【作者】 王炳英；

【导师】 霍立兴；

【作者基本信息】 天津大学 ， 材料加工工程， 2007， 博士

【摘要】 应用动电位扫描技术,测试了X80管线钢及焊接接头在模拟土壤介质(高pH值0.5mol/L NaHCO3+1mol/L Na2CO3溶液和近中性pH值NS4溶液)中的极化曲线,分别考虑离子浓度、扫描速度、测试区域对极化曲线的影响,研究了X80管线钢及其焊缝在典型模拟土壤介质中电化学腐蚀行为。采用慢应变速率拉伸试验(SSRT)和扫描电镜观察研究X80管线钢及焊接接头在上述两种典型土壤介质中的应力腐蚀行为。在0.5mol/L Na2CO3+ 1mol/LNaHCO3溶液中试样断口形貌在阴极电位条件下呈准解理断裂,在自腐蚀电位和阳极电位条件下,试样断口主要是韧性断裂。在NS4溶液中施加阴极电位时,SEM断口形貌呈穿晶准解理断裂,具有明显的应力腐蚀特征。施加阳极电位时,断口形貌为典型的韧性断裂,断口处存在大量的韧窝。两种溶液中SSRT试验结果均表明,随着外加电位的负移,断裂时间、断面收缩率、应变量都明显变小,X80管线钢及焊接接头的SCC敏感性增加。施加相同外加电位时,焊接接头较母材的应力腐蚀敏感性增加,其断裂位置全部落在焊缝或HAZ处。制作楔形张开加载(WOL)试样,在硫化氢介质中进行恒位移应力腐蚀试验,分别测得母材、焊缝和热影响区的临界应力强度因子KISCC和裂纹扩展速率da/dt。实验结果表明,热影响区的KISCC最小,裂纹扩展速率最大,具有较差的抗应力腐蚀开裂的能力。通过对X80管线钢焊接接头的金相显微组织、断口形貌观察以及硬度测试,分析了X80管线钢SSCC性能的影响因素。并对WOL试样进行了有限元分析,得到裂纹尖端应力场分布和氢浓度的分布特征。应力腐蚀试验结果与有限元数值分析结果相互验证。建立了X80钢管道焊接移动热源的三维有限元计算模型,以瞬态温度场分析为基础,考虑材料物理性能参数与温度非线性关系,利用SYSWELD程序进行了焊接温度场和焊接应力场的数值模拟,分析了相变及焊接线能量对管道内外表面的环向及轴向应力的影响规律。以“合于使用”为原则,根据BS7910评定标准,在测试X80管线钢及焊接接头断裂韧度的基础上,对X80管道焊接接头焊趾处的表面裂纹以及焊缝内的深埋裂纹进行了一级、二级安全评定。考虑了应力集中和残余应力的影响,计算了给定载荷条件时的表面容许裂纹尺寸和深埋容许裂纹尺寸。更多还原

【Abstract】 The stress corrosion cracking (SCC) behaviors of X80 pipeline steel in analogysoil solutions(the solution of 0.5mol/L Na2CO3 and 1mol/L NaHCO3 and NS4solution) were studied using electrochemical measurement and slow strain ratetesting(SSRT) and scanning electron microscopy。The susceptibility to stresscorrosion cracking (SCC) of the welded joint of X80 pipeline steel in solution wasanalyzed. The electrochemical corrosion behaviors of the X80 steel and its weldedjoint in the analogy soil solutions were investigated.The stress corrosion cracking (SCC) behaviors of X80 pipeline steel in solutionof 0.5mol/L Na2CO3 and 1mol/L NaHCO3 and NS4 solutions were studied using slowstrain rate testing(SSRT) and scanning electron microscopy. At cathodic potentials,obvious quasi-cleavage fracture was observed in the fracture area of specimens insolution of 0.5mol/L Na2CO3 and 1mol/L NaHCO3. At open circuit potential andanodic potential, ductile fracture was the main fracture pattern. The SEM crackingmode was transgranular with the feature of quasi-cleavage and hold typical feature ofstress corrosion in NS4 solutions when applied negative potential. At anodic potential,fracture appearance was typical ductile fracture and obtained abundant dimples. SSRTresult showed that the general tendency in the studied potential range was that withnegative increasing of potential, fracture time, elongation and reduction in area ofspecimens decreased, mean the susceptibility to SCC increased. When appliedpotentials of welded joint and base metal homology are the same, welded joint ismore sensitive than base metal in SCC, the results showed that all tensile testspecimens cracked in weld metal and heat affected zone (HAZ).The critical stress intensity factor KISCC and crack propagation velocity wereobtained by the Wedge-open loading constant displacement specimens. The resultsshowed that the heat affected zone (HAZ) had the minimal KISCC, largest crackpropagation velocity and hold poor resistant properties of stress corrosion crack. Theinfluential factor of the SSCC property of X80 pipeline steel was analysed throughmetallographic structure、fracture appearance observation and hardness examination .By the numerical analysis of the FEM, stress field and concentration of hydrogendistribution property from the crack tip were obtained. The experimental results showmostly concordance with the FEA results.A three-dimensional finite element numerical simulation is performed on the material physical absorption variables and temperature nonlinear relationship of theX80 steel pipes with SYSWLED program. Three-dimensional FEM using mobile heatsource for analysis transient temperature filed and welding stress filed incircumferential joint of pipes is founded. Influence law of the phase transition andadherent wire energy of axial and hoop residual stresses on inner and outer surface ofpipes are investigated.The primary and second safety evaluation was proceed to toe external crack andweld deep crack of X80 pipe joints with the principle of“fit utilize”,according toBS7910 test, based on the examination of X80 steel and bonding joints fracturetoughness, adopted FAD evaluation method. Considering the effect of stressconcentration and residual stress, the external allowable crack size and deep allowablecrack under the condition of given loading.更多还原