• Alloy steel pipe
  • Ductile Iron Pipe
  • Carbon Steel Pipe
  • OCTG Steel Pipe
  • Stainless Steel Pipe
Product
Contact us

Address:Beijing Road, Yunhe District, Shengji Building #1802 ,Cangzhou City, Hebei

Contact:Lucky

Phone:86-15003171886

Email:sales@btsteelpipe.com


Production Of Stainless Steel Tube

Attention:     Issuing time:2019-11-18 14:36
Production of stainless steel tube
 
 
Generally speaking, the steel resistant to weak corrosive medium such as atmosphere, steam and water is stainless steel, and the steel resistant to chemical corrosive medium such as acid, alkali and salt is acid resistant steel. Stainless steel and acid resistant steel is called stainless steel for short. Chromium is the main alloy element. In addition, nickel, molybdenum, titanium, niobium and molybdenum are often added. Stainless steel pipes are mainly made of austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel and precipitation hardening stainless steel. Stainless steel pipe is widely used in petroleum, chemical industry, papermaking, chemical fertilizer, automobile, aircraft, power station, decoration and other fields.
 
 
The production methods of stainless steel seamless pipe can be hot rolling, hot extrusion, cold rolling and cold drawing. In recent years, due to the progress of continuous casting and rolling technology, as well as the application of various new welding technologies and nondestructive testing technology, the quality of stainless steel welded pipe has been continuously improved, which can partially replace stainless steel seamless pipe in various fields of use, and the price is about 20% lower than that of seamless pipe. At present, 50% of stainless steel pipes are welded and 50% are seamless.
 
 
Production characteristics of stainless steel seamless pipe
(1) plasticity. When martensitic stainless steel is single austenite structure at high temperature, it is not difficult to perforate, but when there are two-phase structure, the perforability decreases. The heating temperature of tube blank is generally 1130-1160 ℃ (center temperature), the temperature at the furnace end shall be less than 900 ℃, the finishing rolling temperature shall be higher than the critical point transition temperature, the low carbon temperature shall not be lower than 850 ℃, and the high carbon temperature shall not be higher than 925 ℃. With the increase of carbon content, the strength and hardness of martensitic stainless steel are increased, and the plasticity is reduced. When cold drawing, it should be drawn with core bar as far as possible, because it is easy to burst after empty drawing.
 
The high temperature plasticity of austenitic stainless steel is related to the residual α phase. The general plasticity decreases with the increase of α phase. In addition to α phase, there are other residual phases in austenitic stainless steel, such as various forms of carbides, intermetallic compounds, etc. These redundant materials have an effect on the plasticity of stainless steel, and the degree of influence depends on their quantity and state. When heated, the excess phase distributed on the grain boundary as a network, which will significantly deteriorate the plasticity of the metal. Austenitic stainless steel has low plasticity and large deformation resistance (see metal deformation resistance) at high temperature. When adopting cross rolling piercing (see two roll cross rolling piercing), special attention should be paid to selecting reasonable deformation parameters and temperature parameters. Austenitic stainless steel is a single-phase austenitic structure after solution treatment (usually after rolling residual heat quenching water), which is characterized by high σ B, low σ s, large ductility and toughness, and good cold deformation performance. Therefore, a large amount of pass deformation can be taken. However, the work hardening is very large during cold deformation, so the continuous processing performance is poor.
 
Ferritic stainless steel is a single phase structure with no critical transition point (phase transformation), so the grain growth is serious when the billet is heated for a long time and at a high temperature, which leads to a significant decrease in the plasticity of the steel. The highest heating temperature of tube blank is 1000-1060 ℃. The steel has good plasticity (perforation) in this temperature range. The heating temperature before cold drawing hammer head is 700-850 ℃, carburizing shall be prevented during heating, and water quenching shall be carried out after the hammer head. Due to the brittleness of ferritic chromium stainless steel at room temperature and poor cold working performance, it is easy to crack and pull out during cold drawing, so it is best to pull out at a certain temperature (see pipe warm drawing), and the pulling speed should not be too large. When the ferritic stainless steel tube is cold rolled, the deformation degree of the tube is not more than 40% ~ 48%. In the later passes (after surface preparation and heat treatment), the deformation degree can be increased to 55% '~ 65% according to the grain refinement degree. In order to avoid the crack of steel pipe during rolling, the temperature rise of pipe during rolling is favorable. Therefore, in most cases, emulsion cooling tools and metals are not used in rolling such steel pipe.
 
 
(2) deformation resistance. Both austenitic and martensitic stainless steels have high deformation resistance, high work hardening tendency, and low recrystallization speed at high temperature. Therefore, special attention should be paid to equipment and motor capacity when cold rolling such steels. Low carbon stainless steel with ferrite or semi ferrite has the same deformation resistance as that of ordinary carbon steel.
 
