Low cost j55 grade oil casing

Abstract

The present application belongs to the technical field of seamless pipe manufacturing, and particularly relates to a low-cost J55 grade petroleum casing, the chemical composition of which is as follows in terms of mass percentage: C: 0.28% to 0.32%, Si: 0.15% to 0.25%, Mn: 0.8% to 1.0%, P: 0.02% or less, S: 0.01% or less, Ti: 0.01% to 0.02%, Al: 0.015% to 0.025%, and the balance being Fe elements and inevitable impurities. The present application adopts round pipe blanks for rolling production to obtain J55 grade petroleum casing, and through single titanium micro-alloying and less manganese content, the stable performance and strong toughness matching of the petroleum casing is achieved through chemical composition and process control for low-cost production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of seamless pipe manufacturing, and particularly relates to a low-cost J55 grade oil casing. BACKGROUND

[0002] In oil and gas drilling and production operations, the oil casing is a steel pipe used to support the wall of an oil and gas well. Generally, according to the use condition, the casing can be divided into a guide pipe, a surface casing, a technical casing and an oil layer casing. The J55 casing mainly serves as a surface casing. During the service, due to the complex topography and the mispositioning stress of the stratum, the surface casing is required to have a high impact toughness on the basis of meeting the tensile property.

[0003] In order to meet the quality standard, steel pipe production enterprises basically add micro-alloying elements such as niobium (Nb), vanadium (V) and titanium (Ti) on the basis of carbon (C), silicon (Si) and manganese (Mn) strengthening. However, the niobium (Nb) and vanadium (V) alloy has a high cost and a large heat processing energy consumption, which is not conducive to improving the product competitiveness. Therefore, there is an urgent need for a method for producing the J55 grade steel pipe with stable performance and high strength and toughness through single titanium (Ti) micro-alloying.

[0004] Patent CN103045944A discloses a high-toughness oil casing steel and an oil casing manufacturing method. The patent adopts a boron-titanium micro-alloying low-carbon high-silicon composition design, obtains a J55 grade oil casing with a bainite structure through hot rolling, and adds the expensive elements of boron and titanium, which increases the alloy cost of the steel pipe. The design of high silicon easily causes the surface quality of the steel pipe to decrease, and the performance of the obtained hot-rolled bainite structure fluctuates greatly.

[0005] Patent CN110205546A discloses an oil casing with a yield strength greater than 450 MPa and a preparation method thereof. The patent adopts a niobium-titanium micro-alloying carbon-manganese composition design, obtains a 55 steel grade oil casing steel plate through hot rolling of the plate, and then makes the oil casing through welding, which increases the process cost.

[0006] Patent CN111485176A discloses a low-cost J55 grade oil casing steel and a production method and application thereof. The patent adopts a niobium micro-alloying composition design, obtains a J55 steel grade steel plate through hot rolling, and then makes the oil casing through welding. The general process is complicated, and the manufacturing cost is high.

[0007] Patent CN1361303 discloses a TP65 steel grade oil casing and a manufacturing method thereof. The patent adopts a medium-carbon low-alloy steel to add vanadium micro-alloying for rolling production to obtain an oil casing with a yield strength of 448 MPa to 586 MPa. However, the manganese content is 1.0% to 1.8%, which is relatively high. In addition, compared with titanium, vanadium is more expensive. SUMMARY

[0008] The technical problem to be solved by the present application is to provide a low-cost J55 grade oil casing, which has stable performance and strong toughness matching by chemical composition and process control.

[0009] To achieve the above-mentioned object, the present application adopts the following technical solutions:

[0010] A low-cost J55 grade oil casing, the chemical composition is as follows in mass percentage: C: 0.28% to 0.32%, Si: 0.15% to 0.25%, Mn: 0.8% to 1.0%, P≤0.02%, S≤0.01%, Ti: 0.01% to 0.02%, Al: 0.015% to 0.025%, and the balance is Fe element and inevitable impurities.

[0011] A low-cost J55 grade oil casing, the microstructure is as follows in volume: 20% to 40% ferrite, 60% to 80% pearlite, the overall grain size is not less than 8.0 grade, and the mechanical properties meet the following requirements: yield strength Rt0.5 is 380 MPa to 550 MPa, tensile strength Rm is 520 MPa to 850 MPa, elongation after fracture is ≥19%, and impact energy is ≥27 J.

