CN112846460A

CN112846460A - Stress-reducing welding method for repairing metal pipeline on site

Info

Publication number: CN112846460A
Application number: CN202110018002.3A
Authority: CN
Inventors: 蒋应田; 黄小诚; 徐世雄; 蒋常铭; 靖爱群; 邓跃兵; 蔡永梅; 蒋新愿; 马喜龙; 魏哲如; 温斌
Original assignee: Liaoning Shihua University
Current assignee: Shenyang North True Vacuum Technology Co ltd
Priority date: 2021-01-07
Filing date: 2021-01-07
Publication date: 2021-05-28
Anticipated expiration: 2041-01-07
Also published as: CN112846460B

Abstract

The invention relates to a stress-reducing welding method for repairing a metal pipeline on site, which comprises the steps of firstly determining a pipe section with relatively good weldability according to the weldability of a dissimilar metal pipe, and arranging a stress-reducing groove at a certain position away from a welding end. When two pipes are in butt welding, the stress groove is subjected to low-rigidity deformation to release the restraint stress during welding, so that the joint is welded in a low-stress state, and cracks at the welding part are avoided. And after the welding of the joints between the dissimilar steel metal pipes is finished, the performance is adjusted, and the welding is qualified through detection, the repair welding of the stress groove can be carried out. The invention can reduce the welding constraint stress of the pipe joint and is beneficial to reducing the difficulty of the repair welding process of the stress groove.

Description

Stress-reducing welding method for repairing metal pipeline on site

Technical Field

The invention belongs to the technical field of equipment pipeline installation and maintenance of large-scale industrial enterprises, and particularly relates to a stress-reducing welding method for repairing a metal pipeline on site, which is mainly applied to the fields of pipeline installation and maintenance of major equipment such as petrochemical industry and industrial boilers. It is especially suitable for welding and maintaining two kinds of pipes with different performance.

Background

In the production of large-scale industrial enterprises such as petrifaction enterprises, boilers, ship manufacturing enterprises and the like, pipeline field installation and maintenance welding are frequently encountered. At this time, the assembly craters are generally difficult to completely meet the ideal state, so that the joint is in a high stress state in the welding process. Especially in the welding of large-caliber thick-walled pipes. In some cases, the welding maintenance is more severe, for example, in the explosion maintenance of the ethylene cracking furnace tube, the performance is deteriorated because the furnace tube is carburized in the running process, and the furnace tube is replaced and welded by the same material, but the actual effect is the same as that of the welding of the furnace tube made of different materials. Therefore, the prior literature or patent technology focuses the solution of the technical difficulty on the welding performance of the material. And a low stress assembly welding process is introduced in the domestic published patent document 202010322690.8. Specifically, a short pipe with the length of 100mm is cut from a lengthened new pipe, the short pipe is welded to an old pipe, and then the new pipe and the short pipe are welded. The purpose of such welding is to prevent the new and old pipe sections from affecting the hot cracks due to additional stresses caused by the assembly and the quality of the new pipe during welding. In addition to this, welding between pipes made of different steel materials, such as low carbon steel/heat resistant steel pipe, low carbon steel/stainless steel, stainless steel/heat resistant steel, etc., is also performed at a welding site. The adjustment of the welding restraint stress between the dissimilar steel metal pipes can be solved by referring to the above patent technology. However, another new problem occurs in field construction, namely, more craters are added, which does not increase the workload of installation assembly, and also increases the difficulty of weld forming, because the newly added craters also need single-side welding and double-side forming. Therefore, the invention provides a new process method to solve the problem.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a stress-reducing welding method for repairing a metal pipeline on site, and solves the problems that the welding operation is complex and the performance is difficult to guarantee when two pipelines made of different materials are installed and maintained in the prior art.

The technical scheme of the invention is as follows:

a stress-reducing welding method for field rehabilitation of metal pipes, comprising the steps of:

step 1, determining a welding method according to the material, the pipe diameter, the pipe wall thickness and the construction conditions of a pipe to be welded, evaluating a welding process according to technical requirements, and determining correct welding process parameters;

step 2, preparing groove machining of the welded pipe fitting according to the process evaluation technical parameters, wherein the groove machining is required to be carried out by adopting machining, and the groove size is executed according to the national standard or the corresponding technical standard;

step 3, selecting one pipe fitting with relatively good welding performance from the two welded pipe fittings, and forming a stress groove on the pipe end of the pipe fitting by using machining equipment;

step 4, assembling butt joint grooves, and assembling between the pipes subjected to dissimilar welding according to technical requirements of process evaluation or related technical specifications, wherein the assembling quality meets the technical requirements of field welding;

step 5, welding the qualified welding seams of the group, and carrying out the welding process according to the technical requirements qualified by pre-evaluation;

and 6, welding and repairing the stress groove, wherein the stress groove is welded and repaired after the butt weld of the dissimilar welding pipe fittings is qualified through inspection and performance regulation, and the welding and repairing process is carried out according to the technical requirement qualified through pre-evaluation.

