Views:2 Author:RONSCO Publish Time: 2021-06-10 Origin:RONSCO
The weldability of nickel-based Inconel 625 alloy is not good, so reasonable welding process and corresponding measures should be selected to avoid defects such as hot cracks and pores during welding. The difficulty of the welding of bimetal composite pipes is to avoid the contamination of the corrosion-resistant alloy by the carbon steel at the bottom layer, which reduces the corrosion resistance of the corrosion-resistant alloy layer weld. If the single-sided welding process is used to complete the welding, nickel-based Inconel 625 welding consumables must be used for the entire weld.
The welding consumables are expensive; at the same time, because of the poor thermal conductivity of nickel-based alloys, the heat is not easy to dissipate, and it is easy to oxidize. Crack sensitivity, welding process limitations are relatively large, generally only two processes of argon arc welding and electrode arc welding, the production efficiency is low.
For nickel-based Inconel 625 alloy composite pipes with a large thickness, it is advisable to use double-sided welding. At this time, relatively cheap carbon steel materials can be selected for the carbon steel matrix. However, it is very important to avoid the first layer welding. The road penetrates the alloy composite layer, dissolving nickel and other alloying elements into the carbon steel weld, causing rated hardening and cracking, and at the same time, the corrosion resistance of the alloy composite layer can be reduced.
For this reason, based on ASME X 21 and ASTM B 31.3 specifications, the important changes in the overall welding process evaluation process in the specifications are discussed, and then the standardized joint planning form is selected, and the carbon steel side is welded with carbon steel welding consumables to complete the carbon steel. After the side cover, enter the tube to weld the nickel bottom layer. The back-side stripping technology eliminates the possibility of carbon steel welding materials penetrating the alloy layer and causing cracks, and the welding process on the carbon steel side can be flexibly selected, such as high-efficiency submerged arc welding.
In addition, in order to avoid the inevitable large misalignment during the on-site construction, the carbon steel welding material contaminates the nickel-based side parent material during the bottoming. Although the actual thickness of the nickel bottom layer of the composite pipe in the project is generally only 3~5mm, However, the groove size of the inner wall of the groove should be planned deeper to ensure that the nickel bottom layer is not affected by carbon steel. The groove depth of this development plan is 13mm. Compared with the more common single-sided welding groove, the compound groove not only saves the amount of welding material, but also uses carbon steel welding material for the carbon steel side.
After the groove processing is completed, it is necessary to clean the surface of the carbon steel on the same side of the Inconel 625 alloy lining with full copper sulfate to acknowledge the complete removal of the nickel-based Inconel 625 alloy residue on the surface of the carbon steel. When pairing, the butted pipes should be on the same axis to avoid deviation. Use argon arc welding for fixed spot welding, and the spot welding seam should be polished and removed during the final weld seam welding. When positioning, use carbon steel welding consumables to weld from the outside.
When welding, the following welding sequence must be strictly followed: ①Carbon steel side seal + hot welding pass: ②Carbon steel side filling cover; ③Nickel-based Inconel 625 liner side surfacing. When performing argon arc welding on the carbon steel side, the p(Ar) in the welding gun reaches 99.99%, and the flow rate reaches 10-25L/min.
After the carbon steel layer is welded, the inner wall of the nickel-based Inconel 625 lining layer is carefully polished before welding to ensure that the root defects and the carbon steel weld reinforcement are completely removed; at the same time, the welding wire and the inner surface of the welded joint are 25mm The area inside is scrubbed with absolute alcohol. During the entire welding process on the nickel-base side, all welding start and end points should be polished.
Suitable welding current should be used when welding the nickel-based side. Excessive welding current may cause pores, reduce the performance of the weldment, and oxidize due to the destruction of alloy elements and deoxidizing elements before entering the molten pool, which may cause twists and turns Failed during the experiment.
In addition, pay attention to filling the arc crater. If the arc crater at the end of the weld is not filled, it will simply cause cracks and the crack will spread to the base metal. You can use back welding or reverse welding at the end about 10mm to prevent the arc crater from being filled. During the welding process, it is necessary to ensure that an ideal convex straight-in weld bead with a small amount of corrugation is generated; a wide and flat weld bead is easy to crack in the middle part, and an ideal weld bead profile is not easy to generate thermal cracks during the cooling process.
After welding process appraisal, outstanding mechanical properties of welded joints have been obtained, and the double-sided welding process of low-temperature carbon steel + Inconel 625 bimetallic composite pipe has been researched and developed, which fills the gap of double-sided welding of bimetallic composite pipe in my country.
The submerged arc welding process and the Tip TIG welding process complete the high-efficiency welding of the bimetal composite pipe, which has changed the inefficient situation of the previous single-sided welding that can only use manual hydrogen arc welding + electrode arc welding.
Compared with single-side welding, the planning of composite groove double-side welding effectively reduces the total amount of welding consumables. At the same time, carbon steel welding consumables are used instead of nickel-based welding consumables to weld the carbon steel side, which greatly reduces the cost of welding consumables.
Inconel 625 alloy round bars, plates, seamless tubes, etc. can be customized and zero-cut
Inconel 625 alloy provides users with finished product specifications:
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