Monday, September 22, 2014

Spiral pipe welding technology

Because spiral pipe is with weld, so as to withstand the pressure of the liquid will be distributed on each side of the tube to enhance the strength of the tube. While generally large pipe if rolled steel plate welded directly straight, need a larger plate, greatly increasing the difficulty of making, it will use a large diameter spiral pipe spiral steel pipe (double-sided spiral submerged arc welded pipe) is a strip coil for raw materials, often warm extrusion molding, automatic double-sided submerged arc welding process wire spiral welded pipe joints. Another one is welded steel pipe, steel roll after it is welded to the vertical seam welds. Spiral welded pipe is welded steel spiral roll, seam spiral shape.
 
Welded steel pipe refers to a steel strip or plate bending round, square, etc. and then welded into the shape of the joint surface of the pipe. Welded steel pipe used is steel or steel billets. Since the 1930s, with the development of high-quality steel rolling production as well as the rapid development of welding and inspection technology, and constantly improve the quality of welds, welding steel pipe increasing varieties and specifications, and in more and more areas instead of non- pipe joints. Seamless steel pipe welded steel pipe is lower than cost, high production efficiency. Seamless steel pipe points, pipe. Points straight seam steel pipe, spiral steel pipe. Longitudinal points ERW (high frequency resistance welding), LSAW (LSAW). Spiral submerged arc welding process is (referred SSAW) and the difference is LSAW weld form, the difference is the difference with the ERW welding process, submerged arc welding (SAW) is to add media (wire, flux), ERW not needs, ERW is melted by frequency heating. Pipe according to production methods can be divided into two categories: seamless and welded steel pipe. Seamless steel pipe according to production methods can be divided into: hot-rolled seamless pipe, cold drawn tubes, precision steel tubes, thermal expansion, cold spinning tube and squeeze tubes. Seamless steel pipe with high-quality carbon steel or alloy steel, hot-rolled, cold-rolled (pull) of the points. Longitudinal production process is simple, high efficiency, low cost, rapid development. Spiral Welded Longitudinal generally higher than high, can narrow the billet production of large diameter pipe, you can also use the same width of the billet production of different pipe diameters. However, compared with the same length of straight pipe seam weld length of 30 to 100%, and lower production rate. Therefore, most of the smaller diameter pipe straight seam welded, large diameter spiral welded pipe for the most.
 
Currently spiral steel pipe products has a new product plastic composite pipe for hot-dip galvanized steel substrate, the powder coating technology in molten inner wall (wall when needed also) made of plastic coating steel pipe excellent performance. Compared with galvanized pipe, with anti-corrosion, no rust, no fouling, smooth smooth, clean, non-toxic, long life and other advantages. It is more than three times the life test, plastic composite pipe is galvanized pipe. Compared with the plastic pipe, with high mechanical strength, pressure, heat resistance and good.

The difference between the spiral welded and straight seam welding

Welded pipe is a gas pipeline in the common pipe, diameter greater than 426mm (or 508mm) of the pipe is generally known as large-diameter pipe, welded pipe in accordance with the way, can be divided into two kinds of spiral welded pipe and ERW.

Spiral welded pipe is carbon steel or low carbon alloy steel strip at a certain helix angle (also known as molding angle) rolled into a tube, and the tube seam welded steel, it can be used a narrower the production of large diameter steel pipe. Mainly spiral submerged arc welded spiral pipes (SSAW), widely used in the construction of various gas pipeline, with a diameter * thickness specifications indicated. There are one-sided spiral pipe welding and double-sided welding, pipe should ensure that hydrostatic test, weld tensile strength and performance of cold-formed to meet the requirements.

Longitudinal is hot rolled coil after molding machine, so that the coil is deformed into a sleek cylindrical, using high-frequency current skin effect and proximity effect or solder layer under the burning arc welding, so that the tube Edge heating and melting, and to a certain compressive force under the action of the fusion, the final cooling of the molding. Which use high-frequency current to melt the edge of the tube is called high-frequency welded pipe (ERW), using arc melting is called LSAW pipe (LSAW).

