How to harden seamless steel pipes

 The hardness of seamless steel pipes is usually determined based on the type of steel used and the heat treatment method. The following are some methods that may harden seamless steel pipes:

　　Heat treatment: By heating and cooling seamless steel pipes, their hardness can be enhanced. There are various heat treatment methods to choose from, such as normalizing, quenching, quenching, tempering, and so on.

　　Work hardening: Mechanical and deformation processes, such as rolling or stretching, can change the crystal structure of steel and enhance its hardness.

　　Adding alloy elements: Adding other metal materials to steel, such as titanium, chromium, nickel, can increase the hardness of seamless steel pipes.

　　It should be noted that heat treatment and work hardening may lead to increased brittleness of seamless steel pipes, so the correct method must be selected. It is recommended that you consult a professional to ensure proper operation before performing any processing.

The main features and advantages of Q345B seamless steel pipe include

 Excellent corrosion resistance: Q345B seamless steel pipe uses suitable alloy additives, which has excellent corrosion resistance, especially in corrosive media such as acid and alkali.

　　High strength: The tensile strength of Q345B steel is as high as 490MPa or more, and the strength of Q345B seamless steel pipe is also very high, which can be used in high-strength industrial fields.

　　Good plasticity: Q345B seamless steel pipe has good plasticity and toughness during processing, and can maintain its integrity in a diverse environment.

　　Smooth surface: Q345B seamless steel pipe has a smooth surface, without obvious burrs, and is generally not prone to heat transfer problems, which can ensure the quality of liquid or gas transportation.

　　Wide application range: Q345B seamless steel pipe is widely used in various fields, such as petrochemical, mining, construction, automobile, machinery manufacturing, and so on.

　　Q345B seamless steel pipe is also widely used in various fields. For example, it can be used in the petrochemical industry to transport chemical liquids, oil, and natural gas, as well as for processing equipment and pipeline systems. In the automotive, construction, and mechanical industries, Q345B seamless steel pipes are commonly used to produce various high-strength components, including bearings, machine structures, and transmission shafts. In summary, due to its various advantages, Q345B seamless steel pipe has found a large number of uses and applications in both industrial and civil fields.

Large-diameter big thickness Grade 20# seamless steel pipe

 Difference in allowable stress of large diameter thick wall 20 # seamless steel pipe at temperatures of 100 ℃ and 225 ℃

　　Allowable stress of No. 20 steel: allowable stress of No. 20 steel at 225 ℃: (16-36 mm) between 111-124 MPa; 117-131MPa between (6-16mm)

　　Allowable stress of 20 # steel at 100 ℃: At 150 ℃, the allowable stress of 20 # steel pipe is 130 MPa, and the allowable stress of 20 # steel forgings is 108 MPa

　　Seamless steel pipes are widely used. General purpose seamless steel pipes are rolled from ordinary carbon (C) plain structural steel, low alloy structural steel, or alloy structural steel, with the largest production, and are mainly used as pipes or structural parts for conveying fluids. 2. Supply is divided into three categories according to different uses:

　　A. Supplied according to chemical composition and mechanical performance;

　　B. Supply according to mechanical performance;

　　C. Supply according to hydraulic test. GB9948 seamless steel pipes are mainly used for the production of pneumatic or hydraulic components, such as air cylinders or oil cylinders, all of which are made of seamless pipes. The chemical components of precision seamless steel pipes include carbon C, silicon Si, manganese Mn, sulfur S, phosphorus P, and chromium Cr. GB5310 seamless steel pipes are divided into seamless steel pipes for structural purposes; Seamless steel pipe for conveying; Seamless steel tubes for boilers; High pressure seamless steel pipes for boilers. Seamless steel pipes are divided into circular and special-shaped pipes according to their cross-sectional shapes. The special-shaped pipes have various complex shapes, such as square, elliptical, triangular, hexagonal, melon seed, star, and finned pipes. Press