[0012] A low-cost J55 grade oil casing, the outer diameter is Φ114.3 mm to Φ177.8 mm, and the wall thickness is 5.69 mm to 12.7 mm.

[0013] The main chemical components have the following effects:

[0014] C is a carbide forming element, which can improve the strength of the steel, and is limited to 0.28% to ensure the necessary strength, but too high carbon content will exacerbate the banded structure, affect the low temperature impact performance and acid corrosion resistance, so the upper limit is 0.32%.

[0015] Si is an effective deoxidizing element, and too low content will lack deoxidizing effect, and too high content will reduce the toughness of the steel, and also affect the surface quality of the steel pipe, therefore, 0.15 to 0.25% is selected as the alloy content range of Si.

[0016] Mn can play a solid solution strengthening effect, which can make up for the loss of yield strength due to the reduction of carbon content, and appropriate Mn can improve the toughness of the steel, reduce the ductile-brittle transition temperature, and too high Mn can easily cause composition segregation and banded structure in the inner wall of the steel pipe, and reduce the uniformity of the microstructure performance of the steel pipe, therefore, 0.8% to 1.0% is selected as the alloy content range of Mn.

[0017] Ti can precipitate TiN in high temperature austenite, can prevent austenite grain growth, refine the grain, improve the strength and toughness of the steel, and the fine TiC precipitated during cooling can play the role of precipitation strengthening, so the Ti content of the application is controlled at 0.01% to 0.02%.

[0018] P is an impurity element, which promotes central segregation, significantly reduces the impact toughness of the steel, and increases the ductile-brittle transition temperature of the steel, so the content of P should be as low as possible, and the content of P is required to be not more than 0.02%.

[0019] S is an impurity element, which is easy to form sulfide and has a greater impact on impact performance, and the content of S in the application is required to be not more than 0.01%.

[0020] Al is a deoxidizing element, and reasonable control of its content can improve the cleanliness of the molten steel and the acid-soluble aluminum of the steel grade can play a role in refining the pipe blank grain, but too high Al will cause cracks on the surface of the pipe blank, therefore, the content of Al in the application is controlled at 0.015% to 0.025%.

[0021] A manufacturing method of a low-cost J55 grade oil casing, specifically comprising the following steps:

[0022] (1) heat the round pipe blank to 1220-1240℃, the furnace holding time is 1.5-2h, the round pipe blank is discharged at a temperature of 1180-1200℃, and after discharging, head and tail centering and piercing are performed, and the piercing temperature is 1170-1190℃;

[0023] (2) after piercing, the inner surface of the pipe body is treated by spraying boron sand, and then PQF continuous rolling is performed, the continuous rolling temperature is 1130-1150℃, the rough pipe is obtained, and the rolling extension coefficient is controlled at 8.5-8.9;

[0024] (3) intermediate cooling is performed on the rough pipe, the cooling speed is 20-30℃ / s, and the rough pipe is cooled to 860-900℃;

[0025] (4) the cooled rough pipe is subjected to sizing reduction, and the steel pipe is obtained, and the sizing temperature is 850-890℃;

[0026] (5) the steel pipe is subjected to rapid water cooling, the cooling speed is 10-15℃ / s, the steel pipe is cooled to 720-760℃, and then the steel pipe enters the heat preservation cover for isothermal treatment, the isothermal time is 3-5min, and after isothermal treatment, the steel pipe is naturally cooled on the cooling bed.

[0027] In step (1), the diameter of the round pipe blank is 210mm.

[0028] In step (1), a plug-type piercer is used for piercing.

[0029] Step (3) sprays and cools the rough pipe by water mist cooling.

[0030] Step (5) uniformly cools the steel pipe in the circumferential direction by spraying the annular water ring.

