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straight seam steel pipe common problems and preventing measures

by:VENTECH     2020-03-03
The straight-seam steel pipe is a steel or steel that is bent and then welded.
It is cut into strips by a steel plate and then packaged into a tubular cold mold.
Welding welds are then welded by specialized welders.
Bright and polished external welds.
The inner tube of the General Burr is not hit.
Burrs can only be made with precision welded pipes.
During the construction of such spiral welded pipe, the line energy generated by welding is small, and the influence on the base metal heat affected area is also small. Multi-
After the wire is welded, the previous wire on the wire can play the role of eliminating the stress generated during welding, thus improving the mechanical performance of the pipe.
Control of extrusion pressure: after heating the two edges of the pipe to the welding temperature, the ordinary metal particles are formed under the extrusion of the extrusion roller, and finally the solid weld is formed.
If the extrusion force is too small to form a small amount of Cocrystal and the strength of the weld metal is reduced, the force will crack. 3.
If the extrusion pressure is too large, the molten metal will be squeezed out of the weld, and the weld strength will be large, resulting in a large number of internal and external burrs, and even defects such as welds.
The role of straight seam Steel Solution treatment: 1. The structure and composition of straight seam welded pipe are uniform, which is a particularly important raw material, because the rolling temperature and cooling speed of the straight seam welded pipe section are different, resulting in inconsistent organizational structure.
At high temperature, the atomic activity increases, dissolves, and the chemical composition tends to be uniform, in a uniform single-
Stage organization.
2. Eliminate the hardening process so as to facilitate the continued cold processing.
Through solution treatment, the lattice recovery of deformation, the grain recrystals of elongation and fracture, the internal stress is eliminated, the tensile strength of the steel wire is reduced, and the elongation is increased.
3. Restore the corrosion resistance of the straight seam welded pipe.
Due to the precipitation of cold carbide, lattice defects are produced, which reduces the corrosion resistance of straight welded pipe.
After the solution treatment, the corrosion resistance of the straight welded pipe is restored to the best state.
The temperature of the solution is mainly determined by the chemical composition.
Generally speaking, alloy elements, high grade content, and solution temperature should be increased accordingly.
In particular, the content of manganese, molybdenum, nickel and silicon in the long straight welded pipe can be fully dissolved only by increasing the solution temperature, and the softening effect can be achieved.
However, stable steel, such as longitudinal welded pipe, when the stability of the carbide element is completely dissolved in the ferrite, the solution temperature will be high, during subsequent cooling, it will appear in the form of cr23c1 precipitation at the grain boundary, causing inter-Crystal corrosion.
In order to stabilize the carbide element, do not decompose or dissolve solution. Generally, the limit solution temperature should be reduced.
The straight-seam steel pipe is simple to manufacture, with high output, few resources and rapid development for students.
The strength of spiral welded pipe is generally higher than that of longitudinal welded pipe. It can be used to manufacture narrow pipe blanks with large diameter, and also to manufacture pipes with the same width of raw materials.
But compared to straight seams of the same length, with a weld length of 30 to 100%, the student\'s productivity is lower.
Therefore, most welded pipes with small diameter accept straight seam welding, and most welded pipes with large diameter accept Spiral welding.
Although the welding steel pipe production line is to create wind
However, there will be some inevitable small problems, so before the test, the steel pipes in the factory will be less, maybe this is also important.
The welding of straight-seam steel pipes should complete the mechanical performance test, flattening test and expansion test, and meet the standard requirements.
If necessary, the pipeline should be able to withstand a certain pressure.
5Mpa pressure test, keep no leakage for a minute.
Eddy current testing is allowed to replace the water pressure test.
Eddy current detection method is to fix the probe on the rack and maintain the detection and weld 3 ~ At a distance of 5mm, the weld is scanned through the rapid movement of the weld pipe, and the flaw detection signal is automatically processed and automatically sorted through the eddy current flaw detector to achieve the purpose of detection.
Application of straight seam welded pipe: it is mainly used in water conservancy engineering, petrochemical industry, electric power industry, agricultural irrigation, urban construction and other industries in China.
Liquid transport for water supply and drainage.
For the transportation of natural gas, steam, liquefied petroleum gas.
