I. Project Overview
With the rapid development of China's economy, the country's development of offshore oil and gas resources has increased in recent years. In 2012, China's offshore oil and gas production has exceeded 52 million tons of oil and gas equivalent. The rapid development of the offshore oil and gas industry has brought enormous challenges to the construction of offshore oil and gas fields. New technologies, new materials and new technologies have been introduced and promoted.
In the Yacheng 13-4 gas field project developed by China National Offshore Oil Corporation Zhanjiang Branch in the western part of the South China Sea, the natural gas is rich in wet CO2 and Cl- ions, and the medium is corrosive, and the conventional carbon steel pipe line design requires corrosion. If the margin is too large, the designer finally chooses the carbon steel pipe and the bimetallic composite pipe lined with corrosion-resistant alloy CRA as the pipeline material of the submarine pipeline, which reduces the weight of the pipe steel, improves the service life of the pipeline and reduces the maintenance cost. After the pipeline material is selected, the high-efficiency welding of the composite pipe becomes the most important link in the construction of the submarine pipeline. The welding efficiency is directly related to the high offshore construction cost. Based on the research of bimetal composite pipe construction and the latest welding technology at home and abroad, this paper selects TIP TIG welding technology and successfully introduces and applies it to the laying and welding of this bimetallic composite pipe submarine pipeline, in welding quality and welding efficiency. It has achieved good results. TIP TIG welding technology has been widely used in industrialized countries such as Europe and the United States. Currently, it is rarely used in China, and related technology research is relatively lagging behind. This welding technology has the weld quality of TIG welding and the welding efficiency of MIG welding, and has broad application prospects.
Second, TIP TIG welding technology
1. Principle of TIP TIG welding technology
The TIP TIG welding system consists of a welding power source, a hot wire power supply, a wire feeding mechanism and a welding torch. TIP TIG adopts a four-roller wire feeding device and a wire feeding system integrated welding torch to realize automatic wire feeding, which effectively solves the shortage of manual wire feeding. The working principle of TIP TIG welding system is shown in Figure 1. The actual welding torch is shown in Figure 2.
Figure 1 TIP TIG welding system works one
Figure 2 TIP TIG torch
The core of TIP TIG welding technology has two main points: First, the automatic wire feeding mechanism of high frequency vibration is added on the basis of conventional TIG welding, so that the forwardly fed welding wire has high frequency linear vibration function at the same time, through high frequency vibration. The welding wire effectively agitates the molten pool and the surface tension of the molten metal, which not only can greatly improve the welding efficiency, improve the welding performance of the metal, but also make the gas and impurities generated and trapped in the molten pool easy to escape. Thereby ensuring the weld metal has excellent metallurgical properties and mechanical properties; secondly, the hot wire mechanism is added on the basis of automatic wire feeding TIG welding, which realizes the advance heating of the welding wire fed into the molten pool, further improves the deposition rate and welding efficiency. The heat input of the weld pool is adjusted to reduce the dilution rate of the base metal. TIP TIG welding technology demonstrates the outstanding technical features of TIG welding quality and MIG welding efficiency, and is semi-automated for one-hand operation.
2. TIP TIG welding technology performance advantages
(1) High welding efficiency realizes the fully automatic wire feeding function of tungsten inert gas shielded welding, and the wire feeding is stable. The welding efficiency of TIP TIG welding technology is comparable to that of pulsed MIG welding.
(2) The weld quality is the same as that of MIG welding, but the same weld quality and excellent metallurgical and mechanical properties as TIG welding can be obtained. Low heat input, low thermal deformation, well-formed weld surface, no need to repair the surface of the weld.
(3) The operability of the welder is very easy to grasp, the welding control is simple, the welder's personal operation skill is low, and the ideal workpiece can be welded after a short training.
Third, bimetallic composite pipe
The composite pipe material of Yacheng 13-4 gas field project is API 5LD X65+S316L bimetal mechanical composite pipe, produced by Xi'an Xiangyang Aerospace Materials Co., Ltd., with the specification of 219mmO.Dx (14.3+3)mm WT, manufactured by explosion welding method. A 50mm long INCONEL 625 alloy composite layer is deposited on the inner wall of the composite pipe, and a localized metallurgical composite pipe made of X65+INCONEL 625 material is formed at the end, and the inner wall of the pipe end is rounded to ensure the pipe through the internal twisting machine processing process. The roundness of the inner wall of the end. Surfacing is generally completed by the pipe manufacturer. The welding process is firstly after the manual sealing and welding. The automatic MIG is divided into two layers. The pipe end structure is shown in Figure 3. The measured chemical composition of the lining layer is shown in Table 1.
Figure 3 Bimetal composite pipe end structure
Table 1 Measured chemical composition (mass fraction) of composite tube lining (%)
Fourth, composite pipe welding test
1. Welding method selection
Combining the common composite pipe welding technology at home and abroad, we compare the three optional welding processes of manual TIG, fully automatic TIG and semi-automatic TIP TIG. The results are shown in Table 2. Among them, the semi-automatic TIP TIG welding process uses high-frequency vibration automatic wire feeding and hot wire process to obtain high cladding efficiency and high quality weld quality, combining the characteristics of traditional TIG high quality and MIG high efficiency to achieve the uniformity of quality and speed. At the same time, the labor intensity of the welder is greatly reduced, the construction cost at sea is reduced, and the narrow gap groove is selected to reduce the filling amount of the welding material, and the groove tolerance is high.
According to the different characteristics and applicability of various processes, combined with the technical characteristics of submarine pipeline laying and the characteristics of composite pipes, it is concluded that the semi-automatic TIP TIG welding process is the best welding process for laying the submarine pipeline of Yacheng 13-4 bimetal composite pipe.
Table 2 Comparison of advantages and disadvantages of welding process of bimetal composite pipe
2. TIP TIG welding process
Two key points of bimetal composite pipe welding: one is to ensure the continuity of the corrosion resistant alloy layer of the weld; the other is to ensure the mechanical strength of the weld joint. When welding the composite pipe, it is possible to use a single alloy metal alloy or a mixed metal welding process compatible with the inner layer of the composite corrosion resistant alloy. In order to control the cost of welding consumables, the welding process of mixed metal is generally used, that is, the bottom welding and the second welding wire are selected as corrosion resistant alloy welding wire, and the third and subsequent filling welding and surface welding are selected to have higher strength than the carbon steel of the substrate. Welding wire. This can meet the requirements of the corrosion resistance of the inner layer and the mechanical strength of the base carbon steel pipe. However, for the laying of thin-walled submarine pipelines, the cost of welding consumables is even negligible compared to the cost of offshore construction operations. Welding quality and low repair rate are more important for submarine pipeline laying construction. (to be continued)
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