[0031] Compared with the prior art, the beneficial effects of the present application are:

[0032] (1) The component design idea of low manganese (Mn) is adopted, and only trace titanium (Ti) is added, avoiding the use of valuable elements such as niobium (Nb) and vanadium (V), so that the production process energy consumption is low, the product performance fluctuation is small, and the production cost is greatly reduced;

[0033] (2) The rough pipe after continuous rolling is intermediate cooled, further refining the austenite grains, improving the fine grain strengthening effect, and improving the strength and toughness of the steel pipe;

[0034] (3) Controlling the rough pipe into the sizing temperature is conducive to achieving the controlled cooling target temperature of the steel pipe after sizing;

[0035] (4) Through rapid water cooling of the steel pipe after sizing, fine equiaxed ferrite is obtained, avoiding the precipitation of net-shaped ferrite in the high-temperature phase transformation zone to reduce the organizational continuity and impact toughness of the steel pipe;

[0036] (5) Through isothermal treatment, the steel pipe is ensured to have sufficient incubation time in the pearlite transformation zone, so that the remaining austenite is fully transformed into pearlite structure with fine interlamellar spacing, avoiding the appearance of bainite structure to reduce the toughness of the steel pipe.

[0037] The present application adopts round pipe billets for rolling production to obtain J55 grade oil casing, through single titanium micro-alloying and less manganese content, and through chemical composition and process control to achieve low-cost production of J55 grade oil casing with stable performance and strength-toughness matching. DETAILED DESCRIPTION

[0038] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Reference herein to "one embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all directed to the same embodiment, or to one or more group of alternative embodiments. It is expressly understood that any of the embodiments described herein can be combined with any of the other embodiments unless specifically noted otherwise. Based on the embodiments herein, all other embodiments that would be obvious to those ordinarily skilled in the art from the disclosure herein are intended to be within the scope of the present application.

[0039] A low-cost J55 grade oil casing with a chemical composition by mass percentage of C: 0.28% to 0.32%, Si: 0.15% to 0.25%, Mn: 0.8% to 1.0%, P≤0.02%, S≤0.01%, Ti: 0.01% to 0.02%, Al: 0.015% to 0.025%, and the balance of Fe elements and inevitable impurities.

[0040] A manufacturing method of a low-cost J55 grade oil casing, specifically comprising the following steps:

[0041] (1) heating a round pipe blank with a diameter of 210 mm to 1220°C to 1240°C, maintaining the temperature in the furnace for 1.5 to 2 hours, and discharging the round pipe blank at a temperature of 1180°C to 1200°C; after discharging, centering the head and tail, and using a plug-type piercing machine to perform piercing at a temperature of 1170°C to 1190°C;

[0042] (2) after piercing, performing boron sand spraying treatment on the inner surface of the steel pipe to prevent oxidation, and after the boron sand spraying treatment, performing PQF continuous rolling at a temperature of 1130°C to 1150°C to obtain a continuous-rolled hollow pipe, and controlling the rolling elongation coefficient at 8.5 to 8.9 to ensure a large rolling deformation of the steel pipe, so that the steel pipe is fully recrystallized to effectively refine the grains;

[0043] (3) further refining the austenite grains by intermediate cooling the continuous-rolled hollow pipe, and using a water mist cooling method to spray cool the hollow pipe at a cooling speed of 20°C / s to 30°C / s to cool the hollow pipe to a temperature of 860°C to 900°C;

[0044] (4) performing a sizing reduction on the cooled hollow pipe to obtain a steel pipe at a sizing temperature of 850°C to 890°C;

[0045] (5) uniformly cooling the steel pipe in the circumferential direction by using a ring-shaped water ring to spray, cooling the steel pipe to a temperature of 720°C to 760°C at a cooling speed of 10°C / s to 15°C / s, and then placing the steel pipe in a holding cover to perform isothermal treatment to convert the remaining austenite into a pearlite structure with a small interlamellar spacing, and naturally cooling the steel pipe on a cooling bed after isothermal treatment for 3 minutes to 5 minutes.

[0046] The produced steel pipe has an outer diameter of Φ114.3 mm to Φ177.8 mm and a wall thickness of 5.69 mm to 12.7 mm, and the main mechanical properties meet the requirements of a yield strength Rt0.5 of 380 MPa to 550 MPa, a tensile strength Rm of 520 MPa to 850 MPa, an elongation after fracture of ≥19%, and an impact energy of ≥27 J (room temperature test temperature, full-size sample).