For structural use: for piling as a bridge;
Terminals, roads, buildings and other buildings.
The general weakness of ordinary welded pipe is: air hole, slag, unwelded, crack, etc.
And measures to prevent defects and evaluation of the essence of internal ills: 1. Air holes: Spiral steel pipes have low echo height in a single air hole, and the waveform is single seam and relatively stable.
Detected from the left side, the reflected waves are almost the opposite, but a cluster of reflected waves occurs at a point of dynamic probes on hidden, dense pores, when the probe is used for fixing, the height of the wave is related to the size of different pores
The rotation of the point will emerge from the scene.
The main reason for this shortcoming is that the welding is not dry at the specified temperature, the electrode coating is degraded and falling off, the welding core is corroded, the wire is not cleaned, the manual welding current is too large, and the arc is too long;
The voltage of submerged arc welding is too high or the network voltage is too strong;
Welding the gas treasure when the purity of the gas is primary.
Assuming that the spiral steel pipe has holes in the weld, not only breaks the shortcomings of the weld metal density difference, but also allows for effective cross-over
The area of the section of the welded cut reduces the performance of the machine, the extra chain
Like pores, there is a clear contrast flight between bending and impact toughness.
The prevention order to prevent such defects is: do not use the peeling, peeling, deformation and corrosion of the wire rod, and must use rust after skill.
The welding materials used shall be dried at the specified temperature, groove and clean on both sides of the cleaning, and shall be used according to the welding current, arc voltage and welding speed. 2, Slag: steel-like point-
The echo signal like slag is similar to the point-
Like air holes.
The echo signal of the slag is mostly the zigzag amplitude is not high, the waveform is mostly branch-like, the main peak edge has a small peak, and the probe has a change in the translation amplitude. When the amplitude is not rejected, the reflection from all directions.
The reason for this failure is: the welding current is too small, too fast, the slag is rising, the weld edge and the weld layer are not clean, the chemical composition of the metal and welding materials is wrong, and there are more sulfur and phosphorus.
The steps to prevent are: correctly select the welding current, the slope of the welding piece should not be too short, the slot must be cleaned before welding, many
Welding slag must be eliminated in layer welding;
Reasonable Decision of welding rate of transportation angle.
3. No penetration: high reflectivity, high volatility, probe translation, more stable waveform, two sides of the weld flaw detection can be similar to the amplitude of the reflection.
Such defects not only enable the machine to discuss the performance of welding, but also in the components of unwelded penetration and stress bonding at the end of the gap, the bearing often leads to cracks, which is a hazard to the disease.
The reason is usually: the edge of the slot is too small, the welding current is too small or the transportation speed is too fast, the slope is small in black and white, the error and the angle of operation of the arc local strike.
The order of prevention is: reasonable use of groove type, Assembly clearance and use of correct welding techniques, etc.
The basic principle of the straight seam steel pipe forming theory is the shape and size of the Strip
The plastic deformation tube that you need to do the external force.
Since the deformation of the steel plate mainly occurs in the continuous transverse and longitudinal direction during the tube surface forming process, its binding force is applied to the roller hole through the layout of the roller slotting machine, in the transverse deformation, the two sides are made of steel plates, are steel plates, the vertical deformation of concrete operation and the model exist many differences in the process of continuous deformation of steel plates through the corresponding Mill.
Longitudinal deformation is the deformation direction of the lateral deformation of the finger plate column, and it is the bending deformation of the tube section.
The development of vertical welded pipe industry, there is no doubt about the achievements, but we can not see the obstacles to the development of the industry.
China\'s longitudinal welded pipe industry in the industry, from the planned economy along the way, has experienced the ups and downs of enterprise restructuring, to now more than 95% of private enterprises, extensive development, the overall level of enterprise quantity, product quality, staff quality and organization management is still low, which is the result of unreasonable industrial structure caused by disorderly market competition.
As can be seen from the industry as a whole, the current vertical seam welded pipe industry market concentration is very low, mainly private small and medium-sized enterprises, the lack of leading enterprises;
The whole industry chain is less involved in enterprises, and the homogenization is serious.
In the future, extending the industrial chain, opening up the central and western regions, and expanding into hot areas such as railways will be the development trend of China\'s straight seam welded pipe industry.
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