[0024] The girth welding method of the dual-phase stainless steel bimetallic composite pipe of the present invention comprises the following steps:
[0025] The first step, groove treatment: such as figure 1 As shown, the duplex stainless steel bimetal composite pipe is composed of a duplex stainless steel lining pipe 2 with a wall thickness of 0.6-2mm and a carbon steel base pipe 1 set outside the lining pipe 2; The surface is processed with a V-shaped groove, and the angle α of the groove is 45-55°, and the length of the part of the lining pipe 2 extending beyond the base pipe 1, that is, the blunt edge 6, is 2-3 mm. In this embodiment, the base pipe 1 is made of 20 steel and its wall thickness is 7 mm. In practice, the base pipe 1 can also be made of 20G steel, L245NB pipeline steel or L360 pipeline steel; the material of the lining pipe 2 is 2205 duplex stainless steel And its wall thickness is 2mm. First, the welding surface of the base pipe 1 is processed into a groove with a groove angle α of 44±4° through conventional machining. After processing, it is necessary to ensure that the groove surface is free from impurities such as cracks and oil stains. The specific machining steps are: first Use a common lathe to process the port of the base pipe 1 according to the determined V-shaped groove angle α, and finally process the welding surface of the base pipe 1 into a V-shaped groove. It should be noted that damage to the lining pipe 2 is avoided. After roughing with a lathe, the final finishing is done with hand-grinding tools. In addition, in this embodiment, the length of the blunt edge 6 of the lining pipe 2 is 2 mm.
[0026] After machining, the welding surfaces of the base pipe 1 and the lining pipe 2 are respectively cleaned with a common cleaning agent. In this embodiment, acetone is used to clean the welding surfaces of the base pipe 1 and the lining pipe 2, and alcohol can also be used as the cleaning agent in practice.
[0027] The second step, sealing welding: use a tungsten argon arc welding machine to perform sealing welding on the connection port between the base pipe 1 and the lining pipe 2. The welding wire used is a duplex stainless steel wire and the welding current is 65-80A. combine figure 2 , In this embodiment, manual argon tungsten arc welding is used for sealing welding, and the selected welding wire is duplex stainless steel welding wire ER2209 and the diameter of the welding wire is 2.0 mm. After the welding is completed, a sealing seam 3 is formed between the blunt edge 6 of the base pipe 1 and the lining pipe 2 . During the welding process, if there are defects such as pores and cracks in the weld, it must be cleaned and then re-welded. It should be noted that the inner lining pipe 2 is not burned through during sealing welding.
[0028] The third step, backing welding: use a tungsten argon arc welding machine to perform backing welding on the connection ports between the lining pipes 2, the welding wire used is duplex stainless steel welding wire and the welding current is 60-90A.
[0029] After the nozzles of the base pipe 1 and the lining pipe 2 are aligned, the four points are evenly spot welded along the pipe circumference of the sealing weld, and then argon gas is introduced into the lining pipe 2 for protection, and then bottom welding is performed. combine figure 2 , in this embodiment, manual tungsten argon arc welding is used for bottom welding, the selected welding wire is ER2209 and the diameter of the welding wire is 2.0mm, and during the welding process, the duplex stainless steel bimetallic composite pipe is passed through the pipe. Argon is used for protection, and the purity of the protection gas argon is ≥99.9%. After the welding is completed, a backing weld 4 is formed between the base pipe 1 and the lining pipe 2 . During the welding process, if there are defects such as pores and cracks in the weld, it must be cleaned and then re-welded. After inspection of the weld and to ensure that the inspection is qualified, the base pipe welding is carried out.
[0030] In addition, the duplex stainless steel welding wire ER2209 used in the second and third steps has the same composition and contains the following chemical compositions by weight: C≤0.03%, Cr 21.5-23.5%, Ni7.5-9.5%, Mo 2.5-3.5%, Mn 0.5-2.0%, Si≤0.9%, S≤0.03%, P≤0.03%, Cu0.08-0.2%, N≤0.75%, the balance is iron.
[0031] In the present embodiment, the lining pipe 2 is the base material and the duplex stainless steel backing weld 4 that is finally formed, except for iron, the other chemical components and contents contained in the two are shown in the table. 1:
[0032] Table 1
[0033] Chemical composition of liner pipe 2 and liner pipe 2 weld (%)
[0034] C Cr Ni Mo Mn Si S P N mother
[0035] It can be seen from Table 1 that the chemical composition of the weld of the lining pipe 2 finally formed meets the requirements of the base metal, which can effectively ensure the corrosion resistance of the lining pipe 2 .
[0036] The fourth step, base pipe welding: use an arc welding machine to weld the connection ports between the base pipes 1, and the electrode used is a duplex stainless steel electrode. combine figure 2 , in this embodiment, the base pipe welding adopts manual arc welding, the electrode used is E2209-17 and the diameter of the electrode is 2.5mm, the base pipe welding adopts multi-layer multi-pass welding, and the slag on the surface of the welding seam is cleaned during the welding process. Check for defects such as undercuts and lack of fusion, and finally form the base pipe welding seam 5 . Likewise, during the welding process, argon gas is introduced into the duplex stainless steel bimetallic composite pipe for protection, and the purity of the protective gas argon gas is greater than or equal to 99.9%. In addition, the duplex stainless steel electrode E2209-17 contains the following chemical compositions by weight: C≤0.04%, Cr21.5-23.5%, Ni 8.5-10.5%, Mo 2.5-3.5%, Mn 0.5-2.0% , Si≤0.9%, S≤0.03%, P≤0.04%, Cu0.08-0.2%, N≤0.75%, the balance is iron.
[0037] To sum up, the present invention divides the welding process of the duplex stainless steel composite pipe into three parts: end sealing welding of the composite pipe, bottom welding of the lining pipe and base pipe welding, that is to say, it combines the traditional transition weld welding and the base pipe welding. Welds are welded together. Specifically: 1. Use argon arc welding to seal the port of the composite pipe. Its main function is to block the diffusion of harmful elements such as carbon in the base pipe 1 and seal the gap between the base pipe 1 and the lining pipe 2. The sealing welding adopts 2. After the sealing welding is completed, the bottom welding of the lining pipe 2 adopts argon tungsten arc welding, and the duplex stainless steel composite pipe is carried out in the welding process. Argon-filled protection, the welding wire adopts the duplex stainless steel wire of the same quality as the base metal of the liner tube 2, and the main purpose of backing welding is to form a corrosion-resistant alloy layer consistent with the chemical composition and performance of the base metal; 3. After the backing welding is completed, The base pipe 1 is welded by manual arc welding, and the welding rod adopts the duplex stainless steel base material of the same quality as the base material of the lining pipe 2, and finally forms the base pipe weld. The duplex stainless steel electrode is used for base pipe welding, which not only ensures the lining The corrosion resistance of the pipe 2 can be improved, and a welded joint with better mechanical properties than the base pipe 1 can be obtained. In order to ensure the quality of the weld, the welding torch is filled with argon for protection during the whole welding process, that is, during the sealing welding, bottom welding and base pipe welding; in addition, during the welding process of bottom welding and base pipe welding , Always keep the duplex stainless steel composite tube for argon filling protection. The purpose of argon filling in the tube is to ensure that the weld of the lining tube 2 in the duplex stainless steel composite tube is not oxidized and ensure its corrosion resistance.
[0038] The above are only preferred embodiments of the present invention and do not limit the present invention. Any simple modifications, changes and equivalent structural changes made to the above embodiments according to the technical essence of the present invention still belong to the technology of the present invention. within the scope of the program.
