The quality of the tube blank has an extremely important influence on the quality of the steel tube. Any tube blank that does not meet the quality requirements must not be fed. The surface defects of the tube blank must be removed.
1. Tube blank quality inspection method:
a. Visual inspection: surface quality
b. Low magnification organization: sulphur printing, acid leaching, industrial hydrochloric acid or copper chloride solution check cracks, bubbles, loose, white spots, inclusions and other distribution.
2. Clearance of tube blank surface defects:
1. Flame cleaning:≤0.4%c Surface defects of tube blank.
2. Air shovel cleaning: suitable for the cleaning of local defects on the surface of tube blanks.
3. Wheel cleaning: mainly used for tube blanks that should not be used for flame cleaning.
4. Turning and cleaning: It is mainly used for the cleaning of surface defect of pipe blanks with high added value and quality requirements, such as stainless steel blanks, rust blanks: such as P91 and P92.
In short, the inspection and inspection of the quality of the tube blanks and the necessary cleaning of the surface defects of the tube blanks are the basic prerequisites for ensuring that the blanks used in the production of seamless steel tubes meet the quality requirements.
The use rate of spiral steel pipe is relatively high, and its application is very extensive. However, the quality should be paid attention to when selecting it. How should we choose it?
Commonly, we use atmospheric pressure and water pressure for testing. This method can detect the working conditions of spiral steel pipe in pressure working environment, and can also detect the sealing performance of spiral steel pipe. Generally, atmospheric pressure testing is adopted because of such safety. It is relatively high, and if the vapor pressure is used for detection, the spiral steel tube needs to be removed after the test, which is troublesome. The second method is also relatively simple, it is through the observation of the surface. With the naked eye found in the spiral pipe in the welding and the size of the problem, if necessary, can also use the standard sample to compare with the product to be purchased to find the problem.
Thick-walled spiral steel pipe refers to a spiral steel pipe whose wall thickness is slightly thicker than ordinary spiral steel pipe. Compared with the ordinary wall thickness spiral steel pipe has the advantages of high compressive strength, high impact strength, high safety performance and longer service life. With the development of industry, engineering has put forward higher requirements for the use of spiral pipelines. The reason why thick-walled spiral pipelines appear is because some of the pressures required to transport the medium are unacceptable to ordinary spiral steel pipes. Straight seam steel pipe or seamless steel pipe will greatly increase the cost of the project. If it is a dangerous medium, we increase the cost is inevitable, so when the choice of pipeline is based on the pressure required by the medium and medium to transport the project needs decided.
The common problems of pre-welding of welded steel tubes, such as erroneous edges, directly lead to the degradation of welded steel tubes or waste materials. Therefore, pre-welding must strictly control the wrong side. When the entire or most of the welded blanks have the wrong edges, the difference is generally due to:
(1) Slit adjustment is not in place;
(2) Joiner rolls (roller adjustment is not on the right side of the circumferential angle, or on the centerline of the tube, the radial roll stretch is approximately asymmetric, or the pressure roll is inconsistent, no pressure circle); Prebend without pre-bend plate in place Feng caused a straight edge phenomenon. When the wrong lateral deviation occurs at the head or tail of the tube blank, it is usually due to the incorrect position of the import/export roller table; the center of the ring is wrong;
(3) Joint pressure rolling circle is not good, individual roller position deviation;
(4) Poor molding (the height of the blank on both sides after forming);
(5) The opening width exceeds 150mm.
(6) Hydraulic system pressure fluctuations. Open slot adjustment is not in place;
2, In the back of the over, after burning and welding if clear and time-consuming, affecting the normal production process; is not clear, steel pipe welding and internal weld tracking welding. Burning, affecting the quality of welding inside and outside, need to be filled. The reasons behind overlap and burning are generally:
(1) The joint is not tight, there may be a low pressure hydraulic system;
(2) Poor molding, large roundness deviation;
(3) Improper selection of pre-welding process parameters. Welding current and arc voltage have proper welding speed, welding speed and line energy are too high or too low, easy to burn and flash back.
Pre-weld porosity causes internal defects in internal and external welds. The formation of porosity in the pre-weld is generally due to:
(1) Poor protection gas quality, such as insufficient water, pressure and flow;
(2) Part of the welding torch is blocked, the hood formed by the shielding gas is not uniform, and the harmful gas is stirred
(3) There are rust and oil contamination on the tank.
