管道焊接过程中克服磁偏吹的方法

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Pipe welding process overcome arc blow method

XuTieHeng FanYongMing

(China petroleum engineering branch, kindly first Hebe langfang 065000)

Abstract: in the oil and gas pipelines in the construction process of welding, often encounter arc partial blow phenomenon. Some arc partial blow causes are difficult to be determined, and the serious influence the welding process of forming and welding, lead to welding flaws. For this analysis of petroleum pipeline welding arc blow in the construction process of the influence on the quality of welding, and connecting with the pipe welding construction experience of several can effectively eliminate and reduce arc blow method.

Keywords: pipeline construction; Welding; Arc blow; degaussing

preface

In oil and gas pipelines in the construction process of welding, often encounter arc partial blow phenomenon. Usually by replacing welding rods, adjust welding arc Angle, down the height, the adjustment ground position, rearrange equipment, such as welding can eliminate or reduce; But there are also some arc blow phenomenon, and the reason is not very clear, in a few kilometers, a few tens of kilometers long pipeline welding construction process has always been there, the serious influence pipe welding quality [1].

A natural gas pipeline construction in China welding during an a lot of arc blow phenomenon, of the welding construction quality has seriously affected. The causes of the arc blow is not very clear, pending further analysis, effective solutions need further investigation.

1 arc blow to the influence of the welding

In the field of welding technology has changed the electric arc welding arc shape, the mother material influence melting and weld forming; Through the electromagnetic stirring role, change the welding pool in the process of liquid metal crystalline mass transfer and heat transfer process, which changes the crystallization of grain size of the method, the mechanics performance of the weld decreased significantly, produce porosity, incomplete fusion, crack welding defects.

1.1 to the arc and the influence of the pool

Welding arc is a continuous gas discharge phenomenon, plasma. Usually, in all kinds of arc force, under the action of arc welding is cone shape. But, in additional magnetic field under the role of arc shape change greatly, which produce the arc blow phenomenon. Because arc shape and metal motion state changes that lead to welding pool change shape. Pool by the liquid metal disk blow of function, rotating around the welding pool. Molten pool front-end liquid metal along the side of the pool to flow, the corresponding molten pool tail liquid metal in the other side of the forward flow. Because the molten pool front-end liquid metal to the high temperature, flow in process make side than the fusion, fusion another side than small, cause welding pool of temperature field of asymmetry and appearance shape molten pool of asymmetry.

1.2 to the organization and the influence on the performance of the weld

According to the solidification theory, grain size and morphology of organization by the nucleation rate and subcooling influence. For a certain ingredients of alloy, its inherent cause composition undercooling solute the enrichment layer by the liquid temperature gradient width and the cooling speed two factors. Usually, the welding joint organization for the cellular crystal or cellular crystal branches.

When a magnetic field effect, because the pool of the asymmetry of the temperature field, make welds on both sides of the liquid temperature gradient G and the cooling speed R are changing, so on both sides of weld bead solute uneven distribution. The distribution of the solute different, cause on both sides of weld bead heterogeneous nuclear particle concentration form differ, nucleation rate different; Lead to different degrees composition undercooling, so in welding seam organization on both sides of the word size, shape markedly different, lead to weld the mechanical properties of the serious decline [2].

1.3 to the influence of the welding defects

Arc blow in arc burning instability, add in arc, the power of the column is not stable, it is shown transition irregular, leading to the weld pool irregular, cause continuous or intermittent bite edge, root in not weld fully, root fusion defect such as bad. The existence of the arc blow undermined arc around the protective atmosphere, make easy pool mingling with the harmful gas such as air, causing porosity, slag defect such as [3].

2 arc blow the reasons of the analysis

2.1 false arc blow phenomenon

Due to the steel pipe in the wild environment long-term sun exposure, the wind blows on the steel tube to produce static charge, and the steel pipe coatings in the earth and steel pipe played the insulation between the effect, make steel tube on a large amount of static charge enrichment. In the mouth, electrostatic induction role in steel, cause welds produce electrostatic field position, as shown in figure 1 b, as shown by the role of the arc electrostatic field from the axis of welding rod, and produced the partial blow phenomenon. Because this is caused by the electrostatic field, so called false arc blow.