Longitudinal main raw material is low carbon steel hot rolled coil, hot-rolled, in petroleum, metallurgy, construction, mining, port, machinery and other industries widely used in oil and natural gas, low water gas transportation, mining fluid transport, belt conveyor roller, automotive transmission and so on.

Friday, September 19, 2014

Square tube welding deformation mode

In the welding deformation theory, we can know, the large size of the weld has led to the greater distortion, welding the same size, welding heat input is greater, will lead to large deformation, large long seam welding, welding deformation will be smaller, the weld asymmetry or asymmetrical arrangement of welding, weld deviation will cause more serious to severe deformation.

Welding specifications through process test and process analysis in determining square tube and rectangular tube butt weld double carbon dioxide gas shielded arc welding is a welding current of the first layer 200-250A, arc voltage of the second layer is 24-26V, its process requirements is the first layer of the weld must be able to ensure good welding, to form, welding current, arc voltage, wire feed speed and welding speed needs to be adjusted more equipment.

Welding sequence to reduce distortion rectangle, welding sequence should be in accordance with the following principles: start with the middle to both sides of the symmetrical hierarchical segmentation welding, it is a good diffusion and release stress, avoiding stress in welding production complex, through the swing welding, soldering at the beginning of the formation of plastic deformation of the narrow region only once, and because of the continuous weaving welding heat input so that the heating area is too large, the compression caused by the large plastic deformation, so large deformation of welding contraction, when welding STAGED because each section is very small, the heat is also very small, each layer is divided into several sections, so each jump welding welding, basically in the cold temperature field reconstruction, each in a narrow corresponding to
the plastic deformation of the longitudinal weld layered linear shrinkage is small, rather than by oscillating continuous-time filling the welding deformation.

Thursday, September 18, 2014

ERW pipe flattening cracking analysis

ERW pipe flattening test weld cracking is mostly due to micro-cracks, brittle phase inclusions, coarse grains, caused by the band structure. Rational design of chemical composition, reducing inclusions in steel and ribbon organization, forming, welding and heat treatment process parameters were optimized control, can effectively reduce the weld cracking index inclusions and improve high-frequency ERW pipe weld cracking performance anti-crush. Ferrite / pearlite banded structure is hot-rolled steel in common a phenomenon banded structure has a great influence on the performance of steel, will decrease the ductility and toughness.

Low magnification analysis does not appear in the weld fracture. The microstructure can be judged by the organization does not have near the fracture due to welding temperature changes, which can determine the cause of the pipe welding process is not squashed fracture. Mechanical properties and the results of the analysis show that the spectral composition of the high-strength steel; plasticity respect, 31.25% of the coils of plastic does not meet the standards, 62.5% of the coils of plastic slightly larger than the standard one percentage point or exactly equal to the standard value , only 6.25% of the coil is greater than 30% of the plastic. Overall, high strength steel to, and low plasticity. According to the inclusion of ratings and scanning electron microscopy analysis can be seen, a lot of steel inclusions, and the level of more than 3.0. Serious is the reason for the non-metallic inclusions in a significant cracking. By microstructure analysis and scanning electron microscope analysis shows that strip banded serious, the highest level reached B4.0 level. Produce these banded structure, there are two reasons, one is not properly controlled during hot rolling process resulting in serious banded, the other is the inclusion became banded nucleation mother. On the microstructure, the hot rolling process control process is aggravated by improper banded structure of the main reasons, so the focus is how to eliminate banded controlled rolling process. From the above analysis shows, quantity and high levels of non-metallic inclusions (sulfides) and severe plastic strip banded structure is leading to the main reason for the low and cracking. So steelmaking process should reduce the content of non-metallic inclusions, especially sulfide. Hot rolling finishing temperature should be adjusted to reduce the banded structure.

