Longitudinal straight seam welded pipe butt weld joint cross-sectional shape, depending on the thickness of the body to be welded before welding groove and then type two sides. When welding thick steel plate, for penetration in contact at the edges out of various shapes of the groove, so that more easily into the welding rod or wire. Groove patterns are one-sided welding the welding groove and the sides of the groove. When you select groove type, in addition to outside should be considered to ensure penetration welding convenient, less filler metal Chi, small welding deformation and beveling of Longitudinal low cost factor. Linker connecting the two is in the welding Longitudinal seam formed called weld. Both sides of the weld in the welding welding heat effect will be, but the organization and performance vary, this area is known as the heat affected zone. Welding due to the workpiece material welding materials, Longitudinal welding current so different, after welding may occur in the weld and heat affected zone of overheating, embrittlement, hardening or softening, but also the weldment performance degradation, deterioration of weldability. This need to adjust the welding conditions, before welding weldment interface preheating, post-weld heat when and weld heat treatment can improve the quality of welding weldment quality. Longitudinal is of two or more homogeneous or heterogeneous material through a combination of diffusion and the question of the atom or molecule is integrally connected to the process, prompting the question of atoms and molecules produce binding and diffusion method is to heat or pressure, or simultaneously heated and pressurized.   In addition, a local weld foot rapid heating and cooling process, the weld zone due to the binding body and four weeks of the workpiece can not freely expand and contract in the weldment after cooling will produce welding stress and deformation. Important product after welding is required to eliminate welding stress, welding distortion correction.

High frequency welder using a unique high-frequency current skin effect and proximity effect, gathered in the welding current at the contact surface, the surface bonding surface temperature rises rapidly, it will be heated to melt solder surface or near-molten plastic state then quickly squeezed into a pressure welding method for joints. This welding method has a number of advantages: the weld heat affected zone of small, fast heating, which can greatly increase the speed and frequency welder weld quality, and available without pickling, shot peening and trimming strip for the blank , while welding high alloy steels and non-ferrous metal pipe, greatly reduce the unit power consumption. We can produce all kinds of metal pipe with a set of welding equipment. Different metals, simply changing the corresponding welding speed and welding power. Depending on the current frequency, high frequency welding machine can be divided into radio frequency current welding and high frequency induction welding, soldering IF current three. Depending on the method of high-frequency current lead tube, high-frequency welding machine can be divided into high-frequency and high-frequency induction welding contact pads in two forms. Offs between the two welding methods are as follows: Advantages of high-frequency welding machine  are: 1) Invalid shunt less; 2) Due to squeeze stick close contact head, high current density, high efficiency; 3) Small heat affected area; 4) The impact of small diameter, can be welded about 8 to 1270 mm diameter tube; 5) Welding speed of up to 100 to 120 m / min, such a high welding speed and groove so that the molten metal layer may not be able to protect the welding light alloy, stainless steel, copper, brass, zirconium and other metal pipe. The disadvantages are: 1) Consumption contact head; 2) There is galvanic corrosion defects; 3) Heating range of small, rapidly melted, detrimental to the tube surface. The advantages and disadvantages of induction welding opposite to the above, in particular the impact of large diameter. In the production practice, usually choose induction welding method. This is due to induction welding contact welding compared with the following significant advantages: 1) Virtually eliminating equipment failure caused by the open, thus increasing equipment utilization and reduce production costs; 2) Stable welding process, welding quality, smooth weld surface; 3) The strip joints and surface quality strict requirements, so as to reduce the labor intensity; 4) Due to the non-electrode pressure, ideal for welding thin-walled tube; 5) No contact electrode consumption, thus saving non-ferrous metals, and saving downtime caused by the replacement electrode; 6) Welding adjustment easy and convenient. However, when the ratio of induction welding contact pads 40 to 50% high power required for the desired power. When the power and welding pipe welding device specifications are the same, induction welding speed of the contact welding speed of 1/2 to 2/3.

