Wednesday, October 29, 2014

Advantages of cement mortar lining anti-corrosion pipe

As the cement mortar lining anti-corrosion steel raw cement mortar use is great, in construction, foundation and masonry wall can be used to make adhesives massive masonry materials, such as rubble, red brick use cement mortar; the second is used for interior and exterior plastering. Cement mortar when in use, but also often incorporated additives such as micro-foam agents, water powder to improve its workability and viscosity. Cement mortar in proportion to join the stones, they become concrete.

The biggest advantage of the cement mortar lining of steel corrosion, since the concrete inside the steel pipe, it is possible to absorb large amounts of heat, so the temperature of the cross section of the steel pipe when subjected to uneven distribution of the fire, increasing the fire resistance of steel, slowing the rate of temperature rise of steel, and once the pipe yield, also be able to withstand most of the dirt load, to prevent structural collapse. The experiment proved refractory three hours to achieve the level of savings compared to the requirements of fire and steel pipe coating 1/3 a 2/3 or even more, as the pipe diameter increases, the more savings paint.

After the cement mortar lining of steel corrosion completion of the last step is particularly important, it is dried, refers to the dried 2-3 days in a natural state, is mainly to prevent the shipment of the process due to the turbulence leads to cracks in the cement mortar.

Testing process of Straight seam steel pipe and straight pull steel tube

For the strip progressively coiled tube and straight seam welded steel pipe, depending on the welding process when used in its production can be divided into a continuous furnace welding (forge welding) pipe, tube and arc resistance welding Li key welding pipe three.

1. The continuous furnace welding (forge welding) riveting
Continuous furnace brazed (forge welding) of the pipe is in the heating furnace for heating the steel strip, and then forming edge Pat mechanical pressing method so that the welding together to form a straight seam having a pipe. Its features are: high efficiency, low production costs; but the weld quality is poor, poor mechanical properties. Currently, it is mainly applied to the design temperature of 0-100 ℃, the design pressure of not more than 0.6 MPa water and compressed air systems.

2. The resistance of bare steel
Pipes are produced by resistance welding riveting resistance or induction welding method, a straight pipe with a seam, which is characterized by high efficiency, high degree of automation, deformation and residual stress after welding small; but its high investment in equipment, the quality of welded joints requirements are relatively high; and because the joint is inevitable impurities, so fitting plastic and low impact toughness. At present, it is mainly applied to the design ju not higher than 200 ℃ of water, gas, air, steam and other heating and oil and gas industry can be fluid and non-tender fluid, low-pressure pipe.

3. The arc tube bad record
Arc welding pipe is produced by electric arc welding steel pipes. Its characteristics are achieved complete metallurgical bond joints, the mechanical properties of the joint can fully meet or achieve the mechanical properties of the base material. After saying after appropriate heat treatment, arc welding straight seam steel pipe seamless steel pipe can be achieved using conditions will replace it with conditions. At present, it is mainly applied to the design not higher than 200 ℃ of water, gas, air, heating and other design pressure less than 5.0 MPa steam pipes.

Tuesday, October 28, 2014

Detection of seamless steel pipe

Detection methods are mainly magnetic particle inspection of seamless steel pipe or penetrant testing can be effectively found surface cracks, folding, surface defects heavy leather, hairline, pinholes. For ferromagnetic materials, magnetic particle testing method should be given priority, because of its high detection sensitivity; for non-ferromagnetic material, such as stainless steel seamless pipe, is used penetrant testing method.

When both ends of the cut is less reserve margin, due to structural reasons, detection means, both ends of the head may not be effectively detected, and the end is the most likely site of the presence of cracks or other defects. If the end of the cracks tend to have potential, weld heat affected during installation is also possible to make a potential crack. Therefore, it should be noted that after the detection of certain seamless steel tubes welded area, the expansion pipe ends to detect defects on the online use of austenitic seamless steel pipe, when the insulation is damaged or there may be rain infiltrated the site, it should be noted penetration testing to find stress corrosion cracking or pitting and other defects, but the magnetic particle or penetrant testing can only be detected on the outer surface of the pipe, internal and surface defects are powerless. Detection of the inner surface, in particular the crack defect class detection must be carried out by ultrasonic testing.

