The heating process of 4140 alloy steel pipe in the walking beam reheating furnace was studied by means of experiment and three-dimensional finite element numerical simulation， the temperature change and distribution of the pipe were analyzed. The results showed that the temperature of the head of the steel pipe entering the furnace first was 30-50 ℃ higher than that of the middle and tail part，and there was uneven heating phenomenon along the circumference of the steel pipe. When the temperature exceeded 800 ℃，the temperature difference between each part of the pipe gradually decreased，and the overall temperature tended to be uniform. Below the austenitizing temperature，the heating rate gradually decreased from 0.35 ℃/s to 0 ℃/s，and when the austenitization was complete，it increased slightly and then decreased again. Compared to the middle section， the temperature was higher at both the end and the head of the steel pipe，and the influencing area was less than 200 mm. When the temperature was about 400 ℃，the temperature difference between the end surface and the middle was the largest，reaching 117 ℃. However，the temperature difference gradually decreased to less than 2 ℃ at the end of the calculation. The simulation results were in good agreement with the measured value. When the inner surface of the steel pipe was treated as adiabatic boundary， it had relatively little influence on the temperature，which could make it possible to simplify the model roughly.

In view of the special working conditions of 350 ℃ high temperature， 17 MPa high pressure and multiple cycles of steam huff and puff in thermal production wells， the mechanical properties of TP110H during the first steam injection and multiple cycles of injection and production are studied. The test shows that TP110H generates thermal stress up to 764 MPa during thermal injection， and the material generates a small amount of plastic strain and stress relaxation effect. The string stress of 15 rounds of steam huff and puff is basically stable， and the strength and elongation at room temperature are basically unchanged before and after the experiment. The high-temperature yield strength at 350 ℃ decreases by about 50 MPa， the tensile strength decreases by about 13 MPa， and the elongation after fracture decreases by about 2%.

In order to explore the problems and improvement methods of the current production process of 37Mn5 steel for oil casing smelting in a steel mill， in this paper the whole process sampling analysis of two consecutive heats in the industrial production of the steel plant， including metallographic specimen， oxygen and nitrogen rod and refined slag sample， was conducted. After optimization and improvement， the final conclusions are as follows：（1）secondary oxidation occurs in different degrees in the LF refining and VD calcium treatment stage， specially feeding calcium line stage reaction is more violent ， which is easy to cause the secondary oxidation of the liquid steel and increasing of Ds inclusions.  By optimizing the refining deoxyoperation， the amount of calcium line feeding is reduced from 1.4-1.7 m/t to 0.95 m/t， and all kinds of inclusions are grade ≤1.5， and the qualified rate is 100%；（2） the composition analysis of refining slag shows that the residue components in the ternary phase diagram are all outside the liquid phase region， which results in poor melting performance and poor liquidity of the refining slag. By increasing SiO ₂ in the slag from to 9%-12%， Al ₂O ₃ to 25%-30%， and controlling the binary alkalinity at 5-8， it can improve the melting and fluidity of the slag， strengthen the coverage capacity of the slag， and effectively prevent secondary oxidation；（3） compared to the VD stage， the oxygen and nitrogen content in the tundish casting stage is basically stable， but the number of inclusions has been increased to a certain extent， and the growth rate of the inclusions is far higher than the endogenous rate of the inclusion， therefore， the source is from slag rolling， the smooth casting of the tundish shall be kept， at the same time to avoid the occurrence of dropping off slag phenomenon of the ladle.

Microstructure and properties of Φ457 mm×70 mm 12Cr1MoVG steel pipe （/% ： 0.13C， 0.21Si， 0.56Mn， 1.07Cr， 0.31Mo， 0.20V， 0.008P， 0.004S， 0.02Ni， 0.004Cu， 0.012 4Al） after 1 000 ℃ normalizing plus using water mist accelerated cooling and 740 ℃ tempering were studied by means of microstructure observation， tensile test ， impact test at room temperature， hardness test and high temperature durability test. The results showed that the microstructure consisted of ferrite and bainite， with the volume of bainite accounting for 65%， and the grain size of 7-5 grade. Yield strength was 416 MPa， tensile strength was 575 MPa， impact energy at room temperature was 206-244 J， brinell hardness was 187HBW. The endurance strength under 575 ℃×10 ⁵ h was 86 MPa. It lasted 51 480 hours at 575 ℃/100 MPa unbroken. After 27 198 hours， it cracked under 575 ℃/120 MPa， and the crack originated from grain boundary creep pores， no serious spheroidization was found in the bainite matrix surrounding. The structure stability was excellent.