　　For steel pipes supplied in categories A and B, if they are used to withstand liquid pressure, they also need to undergo a hydraulic pressure test. 3. There are various types of seamless pipes for special purposes, such as seamless pipes for boilers, chemical and electric power, geological seamless steel pipes, and petroleum seamless pipes. Seamless steel pipes have hollow (zh ō ng k ō Ng) Cross section, widely used as a conduit for transporting fluids, such as oil, natural gas, coal gas, water, and some solid materials. Compared with solid steel such as round steel, steel pipes have a lower weight when their bending and torsional strength are the same, making them an economic cross-section steel. Extensively used for manufacturing structural and mechanical parts, such as petroleum drill pipes, automotive transmission shafts (composed of shaft tubes, expansion sleeves, and universal joints), bicycle frames, and steel scaffolds used in architectural construction. The use of steel pipes to manufacture circular parts can improve material availability, simplify manufacturing processes, and save materials and processing hours, Steel pipes have been widely used for manufacturing.

Specifications of steel grit

 Specifications of steel grit

Products		Steel Grit
Chemical Composition	C	0.70~1.20%
	Mn	0.35~1.20%
	Si	≥0.40
	S	≤0.05%
	P	≤0.05%
Microhardness		Normal:40~50HRC (377~509HV)
		Special:52~56HRC (543~620HV)
		Special:56~60HRC (620~713HV)
Hardness Deviation		Max Deviation ±3.0HRC
Microstructure		Tempered Martensite or Sorbite
Density		7.2g/cm3

What is the effect of shot peening on the material surface?

 　Shot peening is a process that impinges on the workpiece surface by using sand and iron shot sprayed at high speed to improve the mechanical properties of parts and change the surface state. It can be used to improve the mechanical strength of parts, wear resistance, fatigue resistance and corrosion resistance, and can also be used for surface extinction, skin removal and optimization of casting, forging, welding residual stress.

　　Shot peening process is the process of spraying a large number of projectiles to the surface of the parts, like countless small hammer hammer on the surface, therefore, the surface of metal parts produce very strong plastic deformation, the surface of the parts produce a certain thickness of cold hardening layer, known as the surface strengthening layer, the strengthening layer will significantly improve the fatigue strength of parts.

The role of steel shot in the surface treatment of steel pipe

 With the development of economy, the steel pipe is widely used in the transportation industry of various chemical substances. The surface treatment of steel pipe is one of the key factors to determine the service life of the transportation pipe. In addition to coating type, coating quality and construction environment, the surface treatment of steel pipe also has a great influence on the life of anticorrosive layer. This is the steel shot, steel grit will come in handy.

　　Spray derusting is driven by high power motor jet blade high-speed rotation, so that abrasive sand, steel ball under the action of centrifugal force on the surface of the steel pipe spraying (throwing) treatment, so that not only can completely remove rust, oxides and dirt, but also under the action of abrasive fierce impact and friction force, steel pipe can also achieve the required uniform roughness. The mechanical adhesion between the anticorrosive layer and the surface of the pipe is enhanced not only by enlarging the physical adsorption on the surface of the steel pipe but also by spraying the steel pipe. Jetting is an ideal way to remove rust in pipeline. Shot blasting (sand) rust removal is mainly used for pipe inner surface treatment, shot blasting (sand) rust removal is mainly used for pipe outer surface treatment. Several problems should be paid attention to when using spray to remove rust.

　　Abrasives can be selected according to the hardness of the surface of the steel pipe, the original degree of rust, the required surface roughness, the coating type, etc. The mixture of steel sand and steel pellets is easier to achieve the ideal effect of rust removal. Steel shot can strengthen the steel surface, and steel sand can etch the steel surface. The abrasive mixture of steel sand and steel shot, usually the hardness of steel shot is 40 ~ 50HRC, the hardness of steel sand is 50 ~ 60HRC can be used for all kinds of steel surface, even if it is used in C and D grade rust steel surface, the rust removal effect is also very good.

　　The surface treatment of the steel pipe seriously affects the service life of the pipe, is also the most simple and direct treatment method, so we should strictly comply with the requirements of the anticorrosive layer specification on the surface of the steel pipe, and constantly explore, summarize and improve the surface treatment method of the steel pipe.