4, Poor formation of welds.
Welded steel pipe welding seam shape is poor, affecting the internal and external welding tracking, affecting the stability of the welding process, thus affecting the welding quality. Welding formation is closely related to the line. Welding current, constant arc voltage, increased welding speed, weld penetration and weld width decrease, resulting in poor weld formation. When air holes are created in the weld, weld formation is generally poor.
Large diameter welded pipe, more common in industrial and civil construction electrical, water supply and drainage, fire fighting and support structure. Due to the production of such pipes, the rolling, coiling, and straight-line welding processes are used. Most of the welding of the welded pipe uses a high-frequency wave welding process, so it is customarily called a "high-frequency welded pipe." Small-diameter pipe, using this process, the technology is relatively simple, easy to control defects. When the large-diameter welded pipe is manufactured, because of the large size of its blank, some manufacturing defects such as concentricity of the finished product, smoothness of the surface, and surface finish are inevitably caused by some influences of the processing machinery and processes. There are also indicators such as voids, missing welds, and welding defects that may exceed original expectations. In addition, the material weldability index of the pipe is also a major factor affecting the quality of the finished product.
Recently, the large-diameter welded pipe used as a pipe is generally produced by a spiral welding process, which avoids the defects of the longitudinal welded pipe.
Large diameter welded pipe overall heat treatment process
The overall heat treatment is characterized by: in the process of processing, there is no temperature difference in the wall, no residual stress, heating and holding time can be adjusted to adapt to more complex heat treatment specifications, but also can be automatically controlled by a computer, but the roller type furnace equipment is complex and operating costs are high. Large-diameter welded pipe overall heat treatment: it can be divided into online heat treatment and off-line heat treatment.
Welded pipe heat treatment:
After the large-diameter welded pipe is welded, two or more sets of intermediate frequency circular induction heating devices are used to heat the whole pipe. The required temperature is heated to normal temperature within 900-920°C for a short period of time. After normal cooling below °C, the overall tube organization was improved.
Welding pipe offline normal heat treatment in furnace:
The overall heat treatment equipment for the large-diameter welded pipe of the welded pipe consists of a chamber furnace and a roller hearth furnace. Nitrogen or hydrogen-nitrogen mixed gas is used as a protective atmosphere to achieve no oxidation or light. Due to the lower production efficiency of the chamber furnace, a roll-bottom type continuous heat treatment is currently used.
Seamless steel pipe has high pressure resistance, good toughness, long pipe length and less interface, lighter weight under the same strength, no welding seam, and can withstand greater pressure. It has a hollow cross-section and is used in large quantities as a conduit for fluids, such as pipelines for the transportation of oil, natural gas, gas, water and certain solids. The process of the seamless steel pipe determines its limited performance. The general seamless steel pipe has low precision and uneven wall thickness.
Uniform, low brightness inside and outside the tube, high cost of the fixed length, and pits and black spots inside and outside the table are not easy to remove. The advantages and characteristics of seamless steel tubes determine that the requirements for seamless steel tubes for the storage environment are very strict.
1. The site or warehouse where seamless steel tubes are to be preserved should be selected in a clean, well-ventilated area away from factories and mines that produce harmful gases or dust. Weeds and all debris should be removed from the site to keep the steel tubes clean.
2. Seamless steel tubes in warehouses must not be stacked together with acids, alkalis, salts, cement, etc., which are corrosive to the steel tubes. Different types of steel pipes should be stacked separately to prevent confusion and prevent contact corrosion;
3, The warehouse should be selected according to geographical conditions, the general storage of seamless steel pipe using ordinary closed warehouse, that is, a roof with walls, doors and windows tight, with a ventilation device warehouse;
4, The warehouse requires clear attention to ventilation, rainy days, pay attention to close the moisture, and often maintain a suitable storage environment.
The above is the environmental requirements for the storage of seamless steel tubes. The application range of seamless steel tubes is becoming more and more extensive. Therefore, the requirements for seamless steel tubes are also increasingly strict. A good seamless steel pipe must have a good storage environment in order to maintain the advantages of seamless steel pipe.