In the step 3, the distance from the center position of the stress groove to the butt welding groove is within the range of 50-100 mm.

In the step 3, the shape of the stress groove is a V-shaped combined shape with a flat bottom, the width of the flat bottom is 3-4 mm, the angle of the groove is 60 +/-5 degrees, and the thickness of the residual pipe wall of the groove is 2-3 mm.

In the step 3, the slope surface and the flat bottom of the stress groove are in smooth transition, and the transition radius is larger than 10-20 mm.

The invention has the following advantages and effects:

stress grooves with reduced wall thickness are arranged at certain positions away from the welding seam to reduce the restraint degree of the welding joint. The stress reduction groove is required to be arranged at one end with good weldability of steel, so that the welding restraint stress of the pipe joint can be reduced, and the difficulty of the repair welding process of the stress groove is reduced. In addition, the material with good weldability has lower strength and good plasticity and toughness, is easy to deform and is more beneficial to reducing the assembly stress. In addition, the stress groove is arranged at a distance of 50-100 mm from the butt welding groove, so that the heat transfer process of the joint during welding of dissimilar metals is not influenced, and the restraint degree of the joint can be effectively reduced. The shape and size of the stress groove are selected to be proper, so that the restraint degree is reduced, and excessive deformation and even breakage are avoided. In addition, repair welding work for the stress groove and increased economic cost are also considered.

Drawings

FIG. 1 is a schematic structural view of the present invention when welding pipes.

In the figure, 1, an old pipeline base metal, 2, a surfacing transition layer, 3, a welding seam metal, 4, a new pipeline, 5 and a stress groove welding seam;

alpha-groove angle, c-groove bottom width, R-smooth transition radius.

Detailed Description

Examples

step 3, selecting one pipe fitting with relatively good welding performance from the two welded pipe fittings, and forming a stress groove on the pipe end of the pipe fitting by using machining equipment; the distance between the center position of the stress groove and the butt welding groove is within 50-100 mm; the shape of the stress groove is a V-shaped combined shape with a flat bottom, the width of the flat bottom is 3-4 mm, the angle of the groove is 60 +/-5 degrees, and the thickness of the residual pipe wall of the groove is 2-3 mm; the slope surface and the flat bottom of the stress groove are in smooth transition, and the transition radius is more than 10-20 mm;

Application examples

1. Aiming at the explosion welding maintenance of the furnace tube in the radiation section of the ethylene cracking furnace of a petrochemical enterprise, the material of the furnace tube is 25Cr-35Ni-Nb, the specific components are shown in Table 3, and the specification is phi 120 x 8. When the furnace tube is burst, the operation time of the furnace tube is longer, the material of the furnace tube is subjected to a carburizing process, and the performance of the furnace tube is changed to a certain extent. The common practice of the engineering is to process a welding groove on a broken section of an explosion-broken furnace tube for transition surfacing welding and then butt welding with a new connecting tube. The steel pipe with the same grade still needs to be selected in the selection of the new pipe material, but the old pipe changes due to the carburization performance of the inner wall, so a transition layer needs to be overlaid on the bevel surface of the old pipe. And carrying out butt welding with a new pipe after the transitional overlaying layer is overlaid, the groove is finished and is checked to be qualified. In order to reduce the influence of the assembling stress and the welding restraint stress during welding, the technology provides that a stress groove is processed near 80mm away from the edge of a new pipe, and the size of the stress groove is as follows: the width of the flat bottom is 3mm, the depth of the groove is 6mm, the angle of the groove is 60 degrees, the bevel surface and the flat bottom are in smooth transition, and the transition radius is larger than 10 mm. The new and old pipe interfaces were welded according to the welding process given in table 1. And after welding, performing necessary postweld heat treatment, and then performing stress groove repair welding, wherein specific welding technical parameters are shown in the stress groove repair welding of the table 1.