[0047] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application.

[0048] Embodiment 1

[0049] The embodiment provides a low-cost J55 steel grade oil casing manufacturing method, which comprises the following process steps:

[0050] (1) heat Φ210mm round billet to 1220℃, furnace holding time 1.5h, billet discharge temperature 1180℃, after discharging, head and tail centering is performed, and piercing is performed by using a mushroom type piercing machine, and the piercing temperature is 1170℃;

[0051] (2) after piercing, boron sand spraying treatment is performed on the inner surface of the steel pipe to prevent oxidation of the inner wall, and after the boron sand spraying treatment, PQF continuous rolling is performed, the continuous rolling temperature is 1130℃, the as-rolled pipe is obtained, and the rolling elongation coefficient is controlled to be 8.5;

[0052] (3) the as-rolled pipe after continuous rolling is subjected to intermediate cooling, the as-rolled pipe is sprayed and cooled by using a water mist cooling method, the cooling speed is 20℃ / s, and the as-rolled pipe is cooled to 860℃;

[0053] (4) the cooled as-rolled pipe is subjected to sizing reduction, and a steel pipe is obtained, and the sizing temperature is 850℃;

[0054] (5) the steel pipe after sizing is subjected to rapid water cooling, the steel pipe is uniformly cooled in the circumferential direction by using a ring-shaped water ring spraying method, the cooling speed is 10℃ / s, the steel pipe is rapidly cooled to 720℃, and then the steel pipe enters a heat preservation cover to be subjected to isothermal treatment, the isothermal time is 3min, and after isothermal treatment, the steel pipe is naturally cooled on a cooling bed.

[0055] The prepared Φ114.3mm*5.69mm low-cost J55 grade oil casing has a microstructure of 40% ferrite + 60% pearlite, and the overall grain size is 8.5.

[0056] The chemical composition of the oil casing is shown in Table 1;

[0057] Table 1: Chemical composition

[0058]

[0059] The performance of the oil casing is shown in Table 2;

[0060] Table 2: Performance of the oil casing

[0061]

[0062] Embodiment 2

[0063] The embodiment provides a low-cost J55 steel grade oil casing manufacturing method, which comprises the following process steps:

[0064] (1) a Φ210mm round pipe blank is heated to 1230℃, the furnace holding time is 1.7h, the steel blank discharge temperature is 1190℃, after discharge, head and tail centering is carried out, and a mushroom type piercing machine is used for piercing, and the piercing temperature is 1180℃;

[0065] (2) after piercing, boron sand treatment is carried out on the inner surface of the steel pipe to prevent oxidation of the inner wall, after the boron sand treatment, PQF continuous rolling is carried out, the continuous rolling temperature is 1140℃, the as-rolled pipe is obtained, and the rolling elongation coefficient is controlled to be 8.7;

[0066] (3) the as-rolled pipe after continuous rolling is subjected to intermediate cooling, the as-rolled pipe is sprayed and cooled in a water mist cooling mode, the cooling speed is 24℃ / s, and the as-rolled pipe is cooled to 875℃;

[0067] (4) the as-rolled pipe after cooling is subjected to diameter reduction, and the steel pipe is obtained, and the entry diameter reduction temperature is 860℃;

[0068] (5) the steel pipe after diameter reduction is subjected to rapid water cooling, the steel pipe is uniformly cooled in the circumferential direction in a ring-shaped water ring spraying mode, the cooling speed is 13℃ / s, the steel pipe is rapidly cooled to 730℃, and then the steel pipe enters a holding cover to be subjected to isothermal treatment, the isothermal time is 4min, and the steel pipe is naturally cooled on a cooling bed after isothermal treatment.

[0069] The prepared Φ139.7mm*9.17mm low-cost J55 grade oil casing has a microstructure of 30% ferrite + 70% pearlite, and the overall grain size is 8.5 levels.