Wednesday, September 17, 2014

Submerged arc welding pipe welding squeezing roller adjustment

In the production of high-frequency welded, the shaped state of the seam directly affect the quality of the welded tube, wherein the parallelism of the abutting surfaces of the welded joint is particularly important. The seam welding in the steel process, the main reduction by adjusting the squeezing rollers and the roller gap between the rollers to ensure that the degree of the parallel on two of the commissure. Welding the welding characteristics of the squeeze roll grooved extrusion pressing on the frame between the radii of the grooved rollers squeeze rolls other than about 10% larger, and therefore, the squeezing rollers and the roller surface of the outer pipe of circular cross section over creating a gap, the gap known as the "heel gap." In the actual molding, the pipe can not be perfectly circular cross-section. Under normal circumstances, due to the deformation of the strip edges is not sufficient, Peach section was easy, if not adjusted butt weld surface is not parallel to form a butt, seriously affecting the quality of the weld. If the upper squeeze roller and the other using the same pass squeeze roller radius reduction amount when the adjustment by the squeeze roller removes the V-shaped commissures, on the outer surface of the roller pressing the roller against the surface of the pipe will strongly on the tube surfaces likely to cause injuries, and the formation of a more serious V-shaped seam.

Pipe wall thickness, the higher the strength of the material, V-shaped when welding is not easy to eliminate the commissure. If the roller surface on the outside of the roll has caused a significant but still can not achieve an indentation shaped commissure I described adjustment has reached the limit, proceed to the next on the pressure roller will not only cause serious indentation, but also a more severe V-shaped butt seam. The ideal value of the roll gap with the tube wall thickness and strength of the various and different. For example, when the thin wall thickness generally requires the the roll gap is set smaller in order to increase the stability of welding. As the wall thickness is thick, even if the appropriate expansion of the roll gap, it will not affect the stability of welding. Therefore, when the thick-walled high-strength steel or molded in order to obtain greater "gap followed by" on the expansion of the roll gap and the practice, as long as it does not affect the stability of the expansion of a suitable welding.

In the high-frequency modulation type and welding pipe, through the contact surface and the heating mode and butt seam state relations analysis, using the adjustment of welding squeeze rollers roll gap and reduction methods, accurate and timely manner to ensure the steel plate welding edge welded to achieve a good state. When the I-shape commissure when instructions at this time in a substantially parallel state of the abutment surfaces during welding, does not require adjustment of the extrusion pressure roller; commissures when V-shaped abutment surfaces instructions at this time in the welding process, the lower portion of the first contact surface, can increase the amount of reduction rollers squeeze rolls to achieve an I-shaped state; when the inverted V-shaped commissures, the abutting surfaces described case the welding process, the upper surface of the first contact, by reducing squeeze roll reduction amount reaches the I-shaped state.

Straight seam welded pipe flaw detection methods and technical requirements

Magnetic flux leakage testing of high sensitivity, can well distinguish the pipe outer wall defects, but a long tube, large wall thickness of the pipe after degaussing magnetic flux leakage inspection to be done to deal with; eddy current flaw detection speed, but by the skin effect, the difficult to find defects in the depths of the workpiece; ultrasonic flaw penetrating ability, defect positioning accuracy, low cost, high speed, but testing operations to be coupled, the coupling in the northern winter environment welded easy to freeze, causing inconvenience to the inspection work . In the manufacture and use of welded pipe, the non-destructive testing is performed to ensure the weld quality is particularly important. Pipe commonly used non-destructive testing methods are: for more than 5 mm from the pipe surface offline whole tube of magnetic flux leakage testing, eddy current and ultrasonic testing; verify more than 5 mm from the surface of the pipe welding quality online magnetic flux leakage inspection and eddy current inspection; applicable in thick-walled pipe weld the whole tube offline ultrasonic flaw detection; verification thick-walled pipe welding quality ultrasonic flaw detection.

