丙烷溶剂罐鼓泡裂纹成因分析与对策

介绍了丙烷脱沥青装置--丙烷溶剂罐检测过程中发现的鼓泡开裂情况,通过金相组织分析,确定低合金高强度16MnR钢的鼓泡开裂原因是设备在工艺介质H2S含量超标情况下发生了典型的湿硫化氢环境下的氢鼓泡(HB)、氢致开裂(HIC)和应力导向氢致开裂(SOHIC),并从设备选材、工艺防腐蚀、设备防腐蚀等方面提出了改进措施.     

API X52管线钢在饱和硫化氢气田水溶液中的氢渗透与氢致开裂行为

天然气输送管道氢致开裂问题日益突出,而API X52管线钢在气田模拟水溶液中氢渗透和氢致开裂的研究较少。模拟了饱和硫化氢某气田水溶液,采用电化学和恒载荷拉伸试验方法,测定了API X52管线钢在不同充氢电流密度下的氢扩散系数、可扩散氢浓度(ω0)及管线钢氢致开裂临界可扩散氢浓度(ωHIC)。结果表明:API X52管线钢可扩散氢浓度(ω0)与充氢电流密度呈线性关系,即ω0=0.99+0.07J;其恒载荷下开裂临界可扩散氢浓度的对数值(lnωHIC)随拉应力(σ)呈线性下降,即σ=475-450lnωHIC。     

核电站大型巴氏合金轴瓦失效分析

利用光学显微镜、扫描电镜和能谱等分析手段,对巴氏合金轴瓦表面多次发生粘结和开裂进行了检验和分析。结果表明,在巴氏合金层中存在着组织分层,化合物相呈区域性偏析和聚集,轴瓦结合面附近存在大量疏松、孔洞等浇注工艺不当所形成的铸造缺陷;加之结合面附近背底金属中氢含量较高,轴瓦长期在一定温度和应力下工作,氢的不断扩散和聚集最终在巴氏合金表面形成氢鼓泡。上述缺陷的存在,使轴瓦在运行过程中易造成应力集中导致裂纹的萌生和扩展。最终造成局部润滑条件恶化而导致粘结和开裂失效。     

X90管线钢的抗氢致开裂性能

目前有关X90管线钢抗H2S性能的研究报道较少.为此,采用NACE TM 0284-2003方法对X90和X80管线钢进行氢致开裂(HIC)试验以对比研究其抗HIC性能,论述了氢致开裂的机理,并分析了X90管线钢的微观组织和化学成分对氢致开裂的影响.结果表明:X90管线钢的抗HIC性能较X80管线钢差,X90钢的热影响区与焊缝区的抗HIC性能比母材好;X90钢易产生Mn的偏析,且C会加剧其偏析,同时Cr的碳化物析出使氢鼓泡易在此处产生,2种因素均导致X90钢的抗HIC性能降低;适当控制微观组织比例,降低C含量,在保证提高X90管线钢强度的同时,严格控制Mn和Cr的含量,可以提高其抗HIC性能.     

某压力容器封头焊缝开裂分析

某压力容器封头在打压实验过程中焊缝开裂,采用扫描电镜、光学显微镜对断口特征和金相组织进行了观察,并对焊缝的显微硬度、氧和氢含量等进行了检测,在综合分析的基础上,确定了封头焊缝开裂原因.结果表明:封头焊缝开裂是由于在焊接过程中,焊缝内表面保护不良而形成氧化层及富氧α层,加之封头吊耳焊缝与环形焊缝叠加处具有一定的应力集中和相对较高的残余应力,从而在压力实验过程中造成焊缝开裂.     

大型调质输入轴开裂分析

某大型调质输入轴放置约9个月后开裂,采用宏观分析、化学成分分析、低倍检验、断口分析、金相检验以及力学性能测试等手段对输入轴开裂原因进行了分析。结果表明:该输入轴为在组织应力及氢析出所造成内应力共同作用下的氢致延迟开裂;输入轴原材料氢含量高、偏析严重、非金属夹杂物含量高以及锻造不充分,引起零件内部发生了氢气积聚,形成了较大的内应力,这是导致输入轴发生氢致延迟开裂的主要原因。     

304不锈钢低温分离器开裂原因分析

采用残余应力检测、常规力学性能试验以及金相分析等方法对304不锈钢低温分离器的封头开裂原因进行分析。结果表明,开裂是由应力腐蚀引起的;其原因是工作介质中有含量较高的硫,而封头一筒体对接环焊缝区域存在的残余应力促使开裂的发生。     

X52管线钢抗氢致开裂试验裂纹成因分析

针对某段时期出现的X52管线钢产品经抗阶梯型破裂试验后,试样有明显阶梯裂纹,产品检验不合格的问题,对不合格批次的试样进行化学成分、炼钢工艺以及显微组织等方面的分析,分析了该抗硫化氢腐蚀X52管线钢氢致开裂的原因。结果表明:开裂批次试样的钙硫含量比值偏低,导致出现夹杂物偏聚和中心偏析,且夹杂物呈线状分布,是造成该管线钢产品抗氢致开裂试验开裂的主要原因。最后对X52管线钢的生产控制要点提出了相应建议,以提高其抗硫化氢腐蚀的能力。     

