Welding process and treatment of stainless steel cross

Stainless steel cross usually need to be welded when they are installed. Because of the particularity of material, stainless steel cross are different from ordinary pipes when they are welded. And the treatment of welds after welding is also different. The welds of stainless steel cross are not only beautiful but also rusty. What is the welding and treatment process of stainless steel cross?

　　Because of the different sizes of Stainless Steel Equal Butt Welding Cross, according to the unique welding place of stainless steel cross, as far as possible to reduce the heat input, manual arc welding and argon arc welding are used. For d > 159 mm, argon arc welding is used to bottom and manual arc welding cover. D < 159 mm full-purpose argon arc welding, stainless steel cross welding technical requirements are as follows:

　　DC reverse connection is used in manual arc welding and DC forward connection is used in argon arc welding.

　　Before welding, the welding wire should be brushed off with stainless steel cross brush and washed with acetone. The welding wire should be dried at 200-250 C for 1 hour and used as needed.

　　Before welding, the oil contamination in the range of 25 mm on both sides of the groove is cleaned up, and the range of 25 mm on both sides of the groove is washed with acetone.

　　In argon arc welding, the diameter of nozzle is 2 mm, tungsten pole is hollow tungsten pole, specification 2.5 mm.

　　When welding stainless steel cross by argon arc welding, the back must be protected by argon gas to ensure the back forming. The flow rate is 5-14L/min and the front argon flow rate is 12-13L/min.

　　The thickness of weld seam should be as thin as possible during bottom welding. It should fuse well with the root and form a gentle slope when arc closing. If there are shrinkage holes in arc closing, they should be polished by a polishing machine. Arc extinguishing must be initiated in the groove. When arc extinguishing, arc pits should be filled to prevent arc pit cracks.

　　Because the stainless steel cross is austenitic stainless steel cross, in order to prevent carbide precipitation sensitization and intergranular decay, the interlayer temperature and cooling rate after welding should be strictly controlled. The interlayer temperature during welding should be controlled below 60 C. After welding, it must be immediately water-cooled, and sectional welding should be adopted. This symmetrically dispersed welding sequence can increase the cooling rate of the joint and reduce the welding stress.

Rising raw materials lead to rising prices of stainless steel slip-on flanges

At present, all countries in the world are reducing the production of stainless steel slip-on flanges, which not only makes China's iron and steel industry face a more complex situation, but also makes the global steel industry face many problems.

　　It is understood that the primary problem of ASME B16.9 Class 300 Stainless Steel Slip-on Flange in the world is the slowing down of world economic growth, which restrains the increase in demand for stainless steel slip-on flanges. The world economic situation is still facing many uncertainties, so the stainless steel slip-on flanges industry is facing a more complex situation.

　　Developed countries facing sovereign debt crisis will experience low-speed economic growth has become the consensus of all, and although the emerging market of stainless steel slip-on flanges still maintains a good growth trend, the rising inflationary pressure and the risk of economic "hard landing" will increase. At present, the global economy has entered a new dangerous stage, and the downturn of the world economy will be transformed into factors affecting the growth of global stainless steel slip-on flanges market demand in the future.

　　However, the stainless steel slip-on flanges companies are optimistic, "low and high crude steel production, increased pressure on global stainless steel slip- on flange production supply", "stainless steel flange prices will be supported by raw fuel costs, the trend is expected to be low and high" and other perspectives are full of confidence. It is believed that the global production of stainless steel slip-on flanges will rise again. The production of stainless steel slip-on flanges will be low and high throughout the year. The global production of crude steel is expected to surpass the new development of last year.