So far, the main performance can be speculated that the high-frequency welding from the heat affected zone, and according to the welding time - temperature HAZ microstructure and properties of judgment, therefore, in order to study the characteristics of the HAZ, you must understand the welding unit to adjust the V-shaped area of the strip edges influence of temperature distribution unit.      The middle of 1990s, a number of published works in mathematical calculations based on the establishment of a high-frequency welding theory, mathematical theory most representative: speculation is accurate welding speed and welding power according to the length of the V-shaped region, plates and welding frequency relationship. This theory tube welding has been successfully used for several years, has been in Ma Tours company for performance evaluation of welding equipment, the theory accurately speculate over a wide range of different specifications of steel pipe welding power and welding speed. In theory, the V-shaped area of high-frequency welding temperature distribution of the heat due to the current flowing through the first of the V-shaped area of the resulting decision, thermal conduction of heat determines the penetration depth of the high-frequency current distribution of the weld zone is to look at the strip edges it the penetration depth, the depth of weld penetration is a function of frequency. Characteristics of heat transfer process is that heat penetration depth of the V-shaped zone length and the welding speed functions. The actual state of high-frequency welding steel pipe are: ① current penetration depth is greater than the penetration depth of the heat, which is the result of a temperature distribution under; ② heat penetration depth is greater than the penetration depth of the current, which is another result of the temperature distribution under; ③ heat penetration penetration depth, which is a transition temperature distribution. In short, the weld HAZ setup time - temperature curve, combined with high-frequency current heating effect (current penetration depth) and welded V-shaped area heat conduction (heat penetration depth), controls the welding zone temperature distribution. If you can pipe unit according to a number of important parameters (diameter, wall thickness, welding power, welding frequency, V-shaped area of pipe length and performance) to calculate the current penetration depth and thermal penetration depth, then we can predict the temperature distribution of the weld V-shaped area of the strip edges, this method can accurately predict and control weld heat affected zone.

Submerged arc welding of straight seam steel pipe has the following advantages: Submerged arc welding heat concentrated, welding safety metal spatter loss, there is no waste of the electrode head, workpiece thickness h may also be without groove, thus saving metal material. Submerged arc welding can be employed large welding current, arc heat concentration, deep penetration, the wire can be continuously fed unlike electrodes as frequently replaced, so the productivity of 5 to 10 times higher than that of manual arc welding village. Submerged arc welding is not visible arc welding, welding fumes and rarely, but also mechanical automatic operation, and thus the working conditions have been greatly improved. Submerged arc welding is a limitation: since the arc is not visible, thus demanding joint processing and assembly, welding position subject to certain restrictions, are generally always in flat-position welding.

In order to detect LSAW longitudinal weld defects in the weld total length of horizontal or vertical use jet (water column) coupled ultrasonic flaw detection. Jet (water column) ultrasonic flaw detection is between the probe and the pipe coupling by jet, so that the longitudinal wave probe beam emitted by the incident to the interface of water or steel pipe, a steel pipe weld inspection by pure shear wave conversion. Therefore, to achieve the weld pure shear testing, the incident angle of the probe must be between Ⅰ critical angle and the critical angle II, drawn by the law of refraction. Can be obtained by calculating the longitudinal wave is incident from the water to the steel in the first critical angle I and II were critical angle 14.5 ° and 27.3 °. Longitudinal ultrasonic testing: non-destructive testing is on-site detection, rapid non-destructive, without having to reach the lab, greatly improving efficiency. Analysis speed is much faster than desktop spectrometer, only a few seconds to display the results of the analysis. Small size, light weight, easy to carry. NDT ultrasonic flaw detection for very many, testing principle Longitudinal not divided: ultrasonic testing, X-ray testing, testing film. Testing methods are: single-sided double-sided testing, double-sided double-sided testing, single-sided unilateral testing. The choice of which depends on the testing straight seam steel pipe wall thickness and width of the weld, the weld testing if too wide on one side of the double-sided double-sided or double-sided testing (generally used for thick seam width) of Implementation of the standards: GB 11345-89 (most common), GB / T11345-2013. DW1.1 standard inside a two minute testing, usually less demanding steel structure is three testing no matter what standard testing must meet the requirements of customers in accordance with the national standard steel pipe testing to a weld two.