EP1811054A1 - Pipe for petroleum and gas product pipelines and method for the production thereof - Google Patents

Abstract

The invention relates to metallurgy, in particular to producing welded pipes for petrol and gas product pipelines and for other similar constructions (tanks and pressure vessels) used in difficult geological and climatic conditions in the presence of aggressive corrosion media. The inventive pipe for petrol and gas product pipelines is made of a steel hot-rolled sheet, wherein said steel is produced on the base of original or pure charging materials and comprises carbon, manganese, silicon, chromium, nickel, vanadium, niobium, titanium, aluminium, calcium, sulphur, phosphorus, nitrogen, copper, antimony, tin, arsenic, iron and molybdenum with the following component ratio: 0.02-011 mass % carbon, 0.10-1.80 mass % manganese, 0.06-0.60 mass % silicon, 0.005-0.30 mass % chromium, 0.005-1.0 mass % nickel, 0.01-0.12 mass % vanadium, 0.02-0.10 mass % niobium, 0.01-0.04 mass % titanium, 0.01-0.05 mass % aluminium, 0.0005-0.008 mass % calcium, 0.0005-0.008 mass % sulphur, 0.001-0.012 mass % phosphorus, 0.001-0.012 mass % nitrogen, 0.005-0.25 mass % copper, 0.0001-0.005 mass % antimony, 0.0001-0.007 mass % tin, 0.0001-0.008 mass % arsenic, equal or less than 0.5 mass % molybdenum, the rest being iron. The total nickel and manganese content depends on a molybdenum and phosphorus concentration expressed in mass % by the equation (I). The method for producing the inventive pipe consists in producing a steel having above mentioned composition, in treating in a ladle, casting, hot rolling, shaping and welding, wherein hot rolling is carried out on reversing and continuous mills and associated with a subsequent controllable accelerated cooling.

Description

FIELD OF INVENTION
• This invention relates to metallurgy, referring specifically to welded pipe production for oil pipelines, natural gas pipelines, product pipelines and other similar designs (tanks, pressure vessels) which can be safely operated in adverse geological and climatic conditions, and in aggressive corrosive liquids.
STATE OF ART
• The pipe and its method of manufacture is known (Patent of the Russian Federation No. 2180691 , C 21 D9/08, publication of 10.11.1999). It includes steelmaking, ladle processing, steel teeming, hot rolling (several rolling passages with predetermined deformation ratio), shape molding and welding. Steel is molten from first or clean melting stock, with the following component ratio (weight, %):

  Carbon	0.03 - 0.11
  Manganese	0.9 - 1.8
  Silicium	0.06 - 0.6
  Chrome	0.005 - 0.30
  Nickel	0.005 - 0.3
  Vanadium	0.02-0.12
  Niobium	0.03-0.1
  Titanium	0.01-0.04
  Aluminium	0.01-0.055
  Calcium	0.001-0.005
  Sulphur	0.0005-0.008
  Phosphorus	0.0005-0.010
  Nitrogen	0.001-0.012
  Copper	0.005-0.25
  Stibium	0.0001-0.005
  Stannum	0.0001-0.007
  Arsenic	0.0001-0.008
  Iron	remaining share

• At this ratio the content of carbon, nitrogen, copper, phosphorus, stibium, stannum and arsenic shall be as follows: $$\mathrm{C}\mathrm{+}\mathrm{10}\mathrm{N}\mathrm{<}\mathrm{0.14}$$

  

  $$\mathrm{10}\mathrm{P}\mathrm{+}\mathrm{Cu}\mathrm{<}\mathrm{0.14}$$

  

  $$\mathrm{2}\mathrm{P}\mathrm{+}\mathrm{Sn}\mathrm{+}\mathrm{Sb}\mathrm{+}\mathrm{As}\mathrm{<}\mathrm{0.035}$$

  
• During hot rolling deformation ratio in each rolling passage shall be 1.25-2.5 times less than in the previous one, and will be done in the following temperature range: T_bgn-T_end<200,
  where T_bgn and T_end are values of temperature at the start of hot roll and at the finish, accordingly.
• Since this manufacturing method of pipes from hot-rolled sheets lacks fast controlled cooling, it results in sharp limitations on the manufacture of high-strength pipes (class K60 and above), especially with sheet thickness in excess of 12 mm, because such important properties of pipes as impact strength in subzero temperatures, plasticity, weldability, crack resistance and resistance to corrosion decrease. This is due to the fact that fast cooling, which is not envisaged in the invention, can be compensated by temperature reduction in the end of hot rolling down to 700°C -750°C and an increase of carbon and manganese content, in order to provide required strength properties at the level of 60 kg/mm² and more. Both methods provide the strength required, but they result in worse properties pertaining to as impact strength, weldability and resistance to corrosion.
ESSENSE OF INVENTION
• The purpose of this invention is to provide combination of the required strength properties (breaking strength above 620 kg/mm²) and high plasticity, ductility, crack resistance and resistance to corrosion in pipes and other products made from steel sheets up to 50 mm thick.
• Technically, the required result is obtained due to the fact that pipes for oil and gas pipelines are made of steel molten from first or clean melting stock with the following component ratio (weight, %):

