1, Physical quality comparison between Chinaseamless steel pipe and the world advanced level

1.1,The mainsteel standard quality indicators compared with foreign advanced level

Seamless steel quality indicators include the level of the chemical composition control, precision geometry, mechanical properties, process performance, and special service conditions under special requirements.

In recent years, the new system (Amendment) increased the standard of seamless steel set of international standards and foreign advanced standards, tantamount to the adoption of international standards and foreign advanced standards of the national standard is gradually increasing. Provided solely from the standard technical indicators, domestic seamless precision and geometry of the same or similar international advanced level, chemical composition of the deviation is almost the same (Table 1). However, the stability of performance, especially steel quality level there are some gaps in kind, mainly in the inclusion of harmful elements and the lower level of control, poor uniformity of steel microstructure, mechanical properties of fluctuations in the value of large, difficult to adapt well to temperature, pressure, acidity and other conditions of service under special circumstances and so on.

Table 1 Several commonly used main indicators of domestic and foreign steel standard comparative table

1.2, Analysis of the gap between domestic and foreign advanced level on the physical quality of steel

While most of China seamless steel pipe standards have been with foreign advanced level, but the physical quality of steel (including: surface quality, performance, stability, uniformity and composition control the level of harmful elements, etc.) there is a gap compared with foreign products. The main reason causing this gap, not only the technical and management gaps, but also other gaps are still following.

1.2.1 Billet metallurgical quality gap

Currently, in addition to several large-scale professional production of seamless steel pipe manufacturer has an excellent Self blank condition, the manufacturers of some tone rolled billet market to buy only from the tube, even the confession tube business, its smelting, refining capacity and the control of harmful elements in steel by varying levels. Tube provided by some companies of different chemical composition between furnace batches larger deviations, especially in the tube P, S content and quality products abroad, a difference of almost an order of magnitude compared. Inclusion content and residual elements of the control level there are obvious gaps. The tube eating "hundreds of rice" part of the seamless steel pipe plant, steel issue is even more prominent.

Seamless Steel Tube metallurgical quality of a great impact on the physical quality of the finished product, emphasizing the tube is to improve the metallurgical quality of steel purity and reduce the number of inclusions in steel, size, control, and the gas content of harmful elements and to reduce component segregation.

While product standards in developed countries such as API, ASME SA106/ASTM A106, ASME SA335/ASTM A335, ASME SA213/ASTM A213 in the chemical composition of the control of steel has not made very stringent requirements, but they are means through strict process control physical quality of their products to achieve a very high level and very stable. If some of the world-renowned oil well pipe, line pipe procurement of technical conditions, by controlling the content of aluminum or acid soluble aluminum and Al / N ratio to evaluate the level of molten steel deoxidation process, the gas concentration level and confirm whether nature of fine-grained steel; by controlling the Ca / S to ensure that the sulfur content of molten steel and to control the volume and shape of inclusions in the power plant boiler tubes and pipes for pressure vessels in the technical conditions, with high levels of low-temperature impact energy requirements and limitations of [Pb] [Sn] [As] [Sb] [Bi] to reduce the amount of steel in sulfur, phosphorus content and improve the cleanliness of molten steel.

Residual elements in steel copper, lead, tin, arsenic, antimony, bismuth mainly from scrap steel, steel solidification, the residual elements easy to gather in the grain boundary, the temperature temper brittleness in the area, the residual elements have sufficient ability to spread, and gradually within the crystal grain boundary segregation, leading to grain boundary embrittlement and reduce the mechanical properties of steel. Mainly reflects the thermal processing performance for the deterioration of steel, ductile - brittle transition temperature rises and the impact energy decreased, so China's exclusive possession of the corresponding tube and pipe product standards to increase the low times, inclusions, microstructure, Al / N requirements. Self domestic seamless steel billet production capacity of enterprises are the key internal control standards in its business management on species-specific provisions of the tube to allow the value of the residual element. But most enterprises because of the steel smelting equipment level is not high, especially lack of refining capacity, causing the molten steel is not enough clean, standards for residual elements can only reach the lower level and not very stable.

