1. Chemical composition analysis: chemical analysis method, instrumental analysis method
①Infrared C-S instrument: analyze ferroalloys, steelmaking raw materials, C and S elements in steel.
②Direct reading spectrometer: C, Si, Mn, P, S, Cr, Mo, Ni, Cn, W, V, Ti, B, Nb, As, Sn, Sb, Pb, Bi in bulk samples
③N-0 instrument: gas content analysis N, O
2. Seamless tube geometry and shape inspection:
① Steel pipe wall thickness inspection: micrometer, ultrasonic thickness gauge, no less than 8 points at both ends and record.
②Check the outer diameter of the steel pipe and the roundness of the bridge: caliper, vernier caliper, ring gauge, and measure the maximum and minimum points.
③ Steel pipe length inspection: steel tape measure, manual, automatic length measurement.
④Steel tube bending degree inspection: straightedge, level (1m), feeler gauge, thin wire to measure the bending degree of each meter and the bending degree of the whole length.
⑤ Inspection of the bevel angle and blunt edge of the end face of the steel pipe: square ruler, card board.
3. Seamless tube surface quality inspection:
① Manual visual inspection: lighting conditions, standards, experience, signs, steel pipe rotation.
a. Ultrasonic flaw detection UT:
It is more sensitive to the surface and internal crack defects of various materials with uniform materials.
b. Eddy current inspection (electromagnetic induction) is mainly sensitive to point-shaped (hole-shaped) defects.
c. Magnetic powder MT and magnetic flux leakage inspection: magnetic inspection, suitable for the detection of surface and near-surface defects of ferromagnetic materials.
d. Electromagnetic ultrasonic flaw detection: no coupling medium is required, and it can be applied to high temperature, high speed, and rough surface flaw detection of steel pipes.
e. Penetration inspection: fluorescence, coloring, detection of surface defects of steel pipes.
4. Seamless tube management performance inspection:
① Tensile test: measure stress and deformation, determine the strength (YS, TS) and plasticity index (A, Z) of the material, longitudinal, transverse sample pipe section, arc, circular sample (C10, (12.5) small diameter, Thin-walled large-diameter, thick-walled calibration distance.
②Impact test: CVN, notch C type, V type, work J value J/cm2 standard sample 10 × 10 × 55 (mm) non-standard sample 5 × 10 × 55 (mm)
③Hardness test: Brinell hardness HB, Rockwell hardness HRC, Vickers hardness HV, etc.
④Hydraulic test: test pressure, voltage stabilization time, p=2S8/D
5. Technical performance inspection of carbon steel tube :
① Flattening test: round sample C-shaped sample (S/D>0.15)H=(1+2)S/(x+S/D)
L=40~100mm unit length deformation coefficient=0.07~0.08
②Ring pull test: L=15mm without crack is qualified
③Flaring and hemming test: the taper of the top center is 30°, 40°, 60°
④Bending test: can replace flattening test (for large diameter pipe)
6. Metallographic analysis of seamless steel tube:
①High magnification inspection (microscopic analysis) non-metallic inclusions 100xGB/T10561 grain size: grade, grade difference
Organization: M, B, S, T, P, F, A-S
Decarburization layer: inner and outer
A method rating: Class A - Sulfide, Class B - Oxide, Class C - Silicate, D - Spherical Oxide DS Class
②Low magnification test (macro analysis): naked eye, magnifying glass below 10x
a. Acid etching inspection method, b. Sulfur seal inspection method (tube blank inspection, showing low cultured tissue and defects, such as looseness, segregation, subcutaneous air bubbles, turning skin, white spots, inclusions, etc.
c. Tower-shaped hairline inspection method: check the number, length and distribution of hairlines.
Medium carbon steel pipe with seamless is a carbon steel pipe with a carbon content of 0.25% to 0.60%. It includes most of the high-quality carbon structural steel and a part of ordinary carbon structural steel. Most of this type of steel is used to make various mechanical parts, and some are used to make engineering structural parts.
According to the chemical composition of steel, it can be divided into two categories: carbon steel and alloy steel .
Carbon steel is divided into: ① low carbon steel, carbon content is less than 0.25%; ② medium carbon steel, carbon content is 0.25% - 0.60%; ③ high carbon steel, carbon content is greater than 0.6%;
Medium carbon steel has good hot working and cutting performance, but poor welding performance. The strength and hardness are higher than those of low carbon steel, while the plasticity and toughness are lower than those of low carbon steel. Cold-rolled and cold-drawn materials can be used directly without heat treatment, or they can be used after heat treatment. The quenched and tempered medium carbon steel has good comprehensive mechanical properties. The highest hardness that can be achieved is about HRC55 (HB538), and σb is 600-1100MPa. Therefore, among various uses of medium strength level, medium carbon steel is the most widely used, in addition to being used as a building material, it is also widely used in the manufacture of various mechanical parts.
