Straight Seam Steel Pipe Common Problems and Preventing Measures

Dec 22


Marine Lee

Marine Lee

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Straight seam steel pipe is steel or steel after bending molding, and then made by welding. It is cut into strips by a steel strip, and then wrapped into a tubular cold mold. The special welder then welds a seam. Outer weld brightly polished. The inner pipe of the general burr does not hit.


Only precision welded pipe to hit the burr. Such a spiral welded pipe construction process of welding the line energy generated by the small,Straight Seam Steel Pipe Common Problems and Preventing Measures Articles the influence of the base metal heat affected zone is also small. Multi-wire welding after the former wire on the wire can play a role in eliminating the stress generated when welding, thereby improving the mechanical properties of the pipe. Control of squeezing force: After the two edges of the tube are heated to the welding temperature, the common metal grains are formed to penetrate and crystallize under the extrusion of the squeezing roller, and finally the solid weld is formed. If the extrusion pressure is too small, the formation of a small number of common crystals, weld metal strength decreased, the force will produce cracking; if the extrusion force is too large, will make the molten metal is extruded out of the weld, The weld strength, and will produce a lot of internal and external burrs, and even welding seam and other defects caused.

The role of straight seam steel solution treatment:
1, The straight seam welded pipe organization and composition of uniform, which is particularly important raw materials, because the straight seam welded pipe sections of the rolling temperature and cooling rate is not the same, resulting in inconsistent organizational structure. At high temperatures, the atomic activity increases, dissolution, chemical composition tends to uniform, rapid cooling after the uniform single-phase organization.
2, To eliminate the hardening process, in order to facilitate continued cold. Through the solution treatment, distortion of the lattice recovery, elongation and broken grain recrystallization, internal stress elimination, steel wire tensile strength decreased, elongation increased.
3, To restore the inherent corrosion resistance of straight seam welded pipe. As a result of cold carbide precipitation, lattice defects, so that the corrosion resistance of straight seam welded pipe decreased. The corrosion resistance of the straight seam welded pipe after solution treatment is restored to the best condition.

The solution temperature is determined mainly by the chemical composition. In general, alloying elements, high content of grades, solution temperature should be increased accordingly. Especially manganese, molybdenum, nickel, silicon
content of long straight welded pipe, only to improve the solution temperature, to fully dissolve in order to achieve softening effect. However, stabilized steel, such as the Longitudinal Welded Pipe, the solution temperature is high when the stability of the carbide elements fully dissolved in the austenite, in the subsequent cooling will be in the form of Cr23C6 precipitation in the grain boundary, causing intergranular corrosion. In order to stabilize the carbide elements do not break down, not solid solution, generally the lower limit solution temperature. Straight seam steel pipe manufacturing is simple, students to create high yield, low resources, rapid development. Spiral welded pipe strength is generally higher than the Longitudinal Welded Pipe, can be used to create a narrow billet diameter pipe larger pipe, but also with the same width of the raw material to create pipe diameter pipe. However, compared with the same length of the straight seam, the weld length to add 30 to 100%, and students have lower production rate. Therefore, most of the smaller diameter of the welded pipe to accept straight seam welding, large diameter welded pipe is mostly accepted spiral welding. Although the welded steel pipe production line is to create wind-induced security, but there will be some unavoidable small problems occur, so the steel pipe in the factory before doing the testing links will be less, perhaps that is equally important. Straight seam steel pipe welding should be done to complete the mechanical properties test and flattening test and flaring test, and to meet the standards requirements. Pipe should be able to withstand a certain amount of pressure, if necessary, 2.5Mpa pressure test, to maintain a minute without leakage. It is permissible to replace the hydrostatic test with eddy current testing. Eddy current testing method is to probe fixed in the rack, testing and weld to maintain 3 ~ 5mm distance, by the rapid movement of the weld pipe to conduct a comprehensive scan of the weld, the flaw detection signal by the eddy current detector automatic processing and automatic sorting, To achieve the purpose of testing. Longitudinal Welded Pipe Application: In the country is mainly used in water projects, petrochemical industry, chemical industry, power industry, agricultural irrigation, urban construction. For liquid delivery with: water supply, drainage. For gas transportation with: gas, steam, liquefied petroleum gas. For structural use: for piling, as a bridge; terminals, roads, buildings and other structures.