During the production of large-sized P92 ferrite heat-resistant seamless steel pipe by rotary piercing process,the inner surface of the steel pipe is prone to produce small cracks. Through metallographic analysis,high-temperature phase transformation calculation and high-temperature heating test, the studies show that because of the higher heating temperature and the longer heating time,which increases the surface oxidation and decarburization,during the heating process of the P92 billet with a through hole in the center make a large number of high temperature δ ferrite phases near the inner wall and then the cracks generate and propagate around the δ Ferrite phases at the subsequent process of rotary piercing. According to the mechanism of internal surface cracks,through the control of the Cr＜13%,Ni _eq＜4% for P92 pipe chemical composition, the lowering of the billet heating temperature from 1220-1250 ℃ to 1190-1220℃,and the improvement parameters of roll speed,roll distance and the piercing point,the problem of cracks on the internal surface of large-diameter P92 seamless steel pipe is effectively solved,and the yield and production efficiency of P92 seamless steel pipe are improved.

The causes and practical effects of macrostructure “bubbles” in WB36 thick wall seamless steel pipe are analyzed and studied by means of scanning electron microscope,magnetic particle and ultrasonic flaw detection and performance test. The results show that the main reasons for the formation of macrostructure bubbles are poor deoxidation,high pouring temperature,and damp of ladle and refractory materials etc,the bubbles are short linear dark stripes at the macro, and circular or elliptical holes in the micro,it is mainly distributed near the inner wall to 1/2 wall thickness of the steel pipe corresponding to ingot head near hot top. Slight bubbles cannot be detected by magnetic particle,penetration and ultrasonic flaw detection,which has little impact on the mechanical properties of the steel pipe at room temperature. With controlling casting temperature of WB36 steel below 1590℃,holding time of VD refining at 67 Pa should not be less than 15 min,and moisture content of heating agent and thermal insulation material less than 0. 1%,the generation of macrostructure bubble defects can be effectively prevented.

As the diameter of the casing in the reservoir becomes larger and larger， and the well go deeper and deeper， the demand for strength and toughness of large-diameter perforating barrel becomes stronger. In order to ensure the safety of the perforating operation and improve the ability of the perforating barrel to resist external extrusion， it is necessary to improve the strength of the barrel and match higher impact toughness. Tianjin Pipe Corporation has developed big size Φ244.48 mm×11.99 mm high strength TP170P grade gun pipe. After heat treatment， the yield strength is over 1 200 MPa， and CVN 0 ℃ impact energy reaches to 110 J for longitudinal and 85 J for transversal. The gun pipe has good high temperature tensile performance and excellent low temperature impact toughness. At the high temperature condition of 300 ℃， the yield strength still reaches 1 056 MPa， and the low temperature impact toughness and brittle transition temperature is less than -40 ℃，this character assures the gun pipe can be used safely in the high temperature and ultra-deep well ， it has cold toughness in cold areas ， expanding the use range of the products. In addition， the steel grade has good resistance to hydrogen sulfide stress corrosion， hydrogen cracking ability and rolling thermal deformation ability.

SUS410 half martensitic stainless steel (0.08% ~0.15%C , 12.5%~13.5%Cr) is easy to produce inner surface defects in production of hot rolled thick-walled seamless steel tubes. The localization analysis of the crack defects at inner surface of 139.7 mm x 38.1 mm tube, the results shows that the thermoplastic decline of steel is caused by the large precipitation of δ-ferrite in steel near crack. During the deformation process, the deformation of the two-phase region is not coordinated, and finally cracks appear at the boundary between austenite and δ-ferrite. According to tlie Schaeffler phase diagram, the chemical composition of steel is redesigned, the Cr equivalent /Ni equivalent ratio decreases from 4.51 of originel defect tube to ≤ 3.0, the heating temperature of tube bloom decreases from 1200~1300℃ to 1180~1280 ℃ ,the internal surface defects are effectively solved, and the qualified rate of ultrasonic flaw detection increases to 97.9%.

The composition and process flowsheet of deep water oilfield large size deep subsea pipeline steel have been designed and developed. The experimental batch results of X65QO steel seamless tube show that: through the optimization of micro alloy composition (/% ：0.15Mo,0.04Nb,0.09V,0.06Ti),pilger tube rolling process,combined with 930 °C quenching and 670 °C tempering process,the yield strength of X65QO steel grade seamless steel tube for deep sea is ~500 MPa,the tensile strength is ~ 580 MPa, and the low temperature impact at -30°C is more than 300J, the CTOD ( Crack Tip Opening Displacement),welding properties and HIC (Hyrogen-Induced Cracking) properties are good, which fully meet customer requirements.

