Welded pipes are common pipes in gas pipelines. Pipes with a diameter greater than 426 mm (or 508 mm) are generally referred to as large-diameter welded pipes. According to the method of welding into pipes, they can be divided into spiral welded pipes and straight welded pipes. The straight seam welded pipe is formed by forming a hot rolled coil through a molding machine to deform the steel coil into a smooth cylindrical shape, and welding by using the skin effect of the high frequency current and the adjacent effect or the arc under the solder layer to make the blank The edge is heated and melted, and is fused under a certain pressing force, and finally cooled to form. The high-frequency straight seam welded pipe (ERW) in which the edge of the pipe blank is melted by high-frequency current is called a straight seam submerged arc welded pipe (LSAW). The main raw materials for straight seam welded pipes are low carbon steel hot rolled coils and hot rolled strips. They are widely used in petroleum, metallurgy, construction, coal, port, machinery and other industries for oil and gas transportation, low pressure water gas transportation, mining fluid transportation, belt type. Conveyor rollers, automotive drive shafts, etc.
Welded steel pipes, also called welded pipes, are steel pipes made by welding steel plates or strips after being crimped. The welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment, but the general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technology, the quality of welded joints has been continuously improved, the variety specifications of welded steel pipes have been increasing, and more and more fields have replaced Seam steel pipe. Welded steel pipes are divided into straight welded pipes and spiral welded pipes in the form of welds.
The blanks used for welded steel pipes are steel plates or strip steels, which are divided into furnace welded pipes, electric welding (resistance welded) pipes and automatic arc welded pipes due to different welding processes. Due to the different welding forms, it is divided into straight seam welded pipe and spiral welded pipe. Because of its shape, it is divided into round welded pipes and special-shaped (square, flat, etc.) welded pipes. Welded pipes are divided into the following varieties due to their different materials and uses:
GB/T3091-1993 (galvanized welded steel pipe for low pressure fluid transport). It is mainly used to transport water, gas, air, oil and heating water or steam, such as general lower pressure fluids and other uses. It stands for material Q235A grade steel.
GB/T3092-1993 (galvanized welded steel pipe for low pressure fluid transport). It is mainly used to transport water, gas, air, oil and heating water or steam, such as general lower pressure fluids and other uses. Its representative material is: Q235A grade steel.
GB/T14291-1992 (mineral fluid transport welded steel pipe). It is mainly used for straight seam welded steel pipes for mine pressure, drainage and shaft discharge. It stands for material Q235A, B grade steel. GB/T14980-1994 (large diameter electric welded steel pipe for low pressure fluid transportation). It is mainly used to transport low pressure fluids such as water, sewage, gas, air, heating steam and other uses. It stands for material Q235A grade steel.
GB/T12770-1991 (stainless steel welded steel pipe for mechanical structure). Mainly used in machinery, automobiles, bicycles, furniture, hotel and restaurant decoration and other mechanical parts and structural parts. It represents materials 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, and the like.
GB/T12771-1991 (stainless steel welded steel pipe for fluid transportation). Mainly used to transport low pressure corrosive media. Representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, and the like.
Straight seam welded pipe has simple production process, high production efficiency, low cost and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight welded pipe. It is possible to produce a welded pipe with a large diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter by using a blank of the same width. However, compared with the straight pipe of the same length, the weld length is increased by 30 to 100%, and the production speed is low. Therefore, most of the smaller diameter welded pipes are straight seam welded, and the large diameter welded pipes are mostly spiral welded.
Straight seam welded pipe rust maintenance method:
However, the maintenance of straight seam welded pipe equipment has become a headache. Straight seam welded pipe equipment plays a major role in life and work. It is generally required that the surface of straight seam welded pipe fittings reaches near-white level (Sa2.5 practice proves that the construction process of epoxy, vinyl, phenolic and other anticorrosive coatings commonly used in straight seam welded pipe fittings can be almost eliminated by this descaling grade. All oxide scale, rust and other dirt are removed, the anchor depth reaches 40~100μm, which fully meets the adhesion requirements of the anti-corrosion layer and the steel pipe, and the spray (polishing) derusting process can use lower running cost and stable and reliable quality. It reaches the near-white level (Sa2.5 technical condition. When a certain rust is formed in the straight seam welded pipe, it is treated according to a certain descaling method and method to ensure the quality and performance of the straight seam welded pipe, and can be used in different industries and fields. Make an important contribution and role for the construction industry.
Spraying (polishing) abrasives for straight seam welded pipes:
In order to achieve the desired descaling effect, the abrasive should be selected according to the hardness of the straight seam welded pipe equipment, the original corrosion level, the required surface roughness, the coating type, etc. For single-layer epoxy, two-layer or three-layer polyethylene coating The layer, using a mixture of steel sand and steel shots, is easier to achieve the desired descaling effect. Steel shots have the effect of strengthening the steel surface, while steel sand has the effect of etching the steel surface. Mixed abrasive of steel sand and steel shot (usually the hardness of steel shot is 4050HRC. The hardness of steel sand is 5060HRC, which can be used on various steel surfaces. Even if it is used on steel surfaces of grade C and D rust, the rust removal effect is very good. .