300 tons of Stainless Steel Pipes Shipped to Turkey

 300 tons of Stainless Steel Pipes Shipped to Turkey

　　Purchase date: December 17, 2022

　　Delivery date: January 27, 2023

　　Name of purchased product: Hot Rolled ASTM Stainless Steel Pipe

　　Quantity: 300 tons

　　Mode of transportation: sea transportation

　　Port of destination: DILISKELESI

Sealing treatment for leakage of stainless steel flange

 Leakage position and condition The bolts connecting the stainless steel flange on both sides of the DN150 valve body are leaking. Because the connection gap of the stainless steel flange is very small, it is impossible to inject sealant into the gap to eliminate the leakage. The leakage medium is steam, the leakage system temperature is 400~500 ℃, and the system pressure is 4MPA.

　　The sealing construction method is based on the site survey of the leakage site. In order to achieve limited sealing, the fixed clamp method is used to contain the leakage point to form a sealing cavity, and the sealant is injected to eliminate the leakage.

　　1. Fixture design

　　(1) Determination of fixture structure

　　① Contain the leakage point, and establish the sealing chamber between the stainless steel flange of the valve body and the stainless steel flange of the pipe connection nipple. In order to prevent re-leakage at the potential leakage of the gap between the valve body and the stainless steel flange due to pressure holding, an annular cavity is set at the junction of the clamp and the outer edge of the stainless steel flange of the valve body.

　　② During the injection process of reducing diameter stainless steel flange, the fixture is easy to move towards the side of small diameter stainless steel flange, so the limit measure of tooth contact clamping is adopted.

　　2. Sealant selection and dosage estimation

　　(1) TXY-18 # A sealant is selected according to the temperature of the leakage system and the characteristics of the leakage location. The sealant has excellent temperature resistance, medium resistance and injection process performance, is easy to establish uniform and dense sealing structure, and the sealing can maintain long-term stability.

　　(2) The amount of sealant is estimated to be 4.5KG at the leakage point on one side.

　　3. Construction operation

　　(1) During fixture installation, due to the tooth shape contact, the inner diameter of the tooth tip is small. During installation, it is necessary to knock the outer wall of the fixture around the ring to cause the tooth end deformation and clamp the limit.

　　(2) After the injection operation is completed, the clamp, valve body and stainless steel flange annular cavity are injected into the sealing cavity, and then the intermediate cavity is injected. During the injection process, the pressure should be balanced, and attention should be paid to refilling and compaction to prevent stress relaxation.

　　(3) After the sealant is cured, after the effect is observed, local supplementary injection and compaction shall be carried out to prevent stress relaxation, and then the injection hole shall be sealed.

Methods for increasing the heat resistance of stainless steel flanges

 What are the methods for increasing the heat resistance of stainless steel flanges?

　　1. A higher chromium content is required to ensure oxidation resistance to form a dense oxide film. The mass fraction of chromium that can maintain thermal stability at 800 ° C, 1000 ° C, and 1100 ° C is 10% - 12%, 22%, and 30%, respectively. The higher the Cr content, the stronger the oxidation resistance. The addition of alloying elements such as Al and Si to steel helps to enhance the impact of Cr. The surface of steel is formed as an oxide film with a dense structure and firmly binds to the surface of steel, such as alloy oxide films such as Cr2O3, Al2O3, and SiO2. The alloy oxide film has a good protective effect, which can extend the service life of steel or increase the service temperature. In stainless steel flanges, if the oxide film is mainly in the form of (FeCr) 2O3, its ability to resist sudden changes in temperature is most outstanding.

　　2. Measures to ensure thermal strength requirements a. Adding Ni to obtain a stable austenitic structure and using Mo and W solid solution strengthening to increase the bonding force between atoms. However, the addition of Mo is not conducive to antioxidant activity. b。 The formation of a second phase dominated by carbides (MC, MC6) should be appropriately increased in carbon content. C。 Add trace amounts of boron or rare earth to control grain size and enhance grain boundaries, such as heat-resistant austenitic stainless steel flange 0Cr15Ni25Ti2 MOAIVE.