In order to study the normalizing cooling rate and the cooling uniformity of hypoeutectoid steel medium- and thick-walled seamless steel tube with wall thickness ≥30 mm, the water-air circulation cooling model is used for the normalizing structure and performance control of medium- and low-carbon Mn steel medium- and thick-walled seamless tube. Based on analysis on structure and properties of normalized steel tube with fen cooling, water fog forced cooling and water-air circulation cooling, the water-air circulation cooling process-immersing part of the steel pipe body in water and high speed rotating meanwhile, and controlling the depth of immersion, the rotation speed of steel tube and the total cooling time, of medium- and thick-walled pipe, the performance of yield strength ≥500 MPa, -20℃ V-type impact energy≥100 J based on the stable structure of ferrite + pearlite are obtained.

The Φ219 mm x 20 mm seamless tube of 09MnNiD steel (/% ；0.07 ~ 0.10G,0. 25 ~ 0.35Si, 1.35〜1.40Mn,0.49 〜0.51Ni,0.020 ~O.O35A1, ≤0. 02Nb, ≤0.015P, ≤0.006S) has been produced by 20 t EAF—LF + VD→ ingot casting —► rolling Φ270 mm round billet—► cross piercing → CPE rolling tube—► online normalization. By con trolling EAF endpoint [C] ≤ 0.04% and [ P] W≤ 0. 008% , LF refining [S] ≤ 0.005% ,VD≤67Pa, 15 min, ingot cast steel overheating ≤ 45 °C , cooling rate of hot rolled piercing shell 30 ~70 P/min, and steel tube normalizing at 910 °C. The test results show that the microstructure is F + P, grain size grade 10, —70 °C impact energy KV2 3257 J, tensile strength 503 〜508 MPa,yield strength 354~356 MPa,and the chemical composition, mechanical properties, nondestructive testing meet the requirements of GB 150.2-2011 standard.

According to the requirements of SY/T 6952.2-2013 standard and working conditions of heavy oil thermal recovery wells, Daye Special Steel Co Ltd successfully produces a kind of grade 110SH-1 thermal recovery casing with high strength and toughness by using 0.9 ~ 1.2Cr-0.3 ~ 0.6 Mo-based low alloy + Nb-Ti-V respectively 0. 01 〜0. 05 composition design of microalloy to reduce the use of precious alloy and production cost. The Φ 177.8 mmx 9.19 mm seamless steel pipe is produced by process of "70 t EAF →LF + VDC→CM Φ230 mm bloom →CPE mill rolling→quenching and tempering heat treatment" , according to the test results it is defined that the quenching temperature 920 ℃, water cooling, tempering temperature 660℃ ,air cooling process. The results show that the conventional performance, high-temperature anticreep performance, full-size blasting, full-size crushing and other test results of the steel grade thermal recovery casing fully meet the requirements of SY/T 6952. 2-2013 industry standard.

The main material of common medical and industrial gas cylinders is 37Mn steel of Mn series. Normalizing treatment is mainly adopted for cylinder steel. However,the mechanical properties of normalized 37Mn cylinder steel are unstable ,and it yield strength and impact energy cannot meet setting in standards. In this paper, by adding Cr and N micro elements ,the chemical composition of microalloying 37Mn steel is /% ：0.34 ~0.38 C,0.20 ~0.27 Si, 1.60 〜1.70 Mn, 0.10 ~0.20 Cr,0.004 0 ~0.0090N,of normalized rolled;219mm x6mm steel tube,the yield strength≥530 MPa,tensile ≥750 MPa and impact energy 13.2J,fully meet the needs of customer.

Developmental 110SS steel Φ325 mm × 55 mm thick-wall seamless pipe ( /% ：0. 28 ~0.33C,0. 20 ~ 0.30Si, 0.60~1.00Mn, ≤0.015P, ≤0. 005S, 1. 20 ~ 1.45Cr,0. 65 ~0.85Mo,0.01 ~ 0.05Al, 0.01 ~0.05Ti, 0. 01 ~ 0. 05Nb,0. 01 ~0. 10V ) is produced by process of BOF-LF-RH-CC-ASSE1 rolling. By controlling BOF end point [C] ≥ 0. 03% , LF refining slag basicity 3. 0 ~4. 0, HR vacuum treating for ≥30 min, CC steel overheating ≤15 ℃ , continuous casting speed 0, 30 ~ 0. 50 m/min, steel pipe quenching temperature at 880 ℃ and tempering at 650 ℃ , the product inclusion size is less than 20 μm，yield strength is 760 ~820 MPa, at that time, the thick wall seamless steel pipe meets the requirements of hydrogen sulfide-proof.