The working principle of the invention is as follows:

one of the conditions according to which a weld crack is generated is that a certain degree of tensile stress is present in the weld region. If the condition of tensile stress generated in the welding process is reduced, various cracks can be prevented correspondingly. Based on the starting point, the technical key point of solving the related cracks is to reduce the restraint stress in the welding process of the metal steel pipe, particularly when dissimilar steel metal pipes or metal pipes with different properties are welded. The specific method is that firstly, according to the weldability of the dissimilar steel metal pipe, a pipe section with relatively good weldability is determined, and a stress reducing groove with a certain shape is arranged at a certain position away from a welding end. When two pipes are in butt welding, the stress groove is subjected to low-rigidity deformation to release the restraint stress during welding, so that the joint is welded in a low-stress state, and cracks at the welding part are avoided. And after the welding of the joints between the dissimilar steel metal pipes is finished, the performance is adjusted, and the welding is qualified through detection, the repair welding of the stress groove can be carried out. The specific welding method and the specific process of the stress groove can be selected according to the welding performance of the steel pipe, the welding conditions of enterprises and the mastering degree of the process technology.

As for the hot crack, the welding metallurgy shows that the welding hot crack is mainly generated in the later solidification stage of weld metal, and impurities in molten pool metal are extruded to intergranular parts due to the growth of columnar crystals and are largerThe fracture is generated under the action of welding cooling shrinkage tensile stress. If the constraint tensile stress is reduced at the later stage of metal solidification so that the metal rapidly passes through the crystallization solidification point, the grain boundary can not crack, and the thermal crack can not be generated. For cold cracking, the weld of alloy steels often appears as delayed cracks, which are due to the weld metallurgy to three factors, the carbon equivalent, the restraint and the diffusion of hydrogen of the material. If the joint has small restraint, delayed cracks can not be generated or the generation probability is reduced. Therefore, in the case of thermal cracking, reheat cracking, or delayed cracking, if the joint restraint is reduced, the tensile stress in the weld and the heat affected zone is reduced, and the occurrence of cracks in the welded joint is reduced. According to the definition of the restraint degree of the welding joint and the calculation formula R_FAs is known, the joint restraint degree depends mainly on the plate thickness and the restraint length. For butt welding of tubes, the most effective way to reduce the restraint is to reduce the thickness δ of the tube wall. Therefore, a stress groove with reduced wall thickness can be arranged at a certain position away from the welding seam to reduce the restraint degree of the welding joint. The stress reduction groove is required to be arranged at one end with good weldability of steel, so that the welding restraint stress of the pipe joint can be reduced, and the difficulty of the repair welding process of the stress groove is reduced. In addition, the material with good weldability has lower strength and good plasticity and toughness, is easy to deform and is more beneficial to reducing the assembly stress. The constraint, defined in terms of constraint, also depends on the constraint length L, i.e. the distance from the stress slot center to the soldering site. Therefore, the length of the welding groove of the stress groove pitch is appropriate, and if 1/3 with the reduced stress groove wall thickness as the base material thickness is adopted, the second volume 136 pages of the welding manual (the main edition of Chinese society for welding, second edition) is used for the restraint degree R of the inclined Y groove crack resistance test_FThe value is about 700 delta (N/mm. mm) and the constraint length is calculated to be 100 mm. Therefore, the stress groove can be arranged at a position 75-125 mm away from the groove position according to actual conditions. Therefore, the heat transfer process of the joint during dissimilar metal welding is not influenced, and the restraint degree of the joint can be effectively reduced. The shape and size of the stress groove are selected to be proper, so that the restraint degree is reduced, and excessive deformation and even breakage are avoided. In addition, repair welding work for the stress groove and increased economic cost are also considered.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

TABLE 1 welding Process parameters

The welding method comprises the following steps: manual tungsten electrode argon arc welding

TABLE 2 materials for welding trade marks and compositions

TABLE 3 furnace tube Material composition (w,%)

Claims

1. A stress-reducing welding method for repairing a metal pipe in situ, comprising the steps of:

2. The stress-reducing welding method for repairing the metal pipeline on the spot according to the claim 1, wherein in the step 3, the distance between the central position of the stress groove and the butt welding groove is within the range of 50-100 mm.

3. The stress-reducing welding method for repairing the metal pipeline on the spot according to claim 1, wherein in the step 3, the shape of the stress groove is a V-shaped combined shape with a flat bottom, the width of the flat bottom is 3-4 mm, the angle of the groove is 60 +/-5 degrees, and the thickness of the residual pipe wall of the groove is 2-3 mm.

4. The method of claim 3, wherein in step 3, the stress-relief notch surface and the flat bottom are smoothly transited, and the transition radius is larger than 10-20 mm.