 
(3) spread. The width spread (transverse deformation) of stainless steel is larger, that of martensitic stainless steel is 1.3 times of that of carbon steel, that of austenitic stainless steel is 1.35-1.5 times, and that of ferritic stainless steel is 1.55-1.6 times. Therefore, it is necessary to control the transverse deformation and take a smaller ovality. The pass ovality of cold and hot-rolled pipes should be larger, and the small pass deformation should be taken to avoid the ears, etc. the wall thickness of stainless steel pipe is larger when there is no tension reducing (see pipe no tension reducing), and the pass ovality of reducing machine should be larger.
 
 
(4) sensitivity to stress. Ferritic stainless steel has brittleness at room temperature, high sensitivity to cold working stress, low sensitivity to hot rolling stress, and water quenching after rolling. Martensitic stainless steel is more sensitive to cracks, so it can not be cooled too fast after hot rolling, so it is usually used to cool in heaps. Austenitic stainless steel is less sensitive to cracks and can be quenched after hot rolling.
 
 
(5) thermal conductivity. The thermal conductivity of stainless steel is poor at low temperature, and the coefficient of linear expansion is larger than that of carbon steel. In order to ensure the heating quality, low temperature (< 800 ℃) and slow heating should be adopted.
 
 
(6) antioxidation. Due to the oxidation resistance of stainless steel, there is less scale formed by heating. However, the scale contains chromium and nickel oxides and is very dense, so it is difficult to pickling in cold working. HF + HNO3 is often used for pickling or alkali acid composite pickling.
 
 
(7) bonding tendency. The ferritic, AUSTENITIC FERRITIC and austenitic stainless steels are easy to stick to the roll during rolling, which reduces the surface quality of the steel pipe. The phenomenon of sticking roll can be reduced by using cast iron roll in hot rolling mill. In addition, it is very important to use cooling water to cool the roll.
 
 
The production characteristics of stainless steel welded pipe under φ 219mm are basically similar to that of high-frequency straight welded pipe with continuous roll forming, and pressure forming (UOE) or spiral welding (see spiral welded pipe) is adopted for above φ 219mm. After welding, the drawing method is used to produce capillary under φ 4.76mm. Welding methods include high frequency welding, tungsten inert gas welding (TIG or argon arc welding), laser welding, electron beam welding, etc. High frequency welding can not guarantee the welding quality of the weld, but the welding speed is high, which is suitable for the production of stainless steel welded pipe for general structure and decoration. The vast majority of stainless steel welded pipe production uses argon arc welding or combination of argon arc welding and plasma welding. The surface of stainless steel welded pipe for decoration shall be polished. The stainless steel welded pipe for chemical machinery and boiler heat exchanger shall be flat with internal welding prick. After solution treatment, the weld structure needs to be equipped with weld quality monitoring and non-destructive testing system. The production process of argon arc welding stainless steel welded pipe is as follows:
 
Strip Slitting, slitting, flattening, butt welding, looping, forming, argon arc welding, removing external weld pricks, cooling a certain diameter, eddy current testing, flying saw cutting
 
 
 
The cut stainless steel welded pipe can be divided into the following three situations according to the product use:
(1) the welded pipe that does not need heat treatment and drawing shall be straightened, leveled, hydraulically inspected, packed and warehoused;
(2) the welded pipe that needs heat treatment shall be degreased, bright heat treated, straightened, ultrasonically inspected, leveled, hydraulically inspected, packed and warehoused;
(3) the welded pipe that needs drawing shall be degreased, forged, annealed, straightened, pickled, lubricated and drawn, all heads shall be degreased, bright annealed Finishing, inspection, packaging and warehousing;
 
 
The new technology of stainless steel welding pipe includes multi torch welding with multiple electrodes (generally 3 electrodes), or the combination of argon arc welding and plasma welding. Multi torch welding is suitable for welded pipes with a wall thickness of more than 2mm. The welding speed is 3-4 times higher than that of single torch, and the welding quality is also improved. In addition, adding 5% - 10% hydrogen to argon and using high frequency pulse welding power supply can improve the welding speed; in order to ensure the welding quality, the automatic tracking device of welding torch to weld, automatic arc voltage control system (AVC) and computer-controlled welding process are used. The methods to remove the internal welding prick are as follows: (1) the internal wall air support technology, the internal wall is filled with inert gas of a certain pressure to hold the molten liquid drop, so as not to make it droop, so as not to form the welding prick; (2) the internal wall hammering technology is used for the pipe with the diameter of less than 30mm; (3) the internal wall rolling technology is suitable for the welded pipe with the diameter of more than 50mm; the decorative pipe shall be equipped with high-efficiency polishing equipment to improve the surface gloss of the stainless welded pipe Cleanliness.
 


HOME |  Company |  Product |  News |  KnowLedge |  Equipment |  Contact | 

Technical Support:CZWLWL.COM  Address:Beijing Road, Yunhe District, Shengji Building #1802 ,Cangzhou City, Hebei

Phone:86-15003171886   站长流量统计