Refers to the magnetic flux leakage inspection of ferromagnetic material is magnetized, the surface and near-surface defects in material surface leakage magnetic field, discovered by detecting leakage field NDT techniques defects. Magnetic flux leakage inspection of the surface state of the pipe does not ask, detected a greater depth, are widely used in pipe detection abroad, especially oil with domestic pipe detection has also been widely used. When the magnetization is low, the leakage magnetic field is small, and increases slowly; When the magnetic flux density reaches about 80% of the saturation value, the peak of the defect with the increase of the leakage magnetic field the magnetization increases rapidly, but when a ferromagnetic material into the the magnetic saturation magnetization increases outside little influence on the magnetic field strength of the defect. Therefore, the magnetic circuit should be developed so that the material being tested as nearly saturation magnetization state. A huge influence on the direction of the leakage defects in the magnetic detection accuracy when the defect perpendicular to the main plane of the magnetization direction of the magnetic field, generated by the leakage magnetic field is the strongest. The same weakness leakage magnetic field maximum surface of the duct, and with increasing burial depth gradually decreases when the burial depth is sufficiently large, the leakage magnetic field will tend to zero. Defect size is also a great influence on the leakage magnetic field, the same width and the depth when the defect is not the same, with the increase of the leakage magnetic field to increase the depth of the defect in a certain range of the approximate linear relationship between the two.

For pipe weld often produce "inner burr adsorption", eddy current testing equipment often erroneously reported as defects. Frequently appeared in eddy current testing process glitch due to electromagnetic forces adsorbed on the seam, leaving the eddy current magnetic field exposure steel automatic degaussing device, there is no magnetic attraction after the glitch automatically fall, and then manually re-defect detection and no awkward questions displayed. Due to the skin effect, as the distance between the detection coil and the pipe is subject, the detection sensitivity is gradually reduced, so that, for the same size of the defect, as reflected in the pipe wall will be smaller than the amplitude of a signal tube wall defects on. Pipe full pipe eddy current testing equipment capacity in the probe and the inner surface of the outer surface of the pipe defects regard is determined by many factors, but the most important thing is dependent on the wall thickness of the pipe was seized and eddy current excitation frequency and magnetic saturation intensity ; the same time, the choice of instrumental parameters should consider the impact of the physical parameters of the subject to be welded conductivity and magnetic permeability, etc. of the eddy-current flaw detection precision.

Tuesday, September 16, 2014

Double-sided submerged arc automatic welding machine

Straight seam steel pipe double-sided submerged arc automatic welding machine can be divided into internal welding and outside welding of straight seam welded steel pipe

Straight seam steel pipe outside sided submerged arc welding machine, straight seam in the steel industry as "outside welding" outside, the so-called straight seam welded steel pipe refers to closely co-ordinated pre-process after welding, can be understood as follows: When the straight stitch After the pre-weld pipe from the welding process welding procedure is to be outside rather than inside the welding. The reason is: Whether straight seam welded steel pipe outside, or from physical deformation by heat pipe inside straight seam welded steel pipe will shadow, if the first outer seam welded straight seam steel pipe, the data can be the greatest degree of reduced physical deformation of straight pipe joints size. Straight pipe joints due to project needs, require a higher quality of welds, weld start working outside, you can ensure the greatest degree of straight seam welded steel pipe weld penetration resistance, straight seam steel pipe welds beautifully, and straight seam straightness of the linear weld pipe.

Straight seam steel-sided submerged arc welding inside, straight seam in the steel industry as "the weld." Straight seam steel tube welder, Lincoln uses the same equipment imported from Germany, and flux. Straight seam welded steel pipe is straight seam steel pipe welds in priority. The reason: it is not only difficult to weld, the weld requires the highest level of straight seam steel pipe weld inspection on this within the solder can be seen. Straight seam steel pipe welder at work within the current large degree of penetration depth, and less prone to the human eye. Seasoned team leader within the welder can be adjusted from a straight seam steel pipe weld television industry track, as well as outside the hot spot welds when welding from within, in order to make adjustments based on the size of the hot spot welding speeds. Steel-sided submerged arc welding using German into Lincoln automatic welding machine, straight seam welded steel pipe automatic welding flux using straight seam steel pipes imported from Germany, supporting internal and external welding flux, straight seam steel pipe welding equipment before working inside and outside of welding flux through the filter, the filter is too large particles, because when submerged arc flux, exceeding the size of the solder particles will affect straight seam steel pipe welds uniform cooling time, if not straight seam steel pipe welds standard time temperature range, the standard rate of cooling, are may affect the level of straight seam steel pipe welds NDT.