　　3. High temperature embrittlement problem. Heat resistant stainless steel can produce various embrittlement phenomena during high-temperature hot working or long-term work, such as the tempering embrittlement of MoCr13 steel at about 550 ℃, the growth of high chromium ferrite steel, and the embrittlement of austenitic steel. Brittleness caused by precipitation of grain boundary carbides at 475 ℃ and brittleness of ferritic steels σ Phase precipitation brittleness exists even in high CrNi austenitic steels σ Phase precipitation brittleness. When using heat-resistant steel at high temperatures, consideration should be given to the possibility of embrittlement and high-temperature fatigue damage during long-term high-temperature work. Fatigue failure is usually caused by the formation of surface cracks or certain defects beneath the surface. Under the action of alternating load, the crack gradually propagates until it ruptures.

How to do a good job in rust removal of stainless steel elbows

 Stainless steel elbow plays a very important role in pipelines, but stainless steel elbow has a long service life and is inevitably rusty. After rusting, it not only causes damage to the pipeline, but also causes leakage problems, causing serious problems. Due to large economic losses, stainless steel elbows should be protected against rust.

　　Attention to corrosion protection of stainless steel elbows can also extend their service life. However, corrosion prevention practices for stainless steel elbows in different areas are not the same. In southern China, the air is humid, which is chemical hydrogen evolution corrosion. Water is one of the substances that make iron susceptible to rust, only when the oxygen in the air dissolves. In water, oxygen reacts with iron in the water environment to produce something called iron oxide, which is rust. Rust is a reddish brown substance. It's not as hard as iron. It's easy to fall off. After a piece of iron is completely rusted, its volume can expand by 8 times. If rust is not removed, spongy rust is particularly prone to absorbing moisture, which can accelerate corrosion of stainless steel elbows. Therefore, in southern China, due to the impact of humid climate, heavy corrosion protection must be adopted for stainless steel elbows.

Four common derusting methods for spiral welded steel pipes

 1. Cleaning: use solvent and emulsion to clean the steel surface to remove oil, grease, dust, lubricant and similar organic matters, but it can not remove rust, oxide skin, welding flux, etc. on the steel surface, so it is only used as an auxiliary means in anti-government operations.

　　2. Acid cleaning: generally, chemical and electrolytic methods are used for acid cleaning. Only chemical acid cleaning is used for pipeline corrosion prevention, which can remove oxide scale, rust and old coating. Sometimes it can be used as the re-treatment after sand blasting and rust removal.

　　Although chemical cleaning of spiral welded steel pipe can make the surface reach a certain degree of cleanliness and roughness, its anchor pattern is shallow and it is easy to pollute the surrounding environment.

　　3. Tool derusting: mainly use tools such as wire brush to polish the steel surface to remove loose oxide scale, rust, welding slag, etc.

　　The derusting of hand tools can reach Sa2 level, and the derusting of power tools can reach Sa3 level. If the steel surface of spiral welded steel pipe is attached with solid oxide scale, the derusting effect of tools is not ideal, and the depth of anchor pattern required by anti-corrosion construction cannot be reached.

　　4. Spray derusting: spray derusting is to drive the spray blade to rotate at a high speed through a high-power motor, so that abrasive such as steel shot, steel sand, iron wire segment, minerals and other abrasives can spray the surface of the spiral welded steel pipe under the strong centrifugal force of the motor. It can not only completely remove oxides, rust and dirt, but also achieve the required uniform roughness of the spiral welded steel pipe under the strong impact and friction force of the abrasive.

　　After spray derusting, it can not only expand the physical adsorption of the pipe surface, but also enhance the mechanical adhesion between the anti-corrosion coating and the pipe surface. Therefore, spray derusting is an ideal derusting method for pipeline corrosion prevention.

　　Generally speaking, shot blasting is mainly used for inner surface treatment of pipes, and shot blasting is mainly used for outer surface treatment of spiral welded steel pipes.

　　During the production process, the relevant technical indicators of rust removal shall be strictly required to prevent the secondary damage to the spiral welded steel pipe caused by operation errors. After the removal of rust, the appearance of the spiral welded steel pipe will be smoother than that before the removal of rust. The removal of rust from the spiral welded steel pipe is a frequently used technology in the steel pipe industry.

 

The main factors affecting the internal hole finish of cold-drawn seamless steel pipe are as follows:

1. Pungent

　　The manufacturer's experience in piercing is not mature, the piercing temperature is not controllable, the piercing equipment is short, and the uneven heating of round steel causes large temperature difference inside and outside the steel pipe, forming pits, pits, peeling, etc., And the smoothness is not good. PMC has a slender perforating furnace, and the steel pipe is evenly heated.

