化工设备用聚四氟乙烯衬里成型技术简介

聚四氟乙烯是重要的特种工程塑料,其耐蚀性能优异,被广泛用作金属设备的衬里。介绍了聚四氟乙烯衬里的成型技术,简述了聚四氟乙烯衬里的成型工艺,综合分析了聚四氟乙烯衬里渗漏、开裂等的缺陷失效原因,以期提高衬里的寿命。     

大型硫酸储罐耐酸瓷砖衬里开裂原因分析

介绍了某硫酸生产企业大型硫酸储罐耐酸瓷砖衬里发生开裂及处理情况,并提出保障耐酸瓷砖防腐衬里工程质量的相关建议。技术人员对大型硫酸储罐耐酸瓷砖衬里开裂的原因进行综合分析,其主要原因是储罐装满硫酸后,金属筒体受力向外膨胀产生弹性变形,使瓷砖衬里在有施工缺陷的砖缝位置产生裂缝。经技术修复后,该硫酸储罐投入使用,未发生所储存的精制硫酸金属离子含量超标的现象。     

焚烧炉耐火衬里更换过程的管理实践

针对焚烧炉的炉顶、炉壁局部耐火衬里出现开裂并脱落现象,阐述了耐火衬里材料的选用原则和施工过程控制,检修后运行效果良好。     

巴斯夫推出冰箱衬里级的新型HIPS

巴斯夫推出冰箱衬里级的新型ＨＩＰＳ从１９９４年初起，高抗冲聚苯乙烯（ＨＩＰｓ）衬里必须与生产聚氨酯（ＰＵＲ）的冰箱保温层不用ＣＦＣ发泡剂的法规相适应。因目前所用之含氢发泡剂ＨＣＦＣ－１４１ｂ往往会导致传统的ＨＩＰＳ衬里开裂和爆皮。冰箱衬里级的ＨＩＰＳ...     

乙烯装置裂解炉辐射室炉墙衬里处理方法

石油化工装置众多炉类设备在投产后经常出现炉墙衬里层开裂或炉墙倒塌事故,造成轻则设备带病生产,重则设备停产维修和报费的巨大经济损失,本文结合乙烯装置裂解炉辐射室炉墙衬里这一实例,详述炉墙衬里具体处理方法。     

尿素合成塔的修理及衬里改造

1概述 川化第二化肥厂大化肥装置尿素系统采用的是日本东洋工程公司三井东压水溶液全循环改良C法工艺，其尿素合成塔由日本神户制钢制造，分为A、B两台，互为备用，结构为圆筒直立压力容器，外壳为多层包扎，内衬为工业纯钛KS50，钛衬里自上而下厚度分别为3mm、4mm、5mm，上、下封头衬里厚度为5mm，设计压力26MPa，设计温度210℃。经过长期使用，A塔的钛衬里减薄严重，最薄处不到2mm。运行过程中，曾经发生过原料CO2带氢的事故，造成底部衬里吸氢，严重脆化。2001年A塔底部衬里出现开裂，无法进行修复，严重影响了系统的正常生产。为彻底消除隐患，结合尿素系统的改造，公司决定对其衬里进行彻底的改造。另外，B塔在2001年7月发生过一次严重的腐蚀，侵蚀了承压壳体。以下分别对A塔衬里的改造和B塔腐蚀区域的修理进行叙述。     

硫磺反应炉衬里失效原因分析

针对硫磺回收反应炉在生产运行过程中因衬里失效脱落，造成炉壁烧穿，从设计、施工、保护、操作等方面分析了衬里失效的原因。结合衬里失效原因，确定了衬里修复方案，做好施工质量控制和烘炉，保证了衬里修复质量。     

耐环境应力开裂聚苯乙烯树脂及合金的制备、性能和用途

耐环境应力开裂聚苯乙烯树脂及合金,是应用于含油食品、冰箱衬里等方面的市场需求量相当大的一类专用产品。本文通过对耐环境应力开裂聚苯乙烯树脂及其合金有关文献资料进行归纳,得出该类产品的制备原理、产品的性能和用途,并提出了有关的建议。     

尿素合成塔衬里腐蚀原因分析与修复

分析了氨汽提法尿素生产工艺中尿素合成塔不锈钢衬里的腐蚀机理，阐述了不锈钢衬里的修复措施。     

室温自硫化丁基橡胶衬里施工及应用

本文对比了天然橡胶衬里，氯丁胶衬里，预硫化丁基胶衬里，室温自硫化丁基胶衬里的技术优缺点，介绍了室温自硫化丁基胶的特性，并详细总结了室温自硫化丁基胶的施工方法及应用情况。     

PC／PE共混合金尖锐缺口试样的冲击断裂分析

本文研究了ＰＣ／ＰＥ共混合金尖锐缺口试样的冲击断裂行为，并用扫描电镜观察了尖锐缺口试样的微观断裂特征。结果表明：ＰＣ／ＰＥ共混合金尖锐缺口试样在室温下的冲击断裂是一个单一过程的韧性断裂，裂纹扩展时产生毫米级的过程区，裂纹尖端存在着强烈钝化，过程区形变的实质为界面空洞化及基体ＰＣ的剪切形变。本文还给出了ＰＣ／ＰＥ共混合金尖锐缺口试样的宏观及微观断裂模型。     

A Backface Strain Technique for Detecting Fatigue Crack Initiation in Adhesive Joints

A new backface strain technique was developed to detect fatigue crack initiation in adhesive-bonded lap joints. The technique was based on the special strain distribution in single lap joints and detected the fatigue crack initiation by the switch in the direction of the strain variation. Use of this technique not only permits the determination of fatigue crack initiation life in the joint, but also allows the site of crack initiation to be located. With the assistance of this new backface strain technique, a fatigue crack was found to initiate in the adhesive but to propagate towards the interface to continue its growth on the interface and to cause the final separation of the joint along the interface. Measurements of fatigue crack initiation lives at different stress levels indicate that the adhesive-controlled crack initiation took an increasingly greater proportion of the total fatigue life as the stress decreased, so that the lifetime in the long-life regime was dominated by the resistance of the adhesive to fatigue crack initiation.     