Descaling speed of straight seam welded pipe:
That is, the total kinetic energy E of the abrasive applied to the steel pipe per unit time and the kinetic energy of the single-particle abrasive E1 steel pipe depend on the type of abrasive and the displacement of the abrasive. Where: the amount of spray (throwing) of m abrasive; the running speed of V abrasive; the mass of m1 single-grain abrasive. The m size is related to the abrasive breaking rate, and the breaking rate directly affects the interest of the surface disposal operation and the cost of the descaling equipment. When the equipment is fixed, m is a constant, y is a constant, so E is also a constant, but since the abrasive breaks, m1 changes. Therefore, the abrasive with lower loss rate should generally be selected, which is beneficial to improve the cleaning speed and length. The life of the blade.
The particle size and ratio of the abrasive of the straight seam welded pipe:
In order to obtain better uniform cleanliness and roughness distribution, the particle size and proportion design of the abrasive is very important. The roughness is too large, which may cause the anti-corrosion layer to become thinner at the anchor peak; at the same time, because the anchor pattern is too deep, the anti-corrosion layer is easy to form bubbles during the anti-corrosion process, which seriously affects the performance of the anti-corrosion layer.
It is not possible to rely on high-grain impact of large-grain abrasives. If the roughness is too small, the adhesion of the coating and the impact strength will be reduced. For severe internal pitting. It is also necessary to polish the corrosion products by small particles to achieve the cleaning effect, and the reasonable proportioning design can not only slow the abrasion of the pipes and nozzles (blades), but also the utilization rate of the abrasives can be greatly improved. Generally, the steel pellet has a particle diameter of 0.81.3 mm and a steel sand has a particle diameter of 0.41.0 mm, wherein 0.51.0 mm is a main component. In the actual operation where the sand shot is generally 58, the ideal ratio of steel sand and steel shot in the abrasive is difficult to achieve because the hard and brittle steel sand has a higher breaking rate than the steel shot. For this reason, the mixed abrasive should be sampled and tested from time to time in the operation. According to the particle size distribution, a new abrasive is added to the descaling machine, and the amount of steel sand is dominant in the new abrasive.
The main differences between straight seam steel pipe and spiral welded pipe are:
Different functions and differences are produced in actual production and use. Straight seam steel pipes and spiral welded pipes have many differences in the manufacturing process and shape. According to their own characteristics and craftsmanship, straight seam steel pipes can have different functions in use. The following is the main difference between the two types of steel pipes. There are two types of straight seam steel pipes: one is the medium straight seam steel pipe, and the wall thickness is not Too large to use high-frequency continuous welding, to become a high-frequency straight seam welded pipe, and second, large-diameter or straight-slit steel pipe through the hydraulic machine to form a raw steel plate in a preliminary step, and then use submerged arc welding method, and then through thermal expansion and plastic processing, Then the one is a spiral with different helix angles, and the former weld is a straight line. In the consumption of small and medium diameter welded pipes, the former has a greater advantage, and the latter has a comparative advantage in the consumption of large diameter welded pipes. Keeping the spiral welded pipe must choose the appropriate site and warehouse. The spiral welded pipe is formed by spirally forming a raw material strip through a molding machine, and is subjected to internal and external submerged arc welding to consume spiral welded pipes of different specifications. Weeds and all kinds of debris should be removed from the site, and the steel should be clean. 2 The warehouse should not be stacked with acid, alkali, salt, cement and other materials that are corrosive to steel. Therefore, under the opposite task pressure, the uniform diameter of the spiral welded pipe can be reduced compared with the straight welded pipe wall thickness. Different types of steel should be stacked separately to prevent smashing and prevent contact erosion. 3 large steel, rail, smear steel, straight seam steel pipe, forgings, etc. can be stacked in the open air. The warehouse requires clear air on the sunny day, and the rainy days should be closed to prevent moisture, and often adhere to the appropriate storage environment. Be sure to pay more attention to the above various matters, otherwise the quality problems caused are not the self-cause of the quality inspection of the spiral welded pipe, but the careless storage of the internal pressure is not acceptable, 3 because of the different shape of the weld. The weld pipe joint reward stress is 60-85% of the main stress of the straight seam welded pipe, which can be stored in the permeable shed. 2The former has a specific width of raw material strip or steel plate for every straight steel pipe of a specification. The latter can be used to produce small and medium-sized steel, wire rods, steel bars, medium-diameter straight-slit steel pipe wires and steel wire ropes of straight-slit steel pipes of different diameters. However, it is necessary to put on the lower pad 5 some small steel, thin steel plate, steel strip, silicon steel sheet, straight seam steel pipe, all kinds of cold-rolled, cold-drawn steel and high-priced, easily erosable metal products, which can be stored in the warehouse.舆 The premise is selected, generally adopts the ordinary blockade warehouse, that is, there is a warehouse with a wall, a tight door and window, and a ventilation device.
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