Friday, September 26, 2014

LSAW steel pipe heat treatment online and off-line

LSAW steel pipe online heat treatment:
After the steel pipe welding, using two groups or more intermediate ring induction heating equipment to the whole pipe heating, which in a short period of time to often required temperature 900 ~ 920 ℃, and heat preservation time, air cooling below 400 ℃ after normal cooling, make whole tube organizations to improve.

LSAW steel pipe offline often in the furnace heat treatment:
Straight seam steel pipe overall heat treatment device have chamber furnace and roller hearth furnace, using nitrogen or hydrogen nitrogen mixture gas as protective atmosphere, to achieve no oxidation or light condition. As a result of the chamber furnace production efficiency is low, now often use roller hearth heat treatment furnace in succession.Whole heat treatment features are: in the process, the wall inside there is no difference in temperature, won't produce residual stress, heating and holding time can be adjusted, to adapt to the complex heat treatment specification, also can use the computer for automatic control, but the roller-hearth furnace equipment complex, high cost of operation.

According to the production process, straight seam steel pipe can be divided into high frequency straight seam steel pipe and submerged arc welding straight seam steel pipe.Submerged arc welding and straight seam steel pipe according to the different forming methods is divided into UOE, RBE, JCOE steel pipes, etc.Which according to the purpose is different, and different production working procedure, after. (can be roughly divided into the scaffold tube, fluid pipe, wire casing, stent tube, guardrail tube etc) under the wing of bohai xiang straight seam steel pipe manufacturer to introduce one of the most common high frequency straight seam submerged arc weld steel pipe and straight seam steel pipe forming process and production process:
1. The plate used in the manufacture of large diameter submerged-arc welding straight seam steel pipe, steel plate into the production line after the first full plate ultrasonic inspection;

2. The edge milling: through the two edges of the steel plate edge milling machine double-sided milling, make it meet the requirements of plate, plate edge parallelism and groove shape;

3. The bending edge: the use of bending machine for plate bending, make the edge of curvature;

4. Molding: on the JCO forming machine bending of the plate after half after many step punching, pressure into a "J" shape, and the other half of the steel plate bending, same pressure into a "C" shape, eventually forming the opening "O" shape
5. Early welding: the forming of straight seam welded steel pipe joint with gas protection welding and continuous welding (MAG);

6. The welding: the columns more wire submerged arc welding wire (up to 4) in the straight seam welded steel pipe inside;

7. The welding: adopting many wire submerged arc welding of columns in the side of straight seam submerged arc welding steel pipe welding;

8. Ultrasonic inspection Ⅰ: inside and outside of straight seam welded steel pipe weld and weld on both sides of the base of 100% of the check;

9. X-ray Ⅰ: 100% of inside and outside weld X-ray industrial TV inspection, using image processing system to ensure the sensitivity of detection;
10. Hole enlargement of submerged arc welding and straight seam steel pipe length hole diameter in order to improve the size precision of steel tube, and improve the distribution of stress in steel tube;

11. Hydraulic pressure test: steel pipe after hydrostatic testing machine for hole enlargement by root inspection to ensure the test pressure of steel tube meet the standard requirements, the machine has the function of automatic recording and storing;

12. Chamfering: after the inspection of steel pipe to pipe processing, meet the requirements of tube end groove size;

13. The ultrasonic inspection Ⅱ: root by ultrasonic inspection to check again after the straight seam welded steel pipe in the hole diameter, water pressure may produce defects;

14. X-ray Ⅱ: for hole enlargement and after water pressure test of tube X-ray industrial TV inspection and pipe weld shooting;

15. The pipe magnetic powder inspection: check on this to find out the pipe defect;

16. Corrosion protection and coating: qualified steel pipe according to user requirements for corrosion protection and coating.

The requirement of the production line of galvanized steel pipe

Galvanized steel pipe to the requirement of the production line has a special, especially in the production environment, a good environment can help us better production, improve production efficiency and production quality, especially the galvanized steel pipe product of this need a stable environment.

Firstly, it shouled ensure the production line for process, equipment, heating, ventilation, drainage and other aspects of meticulous work, all work must be around the center of the quality of the galvanized steel pipe, as long as the quality assurance of galvanized steel pipe is good, all other factors we can all achieve.

Galvanization steel tube is very wide USES, especially in some natural gas pipeline, heating and so on need high strength and quality of pipeline industry, galvanized steel pipe has more obvious advantages than other steel pipe.Galvanized steel pipe used as water heating, generate a lot of rust scale, after a few years tube flow including not only pollute the sanitary ware, and mixed with smooth wall not breed bacteria, heavy metal corrosion caused by the water content is too high, cause serious damage to human body health.In order to make the galvanized steel pipe has a bright appearance and good corrosion resistance, in addition to the hot galvanizing technology on, also can use electric galvanizing technology.

Thursday, September 25, 2014

Problems of steel pipe concrete structure

With excellent seismic performance is an important feature CFT for reasonable and safe to promote this type of structure in the earthquake zone, must be studied in depth the dynamic performance. However, recently studied abroad basically only ten experimental study on the dynamic performance of concrete pipe, still does not provide design formulas for calculation of the theoretical and specifications used; while relatively little research on steel concrete creep and fatigue properties, mainly in Experimental study mainly due to lack of reasonable design training methods, to a certain extent, restricted the steel concrete in high-rise buildings and railway bridges and other projects.

As a new steel concrete structure, China has not yet formulated the relevant steel and concrete structural fire design side provisions, so restrict the application of such structures. The structure has been built on, whether it is outsourced to concrete or coated with fire-resistant coating to ensure the safety and structural fire protection requirements are biased ten conservative and wasteful, the lack of scientific and unity. Therefore, on the basis of theoretical research and engineering practice, should be worked out for our country's steel concrete structure fire code as soon as possible.

N-point steel beams of concrete structures has been a focus of engineering applications and research. Although the design rules and many researchers recently made a number of nodes in the form, but it should be incorporated into the design rules as soon as possible, to provide a foundation for the promotion and application of steel pipe concrete structure. In addition, the dynamic performance of the node structure set up training as a key, relatively few studies of construction difficulties static properties.

Since most ordinary steel concrete structure is characterized by high Bian to a few anti-bearing capacity and good ductility, toughness, and can only be used as a pillar, not used as flexural members, it is of limited use. From the research literature at home and abroad to see prestressed steel concrete composite spatial structure and the advantages of prestressed concrete steel combination of technology, generally used only as a building pillars and arches of the bridge, not applied to the space frame or net title medium-sized racks space structure or member. If its in-depth study to ascertain the force deformation characteristics and failure mechanism of prestressed concrete steel structure, the establishment of computing theory and design methods, you can expand the applications of this new type of composite structure.

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.