　　2. Cold drawing die

　　There are defects in the cold drawing die itself, resulting in poor internal finish of the finished seamless pipe. PMC adopts professional customized precision molds with high precision and good internal and external surface quality of the finished products after cold drawing.

　　3. Pickling

　　Due to the strict environmental protection requirements in recent years, many manufacturers have no pickling process and can only be processed outside without professional experience. However, there is no data accumulation on the pickling time of steel, so the processing plant is allowed to process at will. The internal impurities of the cold-drawn seamless pipe cannot be thoroughly cleaned, or there are too many acids to form pits and pits. Since its establishment, PMC has a fully closed environmental protection pickling tank. After more than ten years of data accumulation, different steel grades have different pickling methods and times, which can ensure the internal hole finish.

What is the purpose of Q345C seamless steel pipe

 　Q345C seamless steel pipe is a kind of seamless steel pipe. Alloy pipe is divided into seamless pipe for structure and high-pressure heat-resistant alloy pipe.

　　It is mainly different from the production standard and industry of alloy tube. The mechanical function of Q345C alloy tube is modified by annealing and tempering. Meet the required processing conditions. Its function is higher than that of the ordinary seamless steel pipe. The chemical composition of the alloy pipe contains more Cr. It has the function of high temperature resistance, low temperature resistance and corrosion resistance.

　　The common carbon seamless pipe does not contain alloy components, and may have few alloy components. The reason why alloy pipes are widely used in petroleum, aerospace, chemical, power, boiler, military and other industries is that the mechanical functions of alloy pipes are changed and adjusted.

　　① No matter what steel pipe is carbon steel pipe, it is just that the carbon content of steel pipes of different specifications is different, and whether other trace elements are added to form steel pipes with special performance, such as stainless steel pipes

　　② Ordinary carbon steel pipes are very easy to rust in humid and corrosive environments, so surface treatment is usually required. The general treatment includes galvanizing, plastic plating, painting anti-corrosion paint, etc. Galvanizing is divided into hot galvanizing and cold galvanizing. The processing process is different. Hot galvanizing has better corrosion resistance and longer service life than cold galvanizing, but the price is high

　　③ Steel pipes are divided into welded steel pipes and seamless steel pipes according to different processing technologies. Generally, the steel pipes we use are welded steel pipes, and the seamless steel pipes are rarely used. Please refer to the design requirements, design documents, or consult the designer.

Analysis and Preventive Measures of Cold Working Cracks in Seamless steel pipes

 Seamless steel pipes are mostly medium carbon and high carbon alloy steels. After quenching, some undercooled austenite does not convert to martensite and remains in service as residual austenite, affecting service performance. If placed below zero degrees Celsius and continued cooling, martensitic transformation of residual austenite can be promoted. Therefore, the essence of cold treatment is to continue quenching. The superposition of room temperature quenching stress and zero quenching stress forms cold treatment cracks when the pile response force exceeds the strength limit of the material.

　　Preventive measures:

　　(1) After quenching and cold treatment of seamless steel pipes, placing them in boiling water for 30-60 minutes can eliminate 15% to 25% of the internal quenching stress, stabilize the residual austenite, and then conduct conventional cold treatment at - 60 ℃ or deep cold treatment at - 120 ℃. The lower the temperature, the more residual austenite can be transformed into martensite, but it is impossible to complete the transformation. The experiment shows that the residual austenite is about 2% - 5%. It is necessary for a press to retain a small amount of residual austenite to relax the stress and play a buffering role. Due to the softness and toughness of residual austenite, it can partially absorb the energy of rapid expansion of martensite and alleviate transformation stress;

　　(2) After the cold treatment is completed, take out the seamless steel pipe and heat it in hot water, which can eliminate 40% - 60% of the cold treatment stress. After the temperature rises to room temperature, it should be tempered in a timely manner. The cold treatment stress is further eliminated to avoid the formation of cold treatment cracks and obtain stable microstructure and properties. Ensure that seamless steel pipe products do not deform during storage and use.