[0070] The chemical composition is shown in Table 3;

[0071] Table 3: Chemical composition

[0072]

[0073] The performance of the oil casing is shown in Table 4;

[0074] Table 4: Performance of the oil casing

[0075]

[0076] Embodiment 3:

[0077] The embodiment provides a low-cost J55 steel grade oil casing manufacturing method, which comprises the following process steps:

[0078] (1) Φ210mm round billet is heated to 1240℃, the furnace holding time is 1.6h, the billet temperature is 1200℃ when it is discharged, after discharging, head and tail centering is carried out, piercing is carried out by using a mushroom type piercing machine, the piercing temperature is 1190℃;

[0079] (2) After piercing, boron sand is sprayed on the inner surface of the steel pipe to prevent oxidation, after boron sand spraying, PQF continuous rolling is carried out, the continuous rolling temperature is 1150℃, the rolling elongation coefficient is controlled at 8.8;

[0080] (3) After continuous rolling, the intermediate cooling of the rolled pipe is carried out, the pipe is sprayed and cooled by using water mist cooling, the cooling speed is 27℃ / s, the pipe is cooled to 880℃;

[0081] (4) The pipe after cooling is subjected to diameter reduction by stretching, the pipe is obtained, the entry temperature of the diameter reduction is 870℃;

[0082] (5) The pipe after diameter reduction is subjected to rapid water cooling, the pipe is uniformly cooled in the circumferential direction by using annular water ring spraying, the cooling speed is 14℃ / s, the pipe is rapidly cooled to 745℃, then the pipe enters the heat preservation cover to carry out isothermal treatment, the isothermal time is 3min, after isothermal treatment, the pipe is naturally cooled on the cooling bed.

[0083] The microstructure of the prepared Φ168mm*8.94mm low-cost J55 grade oil casing is 25% ferrite + 75% pearlite, the overall grain size is 8.5 grade.

[0084] The chemical composition is shown in Table 5;

[0085] Table 5: Chemical composition

[0086]

[0087] The performance of the oil casing is shown in Table 6;

[0088] Table 6: Performance of the oil casing

[0089]

[0090] Example 4:

[0091] The embodiment provides a low-cost J55 steel grade oil casing and a manufacturing method thereof, which comprises the following process steps:

[0092] (1) Φ210mm round billet is heated to 1230℃, the furnace holding time is 2h, the billet temperature is 1200℃ when it is discharged, after discharging, head and tail centering is carried out, piercing is carried out by using a mushroom type piercing machine, the piercing temperature is 1190℃;

[0093] (2) After the piercing, the inner surface of the steel pipe is treated by spraying boron sand to prevent the inner wall from being oxidized, and after the spraying boron sand treatment, PQF continuous rolling is performed at a continuous rolling temperature of 1150°C to obtain a rolled pipe, and the rolling extension coefficient is controlled at 8.9;

[0094] (3) The rolled pipe is subjected to intermediate cooling, and the pipe is sprayed and cooled by water mist cooling at a cooling speed of 30°C / s to cool the pipe to 880°C;

[0095] (4) The cooled pipe is subjected to sizing reduction, and a steel pipe is obtained at a sizing temperature of 870°C;

[0096] (5) The steel pipe after sizing is subjected to rapid water cooling, and the pipe is uniformly cooled in the circumferential direction by spraying with an annular water ring at a cooling speed of 15°C / s to rapidly cool the pipe to 750°C, and then the pipe enters a heat preservation cover for isothermal treatment for 5 min, and after isothermal treatment, the pipe is naturally cooled on a cooling bed.

[0097] The microstructure of the prepared Φ177.8mm*9.19mm low-cost J55 grade oil casing is 23% ferrite + 77% pearlite, and the overall grain size is grade 9.

[0098] The chemical composition is shown in Table 7:

[0099] Table 7: Chemical composition

[0100]

[0101] The performance of the oil casing is shown in Table 8;

[0102] Table 8: Performance of the oil casing

[0103]

[0104] Example 5:

[0105] The present embodiment provides a low-cost J55 steel grade oil casing and a manufacturing method thereof, which comprises the following process steps:

[0106] (1) A Φ210mm round billet is heated to 1220°C, the furnace holding time is 2h, the billet discharge temperature is 1180°C, after discharge, the head and tail are centered, and a plug-type piercer is used for piercing at a piercing temperature of 1170°C;