Inspection of pipe fitting cap weld

The main production equipment of pipe fitting cap is maintenance. Maintenance as a supplement. Local disassembly and inspection of the equipment are carried out as planned. Clean the prescribed parts and dredge the roads and pipelines. Replace or clean the oil washing line and oil filter, adjust the fit clearance between the parts of Stainless Steel 304 Schedule 40 Butt Weld Pipe Fitting Cap equipment, tighten the loose bolts, and replace the unusable bolts in time. Ordinary maintenance can be done once a month. The large-scale maintenance is mainly based on maintenance workers, with specific operators participating and included in the monthly maintenance plan of the equipment. Such major maintenance is to repair and inspect some key parts of the cap, replace some vulnerable parts, and repair the electrical parts. The local key position recovery accuracy can satisfy the minimum requirement for processing parts. We just want the equipment to run, not to maintain it. It's not possible. Only by combining use with maintenance and maintenance, can the pipe fitting cap be better served for the factory.

　　As a sealing and fastening connector, pipe fitting cap is easy to install, flexible in position and long in service life. It is widely used in large containers in aerospace, petroleum, chemical and other fields.

　　First of all, the weld of pipe fitting cap should be inspected by 100% ultrasound or X-ray. There should be no cracks or other flange connection or strength reduction defects on the surface of the pipe fitting cap. Ultrasound inspection of pipe fitting cap shows that grade I is qualified product and grade II is required for radiation. If the pressure vessel pattern where the pipe fitting cap is located fails to meet the above requirements for the inspection of the vessel shell, it should be carried out according to the contract or the label in the pattern.

Factors affecting corrosion of seamless steel pipe

1. For seamless steel pipes, 0, 10 and F are the main alloying elements which make the have good resistance to pitting corrosion. Other elements may also have some effect, while K and other elements will reduce the pitting corrosion resistance of Q235 Black ERW Welded Seamless Steel Pipe. It is certain that the effect of elements on the corrosion resistance of materials is summarized briefly. The impact of 13 and 0 is changing. 3 is beneficial in solid solution, but harmful when precipitated as intermediate metal phase, 0 is harmless in solid solution and harmful when precipitated with carbide, but slightly harmful.

　　2. The microstructure of seamless steel pipe plays an important role in the resistance to pitting corrosion of alloys. Various phases, such as sulfide inclusions and 3 ferrite. Phases, sensitized grain boundaries and welds may have a decisive impact on the pit corrosion resistance of steel. They are the most sensitive sites for pit corrosion. For the cast seamless steel pipe with complex microstructures and martensitic seamless steel pipe with sensitive microstructures to heat treatment process, the relationship between pitting corrosion and constituent phases is more close. It should be noted that the composite manganese sulfide inclusions are more sensitive to spot corrosion. Therefore, aluminum deoxidizer should be avoided when smelting seamless steel pipe.

　　3. The research on cold-working of austenitic seamless steel pipe shows that the number of pits on the surface of samples increases and the size of pits decreases after cold-working. This is due to the increase of dislocation density in cold processing, dislocation in the surface outcrop is prone to cause pitting corrosion, cold processing has the trend of increasing pitting corrosion.

　　4. For a given alloy environment system, the factor determining the pitting corrosion potential of the alloy is the smoothness of the material surface. In fact, it is meaningless to compare the pitting corrosion tendency of carbon with different surface finish. The effect of surface finish on the spot corrosion properties of seamless steel pipe is shown in the figure. It shows that in the same material environment system, if the surface finish is different, the difference of pitting corrosion potential can be more than 14.

　　The oxide formed by heating in seamless steel pipe in air may have a significant impact on the pitting corrosion resistance. The oxide film produced by welding may be detrimental to the pitting corrosion resistance of the in strong chloride solution.

　　The main function of passivation treatment is to dissolve the inclusions and contaminants on the surface of seamless steel pipe and make them clean. It can also remove the manganese sulfide inclusions on the surface. Such inclusions may become the source of pitting corrosion and thus improve the pitting corrosion resistance of seamless steel pipe. It should be noted that the seamless steel pipe is cleaned by sodium hydroxide solution after passivation.

End demand for welded steel pipe prices has not improved significantly

At the end of the month, the pressure of steel traders also showed very weak thoughts on the very price. After all, when the end of the month comes, most of the merchants are under the pressure of drawing money from the API 5L X42 Seamless Welded Steel Pipe. Under the pressure of capital return, it is inevitable to loosen the operation of moving goods. In addition, the raw materials continue to weaken. Therefore, this is very unfavorable to the recent trend of welded steel pipe prices.