  Carbon	0.02 - 0.11
  Manganese	0.10-1.8
  Silicium	0.06-0.6
  Chrome	0.005-0.30
  Nickel	0.005-1.0
  Vanadium	0.01-0.12
  Niobium	0.02-0.1
  Titanium	0.01-0.04
  Aluminium	0.01-0.05
  Calcium	0.0005-0.008
  Sulphur	0.0005-0.008
  Phosphorus	0.001-0.012
  Nitrogen	0.001-0.012
  Copper	0.005-0.25
  Stibium	0.0001-0.005
  Stannum	0.0001-0.007
  Arsenic	0.0001-0.008
  Molybdenum	0.0001-0.5
  Iron	remaining share,

  this being the case, total content of nickel and manganese is related to molybdenum and phosphorus content (weight. %) according to the following equation: $$\frac{Ni+Mn}{1+Mo}\cdot P<0.03$$

  
• Also, the required result is obtained due to the fact that the method for production of the above pipe includes steelmaking with the above content ratio, ladle processing, hot rolling, shape molding and welding of pipes. This being the case, hot rolling is performed in reversing mill or continuous mill with subsequent fast controlled cooling, its rate being determined by the following equation: $$\frac{\left(T_{\mathit{hot}}-T_{\mathit{cold}}\right)}{Ls}{V}_s,\mathrm{°C}/\sec$$

  
• Rate value in the process shall be according to the following: $$\frac{\left(T_{\mathit{hot}}-T_{\mathit{cold}}\right)}{Ls}{V}_s>4,$$

  

  
  where
  T_hot is the temperature of steel sheet or steel band in the end of rolling, its value being within 750°C -850°C range;
  T_cold is the temperature of steel sheet or steel band in the end of fast controlled cooling, its value being within 500°C -700°C range;
  V_s is the steel sheet or steel band speed in the sprinkler or laminar flow, m/sec;
  L_s is the length of sprinkler or laminar unit (can be changed in the 10-100 m range).
• These inventions can simultaneously provide the required strength properties (breaking strength increases) of steel sheets up to 50 mm thick, their ductility in subzero temperatures, weldability, crack resistance and resistance to corrosion, provided the above component ratio is observed.
EXAMPLES OF REALIZATION OF INVENTION
• Table 1 shows the chemical composition of steel in two pipes, one made in accordance with the composition offered and the other one - of a different composition. The compositions were selected in such a way so as to estimate molybdenum and nickel contribution to steel sheet strength in different cooling conditions after rolling. Melting process was performed in a vacuum induction furnace. Furnace charge consisted of armco iron and, depending on variant of composition, of nickel, ferromolybdenum, copper and other charge materials. When the required underpressure in the furnace was achieved charge meltdown was started. After complete meltdown and metal heating up to 1630°C -1650°C the charge was degasified and the required predetermined amounts of manganese, ferrovanadium and ferroniobium were added to the molten pool; then deoxidizing agents (ferrosilicium, aluminium and ferrotitanium) were added. As the temperature of liquid steel reached the required level (1560°C -1580°C) the airfree metal was run off directly from the smelting crucible to the casting mold.
• On the whole, 12 trial heats have been performed in the vacuum induction furnace. Analysis of metal chemical composition has been performed for each heat. On the basis of its results three heats have been selected where the ratio between the total content of nickel and manganese and the concentration of molybdenum and phosphorus for heats 1,2 and 3 is 0.01, 0.0057 and 0.0064, respectively, i.e. less than 0.03.
• The ingots selected and the molten steel of a given pipe were forged into 80-430 mm plates; then they were rolled in a reversing mill to become 50 and 20 mm thick. After that the plates were fast-cooled at a rate of 10 and 20 degrees per second and alternately cooled in the open air. The latter cooling procedure corresponds to hot-rolled sheet conditions while the first two - to controlled fast cooling. The resulting sheets were then shaped and welded into pipes.
• Table 2 shows the properties of these heats in comparison with heats of a known composition. The obtained results demonstrate that the new steel of the above composition made in accordance with the offered rolling technology, which involves controlled cooling at a rate of 4°C per second, has the required combination of properties, such as high strength in 50-mm cross-sections and high tenacity, and therefore, good crack resistance and ductility in subzero temperatures. The 10 m/sec sheet passage speed in controlled cooling has been obtained in a wide-strip rolling mill. The sheet surface temperature at the end of rolling mill was 840°C; The sheet surface temperature at the end of controlled cooling procedure was 640°C; the length of laminary machine - 60 m; the steel strip movement speed in the laminar stream - 3 m/sec. The 20 m/sec sheet passage speed in controlled cooling has been obtained in a reversing mill. The sheet surface temperature at the end of rolling mill was 800°C; The sheet surface temperature at the end of controlled cooling procedure was 600°C; the length of quench sprinkler was 10 m, the steel strip movement speed in the sprinkler was 1 m/sec. The rate of steel sheet air cooling was approximately 2-3°C/sec. After cooling the sheet is shaped into pipe and its edges are welded.