ASME B36.10M Standard for Hot Rolled Seamless Steel pipes

　Welded and seamless steel pipes

　　Range

　　This standard covers the standardization of the dimensions of welded and seamless rolled steel pipes for high, low, and various pressure applications. The term "pipe" used is different from the term "tube" and is applicable to commonly used tubular products of pipeline and pipe system sizes. The outer diameter of pipes with "PIPE" specifications less than or equal to NPS12 (DN300) is larger than their corresponding dimensions. On the contrary, the outer diameter values and corresponding dimensions of the tube "TUBE" are the same for all specifications.

　　size

　　The dimensions of all pipes are identified by the nominal pipe diameter.

　　The production of tubes NPS ⏵ (DN6) through NPS 12 (DN300) (including NPS 12) is based on a standardized outer diameter (OD). This OD was initially selected to facilitate a standard outside diameter pipe having a wall thickness with periodic characteristics, which would have an inside diameter (ID) approximately equal to the nominal pipe diameter. Although there is no such relationship between the current standard thickness and the outer diameter and nominal pipe diameter, these nominal pipe diameters and standard OD continue to be used as "standards". The production of pipes larger than and equal to NPS 14 (DN350) is based on OD corresponding to the nominal pipe diameter.

Methods for increasing the heat resistance of stainless steel flanges

 What are the methods for increasing the heat resistance of stainless steel flanges?

　　1. A higher chromium content is required to ensure oxidation resistance to form a dense oxide film. The mass fraction of chromium that can maintain thermal stability at 800 ° C, 1000 ° C, and 1100 ° C is 10% - 12%, 22%, and 30%, respectively. The higher the Cr content, the stronger the oxidation resistance. The addition of alloying elements such as Al and Si to steel helps to enhance the impact of Cr. The surface of steel is formed as an oxide film with a dense structure and firmly binds to the surface of steel, such as alloy oxide films such as Cr2O3, Al2O3, and SiO2. The alloy oxide film has a good protective effect, which can extend the service life of steel or increase the service temperature. In stainless steel flanges, if the oxide film is mainly in the form of (FeCr) 2O3, its ability to resist sudden changes in temperature is most outstanding.

　　2. Measures to ensure thermal strength requirements a. Adding Ni to obtain a stable austenitic structure and using Mo and W solid solution strengthening to increase the bonding force between atoms. However, the addition of Mo is not conducive to antioxidant activity. b。 The formation of a second phase dominated by carbides (MC, MC6) should be appropriately increased in carbon content. C。 Add trace amounts of boron or rare earth to control grain size and enhance grain boundaries, such as heat-resistant austenitic stainless steel flange 0Cr15Ni25Ti2 MOAIVE.

　　3. High temperature embrittlement problem. Heat resistant stainless steel can produce various embrittlement phenomena during high-temperature hot working or long-term work, such as the tempering embrittlement of MoCr13 steel at about 550 ℃, the growth of high chromium ferrite steel, and the embrittlement of austenitic steel. Brittleness caused by precipitation of grain boundary carbides at 475 ℃ and brittleness of ferritic steels σ Phase precipitation brittleness exists even in high CrNi austenitic steels σ Phase precipitation brittleness. When using heat-resistant steel at high temperatures, consideration should be given to the possibility of embrittlement and high-temperature fatigue damage during long-term high-temperature work. Fatigue failure is usually caused by the formation of surface cracks or certain defects beneath the surface. Under the action of alternating load, the crack gradually propagates until it ruptures.

How to do a good job in rust removal of stainless steel elbows

 　Stainless steel elbow plays a very important role in pipelines, but stainless steel elbow has a long service life and is inevitably rusty. After rusting, it not only causes damage to the pipeline, but also causes leakage problems, causing serious problems. Due to large economic losses, stainless steel elbows should be protected against rust.

　　Attention to corrosion protection of stainless steel elbows can also extend their service life. However, corrosion prevention practices for stainless steel elbows in different areas are not the same. In southern China, the air is humid, which is chemical hydrogen evolution corrosion. Water is one of the substances that make iron susceptible to rust, only when the oxygen in the air dissolves. In water, oxygen reacts with iron in the water environment to produce something called iron oxide, which is rust. Rust is a reddish brown substance. It's not as hard as iron. It's easy to fall off. After a piece of iron is completely rusted, its volume can expand by 8 times. If rust is not removed, spongy rust is particularly prone to absorbing moisture, which can accelerate corrosion of stainless steel elbows. Therefore, in southern China, due to the impact of humid climate, heavy corrosion protection must be adopted for stainless steel elbows.

