Method of heat treatment of pipes

 

The invention relates to the manufacture of high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant oil country tubular goods from carbon and alloyed strong carbidopa elements (Cr, Mo, V, Nb, etc.) steels. The method of thermal processing of tubes includes heating to a temperature AU₃+20-50With cooling water in the sprayer in three stages, the first of which pipe is cooled at an average speed of 60-85With a/C for 2-4 with; the second with an average speed of 35-50With a/C for 6-8, the third with an average speed of 10-15With a/C for 10-13 with temperatures of 100-150And vacation is performed with the shutter speed not less than 30 minutes the Invention provides the desired hardenability martensitic in pipes made of carbon and alloyed steel and eliminates the chance of warping and cracking. table 1.

The invention relates to the metallurgy of steel and can be used in the manufacture of high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant pipe oil gauge from carbon and alloyed and from low-carbon manganese steels namely, that the pipe temperature end of rolling is cooled in the air, is heated to temperatures 760-790C, cooled in water, then provide additional heating to 670-700With cooling [U.S. Pat. Of the Russian Federation No. 2048542, M CL 21 D 8/10, publ. 20.11.95].

The method is used for thermal processing of oil country tubular goods with the yield strength 379-552 N/m²resistant to sulfide cracking under tension in environments containing natural and bacterial sulfide.

However, as practice has shown, this method is not suitable for the manufacture of pipes of higher groups, the strength, the production of which use steel, chromium, molybdenum, vanadium. Due to the increased resistance of steel to supply additional heating after quenching to temperatures 670-700With no exposure is not possible to obtain the desired softening and, accordingly, the necessary resistance to sulfide cracking.

The closest in technical essence and the achieved result to the present invention is a method of heat treatment of pipes made of low-alloy steels containing chromium, molybdenum and vanadium, including load, the HUS and cooling [U.S. Pat. Of the Russian Federation No. 2112050, M CL 21 D 8/10, publ. 27.05.98].

This method allows the tube to get groups strength L-80 API 5 CT and Cs, Its on THE 14-161-173 resistant to sulfide cracking.

The disadvantage of this method is the application of heat in microtecnica temperature range (760-810C), that is, in the structure of hardened pipe is 10-20% commecting ferrite, which is unacceptable for pipes groups strength L-80, C-90, T-95, manufactured according to API 5 CT. Increasing the temperature above AU₃when the cooling water leads to the appearance in the pipes of alloy steel end quenching cracks and invalid warp ends. For steels alloyed with chromium, molybdenum and vanadium, is usually applied hardening in technical oil or special hardening environments, the use of which is not possible with continuous-sequential sprayer cooling. In addition, the use of a double-vacation (without aging and with aging) ethnologica as broken continuity of the process and significantly increase the energy consumption and the cost of production.

The objective of the invention is to develop a method of thermal processing, by controlling the cooling process stably ensure the Ali and eliminates the possibility of cracking.

This object is achieved in that in the method of heat treatment of pipes, including heat exposure, the cooling water in the sprayer and leave with exposure, heat leading to a temperature AU₃+20-50And the cooling is carried out in three stages, the first of which pipe is cooled at an average speed of 60-85With a/C for 2-4 s; the second with an average speed of 35-50With a/C for 6-8 with; the third with an average speed of 10-15With a/C for 10-13 with temperatures of 100-150And vacation is performed with the shutter speed of at least 30 minutes

This method allows the use for the manufacture OCTG pipe with a yield strength 379-965 N/m²the different chemical composition of the steel. Increasing the heating temperature to AU₃+20-50Compared to the prototype caused by the need to fully austenitization inadmissibility in the structure of high-strength pipes, tubes, resistant to sulfide cracking, cold-resistant and corrosion-resistant commecting ferrite.

The cooling mode according to the proposed method provides to ensure the required proquali the second field transformation) and a slower speed in the lower temperature range of the metal. This is because the martensite point most used in the manufacture of these pipes steels lies in the temperature range of ~350-200And in the case of cooling with high speed in the lower temperature range is the sum of thermal and structural stresses, resulting in the occurrence of quenching cracks or strong warp (longitudinal curvature and ovalization ends). The cooling parameters according to the method selected with regard to the structure and properties of high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant pipes and are generic to used in their manufacture carbon and alloy strong carbidopa elements (Cr, Mo, V, Nb, etc.) steel grades.

The first stage of cooling occurs at a rate of 60-85With a/C for 2-4 C. at the steel of the type 20,20 f low hardenability to martensite, a suppression of diffusion ferrito-pearlitic decay. The decrease in the intensity of cooling in this range leads to an invalid for cold-resistant, corrosion-resistant and resistant to sulfide cracking pipes structural components - DOMTECH water consumption.

In the second stage cooling speeds of 35-50With a/C for 6-8 is provided with almost complete suppression of bainite collapse, allowing you to get hardenability martensitic required standards for high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant pipes made of steel of the type MF and MA.

The third stage of cooling is carried out in the area of martensite transformation with a rate of 10-15With less than technical oil during 10-13 C. At this speed and cooling, as the temperature of the cooled tube does not fall below 100-150With the level of residual stresses is significantly less than traditional cooling water to the shop temperature (the prototype).

Thus, when offered in the way the cooling conditions can provide the required hardenability used for the manufacture of high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant pipe steel grades and the likelihood of warping and cracking of the pipe is minimized, i.e. it gives a solution in the invention of the task.

When you vacation with visseren and evenly distributed spheroidizing carbides. This structure guarantees the receipt of the pipes required level of mechanical and corrosion properties.

The proposed method of heat treatment of pipes is carried out as follows.

Pipes made of carbon and alloyed steel is heated in the furnace of the walking beams to temperatures in the range 820-920With depending on the values of the AU₃the particular steel. Precision heating of the metal in the furnace is ±7C. the Cooling pipes is carried out in a sprayer, comprising four adjustable sections. To prevent wrinkling, and exclude the ingress of water inside the pipe during cooling changes the direction of flow of the water jets with the passage of the pipes in the first three sections. The cooling rate along the length of the sprayer is controlled by varying the water flow in sections. This allows the cooling from the temperature of austenitization on for 3 seconds with an average speed of up to 85C/C, then for 6 with speeds of up to 50C/C and then for 12 with speeds up to 15C/C to a temperature of 120-140C. Next, the pipe comes into the furnace walking beam for a vacation �="https://img.russianpatents.com/chr/176.gif">C.

The method was tested in an industrial environment OAO “Sinarsky pipe plant” and gave the following results shown in the table. From the data tables are visible high results related to the invention in comparison with the prototype. The method allows to obtain after a single vacation to extract high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant pipe (higher groups strength L-80, C-90, T-95, P 110) than after two leave the prototype, in addition, offer adjustable cooling water, guarantees the absence of quenching cracks and unacceptable warpage.

Thus, the problem of creating a method of heat treatment, allowing the use of carbon and alloy steels for the manufacture of high strength, resistant to sulfide cracking, cold-resistant and corrosion-resistant pipes, which consistently provides the required hardenability martensitic, high-level properties and eliminates the possibility of cracking and unacceptable warpage.

Claims

Method of heat treatment of pipes, including heating, cooling water sprayer and vacation 2D/chr/176.gif">And the cooling is carried out in three stages, the first of which pipe is cooled at an average speed of 60-85With a/C for 2-4, the second with an average speed of 35-50With a/C for 6-8, the third with an average speed of 10-15With a/C for 10-13 with temperatures of 100-150And vacation is performed with the shutter speed of at least 30 minutes