加氢换热器用321不锈钢、镍基合金825氢脆敏感性研究

Research on Hydrogen Embrittlement Sensitivity of 321 Stainless Steel and Nickel-based Alloy 825 for Hydrogenation Heat Exchanger

加氢换热器作为加氢装置的核心设备,其安全运行对我国石化行业发展有着重要意义。由于加氢换热器长期运行于高温、高压、临氢等恶劣工况条件下,因氢脆等原因引起的泄漏、开裂事故频繁发生,造成非计划停工。因此,本工作选取加氢换热器常用材料镍基合金Incoloy 825和AISI 321不锈钢作为研究对象,采用电化学动态充氢慢应变速率拉伸试验(SSRT),同时借助SEM对样品进行断口分析,借助XRD分析充氢前后样品的物相变化,比较研究了两种材料在氢环境下的力学性能劣化趋势、断裂行为及抗氢性能。研究结果表明:(1)321不锈钢在氢的作用下会发生马氏体相变,而镍基合金825则会生成氢化物。(2)氢会显著降低321不锈钢和镍基合金825的塑性,且随充氢电流密度增大,氢致塑性损失程度增大。(3)不锈钢321和镍基合金825在空气中拉伸时均为韧窝型断裂,随充氢电流密度增大321不锈钢的断裂模式转变为沿晶开裂和准解理型穿晶开裂共存的混合断裂,镍基合金825的断裂模式转变为准解理断裂。因此,321不锈钢在应力/氢的交互作用下会使抗氢性能较好的奥氏体发生马氏体相变,故321不锈钢的抗氢性能比镍基合金825差。

As the core equipment of the hydrogenation unit,the safe operation of the hydrogenation heat exchanger is of great significance to the development of petrochemical industry in China.Due to the long-term operation under severe working conditions such as high temperature,high pressure and hydrogen exposure,the hydrogenation heat exchanger is frequently subject to leakage and cracking accidents caused by hydrogen embrittlement,resulting in unplanned shutdown.Therefore,the nickel-based alloys Incoloy 825 and AISI 321 stainless steel for hydrogenation heat exchangers were selected as the research objects.The electrochemical dynamic hydrogen charging slow strain rate tensile test(SSRT)was used.At the same time,the XRD and SEM was used to analyze the change of the samples’physical properties and fractures before and after hydrogen charging.The com parative study on deterioration tendency,fracture behavior and hydrogen resistance under hydrogen environment of two kinds of materials is carried out.As test results shown,(ⅰ)321 will convert to martensite while 825 produce hydrides under the action of hydrogen;(ⅱ)hydrogen can significantly reduce the plasticity of 321 and 825 materials,and the plastic loss caused by hydrogen will increase with the increase of hydrogen charging current density;(ⅲ)both 321 and 825 show dimple type fractures when stretched in air.With the increase of hydrogen charging current density,321 transforms into a mixed fracture mode of intergranular cracking and quasi-cleavage type transgranular crac-king,and 825 transforms to quasi-cleavage fracture.In conclusion,under the stress/hydrogen interaction,the austenite with good hydrogen resistance of 321 stainless steel is converted to martensite,so the hydrogen resistance of 321 stainless steel is worse than that of 825 nickel-based alloy.