Small diameter seamless steel pipe

 In general, seamless steel pipes used in daily life are of normal caliber, and small caliber seamless steel pipes are used in some special places. Today, I'd like to introduce the relevant knowledge of small-diameter seamless steel pipe, which will help you better use this kind of pipe in the future. Generally speaking, seamless steel pipes with small outer diameter are collectively referred to as small-diameter seamless steel pipes, but there is still a specific range. Generally, those with steel diameter less than 89mm and more than 4mm can be called small-diameter seamless steel pipes.

　　In most cases, small-diameter seamless steel pipe is also used as a pipe for conveying fluid. Compared with solid steel such as round steel, it is light in weight when its bending and torsional strength is the same. It is a kind of economic section steel, which is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, steel scaffolds used in construction, etc.

　　The general specification of small-diameter seamless steel pipe is that its outer diameter is between 6-89mm, and its diameter is relatively small. The wall thickness of 1-12mm can also be divided into small-diameter thick wall seamless pipe and small-diameter thin-wall seamless pipe. Its weight calculation formula: [(outer diameter - wall thickness) * wall thickness] *0.02466 = kg/ meter (weight per meter)

　　In order to produce seamless pipes with smaller size and better quality, cold rolling, cold drawing or a combination of the two methods must be used. Cold rolling is usually carried out on a two high mill. Steel pipes are rolled in an annular pass consisting of a variable cross-section circular groove and a fixed conical plug. Cold drawing is usually carried out on a single chain or double chain cold drawing machine, that is, the hot tube blank is placed in a closed extrusion cylinder, and the perforated rod moves together with the extrusion rod to extrude the extruded part from the smaller die hole, so that small-diameter seamless steel pipe can be produced.

Desulfurization process of carbon steel elbow

 Desulfurization in oxygen converter is difficult and uneconomical. In recent years, the supply of high-quality metallurgical coke is insufficient, the sulfur content of coke is the highest, and the sulfur content of heavy oil injected to strengthen blast furnace smelting is also high, which makes the quantity and cost of low-sulfur molten iron meeting the requirements of steelmaking increasingly problematic. The practice has proved that it is a good way to solve the above contradiction to take off the bowl of molten iron outside the furnace between the blast furnace and the converter.

　　It can improve the technical and economic indicators of ironmaking and carbon steel elbow at the same time. It is particularly important for the converter to simplify operation and realize automatic control. It is developing rapidly in many countries. The basic principle of desulfurization outside the furnace is the same as that of desulphurization inside the furnace. That is to use elements or compounds with greater affinity to sulfur than iron and sulfur to transform iron sulfide into more stable, rarely soluble or completely insoluble sulfide in molten iron; At the same time, create good kinetic conditions to accelerate the diffusion of sulfur in molten iron to the reaction area and expand the reaction area between desulfurizer and molten iron. ASTM 440 is called high-strength carbon steel elbow.

　　It includes Mn-Cu high-strength low-alloy steel profiles, plates and bars. It is mainly used for riveting or bolting bridges and buildings. Generally, welding is not suitable. However, the material can also be welded after taking certain measures. Since it contains a minimum of 0.2% Cu, its atmospheric corrosion resistance is about twice that of carbon structural steel without Cu. The minimum yield strength of steel plate with thickness less than 19mm is 345MPa.

Desulfurization process of carbon steel elbow

 Desulfurization of carbon steel elbow in oxygen converter is difficult and uneconomical. In recent years, the supply of high-quality metallurgical coke is insufficient, the sulfur content of coke is the highest, and the sulfur content of heavy oil injected to strengthen blast furnace smelting is also high, which makes the quantity and cost of low-sulfur molten iron meeting the requirements of steelmaking increasingly problematic. Practice has proved that the carbon steel elbow is a good way to solve the above contradictions by taking off the bowl of molten iron outside the furnace between the blast furnace and the converter.

