High-frequency electric resistance welded (ERW) pipe as a whole without heat treatment, to achieve circumferential weld residual stress around 350MPa, close to the yield strength of the pipe. When the weld processing into working electrode, the residual stress is reduced to 100MPa or less. Circumferential tensile stress can reduce the corrosion potential of welds, accelerated corrosion, increased sensitivity coefficient trench etching after the heat treatment of the welded pipe, the circumferential weld tensile residual stress is small, to 10 ~ 100MPa, after processing into a working electrode its circumferential tensile stress is little change. Trench etching is generally believed that acute heat in the welding process, the results of local tissue metal and chemical change caused by quenching. In the high frequency resistance welding process, within the initial 0.1s, temperature was raised to 1600 ℃, the integration process section MnS decomposed into S or converted to FeS, within the next 4 ~ 6s, the temperature dropped to 400 ℃, then water-cooled to room temperature. S and sulfide-rich seam zone is through the rapid heating, rapid cooling to achieve. For high sulfur content (mass fraction> 0.01%) steel, the corrosion of the trench produce MnS inclusions about; the loss of low sulfur content steel trench produces solder alloy, residual stress and increase the carbon content related. Uneven temperature field of welding process is a root cause of welding stress and deformation. In the small thickness of the weldments, welding residual stress is substantially plane stress, stress in the thickness direction is small. In the free state the welding plate, in the vicinity of the weld and the tensile stress is generally in the stress away from the weld compared. Residual Stress can affect the strength of the weldment, stiffness, stability, accuracy and corrosion resistance. The elimination of residual stress, the general overall heat treatment. Since the annealing temperature is too high will result in material strength and organizational changes or the second phase precipitates, the annealing temperature is too low to remove the effects of residual stress is unlikely, therefore, to the steel to stress annealing 500 ℃ 1h, after slow cooling, reducing the welding residual stress member, improve the uniformity of the organization and composition. Correspondence between before and after heat treatment corrosion current density and tensile stress, it can be seen, not heat-treated samples corrosion current density increases with the tensile stress significantly increased, and the corrosion current density is much larger than the sample after the heat treatment. It showed that after heat treatment, corrosion resistance ERW welded plate significantly improved.

The ultrasonic probe to be completed by the power of sound energy between each other and transform the physical characteristics of ultrasonic waves in an elastic medium to convey when the pipe ultrasonic flaw detection principle foundation. Experiencing disadvantage emitted ultrasonic beam directed to convey in a tube, reflecting both the occurrence of waves and wave attenuation occurs. After signal processing flaw detector, such as the selection reflection detection, echo signal can be obtained shortcomings, such as the use penetration testing method can be achieved by virtue of shortcomings signal attenuation through the waves. Both can give quantitative shortcomings indicated by the instrument. Using the principle of electromagnetic induction or piezoelectric effect can stimulate the inner tube is not the same type of ultrasound. Thus, the piezoelectric ultrasonic and electromagnetic ultrasonic pipe can be used for ultrasonic  inspection. But EMAT only for ferromagnetic materials. Selection of shear (or plate wave) reflection method (or penetration method) in the probe and the pipe relative movement active state inspection, as long as the special large-diameter pipe inspection technology can be conducted. Should take the initiative to check the time or skill to ensure that the beam tube full scan appearance. Such inspection shortcomings longitudinal beam conveyed in the tube wall along the circumferential direction; disadvantage when checking lateral beam conveyed in the wall along the tube axis. Longitudinal and transverse defects inspection should be carried out in two opposite directions of the tube. When the demand side did not make identification lateral side only drawback for inspection longitudinal shortcomings. Endorsed by both sides to negotiate, longitudinal and transverse defects inspection can be carried out only in one direction of the tube. Choose a good coupling active or craft examining them, and not detract from the appearance of the pipe coupling medium.

Leveler is metal profiles, bars, tubes, wire, etc. straightening equipment. Straightening roll straightening machine by pressing on the bars and so it changes straightness. Usually there are two rows of straightening rollers, varying amounts. There are also two roll straightener, relying on two roll angle (intermediate concave hyperbolic rolls) material changes in different diameters straightening. The main types of pressure straightening machine, balancing roller straightening machine, shoe roll straightening, rotating anti-leveler and so on. Principle of straightening machine Roller position with the movement direction an angle straightening products, two or three large active pressure roller, driven by a motor for rotation in the same direction, on the other side of a number of small rolls are driven pressure rollers which It is relying on the rotating rod or tube to be rotated by the frictional force. In order to achieve compression roller products required, these small rollers may be simultaneously or separately adjust the forward or backward position, the more general the number of rollers, the higher the precision straightening products. After the article is roll bite, we continue to make linear or rotary motion, thus making all aspects of the product to withstand compression, bending, flattening and other deformation, and finally achieve the purpose of straightening.

Comparison of mechanical expanding and hydraulic expanding has the following advantages: (1) The production of large diameter steel pipe aging rate. Since the water pressure expanding low-pressure water need to be filled, then pressurized to achieve further boosted when steel yield. As production gradually increasing diameter, efficiency is greatly reduced, for example, to pipe length 12m dollars, when 609.6mm (24in) diameter steel pipe hydrostatic expansion, 36 per hour, while the mechanical expanding, each 28 hours. Of 1067mm (42in) pipe, expanding the use of water pressure, 18 per hour, while 23 per hour when the mechanical expanding. That mechanical expanding, and its efficiency is not the size of the diameter relationship, so relatively speaking increased diameter and also high efficiency. (2) Easily meet the stringent requirements for steel pipe inner diameter. When long-distance pipeline laying, welding steel pipe installed in the field site, with an inner diameter of the base, the smaller the inner diameter of the wrong side two steel tube end after docking, the smaller transport resistance, so the pipe inner diameter accuracy requirements increasingly stringent, while expanding pressure is precisely controlled by the outer mold jacket pipe diameter, the inner diameter dimensional accuracy can not be guaranteed. Mechanical expanding head is inserted into the enlarged diameter steel pipe was expanding, therefore, you can control the precision steel pipe inner diameter, regardless of wall thickness variation. (3) Ovality good. Expanding water pressure, because outside of the welds in contact with the outer mold jacket to near the recessed wall, destroyed the pipe ovality. Mechanical expanding, as long as the weld head aligned expanding segments of the trench, when expanding unfettered welds to form a smooth surface, thus effectively reducing the damage caused by the welded parts. (4) Pipe end shape and high dimensional accuracy. Weld effect expanding the comparison ends pressed into conical steel required pressure head against the head of the press insert seal ring radial seal up, so that the steel pipe and tube end indenter contact portion with expanded diameter steel pipe effect tubular body portion inconsistent. The mechanical expanding not have this phenomenon, pipe ends good shape and dimensions of the field site installation and butt are favorable.

① Pipe wall thickness check: micrometer, ultrasonic thickness gauge, ends not less than 8:00 and recorded. ② Pipe diameter, ovality check: calipers, vernier caliper, ring gauge, measure the maximum points and minimum points. ③ Length of pipe inspection: steel tape, manual, automatic length measurement. ④ Pipe bending degree examination: ruler, the level of foot (1m), feeler, thin measuring curvature per meter, length of curvature. ⑤ Pipe end beveling angle and blunt edge check: Square, pallets.