High-pressure boiler tubes clear the depth effect

Severe temperature change occurred after burning high sulfur anthracite through the boiler corrosion. Analysis of water wall tube at a high temperature corrosion temperature conditions in a reducing atmosphere high temperature sulfur corrosion mechanism of chlorine corrosion and high-temperature corrosion and corrosion mainly produce, combined use of low sulfur coal than the Yangquan Datong bituminous coal the actual situation, the combustion system transformation. High pressure boiler tube clear the depth shall not exceed the nominal wall thickness of the negative deviation, its cleanup at the actual wall thickness of not less than the minimum allowed. Prevent high-pressure boiler in the fire rapidly warming deformed slump, its measures are varied, the key is to take different approaches depending on the circumstances, such as the use of insulation, refractory steel barrier direct flame burning, reduce the speed of heat transfer postpone the steel temperature, the strength becomes weak time. But no matter what method adopted, the principle is the same. Fire retardant paint is a kind of fire in recent years, more advanced technical measures. Since the impurity elements for high-pressure boiler quality impact, high levels of harmful elements in steel products and the inclusion of control has very strict requirements, to try all kinds of impurity elements are required to control at very low levels, often in production using secondary refining the production process in order to protect its cleanliness.

Special reminder, high pressure boiler tube One installation is difficult, especially supercritical once-through boiler no drum, increasing the starting system, heating pipe systems, bulky traditional subcritical boiler rigid beam than quantity, and all with the heating surface welding installation difficult. High-pressure boiler tubes often in high temperature and pressure conditions when using the tube under the action of high temperature gas and water vapor, oxidation and corrosion will occur.

Friday, October 24, 2014

The cause of the pipeline peeling

Line pipe having a high compressive strength is required, they also require a higher low temperature toughness and excellent weldability. However, in the production and use of the Central Standing Committee found that certain finished steel pipe welds on both sides and there are a lot of varying lengths from the skin defect, seriously affecting the material properties.

Under the inspection and analysis, from the skin defect causes are the following:
(1) oxide inclusions. Slab of large inclusions mainly from powder entrapment. In analyzing the composition of slab surface cracks found near the crack contains a lot of O, Ca, Al and Si and other elements, brittle inclusions composed of high melting point such elements can not easily be adsorbed on the protection of molten slag, it is easy into the liquid steel billet and thus remain in the interior. In the casting process, the large inclusions (such as Al2O3 inclusions) will first be peeled and shell matrix form nascent microcracks, this crack propagation along the strand matrix shell spherical inclusions, and then in the slab surface cracks. Such cracks can lead to lamellar tearing, serious damage to the welding properties of the material, thick steel plate to reduce ductility.

(2) the impact of Cu. Cu case of low melting point elements, easy to segregation at the austenite grain boundaries, and precipitates between the iron oxide layer and the substrate layer, resulting in the formation of low-melting slab surface enrichment-rich phase. Meanwhile, Cu segregation reduces the austenite grain boundary energy to reduce the grain boundary strength.

(3) N elements effect. Steel [N] content and plays a significant layer defects correspondence. The parameters in the mold and cooling the same water flux performance is substantially the same conditions, with the steel [N] content is reduced, significantly reduced from the skin defect. Tests showed that the steel of the [N] is the mass fraction of less than 60 × 10-6 from the skin when the defect rate of 5.8%, [N] is equal to the mass fraction of from greater than 60 × 10-6 at a substantial increase in the defect rate of the skin, can be as high as 76.2 %. For aluminum-containing steel, since Al forms AlN precipitation can reduce the low temperature ductility of the steel, at the same time, AlN tend along the austenite grain boundaries under stress in the vicinity of precipitates will form micro-cracks, leading to crystallization boundary embrittlement. This can be found from the detection of high aluminum slab cracks containing proven.