1.2.2 Supporting capacity lacking of steel pipe finishing area and heat treatment processes

As the surface quality of seamless steel tubes, geometry, mechanical properties are higher, so be (by) diameter seamless steel pipe after the cooling bed must also cooling, straightening, cutting heads, inspection, testing (grinding, hydraulic pressure test , NDT), anti-corrosion, packaging, printing and other finishing and testing processes. Seamless steel tubes for special purposes (such as oil casing, tubing, submarine pipelines, power station boilers and the military use of alloy pipe, high pressure gas cylinder tube), respectively related technical standards by heat treatment, sizing, thickening of the pipe end, pipe end sizing, pipe end threading, rust inhibitor and painted inside and outside the vehicle (ground) cut strips and other finishing processes.

Finishing and heat treatment process is to ensure that the important process is one of seamless quality of metal materials to explore and improve the performance potential of the life of seamless steel tubes, seamless steel pipe used to improve performance are an extremely important role. In general, the required high-end products and require more finishing heat treatment process, if the lack of processing capacity in these processes, process flow configuration poor or low level of equipment, are difficult to meet the requirements of producing high-quality steel.

Apart from a few large seamless steel pipe production enterprises, China has a considerable number of seamless enterprise zone equipment configuration finishing lower level, lack of heat capacity, and some companies do not even have steel heat treatment equipment. These processes for the upgrading of product quality and variety of restructuring plays an important role. The reason why some high value-added products of mass production is difficult, in addition to technical reasons, and these processes have great equipment, low-level configuration relationship.

2. Improve the billet quality, and increase the finishing and heat treatment processes of investment, the seamless steel pipe manufacturing power of China into the world

 As mentioned above, to improve the quality and attention to finishing tube and heat treatment processes the input area is to achieve the quality upgrading and varieties of steel products is one important way of structural adjustment.

As users of seamless steel pipe products, physical and chemical properties, processing performance, precision geometry, and the apparent quality requirements increase, seamless steel pipe production enterprises should be based on their product positioning, refining the system attaches great importance to the tube, steel pipe finishing lines, heat treatment line configuration. The steel finishing lines, heat treatment processing line and equipment levels to match the hot line for the production of high value-added products, and create favorable conditions for adjustment of product structure.

2.1, To improve the quality of tube metallurgy and continuous casting

 Self billet with seamless steel pipe production capacity of enterprises should strengthen the raw material supply chain management, procurement of raw materials for refining tube, we must uphold the principle of concentrate to ensure the stability of low-As, Sn high-quality supply of scrap steel and ore resources.

Improve the system, especially in hot metal pretreatment, smelting, refining molten steel system and equipment level and production capacity, through the use of high-quality scrap and high-quality hot metal to reduce the content of residual elements in steel to enhance steel cleanliness, good quality for the manufacture of seamless steel tubes to provide physical protection.

Electromagnetic stirring, level control, protection and pouring, LCR and other technologies to improve the continuous casting billet continuous casting in particular the large-diameter tube of the chemical composition uniformity and uniformity of the organization, reducing the casting tube crack improve the internal quality of continuous casting billet, tube should reach YB/4149 the level of a class of blanks. Slow cooling tube configured as required, surface cleaning, grinding and other equipment.

2.2, Device configuration to improve the level of the finishing area

Heat Pipe Line Finishing Line and many processes, the pipe straightening, cutting and chamfering, internal and external surface processing, heat treatment, nondestructive testing, protection and printing, packaging, finishing a second part of the pipe needed.

Steel heat treatment is an important means of mining the performance of steel pipe. The level of heat pipe assembly line configuration should ensure that the control requirements of steel heat treatment parameters to achieve automatic monitoring and adjustment of temperature. For those on the steel surface quality (surface finish, surface oxide scale), there are strict requirements of steel should be used in the furnace with protective atmosphere, its heat.

