快堆高温P91管道焊接热处理及金属监督研究

Research on Welding Heat Treatment and Metal Supervision of High Temperature P91 Steel in Fast Reactor

示范快堆是我国首座钠冷快堆电站,其主蒸汽管道设计压力为17 MPa,设计温度为530℃,属于高温高压管道,鉴于目前核电厂对于高温管道的监督并无明确标准规范要求,故基于P91钢焊接热处理过程中出现的问题研究高温P91管道的金属监督要求。通过分析P91钢焊接过程中常出现的热处理问题,发现当回火温度过高时,焊接部位会发生马氏体分解、碳化物聚集现象,导致焊接接头硬度过高;预热温度及层间温度过高会延长焊缝从800℃冷却至500℃的时间,降低焊接接头韧性。同时,P91钢在焊接过程中,操作不当会导致焊接接头力学性能降低,因此对P91钢的焊接及焊后热处理工作必须经过严格的工艺评定合格后方可实施。此外,在役阶段金属监督应加强硬度检测、金相检测的手段,建立焊缝检测数据库,以判断P91焊缝金属力学性能是否发生变化。

The demonstration fast reactor is the first sodium cooled fast reactor power plant in China.Its main steam pipeline is designed with a pressure of 17 MPa and a temperature of 530℃,which belongs to high-temperature and high-pressure pipelines.Considering that there is currently no clear standard specification requirement for the supervision of high-temperature pipelines in nuclear power plants,the metal supervision requirements of high-temperature P91 pipelines are studied based on the problems that occur during the welding and heat treatment process of P91 steel.By analyzing the common heat treatment problems that occur during the welding process of P91 steel,it was found that when the tempering temperature is too high,martensite decomposition and carbide aggregation occur at the welding site,leading to high hardness of the welded joint.When the preheating temperature and interlayer temperature are too high,it will extend the time for the weld seam to cool from 800℃to 500℃and reduce the toughness of the welded joint.Meanwhile,improper operation during the welding process of P91 steel can lead to a decrease in the mechanical properties of the welded joints.Therefore,the welding and post weld heat treatment of P91 steel must undergo strict process evaluation and be qualified before implementation.In addition,during the in-service phase,metal supervision should strengthen the means of hardness testing and metallographic testing,establish a weld seam testing database,and then determine whether the mechanical properties of P91 weld metal have changed.