Why are high-pressure pipelines on ships welded using gas shielded welding?
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Dear teachers, in the shipbuilding industry, gas shielded welding is commonly used for welding the flanges and connections of high-pressure hydraulic hoses (those hoses with flanges). The pressure in such hydraulic hoses can reach hundreds of kilograms, and classification societies have not issued any explicit prohibitions regarding this practice. Therefore, a question arises: since gas shielded welding is still considered off-limits in the pressure vessel industry, why is it being used in the shipbuilding industry where similar high pressures are present? Is it because, despite being under high pressure, what are the differences in the mechanical property requirements for high-pressure pipelines in the shipbuilding industry compared to those for pressure vessels?
The main reasons for using gas shielded welding for high-pressure pipelines on ships are as follows: 1. High-pressure pipelines on ships typically carry media such as seawater, fresh water, or hydraulic oil; compared to the media in pressure vessels with higher chemical corrosivity, the corrosiveness of these materials is lower. Moreover, the service life of ships is generally short, so the requirements regarding welding quality are relatively low. 2. The mechanical property requirements for high-pressure pipelines on ships are lower compared to those for pressure vessels, as ships have to withstand various complex dynamic loads while operating at sea, resulting in often complex stress conditions in the pipelines. At the same time, the steel used in the shipbuilding industry still meets regulatory standards, ensuring its reliability under high pressure. 3. The shipbuilding industry employs relevant process control measures when using gas shielded welding, such as controlling the flow rate of the shielding gas and regulating the welding current and time, to ensure welding quality. In short, using gas shielded welding for high-pressure pipelines on ships is not without risks, but when it is employed within the limits permitted by industry standards, there are corresponding control measures in place to ensure its reliability. .
The regulations and standards for special equipment and pressure vessels do not prohibit gas shielded welding; it is rather the industry itself that resists the use of carbon dioxide gas shielded welding. The reason for this is that this welding method requires high skills from the operators, and it has its limitations (it cannot be used for welding non-ferrous metals). Additionally, welders in this industry are often mobile, making them difficult to manage, so the industry chooses not to use this method in order to ensure product quality and simplify management.
The wording is too straightforward; the official stance of the pressure vessel industry regarding gas metal arc welding is that it is neither recommended nor prohibited at present； Although it is not prohibited, the authorities currently do not provide any standards that specify practical methods and procedures for testing and ensuring the quality of gas shielded welding. As a result, it is up to each manufacturing plant to be responsible for its own processes, with no official standards to provide coverage; in such circumstances, it is effectively equivalent to a prohibition.