　　It is the most embarrassing situation that steel prices can not enter a rebound period when the macro-level is good. Once the economy weakens again, the pressure steel prices are facing can be imagined. As for why the macro-level of welded steel pipe price can not drive the steel price to rise, we believe that this is still related to the weak demand side of the steel industry, we know that the downturn of the real estate industry has a great drag on the welded steel pipe market. However, in recent years, in real estate, the relaxation of real estate restrictions and government repurchase of commercial housing for housing resettlement shows that the real estate rescue started, which is good news, but as to whether the market can be boosted, we still have to see the specific implementation of the latter.

　　At present,welded steel pipe prices continue to hover at the bottom of the price, reluctant to fall, lack of hard reasons for rising, so we can only wait for opportunities in the continuous narrow consolidation, the market is in fact very painful. The terminal demand of welded steel pipe price has not improved significantly, and the shortage of funds has restricted the speculative market in the early stage of welded steel pipe price; the tangled market of concussion and consolidation is hard to break; although the expectation of steady growth is high, it can bring the welded steel pipe price to what height, the bottom gas of welded pipe price market is seriously insufficient; the businessmen are eager to "profitable shipment, bagging" For safety, there is a temporary lack of opportunity.

Heat treatment technology for oil pipe

The heating temperature of 27MnCrV steel at AC1=736 C, AC3=810 C and sub temperature quenching of oil pipe is selected at 740-810 C. The heating temperature for sub-temperature quenching is 780 C and the holding time for quenching heating is 15 min. After quenching, the tempering temperature of oil pipe is 630 C and the holding time for API 5L Gr.B X52 Seamless Carbon Steel Oil Pipe is 50 min.

　　Because sub-temperature quenching is heated in the two-phase region of alpha+gamma and quenched in the condition of retaining part of undissolved ferrite, the toughness is improved while maintaining high strength. At the same time, the low-temperature quenching is lower than the conventional temperature, which reduces the stress of quenching, thus reducing the deformation of quenching, which ensures the smooth operation of heat treatment of oil pipe, and provides good raw materials for subsequent wire processing.

　　At present, the process has been applied in China. The quality assurance data show that the yield strength Rt0.6 after heat treatment is 820-860 MPa, the tensile strength Rm is 910-940 MPa, the impact toughness Akv is 65-85J, and the destruction resistance is 100% qualified. The data show that 27MnCrV oil pipe is a high-quality high-grade oil pipe. On the other hand, it also shows that the intercritical quenching process is an excellent method to avoid high temperature brittleness in steel products production.

Preservation of seamless steel pipe

　Choose suitable sites and storehouses:

　　1. The site or warehouse for seamless steel pipe storage should be clean and well drained away from factories and mines that produce harmful gases or dust. Remove weeds and sundries on the site and keep the steel clean.

　　2, in warehouses should not be stacked together with acid, alkali, salt, cement and other corrosive materials on steel. Different types of seamless steel pipe should be stacked separately to prevent confusion and prevent contact corrosion.

　　3. Large size steel, rail, steel plate, DIN17175 Carbon Seamless Steel Pipe and forgings can be stacked in open air.

　　4. Small and medium-sized steel, wire rods, reinforcing bars, medium-sized seamless steel pipes, steel wires and wire ropes can be stored in well-ventilated material shed, but they must be uprooted and underlayed.

　　5. Some small steel products, thin steel plates, steel strips, silicon steel sheets, small-caliber or thin-walled seamless steel pipe, various cold-rolled and cold-drawn steel products, as well as high-priced and corrosion-prone metal products, can be stored in storage.

　　6. Warehouses should be selected according to geographical conditions. Generally, ordinary closed warehouses are used, which have roofs with walls, close doors and windows, and ventilation devices.

　　7, the warehouse requires clear weather to pay attention to ventilation. When wet, close the damp proof and keep the suitable storage environment. Seamless steel pipe can solve the related problems directly.