高含H2S天然气集输管线氢鼓泡失效评价

针对酸性环境下硫化物造成天然气集输管线严重腐蚀开裂的失效现象,根据高含H2S天然气集输管线材质选择、力学性能、显微形貌等综合性能数据结果,对其失效行为进行深入分析和评价。结果表明,在高含H2S、CO2和水等腐蚀介质的集输管线内壁发生腐蚀失效和氢鼓泡的危险性极大,提出产生氢鼓泡现象的影响因素及其预防措施从而指导集输管线的安全运行。     

高含H_2S天然气集输管线氢鼓泡失效评价

针对酸性环境下硫化物造成天然气集输管线严重腐蚀开裂的失效现象,根据高含H2S天然气集输管线材质选择、力学性能、显微形貌等综合性能数据结果,对其失效行为进行深入分析和评价。结果表明,在高含H2S、CO2和水等腐蚀介质的集输管线内壁发生腐蚀失效和氢鼓泡的危险性极大,提出产生氢鼓泡现象的影响因素及其预防措施从而指导集输管线的安全运行。     

纵肋与横隔板交叉构造细节穿透型疲劳裂纹扩展特性及其加固方法研究

纵肋与横隔板交叉构造细节是正交异性钢桥面板最易发生疲劳开裂的构造细节,通过建立有限元数值模型,采用断裂力学方法,研究栓接角钢加固方式对该处疲劳易损细节穿透型裂纹的加固效果。基于疲劳试验足尺节段模型相对应有限元模型,建立了纵肋与横隔板焊接处穿透型疲劳裂纹模型,针对栓接角钢和纵肋外侧栓接钢板两种加固技术的加固效果进行评估。研究结果表明:钢桥面板纵肋与横隔板交叉构造细节的疲劳裂纹扩展至一定长度后将发展成穿透型裂纹,裂纹面受力复杂,纵肋腹板内外侧疲劳裂纹扩展特性表现的不一样,但是随着裂纹扩展的逐步进行,裂纹尖端的开裂模式均以复合型开裂为主;栓接角钢加固方式主要抑制纵肋与横隔板交叉构造细节易损部位疲劳裂纹的I型开裂,因此能很好地抑制短裂纹的扩展,但对于该细节处以复合形式扩展的穿透型疲劳裂纹的加固效果并不显著;在纵肋外侧栓接半U形钢板的加固方法能有效改善穿透型疲劳裂纹的等效应力强度因子,并且加固之后均保持在裂纹扩展阈值以下,表明该加固方式对穿透型疲劳裂纹有良好加固效果。     

Formation and analysis of stack cracks in a pipeline steel

Extensive cracking of the type known as stack cracking was demonstrated in a cathodically charged X65 microalloyed pipeline steel containing a weldment. It is shown that the formation and propagation of rolling-plane cracks, which constitute the primary stages of the stack cracking, is due to local concentration of hydrogen gas pressure and a lowering of the cohesive strength of a number of interfaces by hydrogen. The characteristic S-shape of individual cracks which occurred during the linking up of cracks was attributed to stress interactions at crack tips and cleavage cracking normal to the rolling plane. An explanation of hydrogen embrittlement fracture is given in terms of electronic state modifications of the steel, including charge polarization.     

Research into aperture parameters of point bonded roof waterproofing membranes

Roofing membranes bonded to the substrate of a structure generally tend to blister, crack, etc., which often causes failure. The reasons for this are that it is almost impossible to eleminate risk of blistering from the moisture-bearing substrate [1], and that the membrane, with a free deformation length approaching zero, will certainly rupture when stretched as a consequence of cracking occurring in the substrate to which the membrane is bonded [2]. This situation can be improved by using a waterproofing membrane made of perforated asphalt felt that may have a higher resistance to bulging and cracking. However, aperture parameters of the perforated asphalt felt are as different as the countries where they are manufactured. A satisfactory method of determining the aperture parameters is yet to be found. The paper, based on data obtained from laboratory research, deals quantitatively with the rheological properties of the asphalt felt, analyzes the state of the bonded points, and then derives a group of formulas to determine the aperture parameters in a comparatively reasonable way. Moreover, a feasible method is advanced to extend the free deformation length of the membrane so as to deal with larger cracks in the substrate.     

等离子熔覆铁基涂层开裂行为研究

本文采用正交对比试验,研究了多种因素对等离子熔覆铁基涂层开裂敏感性的影响.试验结果表明,基体材料及其表面状态、工艺参数和熔覆材料成分等都对熔覆层的开裂敏感性产生重大影响,通过改变这些因素可以减少裂纹的产生,扩大等离子熔覆技术的应用范围.     