Medium carbon steel pipe belongs to hypoeutectoid steel, and its annealed structure is pearlite and ferrite. As the carbon content in the steel increases, the amount of pearlite in the microstructure increases, while the amount of ferrite decreases. The quenched structure of steel with carbon content greater than 0.40% is martensite; when carbon content is greater than 0.40%, there is a small amount of retained austenite in addition to martensite, and the amount of retained austenite increases with the increase of carbon content in the steel.
Heat treatment of medium carbon steel:
The final heat treatment methods of medium carbon steel include quenching and tempering, low temperature tempering after quenching, low temperature tempering after high frequency quenching, isothermal quenching and medium temperature tempering after quenching.
(1) Quenching and tempering. The organization is tempered sorbite. This structure has good comprehensive mechanical properties, high strength, good plasticity and toughness. The quenched and tempered steel should have good hardenability to ensure uniform structure and performance on the entire section of the quenched and tempered part. Compared with alloy steel, carbon steel has poor hardenability, so it is only suitable for quenching and tempering of medium carbon steel parts with small section size.
(2) Low temperature tempering after quenching. The organization is tempered martensite, which has high strength and appropriate plasticity and toughness.
(3) Low temperature tempering after high frequency quenching. The microstructure of the high-frequency quenching layer is extremely fine hidden needle martensite, and tempered martensite is obtained after low-temperature tempering. This treatment can obtain similar effects to carburizing treatment. Quenching and tempering or normalizing are generally carried out before high-frequency quenching. Therefore, after high-frequency quenching and tempering, the core of the part has high strength, good plasticity and toughness, and its surface layer has high hardness and good wear resistance. In addition, the surface layer of high-frequency quenched parts produces compressive stress, which has a high fatigue limit and a long service life.
(4) isothermal quenching. The organization is bainite, which has high strength and good plasticity and toughness.
(5) Temper at medium temperature after quenching. The organization is tempered sorbite.
Husteel Industry Group is a leading seamless pipe and welded pipe manufacturer & supplier serving diverse industries with multiple types, grades, diameters and lengths of pipe.
Low carbon steel pipe with seamless refers to carbon steel pipe with a carbon content of less than 0.25%. Because of its low strength, low hardness and softness, it is also called mild steel. It includes most ordinary carbon structural steel and some high-quality carbon structural steel, most of which are used for engineering structural parts without heat treatment, and some are used for mechanical parts requiring wear resistance after carburizing and other heat treatment.
The annealed structure of low carbon steel pipe is ferrite and a small amount of pearlite, its strength and hardness are low, and its plasticity and toughness are good. Therefore, its cold formability is good, and cold forming can be carried out by methods such as hemming, bending, and stamping. This steel also has good weldability.
Low carbon steel generally refers to steel with a carbon content between 0.10 and 0.25%. This type of steel has low hardness and good plasticity, which is convenient for cold plastic deformation forming process, welding and cutting, and is often used in the manufacture of chains, rivets, bolts, shafts, etc.
Low carbon steel heat treatment:
Low carbon steel has a greater aging tendency, both quenching aging tendency and deformation aging tendency. When the steel is rapidly cooled from a high temperature, the carbon and nitrogen in the ferrite are in a supersaturated state, and it can also slowly form iron carbonitride at room temperature, so the strength and hardness of the steel increase, while the ductility and toughness decrease. This phenomenon is called quench aging. Low carbon steel will age even if it is not quenched and air cooled.
Low carbon steel produces a large number of dislocations after deformation, and the carbon and nitrogen atoms in the ferrite interact elastically with the dislocations, and the carbon and nitrogen atoms gather around the dislocation line. This combination of carbon, nitrogen atoms and dislocation lines is called the old Coriolis air mass (Korpal air mass). It will increase the strength and hardness of the steel while reducing the ductility and toughness, a phenomenon called deformation aging.
Deformation aging is more harmful to the plasticity and toughness of low carbon steel than quenching aging, and there are two obvious upper and lower yield points on the tensile curve of low carbon steel. From the appearance of the upper yield point to the end of the yield extension, a surface wrinkle band, called the Lüders band, appears on the surface of the specimen due to uneven deformation. Many stamping parts are often scrapped because of this. There are two ways to prevent it. A high pre-deformation method, the pre-deformed steel will also produce Lüders strips during stamping after being placed for a period of time, so the pre-deformed steel should not be placed for too long before stamping. The other is to add aluminum or titanium to the steel to form a stable compound with nitrogen to prevent the deformation and aging caused by the formation of Coriolis gas masses.