General weaknesses in the common weld pipe are: pores, slag, not penetration, not fusion and cracks. And the prevention of measures against the occurrence of defects and the evaluation of the substance of internal ills:

1, Stomata: spiral steel pipe in a single stomatal echo height is low, the waveform is a single seam, more stable. From the left side detection, the reflected wave is almost the opposite, but a little dynamic probe on the hidden, dense pores will emerge a cluster of reflected waves, wave height with the size of different pores, when the probe for fixed-point rotation, will emerge from the scene . The main reason for the occurrence of such shortcomings is not welding the prescribed temperature drying, electrode coating degeneration fall, welding core corrosion, wire cleaning is not clean, manual welding current is too large, the arc is too long; submerged arc welding voltage Too high or the network voltage is too strong; gas treasure when welding gas purity primary. Assuming the spiral steel pipe with a hole in the weld, not only broken the poor weld metal density, but also allows the effective cross-sectional area of the weld cut, reducing the performance of the machine, the additional chain-like pores, the bending and attack toughness There is a clear contrast flying. To prevent such flaws to prevent the order are: do not use the skin cracking, peeling, transformation and corrosion of welding wire rod, rust wire rust must be used after the skills. The welding material used should be dried at the specified temperature, groove and clean on both sides of clean, and to use in line with the welding current, arc voltage and welding speed.

2, Slag: steel-like point-like slag echo signal is similar with the point-like stomata, strip-shaped slag echo signal is mostly zigzag amplitude is not high, the waveform mostly dendritic, the edge of the main peak of a small peak, the probe There are changes in the translation amplitude, reflection from all directions when the amplitude does not repel. The causes of this fault are: welding current is too small, too fast, the slag to rise, the edge of the welding seam and the layers of the weld is not clean, the metal and welding material chemical composition is not right, sulfur , Phosphorus and more. To prevent the pace are: the correct selection of welding current, welding pieces of the slope of the song straight length of not too short, must be cleaned before welding groove picking, multi-layer welding must be the eradication of welding slag; and a reasonable decision to transport angle welding rate .

3, Not penetration: high reflectivity, volatility is also high, the probe translation, the waveform is more stable, both sides of the weld flaw detection can be similar to the amplitude of the reflection. Such defects not only soar the machine to discuss the performance of welding, but also in the lack of penetration at the end of the gap and the composition of stress rendezvous, bearing often lead to cracks, is a harm of ills. The reason is usually: groove edge is too small, the welding current is too small or too fast transport speed, slope black and white degree is small, the operating angle of the error and arc partial blow. To prevent the order are: the rational use of groove type, assembly gap and the use of the correct welding skills and so on.

The basic principle of the straight seam steel tube forming theory is the shape and size of the strip elasto-plastic deformation tube produced by the action of the external force you need to do. As the deformation of the steel sheet during the forming of the tube surface occurs mainly in the continuous transverse and longitudinal directions, and its binding force is exerted through the roll grooving machine layout applied to the roll hole in the lateral deformation of the two sides is made of steel plate, Is a steel plate, the vertical deformation of the concrete operation and the model there are many differences in the process of continuous deformation of the steel plate through the process of the corresponding mill. Longitudinal deformation refers to the direction of deformation of the deformation of the plate column lateral deformation is the bending deformation of the tube section. Longitudinal Welded Pipe industry development, the achievements of no doubt, but we can not help but see obstacles to the development of the industry. China's longitudinal seam welded pipe industry in terms of industry, from the planned economy along the way, experienced the ups and downs of corporate restructuring, and now more than 95% of private enterprises to enterprises, extensive development, so that the number of enterprises too, Product quality, staff quality, organization and management of the overall level is still low, the result of irrational industrial structure caused by disorderly market competition. From the industry as a whole can be seen that the current pattern of vertical seam welded pipe industry market concentration is very low, mainly small and medium enterprises mainly of private, the lack of leading enterprises; enterprises involved in the whole industry chain less homogenization serious enterprises Lack of core competitiveness. The future, to extend the industrial chain, to open up the central and western regions, to the railway and other hot areas of demand expansion will be China's Longitudinal Welded Pipe Industry trends.