　　It can improve the technical and economic indicators of ironmaking and carbon steel elbow at the same time. It is particularly important for the converter to simplify operation and realize automatic control. It is developing rapidly in many countries. The basic principle of desulfurization outside the furnace of carbon steel elbow is the same as that of desorbing inside the furnace. That is to use elements or compounds with greater affinity to sulfur than iron and sulfur to transform iron sulfide into more stable, rarely soluble or completely insoluble sulfide in molten iron; At the same time, create good dynamic conditions to accelerate the diffusion of sulfur in molten iron of carbon steel elbow to the reaction area and expand the reaction area between desulfurizer and molten iron. ASTM 440 is called high-strength carbon steel elbow.

　　It includes Mn-Cu high-strength low-alloy steel profiles, plates and bars. It is mainly used for riveting or bolting (non welded) bridges and buildings. Generally, welding is not suitable. However, the material can also be welded after taking certain measures. Since it contains a minimum of 0.2% Cu, its atmospheric corrosion resistance is about twice that of carbon structural steel without Cu. The minimum yield strength of steel plate with thickness less than 19mm is 345MPa.

Analysis and preventive measures for cold working cracks of seamless steel pipes

 Most seamless steel pipes are medium carbon and high carbon alloy steel. After quenching, some undercooled austenite does not change into martensite, and remains in service as residual austenite, which affects the service performance.

　　If it is cooled below zero, the martensitic transformation of retained austenite can be promoted. So the essence of cold treatment is to continue quenching. The room temperature quenching stress and zero quenching stress are superimposed. When the reactor response force exceeds the strength limit of the material, a cold treatment crack is formed.

　　Precautions:

　　(1) After quenching and cold treatment, the seamless steel pipe can be placed in boiling water for 30-60 minutes to eliminate 15% - 25% of the internal quenching stress, stabilize the residual austenite, and then carry out conventional cold treatment at - 60 ℃ or - 120 ℃ cryogenic treatment. The lower the temperature, the more residual austenite will be transformed into martensite, but it is impossible to complete the transformation. The experiment shows that the residual austenite is about 2% - 5%. It is necessary for the press to retain a small amount of residual austenite to relax the stress and play a buffering role. Because the residual austenite is soft and tough, it can partially absorb the energy of rapid expansion of martensite and relieve the transformation stress;

　　(2) After the cold treatment, take out the seamless steel pipe and heat it in hot water, which can eliminate 40% - 60% of the cold treatment stress. Temper in time after the temperature rises to room temperature. The cold treatment stress is further eliminated to avoid the formation of cold treatment cracks and obtain stable microstructure and properties. Ensure that seamless steel pipe products do not deform during storage and use.

Pre-welding process of LSAW steel pipe

 The pre-welding technology of LSAW steel pipe consists of three technical supports: pre-welding process, pre-welding equipment and common problem treatment.

　　In the pipeline construction, the long-distance oil and gas pipeline is developing towards large-diameter, high-pressure transportation and thick-walled subsea pipeline. More and more pipelines require the use of LSAW steel pipes. With the introduction and production of LSAW steel pipe production line, it is particularly important to master advanced LSAW welding technology.

　　1. Pre-welding process of LSAW steel pipe

　　During pre-welding, the steel pipe blank shall be welded first, and then the continuous gas shielded welding shall be carried out. At the same time, the weld state and welding quality shall be monitored and fed back. The specific process is as follows: the inlet roller table receives the tube blank → adjusts the opening position of the tube blank → the conveying device delivers the tube blank → the tube blank closes → confirms the joint quality → the welding gun drops to prepare for welding → starts the laser tracker to track → opens the protective gas and cooling water valve → starts the welding (the tube blank is fed at the welding speed) → stops the welding at the end of the arc extinguishing → lags off the protective gas → the welding gun rises and returns → the tube blank is transferred to the next process. At this point, a pre-welding cycle is completed.

　　In the above process, adjusting the opening position of the tube blank means adjusting the opening seam position to the required position, which can be done through the camera monitoring system in the electronic control system.

　　To confirm the quality of the joint is to confirm the misalignment of the joint and the gap of the joint. Only after confirmation can the joint be tracked and welded.