2.2 itself of the magnetic field of the current to produce cause arc blow

Welding arc arc beam is a certain degree of ionization of gas, to certain direction form current in arc around produce a magnetic field. For some reason that arc itself the magnetic fields produced by the distribution uniformity was broken, the arc due to uneven deviating from the electrode force around the axis of the direction, which produce the phenomenon of arc blow (4, 5), as shown in figure 1 c below.

2.3 pipe caused by residual magnetism arc blow

Pipeline steel for hard magnetic materials, its characteristic is easy to keep some magnetic after magnetization, the construction work environment magnetic field, and construction process of magnetic material and met will allow welding residual magnetism, so that the back of the welding process produces arc blow. If HanKou remanent over a certain value, arc blow phenomenon will very serious, can't even welding process.

2.4 the effects of environmental factors

Long distance pipeline welding construction site in the wild are mostly environment, along the pipeline construction site the extension direction changes, so the magnetic field around construction sites from arc blow nots allow to ignore. Usually, this because the magnetic field around construction sites from arc blow is not very serious, but because of the cause caused difficult to judge, often difficult to eliminate, is often a long pipe welding construction process has always been there, welding process cause major problems.

3 solve arc blow method

3.1 grounding method

The welding when construction, will the welding power always connect to welding of groove, and again from mainland line connection point welding grooves place receives a metal line even to the earth, as shown in figure 2 shows. This method for ground position not correct, groove cut causes such as static charge cause false arc blow have better effect.

3.2 adjust welding dip Angle, short arc welding method, segmentation method back welding

In operation on appropriate adjustments to the electrode Angle, the electrodes to arc blow direction tilt, or by using welding method and short back arc welding method can effectively overcome arc blow.

3.3 heating

Welding of the residual magnetism on the main is arranged in order of magnetic atoms dependence and cause. For the disorders of welding magnetic w. to reduce or prevent arranged the purpose of arc blow, can exist on a butt weld ends to the parts of the residual magnetism, local heating, general heating temperature of 250 ~ 300 ℃. The production use in addition to good effect.

3.4 cable winding method

According to the arc blow judge the direction of the magnetic field direction, will be in charge of the central part of the welding torch cable of the mouth RenYiDuan winding few laps in the coil electricity at the same time welding.

3.5 plus the ferromagnetic materials' method

In the welds and near ferromagnetic materials, a ferromagnetic materials side, because the ferromagnetic materials permeability, most made of ferromagnetic material field lines through, so that this side of space field lines goes lean, will reduce the influence of electric arc. So put the magnetic field of the ferromagnetic materials produced symmetrical, try to make arc of ferromagnetic material distribution around even, so that the field of electric arc reduce the influence of even disappear.

summary

(1) long pipeline construction in welding often adjust Angle or the welding with subsection welding method to return to reduce or eliminate arc blow, general can get satisfactory effect.

(2) heating and also of the ferromagnetic materials and can greatly reduce arc blow to the influence on the quality of welding.

(3) cable winding method in operation because it is difficult, in with the construction of pipe welding.

reference

[1] new etc. Use of magnetic resistance properties of steel pipe welding residual magnetism reduce the influence. Welded pipe. 2008, 35 (3) : 76 ~ 77

[2] ZhangZhongDian etc. Additional magnetic field the welding process. The effect of welding. 2002 (3) : 10 ~ 14

[3] SuiYongLi etc. Oil and gas pipe welding the construction process of arc blow. Technology and new technology. 2005 (special issue 4) : 33 to 34

[4] WangGuiSheng. Overcome and eliminate arc blow for welding arc influence method. The welded pipe. 2000, (2) : 51 ~ 53

[5] ZhuYongGuo. Overcome and eliminate arc blow for welding arc. The effect of petrochemical construction. 2007, 29 (3) :-43