(4) mold cooling water, pouring temperature and casting speed impact. Appropriate to reduce the amount of water can reduce mold slab surface microcracks, improve the slab quality, reducing hot-rolled sheet rolled skin defects. Reduce the amount of water mold, in essence, with the use of high crystallization rate fluxes similar effect is to reduce the heat transfer rate, slow to realize the slab in the mold of cold, promote uniform growth of shell to improve slab quality. The ability to reduce the pouring temperature and casting speed will help to improve the slab quality, which is a slab mold shell thickness related to high pouring temperature and casting speed will increase the heat flux density, shell thickness thinning, solidified shell to withstand external forces lower, the larger the probability of cracks.

Passivation process of line pipe

Where the line pipe parts, such as electroless plating or other coating requirements, are generally required in pretreatment (including pickling go black, polished, etc.) through the passivation treatment to use when finished or assembled parts. Passivation can improve the thermodynamic stability of line pipe in environmental media, localized corrosion prevention line pipe, line pipe surface so that cleanliness has sufficient and can also eliminate thermal processing line pipe surface oxide.

Passivation process line pipe can be divided into two types of wet and dry. Concrete can be divided into many types. Passivation effect depends both on line pipe passivation process, but also on line pipe material itself, the specific factors are contained elements line pipe, line pipe metallurgical structure, line pipe processing status. In the composition of the elements, chromium, nickel and strong elements belonging passivating iron followed by passivation, and therefore, chromium and nickel content, the higher, the stronger the passivation of the line pipe. Austenitic, ferritic steel pipeline with a more uniform structure, can be passivated better, martensitic steel pipeline through heat treatment to strengthen its multi-phase microstructure of the organization, thus passivation is not strong. Line pipe by passivating the surface finish after machining is preferably, casting, sand blasting, etc. The resulting surface roughness is not conducive to passivation.

Monday, October 20, 2014

The superiority of spiral pipe in uses

According to the nature of doing HDPE plastic spiral coil, with a light texture, high strength, good toughness, easy to lay, water resistance, low cost, corrosion resistance, etc., its performance and economic benefits far exceed the reinforced concrete pipe and general specifications iron pipe, engineering pipe replacement products. In metallurgy, petrochemical and other industries exchanger design, there are various forms of heat, but the presence of a conventional heat exchanger ineffective, difficult to clean, fouling resistance and large more drawbacks, can not meet production of customer needs. According to the spiral knot spiral hose heat exchanger to do its good effect of heat transfer, easy to clean, low fouling resistance, compact structure and so on.

Plastic spiral steel pipe (also called hollow wall winding plastic tube) is a wall structure is very reasonable plastic tube. The overall use spiral structure. In for urban drainage projects, improve drainage capacity facility (or narrow diameter) and engineering service life, easy construction, shorten the construction period, when the water table is high, the depth of excavation and restoration of large or require high road, the project cost significantly reduced. Spiral has many superior heat transfer characteristics and structural features straight tube. Heat transfer coefficient is higher than the straight tubes, more heat transfer area can be obtained in the same space, the longer the pipe is arranged to reduce the seam to improve the safety. So spiral heat exchangers and steam generators in the field of power engineering, chemical, aerospace, and nuclear energy has been widely applied.

Large plastic spiral steel pipe is formed with a "T" shaped ribs with a sheet of polyvinyl chloride (UPVC) mixing the carbon black or high density polyethylene (HDPE) using a hot press method. Then on the volume of the machine roll cut into spiral. By quickly locking mechanical connection, the application of an adhesive or melted PVC reinforced molded plastic spiral. It has a large diameter, high corrosion resistance, good anti-leakage effects, quick construction and other characteristics.