Spiral pipe (SSAW/SAWH) is also called spiral steel pipe or spiral welded pipe. It is made by rolling a low-carbon structural steel or low-alloy structural steel strip into a tube blank at a certain helical angle (called a forming angle), and then welding the tube seams. It can produce large diameter pipes from narrower strips. Its specifications are expressed by outer diameter * wall thickness, and the welded pipe should ensure that the hydraulic test, the tensile strength of the weld and the cold bending performance meet the requirements.
The production process of spiral steel pipe (SSAW) :
(1) The raw materials are strip coil, welding wire and flux. They must undergo strict physical and chemical inspections before being put into use.
(2) The head and tail of the strip are butted by single-wire or double-wire submerged arc welding, and automatic submerged arc welding is used for repair welding after rolling into a steel pipe.
(3) Before forming, the strip is leveled, trimmed, planed, surface cleaned and conveyed and pre-bending.
(4) The electric contact pressure gauge is used to control the pressure of the cylinder on both sides of the conveyor to ensure the smooth conveying of the strip.
(5) Adopt external control or internal control roll forming.
(6) The weld gap control device is used to ensure that the weld gap meets the welding requirements, and the pipe diameter, the amount of misalignment and the weld gap are strictly controlled.
(7) Both internal welding and external welding are used for single-wire or double-wire submerged arc welding by the American Lincoln welding machine, so as to obtain stable welding specifications.
(8) The welded seams are all inspected by an online continuous ultrasonic automatic flaw tester, which ensures 100% non-destructive testing coverage of the spiral welds. If there is a defect, it will automatically alarm and spray the mark, and the production workers can adjust the process parameters at any time accordingly to eliminate the defect in time.
(9) Use an air plasma cutting machine to cut the steel pipe into single pieces.
(10) After cutting into a single steel pipe, each batch of steel pipes must undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion status of the welds, the surface quality of the steel pipes and non-destructive testing to ensure that the pipe-making process is qualified Only then can it be officially put into production.
(11) The parts with continuous sonic flaw detection marks on the welds shall be re-examined by manual ultrasonic wave and X-ray. If they are indeed defective, after repairing, they shall undergo non-destructive inspection again until it is confirmed that the defects have been eliminated.
(12) The tube where the strip butt weld and the T-joint intersecting with the spiral weld are all inspected by X-ray television or filming.
(13) Each steel pipe undergoes a hydrostatic pressure test, and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. The test parameters are automatically printed and recorded.
(14) The pipe end is machined so that the verticality of the end face, the bevel angle and the blunt edge are accurately controlled.
Husteel Industry Group is a leading manufacturer and supplier of carbon steel pipe s (seamless and welded), supplying many types, grades, diameters and lengths of pipe to a variety of industries.
Due to the increasing bearing pressure of the pipeline, the use conditions are becoming more and more severe, and the service life of the pipeline should be extended as much as possible. In order to improve competitiveness, carbon steel tube manufacturers should research and innovate in what aspects, and what are the main development directions of spiral welded pipes?
(1) Production of large diameter thick-walled pipes to improve pressure resistance;
(2) Design and produce steel pipes with new structures, such as double-layer spiral welded pipes, that is, double-layer pipes are welded with strip steel with half the thickness of the pipe wall, which not only has higher strength than single-layer pipes of the same thickness, but also does not appear brittle failure;
(3) Develop new steel grades, improve the technical level of smelting technology, and widely use controlled rolling and post-rolling residual heat treatment technology to continuously improve the strength, toughness and welding performance of the pipe body;
(4) Vigorously develop coated pipes, such as coating the inner wall of the pipe with an anti-corrosion layer, which can not only prolong the service life, but also improve the smoothness of the inner wall, reduce fluid friction resistance, reduce wax accumulation and dirt, reduce pigging times, and reduce maintenance cost.
The spiral welded pipe plays a great role in conveying gas and transportation. With the planning and construction of a number of major pipeline projects at home and abroad, high value-added products such as large-deformation pipeline steel, high-strength hot-simmering elbows, and thick-specification low-temperature pipe fittings have shown good market competitiveness and large market demand. However, domestic enterprises are relatively slow in developing this series of products. They should develop high-value-added large-deformation pipeline steel, steel for hot simmering and bending, steel for low-temperature pipe fittings for pipeline stations, and X100 straight seam suitable for industrial applications as soon as possible. Submerged arc welded pipe, spiral seam submerged arc welded pipe and hot simmered spiral welded pipe.