Welded joint structure of thick-walled large-diameter pipe and its welding construction method

Abstract

A pair of thick-walled large-diameter base pipes (1) constituted of an Ni-based alloy which comprises, in terms of wt%, 20-35% Cr, 0.1-10% Mo, 0.1-3% Al, 0.11-3% Ti, and Ni as the remainder and intermediate pieces constituted of the same material and having a width of about 60 mm are subjected beforehand to hot working or cold working, thereby giving a solution treatment to a range including portions to be finally welded on a site where at least a boiler has been installed. Thereafter, the intermediate pieces are finally welded to each other on the site where a boiler has been installed. With this method, it is possible to obtain a highly reliable welded-joint structure in a thick-walled large-diameter pipe.

Description

technical field [0001] The invention relates to a welded joint structure of thick-walled and large-diameter pipes and a welding method thereof. The welded joint structure of the thick-walled and large-diameter pipes is formed of a Ni-based alloy and is used in a new generation of pipes with a main steam temperature of about 700°C. In the main equipment of ultra-supercritical pressure power generation equipment, that is, the header of the high-temperature part of the boiler, the main steam pipe, and the reheat steam pipe; especially when there is no large-scale heat treatment equipment such as a manufacturing plant on the site where the boiler is installed, A welded joint structure and its welding construction method that are less likely to cause reheat cracks when welding the final welded part at the aforementioned site where the boiler is installed. Background technique [0002] In the high-temperature portion of the boiler for power generation equipment described above, he...

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Problems solved by technology

[0010] Especially in the thick-walled large-diameter pipes used as main steam pipes and reheat steam pipes in boilers, there are welded joints at many locations, and there are welded heat-affected parts near the welded part of the welded joints that undergo the heat cycle caused by welding. , but the crystal grains here are coarser than that of the non-welded part, and the following problem has also been pointed out: due to the residual stress during welding, the risk of reheat cracking is high (potentsial)

[0016] Under such heat treatment conditions, the actual work is technically difficult and difficult in terms of the working environment.

For example, the actual heat treatment work site is mostly at a high position of the boiler, so of course sufficient safety measures need to be taken, and since the heat treatment is extremely high temperature, there are restrictions on the installation place of the heating power supply and the length of the heating wire. , it is necessary to equip sufficient insulation materials for maintaining high temperature for a long time, etc.

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