Double wire welding wire extension length on welding quality as well. Wire elongation is too large, the resistance is large, the heat resistance will increase, resulting in reduced penetration, poor fusion, flux than the height of the stack increases, increase the amount of weld projections. In addition, the contact tip heat increased, even red-hot oxide overheat and shorten the life of the contact tip. Wire elongation amount is too small, the impact of flux than the height of the stack, or even open arc, penetration increases, projecting height decreases, affecting weld. Spiral welded pipe production, the first multi-purpose wire diameter 4 mm, the diameter of the wire after the multi-purpose 3 mm. Former wire in order to ensure penetration, DC reverse, requiring high current, low voltage, so the first wire elongation should try to choose shorter, but not too short, usually 28 ~ 40 mm. After AC wire, requiring low current, high voltage, in order to increase the weld width to ensure good weld, so after the wire elongation choose slightly longer. Because after the wire diameter is generally thinner than before the wire and welding wire around the pitch and they have a small inclination, prone to cross two wire contacts and seriously undermine the stability of the welding process, so the elongation should not be too long, the general choice 24 ~ 36 mm.

There are many longitudinal quality inspection method, wherein the physical method is the most commonly used test methods, physical examination is the use of some physical phenomena or measurement methods were tested. Longitudinal Q235B material or internal defects and inspection, it is generally used NDT methods. The current non-destructive testing with a magnetic detection, ultrasonic flaw detection, radiation detection, penetration testing and so on. Magnetic inspection Magnetic testing can only find defects Longitudinal magnetic surface and near surface defects and can only do quantitative analysis, the nature and depth of the defect can only be estimated based on experience. Test is the use of magnetic leakage magnetic field generated by the magnetization of ferromagnetic Longitudinal to discover defects. Press the measurement of magnetic flux leakage methods can be divided into magnetic particle method, the magnetic induction method and a magnetic recording method, in which the magnetic particle method most widely used. Penetrant inspection Penetration testing is the use of permeability and other physical properties of certain liquids to discover and display defects, including coloring test testing two kinds of fluorescence can be used to detect defects of ferromagnetic and non-ferromagnetic material surface. Ray detection Ray detection is the use of substances and attenuation in the material properties rays penetrate to discover a flaw detection method for defects. Press ray detection used can be divided into X-ray detection, γ-ray detection, energy-ray detection of three. Because of their different methods of displaying defect, each ray detection are divided ionization method, screen observation, photographically and industrial Television Act. Ray inspection is mainly used to test the internal Longitudinal welds crack, incomplete penetration, porosity, slag and other defects. Ultrasonic Inspection Ultrasonic metal and other media spread evenly, since the interface of different media will produce reflection, it can be used to test internal defects. Ultrasonic welding can test any piece of material, defects in any part of, and can be more sensitive to the position of a defect is discovered, but the nature of the defect, the shape and size difficult to determine.

For large-caliber straight seam steel pipe, the three elements of the solution treatment temperature, holding time and cooling rate. Stainless steel seamless solution treatment effect is as follows: 1: Make large diameter pipe joints and tissues of uniform composition, which is particularly important for raw material, hot-rolled tubes because each section rolling temperature and cooling rate are not the same, resulting in tissue structure is inconsistent. Increased at a high temperature atomic activities, σ phase dissolved chemical composition tends to be uniform, after rapid cooling to obtain a homogeneous single phase. 2: Eliminate work hardening, in order to facilitate continued cold. By solution treatment, recovery distorted lattice, elongated and broken grains recrystallization, to eliminate the internal stress, the wire tensile strength decreases and the elongation increases. 3: Recover large diameter pipe joints inherent corrosion resistance. Because cold causes carbide precipitation, lattice defects, the corrosion resistance of stainless steel pipes decreased. After solution treatment corrosion resistance of stainless steel seamless return to top condition. Solution temperature is mainly determined by the chemical composition. In general, many kinds of alloying elements, high levels of grades, the solution temperature should be increased accordingly. Especially manganese, molybdenum, nickel, silicon content of steel, only the solution temperature to fully dissolve in order to achieve a softening effect. But stable steels, such as 321 stainless steel pipe, large diameter straight seam steel high temperature solid solution of carbide stabilizing elements sufficiently dissolved in austenite, will Cr23C6 form in grain boundary precipitates in the subsequent cooling, the resulting crystals intergranular corrosion. For the stabilizing element carbides (TiC and NbC) does not decompose solution, generally use the lower solution temperature.

Preliminary quality of lsaw steel pipe is including joint quality and welding quality (1) Commissure (ie molding seam) no wrong side or wrong side is less than the predetermined value, the general provisions of the wrong side of the plate thickness ≤ 8%, the maximum does not exceed 1.5mm. (2) To ensure that there is proper weld penetration depth and deposition rate, it is necessary to ensure that no cracks after welding, no burn-through phenomenon, but also to control the height of the weld, the external weld reinforcement does not have an impact. (3) Continuous bead, good shape, in order to facilitate the final outer guarantee welding quality. (4) There is no weld seam side, pores, cracks, slag, and burn the back of weld defects such as weld center requires deviation ≤1 mm. (5) No arc burns, small splash, do not affect the pipe end beveling and surface quality. (6) Weld metal matching the physical and chemical properties of the weld metal to meet quality requirements.

Oil casing according to the different ways can be divided into: surface casing, the intermediate casing, the production casing. the well casing. The main surface of the sleeve is: through the top of the casing head installed to support the suspension and subsequent layers of the casing. There is a shallow surface layer and the front portion of the complex formation isolation, protection against drilling shallow layer of pollution. Intermediate casing or a casing technology, is used to the different strata formation pressure or can be easily collapse and easy to leak complex formation isolation. Production casing layer is used to protect the production, as well as the oil and gas transportation from the production floor to the ground provided by the channel. After drilling liner is used to reduce the time and casing cementing, rig loads and loads of the sleeve after the post-production, saving casing and cement, to reduce the cost of cementing. Using industries and fields, the oil casing to show the important role and good performance.