  Table 1
  Component	Content (weight %)
  	Heat 1	Heat 2	Heat 3	Heat of known steel
  carbon	0.02	0.04	0.09	0.06
  manganese	1.5	1.0	0.3	1.4
  silicium	0.1	0.18	0.25	0.25
  chrome	0.05	0.28	0.2	0.15
  nickel	0.5	0.1	0.9	0.1
  vanadium	0.1	0.05	0.01	0.07
  niobium	0.032	0.06	0.087	0.06
  titanium	0.01	0.015	0.035	0.015
  aluminium	0.012	0.021	0.028	0.024
  calcium	0.0005	0.003	0.006	0.005
  sulphur	0.0035	0.004	0.008	0.003
  phosphorus	0.005	0.007	0.008	0.005
  nitrogen	0.005	0.006	0.007	0.007
  copper	0.23	0.1	0.01	0.15
  stibium	0.0003	0.0009	0.004	0.005
  stannum	0.0005	0.005	0.007	0.005
  arsenic	0.0002	0.004	0.008	0.006

  Table 2

  Steel properties
  Heat	Sheet thickness, mm	Breaking strength, N/mm2			Ductile-brittle transition point, °C
  		Cooling rate, °C			Cooling rate °C
  		20	10	Air	20	10	Air
  1	20/50	836/687	780/730	550/470	-90/-80	-80/-70	-50/-40
  2	20/50	807/712	750/650	540/460	-90/-80	-80/-70	-50/-40
  3	20/50	767/657	720/630	530/450	-90/-80	-80/-70	-50/-40
  Heat of known steel	20/50	621/528	500/410	420/340	-80/-30	-50/-20	-20/-10

Claims (2)

1. Pipe for oil products, natural gas products, product pipelines, made of steel molten from first or clean melting stock, containing carbon, manganese, silicium, chrome, nickel, vanadium, niobium, titanium, aluminium, calcium, sulphur, phosphorus, nitrogen, copper, stibium, stannum, arsenic and iron, characterized by that steel additionally contains molybdenum, with the following component ratio (weight %): Carbon 0.02 - 0.11 Manganese 0.10 - 1.8 Silicium 0.06 - 0.6 Chrome 0.005 - 0.30 Nickel 0.005 - 1.0 Vanadium 0.01-0.12 Niobium 0.02-0.1 Titanium 0.01-0.04 Aluminium 0.01-0.05 Calcium 0.0005-0.008 Sulphur 0.0005-0.008 Phosphorus 0.001-0.012 Nitrogen 0.001-0.012 Copper 0.005-0.25 Stibium 0.0001-0.005 Stannum 0.0001-0.007 Arsenic 0.0001-0.008 Molybdenum 0.0001-0.5 Iron remaining share, this being the case, total content of nickel and manganese is related to molybdenum and phosphorus content (weight %) according to the following equation: $$\frac{Ni+Mn}{1+Mo}\cdot P<0.03$$

   
2. Method for the production of pipe for oil products, natural gas products, product pipelines, including steelmaking said steel having the composition according to claim 1, ladle processing, steel teeming, hot rolling, shape molding and welding, characterized by that hot rolling is realized in reversing mill or continuous mill with subsequent fast controlled cooling, its rate being determined by the following equation: $$\frac{\left(T_{\mathit{hot}}-T_{\mathit{cold}}\right)}{Ls}{V}_s,\mathrm{°C}/\sec ,$$

   

   said rate value in the process shall be according to the following: $$\frac{\left(T_{\mathit{hot}}-T_{\mathit{cold}}\right)}{Ls}{V}_s>4,$$

   

   
   where
   T_hot is the temperature of steel sheet or steel band in the end of rolling, its value being within 750°C -850°C range;
   T_cold is the temperature of steel sheet or steel band in the end of fast controlled cooling, its value being within 500°C -700°C range;
   V_s is the steel sheet or steel band speed in the sprinkler or laminar flow, m/sec;
   L_s is the length of sprinkler or laminar unit (can differ between 10-100 meters), m.