The role of straightening is to eliminate the rolling process, delivery, heat treatment and cooling process of bending steel produced, in addition to reducing the role of pipe ovality. Q125 and above with high strength and toughness of high strength casing, a continuous casing, expandable casing, and anti-carbon dioxide, hydrogen sulfide, such as corrosion of the casing and special threaded casing pipe on the residual stress after straightening, there are strict requirements . Therefore, under normal circumstances, to configure the warm and cold Jiao Jiao 2 sets of straightening machine. Steel for temperature correction, they should be the standard requires a temperature above 400 ℃ for straightening, and then place the tube can rotate the cooling bed for cooling, to prevent the steel produced in the subsequent cooling and then bending. To avoid straightening roller flattening of the pipe end, bite wounds, should be equipped with hydraulic quick roll straightening function, adjust the high precision and stable performance straightener.

Tube-side groove shape, blunt edge, cut the size of slope and ellipticity of the pipe end to reflect an important indicator of quality, especially in the construction line pipe due to welding operations and the need to improve the quality of welding of pipe end roundness and wall thickness accuracy , cut slope requirements are higher, the steel tube finishing line should be configured efficient sizing pipe end chamfering machine and milling equipment to pipe sizing rules round side, end milling, processing and other back groove.

Special threaded oil well pipes are widely used in deep and ultra deep, high pressure gas, heavy oil thermal recovery wells, directional wells, horizontal wells, severe corrosion well. Currently, the worldwide production of oil well pipes of special threaded and use of oil well pipes for more than 30% of the total, many famous foreign oil well pipe production plant has successively developed more than 100 patented technologies in the special connection threads. Although China has developed its own brand of special threaded oil well pipes, but because the market (especially the foreign market) is still limited degree of recognition, coupled with the exclusive features of a special connection thread, resulting in larger imports of such products. Thus, the domestic steel production enterprises should intensify the development of special oil well pipe threaded and marketing efforts, and the importance of supporting the processing equipment and capacity. .

Improve the steel quality inspection and nondestructive testing methods to test the products quality meets the requirements of an important means of product standards. In addition to the performance of steel mechanical properties and process performance, compactness, some products should also have some special physical properties, such as corrosion resistance (resistance to hydrogen sulfide corrosion, carbon dioxide corrosion resistance, corrosion resistance to chloride ion, etc.), high temperature performance, collapsing properties, welding properties. OCTG, line pipe supported not only by hydraulic test requirements and test purposes are not only testing the density of steel, but also the performance of one of the means test. Therefore, steel production enterprises should be based on product inspection requirements to establish the physical properties of the corresponding lab, product positioning configuration according to the ability of the hydraulic testing machine, perfect testing measures.

Non-destructive testing equipment is essential and important steel production line test equipment, the use of one or more combinations of tube testing method for online automatic detection of non-destructive flaw detection and wall thickness, has become in recent years, steel production, in particular the species-specific management tools must be produced. In recent years, various non-destructive testing of international standards on the increasingly stringent requirements more detailed testing in the pipe automatically put forward higher requirements, such as the oblique injury test tube with wall thickness by 10% of the depth of Φ3. 2 FBH calibration equipment to detect defects in laminated, steel production testing DAC curves, super-thick steel automatic testing and so on. All of these require not only testing the accuracy and reliability of the host device later, and ancillary equipment and the host of the match and the stability and non-destructive testing personnel skill levels are put forward higher requirements. Non-destructive testing of domestic enterprises in improving the capacity, should pay more attention has been testing the system and made the introduction of auxiliary matching problems and improve the detection accuracy and stability; to strengthen the technical training of NDT personnel to adapt to the rapid development of detection technology and user requirements improved.

3、Conclusion

With the rapid growth of China's output of seamless steel pipe, seamless steel quality level in China has made significant progress, most of the steel standards and advanced foreign standards has been, the physical quality has been improved. But the species was incomplete, unstable quality problems remain, the low-end products, excess capacity is very conspicuous contradictions, product structure adjustment task is very arduous.

Variety of domestic seamless steel pipe caused incomplete, unstable quality of the reasons, in addition to the technical and management gaps, the tube is not high quality and finishing, heat treatment line of low levels of incomplete or configuration is the main reason.

Seamless steel pipe production enterprises should be based enterprise product positioning, refining the system to the tube, steel finishing lines, heat treatment line and pipe inspection and testing equipment, the configuration enough attention, so that phase is equipped with hot wire, steel product structure for the realization of adjusted to provide protection.