The mechanical response of tetragonal zirconia polycrystal to conical indentation

Blocks of 3Y-TZP were indented with conical diamond indenters. Indentation caused tetragonal to monoclinic phase transformation in a subsurface. Of the cracks generated in the subsurface, radial and lateral cracks can be accounted for by a continuum model of the indented subsurface, built using a combination of the Boussinesq and blister stress fields. Additional ring, median and cone cracks were also observed. It is hypothesized that the latter are motivated by the reduction in blister strength or residual energy brought about by the material damage caused by the phase transformation. This damage reduces the load bearing capacity of the material progressively with increasing normal load.     

Mesomechanics of multiple cracking of brittle coatings in a loaded solid

The paper deals with an analysis of two kinds of multiple cracking in a loaded solid with a brittle coating. First is the front-wise development of opening mode cracks, while the second is the formation of a system of sliding mode cracks along conjugate directions of maximum tangential stresses τ _max. The mesomechanics of each kind of multiple cracking is discussed. The conditions which provide an increase in both the strength and the ductility of a loaded solid experiencing multiple cracking are formulated; the essence of the model is the growth of cracks in the sliding mode along conjugate directions of maximum tangential stresses     

Energy-based mechanistic approach for damage characterization of pre-flawed visco-elasto-plastic materials

Damage characterization plays a significant role in producing durable and high performance structural materials. However, it is somewhat complicated because of the particular characteristics of many materials, such as pre-existing flaws, time-dependent behaviors, and coexistence of cracking and permanent deformation. This kind of materials is pre-flawed visco-elasto-plastic material. In order to characterize damage in such materials, this paper proposes an energy-based mechanistic (EBM) approach that provides a complete solution to these problems. As typical pre-flawed visco-elasto-plastic materials, asphalt mixtures are selected to demonstrate the principles and applications of the EBM approach.When an asphalt mixture is not damaged, the pre-existing flaws are air voids, characterized by the average air voids size and number of air voids calculated by the EBM approach. The calculated values are more accurate than those measured by the X-ray Computed Tomography system. Due to the increased accuracy, it is discovered that the air voids becomes smaller when the mixture is aged, which serves as an evidence of the change of the internal structure of the material due to aging.When an asphalt mixture is damaged, the damage includes cracking and permanent deformation. The cracking damage is a multitude of randomly distributed cracks. A new concept, distributed continuum fracture (DCF), is introduced to model the distributed cracks in the EBM approach. Development of cracking damage is quantified by the evolution of damage density, average crack size and number of cracks. The damage densities of eight different mixtures are proven to correctly reflect the effect of mixture composition and aging. New features of number of cracks discovered lead to new definitions of cracking history in pre-flawed materials. The energy for permanent deformation is separated from that expended for cracking in the same asphalt mixture. Such a separation acknowledges the fact that cracking and permanent deformation always occur simultaneously. The separated energy for cracking is used to define a cracking energy dissipation rate, a direct indicator of cracking susceptibility of asphalt mixtures.In a word, the EBM approach is able to characterize damage in asphalt mixtures under various conditions using one type of test on one specimen. It requires simple inputs: stress, strain, and time, and all the calculations are performed automatically by the Excel. Using this approach to analyze the test data is more efficient than some alternative methods because of less testing effort and more informative results with improved accuracy.     

Mesh-independent modeling of both distributed and discrete matrix cracking in interaction with delamination in composites

A finite element model is presented for failure analysis of composite laminates with the phantom node method for matrix cracking and interface elements for delamination. The phantom node method allows for mesh-independent representation of straight intraply cracks in laminates. In laminates two different phenomena that both involve such cracks are distinguished, namely distributed matrix cracking and discrete splitting, where the transition between the two is related to delamination. It is investigated how both phenomena and their transition can be represented in a single computational framework. Objectivity of the results with respect to element size and the introduced crack spacing parameter is examined.     

煤颗粒表面形态及其对超细粉碎的影响

利用扫描电镜对煤颗粒的表面形态、结构、开裂形式等进行研究。结果表明,煤颗粒的表面形态对超细粉碎过程有重要影响,颗粒表面存在的大量孔隙是开裂的起源,粗颗粒呈脆性断裂,粉碎较容易;随着颗粒的细化,开裂形式从脆性向塑性开裂转变,细颗粒煤微观断裂形态呈撕裂状,粉碎难度增大;煤超细颗粒与其它颗粒有表面和结构上的相似性,具有分形的基本特征。     

Sliding microindentation fracture of brittle materials: Role of elastic stress fields

An analytical model of the stress field caused by sliding microindentation of brittle materials is developed. The complete stress field is treated as the superposition of applied normal and tangential forces with a sliding blister approximation of the localized inelastic deformation occurring just underneath the indenter. It is shown that lateral cracking is produced by the sliding blister stress field and that median cracking is caused by the applied contact forces. The model is combined with measurements of the material displacement around an indentation to show that the relative magnitude of tensile stresses governing lateral crack and median crack growth varies with the magnitude of the applied load. The model also predicts a range of loads at which the lateral crack will grow only after the indenter is removed from the surface. These predictions are consistent with observations of the different regimes of cracking observed under a sliding pyramidal indenter in soda–lime glass and other brittle solids.