracks during hot deformation;

- ensured cold resistance, estimated by the values of impact strength at a test temperature of minus 60 ° C, which is more than 70 J / cm ² .

Claims (7)

1. The pipe of the oil gauge, made of corrosion-resistant steel of martensitic class, subjected to hardening and tempering, characterized in that it is made of steel containing components in the following ratio, wt.%: carbon 0.05-0.15 silicon 0.15-1.00 manganese 0.30-1.00 chromium 12.0-14.0 nickel 2.5-4.0 molybdenum 0.5-1.5 niobium 0.02-0.10 titanium no more 0.05 vanadium 0.02-0.10 sulfur no more 0.01 phosphorus no more 0.02 aluminum 0.02-0.05 copper no more 0.25 nitrogen no more 0,025 iron and inevitable impurities rest, however, it has a yield strength of at least 758 MPa and impact strength at -60 ° C (KCV _{-60 ° C} ) of at least 70 J / cm ² . 2. The pipe under item 1, characterized in that the content of chemical elements in the steel meets the conditions: (1.1 × [Ti] + 0.5 × [Nb] + 0.5 × [V]) ≤0.10, 5.50≤ (30 × [C] + 30 × [N] + 0.5 × [Mn] + 1 × [Ni]) ≤7.00, where [Ti], [Nb], [V], [C], [N], [Mn] and [Ni] are the contents in the steel of titanium, niobium, vanadium, carbon, nitrogen, manganese and nickel, respectively, wt. %