海洋油气管道高强管线钢超音频脉冲TIG焊电弧行为及适用性

The weld seam and the heat affected zone of high strength pipeline steel are easy to produce structural embrittlement and inhomogeneous distribution of chemical composition which could cause stress corrosion and toughness decrease. So far high strength pipeline steel such as X80 has still not been used for the construction of domestic submarine oil and gas pipeline, and the related research on submarine pipeline laying welding and hyperbaric welding repair procedure is blank. Arc ultrasonic excited by ultra-sonic frequency pulse TIG welding power has strong molten pool electromagnetic stirring and vibrating action effects proved to be effective on the grain refinement of weld seam, which could obviously improve welding quality and welding efficiency. Ultrasonic current can greatly increase the stiffness of the arc, and therefore improve welding arc stability under high pressure environment. The arc behavior characteristics during ultrasonic frequency pulse TIG welding process of high strength pipeline steel under atmospheric environment, such as temperature field distribution, arc shape and melting metal flow, were studied for exploring the promotion mechanism of welding performance during ultra-sonic pulse TIG, such as welding efficiency, welding quality and anti-corrosion capability. The above research can lay foundation for formulating high strength pipeline steel laying welding procedure of submarine oil and gas pipeline. During the ultrasonic pulse TIG welding process under high pressure environment the relationship of arc stiffness, arc stability and melting metal flow was analyzed. Furthermore, the influence rule of ultrasonic pulse TIG welding on reducing the hydrogen embrittlement under humid and underwater environment, and the underwater service performance including anti-corrosion capability of hyperbaric welding joint under high pressure environment were also studied so as to provide technology accumulation for developing a new submarine high strength pipeline steel welding repair technology.

高强管线钢（X80等）焊缝及热影响区易出现化学成分不均匀和组织脆化，导致发生应力腐蚀、韧性下降，迄今仍未用于国内海洋油气管线建设，海底管道铺设焊接和干式高压焊接维修工艺研究仍属空白。超音频直流脉冲TIG焊激发的电弧超声会对熔池产生强烈的搅拌和振动作用，能细化焊缝晶粒，显著提高接头性能和焊接效率；超音频电流能大大提高电弧挺度，从而改善高气压环境焊接电弧稳定性。本课题拟研究常压下高强管线钢超音频脉冲TIG焊电弧形态、温度场分布和熔池流动等电弧行为，得到该方法提高高强管线钢焊接效率、焊接接头性能及耐腐蚀能力的规律和机理，为制订海洋油气高强钢管道铺设焊接工艺奠定基础；课题还研究高气压环境下超音频脉冲TIG焊电弧挺度、电弧稳定性增加与熔池流动改善之间的关系，水下潮湿环境超音频焊接减少氢脆影响的规律，水下干式高压焊接接头水中服役行为特别是改善耐腐蚀性能机理，为开发水下高强管线钢焊接维修新技术提供积累。

高强管线钢焊缝区和热影响区易出现化学成分不均匀和组织脆化等现象，进而产生应力腐蚀和韧性下降等问题，再加上高气压环境下焊接电弧的不稳定性也会严重影响焊接接头质量，因此高强管线钢（X80等）迄今仍未用于国内海洋油气管线建设。本项目研制成功适用于水下干式焊接的超音频直流脉冲TIG焊接电源；通过理论分析和工艺试验，分析了常压环境超音频直流脉冲TIG焊电弧峰值电流、基值电流、脉冲频率、占空比对电弧形态和焊接过程的影响规律，完成常压下X80高强管线钢超音频直流脉冲TIG焊接工艺参数的优化工作；在高压干式舱中试验分析了高气压环境超音频直流脉冲TIG焊电弧峰值电流、基值电流、脉冲频率、占空比对焊缝组织的影响规律，完成高气压环境下X80高强管线钢超音频直流脉冲TIG焊接工艺参数的优化工作。常压和高压环境的超音频直流脉冲TIG焊电弧均具有稳定性强和挺度高等优点，其激发的电弧超声对熔池产生强烈的搅拌和振动作用，能细化焊缝晶粒，提高接头性能和焊接效率。项目研究成果将为我国提供一种经济高效的高强管线钢焊接工艺，加快高强管线钢在海底油气管线中的应用步伐；同时提供一种接头质量与母材基本相当的水下高强管线钢焊接维修新技术，为众多涉及水下工程的行业提供技术积累。