[0107] (2) After the piercing, the inner surface of the steel pipe is treated by spraying boron sand to prevent the inner wall from being oxidized, and after the spraying boron sand treatment, PQF continuous rolling is performed at a continuous rolling temperature of 1140°C to obtain a rolled pipe, and the rolling extension coefficient is controlled at 8.5;

[0108] (3) Intermediate cooling is performed on the as-drawn pipe after continuous rolling, and the as-drawn pipe is sprayed and cooled by water mist cooling at a cooling speed of 30°C / s to cool the as-drawn pipe to 900°C;

[0109] (4) The as-drawn pipe after cooling is reduced in diameter by stretching to obtain a steel pipe at a sizing temperature of 890°C;

[0110] (5) The steel pipe after sizing is rapidly water-cooled by spraying in a ring-shaped water ring to uniformly cool the steel pipe in the circumferential direction at a cooling speed of 15°C / s, and the steel pipe is rapidly cooled to 760°C, and then the steel pipe is subjected to isothermal treatment in a heat preservation cover for 5 minutes, and the steel pipe is naturally cooled on a cooling bed after isothermal treatment.

[0111] The microstructure of the prepared Φ127mm*12.7mm low-cost J55 grade oil casing is 20% ferrite + 80% pearlite, and the overall grain size is grade 9.

[0112] The chemical composition is shown in Table 9;

[0113] Table 9: Chemical composition

[0114]

[0115] The performance of the oil casing is shown in Table 10;

[0116] Table 10: Performance of the oil casing

[0117]

[0118] Although the embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low cost J55 grade oil casing characterized in that, The chemical composition is as follows in mass percentage: C: 0.28%~0.32%, Si: 0.15%~0.25%, Mn: 0.8%~1.0%, P≤0.02%, S≤0.01%, Ti: 0.01%~0.02%, Al: 0.015%~0.025%, and the balance is Fe element and inevitable impurities; The microstructure of the oil casing is 20%~40% ferrite, 60%~80% pearlite in volume, the overall grain size is not less than 8.0 grade, and the mechanical properties meet the following requirements: yield strength Rt0.5 is 380MPa~550MPa, tensile strength Rm is 520MPa~850MPa, elongation after fracture is ≥19%, and impact energy is ≥27J; The oil casing has an outer diameter of Φ114.3mm~Φ177.8mm and a wall thickness of 5.69mm~12.7mm; The manufacturing method of the oil casing specifically comprises the following steps: (1) heating a round pipe blank to 1220℃~1240℃, keeping the round pipe blank in the furnace for 1.5~2h, and taking the round pipe blank out of the furnace at a temperature of 1180℃~1200℃, and then performing head and tail centering and piercing after taking the round pipe blank out of the furnace, and the piercing temperature is 1170℃~1190℃; (2) after piercing, performing boron sand spraying treatment on the inner surface of the pipe body, and then performing PQF continuous rolling, and the continuous rolling temperature is 1130℃~1150℃, to obtain a rough pipe, and the rolling elongation coefficient is controlled to be 8.5~8.9; (3) performing intermediate cooling on the rough pipe at a cooling speed of 20~30℃ / s, and cooling the rough pipe to 860℃~900℃; (4) performing diameter reduction on the cooled rough pipe, to obtain a steel pipe, and the diameter reduction temperature is 850℃~890℃; (5) performing rapid water cooling on the steel pipe, and uniformly cooling the steel pipe in the circumferential direction by adopting the way of spraying the steel pipe with annular water ring, and the cooling speed is 10℃ / s~15℃ / s, and the steel pipe is cooled to 720℃~760℃, and then the steel pipe enters a heat preservation cover to perform isothermal treatment, and the isothermal time is 3min~5min, and the steel pipe is naturally cooled on a cooling bed after isothermal treatment.

2. A low cost J55 grade oil casing according to claim 1, characterized by, The diameter of the round pipe blank in step (1) is 210mm.

3. A low cost J55 grade oil casing according to claim 1, characterized by, Step (1) adopts a plug piercing mill to perform piercing.

4. A low cost J55 grade oil casing according to claim 1, characterized by, Step (3) sprays and cools the rough pipe by adopting the way of water mist cooling.

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