Fatigue Crack Growth in Ferroelectric Ceramics Driven by Alternating Electric Fields

Electric-field-induced fatigue crack growth in ferroelectric ceramic PZT-5 with precracks was investigated. The experimental results showed that there were two distinct characteristics in the crack growth under electric loading. Under low electric loads, microcracks located ahead of the main crack emerged and grew and, as a result, impeded the growth of the main crack. On the other hand, under high electric loads, microcracks were absent, and the main crack was the only mode of fatigue cracking. The main crack grew macroscopically along the original path perpendicular to the electric field. Microscopically, the crack grew along the grain boundaries and grain breakaway was observed. The crack growth rate was nonlinearly related to the cyclic electric load. Similar to mechanical fatigue, there existed a crack growth threshold in the applied electric-field amplitude below which the crack ceased to grow. A steady crack growth occurred when the applied electric field exceeded this threshold. An empirical model for crack growth was obtained. Domain-switching effect and fracture-mechanics concepts were used to explain the observed crack closure and crack growth under electric loads.     

Initial slow crack growth behavior followed by rapid brittle fracture in a viscoelastic solid

Initial dynamic crack propagation behavior in a viscoelastic solid just after crack initiation was investigated by newly devised instrumentation at different temperatures. It was observed that initial slow crack growth precedes rapid brittle fracture. The very initial slow crack growth first appears as ductile fracture and successively as brittle crack propagation, and the latter only exists within very short crack passage. It is also recognized that this slow crack growth in a brittle manner greatly depends on the temperature.     

Cohesive Crack Models for Cement Mortar Examined Using Finite-Element Analysis and Laser Holographic Measurements

Unlike classically brittle materials, concrete and mortar toughen as cracks propagate. One of the methods to account for this quasi-brittle response is to use cohesive crack models. Closing pressure, which is assumed to be a function of crack-opening displacement, is applied on the crack faces in such models. In this paper, measurements of crack-opening profiles by laser holography were used to examine the various closing-pressure models. An iterative process based on linear elastic finite-element analysis with singular elements was used to compute crack profiles when the closing pressure was applied to the crack faces. The predicted crack profiles were compared with the experimental values for evaluation. The validity of the assumption of eliminating crack tip singularity was studied. A crack-length-dependent cohesive model is proposed based on experimental measurements of the crack profile.     

Mixed-Mode Fracture in Soda-Lime Glass Using Indentation Flaws

Mixed-mode failure of soda-lime glass under inert and fatigue test conditions was studied using Knoop indentation flaws. For annealed cracks (residual stress-free) crack extension (catastrophic or subcritical) is by an abrupt transition from the initial crack plane to a noncoplanar crack plane followed by a reorientation of the crack normal to the applied stress. Although fatigue strength of these inclined flaws increased linearly with respect to orientation of the flaws to the applied stress up to an angle of 60°, this increase was considerably less than what was predicted by existing theories. It is believed that subcritical crack growth causes the crack to be realigned perpendicular to the applied stress before failure for all orientations; hence, fatigue strength does not show the dramatic increase at orientation angles as predicted by theory. For as-indented cracks the contact residual stress causes the crack extension to be less inclined to the initial crack plane than for annealed cracks, but in this case also, the crack realigns itself perpendicular to the applied stress. Again, fatigue strength is relatively insensitive to the orientation angle as predicted by theory and subcritical crack growth is believed to play a primary role in determining this strength dependency.     

Effect of process parameters on crack characteristics in laser welding of Al2O3 ceramic

The crack of ceramic weld is a worldwide problem for brittle material, high energy laser beam is expected to solve this problem. In this paper, the crack of fiber laser welding of Al₂O₃ ceramics was studied. The weld crack rate was used to characterize the crack condition of weld, and the influences of laser power, welding speed and defocusing distance on crack characteristics were carried out. The results showed that Al₂O₃ ceramics weld has obvious crack tendency, and the cracks mainly appeared on the weld center line. When the crack appeared on the weld center line, there was crack-free on the base metal. When the defocusing distance increased from +3 mm to +20 mm, the number of cracks gradually decreased. When the defocusing distance was greater than +17 mm, cracks-free appeared on the weld and base metal. Abaqus software was used to simulate the relationship between crack and stress based on thermal elastoplastic theory. The high crack areas, few crack areas and free crack areas were divided according to the maximum principal stress value. No matter what welding conditions, as long as the maximum principal stress was less than 1576 MPa, there was crack-free on the weld and base metal.     

工业管道应力腐蚀裂纹的检验

概述了金属材料应力腐蚀裂纹的特点,提出了工业管道对其检验的内容和方法,通过对应力腐蚀裂纹宏观和微观特征的检查和分析,基本可以区别应力腐蚀裂纹和其他裂纹.应力腐蚀裂纹是比较危险的缺陷,因此在管道检修和设计时应采取必要的改进措施,防惠于未然.     

Fatigue crack growth model and mechanism of a random fiber SMC composite

The primary purpose of this study is to investigate the fatigue crack growth rate and mechanism in a random fiber sheet molding compound (SMC) composite. The fatigue crack growth rate in this study was measured using a compliance approach. The fatigue crack growth rate in the SMC studied here shows a good agreement with a new power law model proposed earlier. This new model takes into account not only the effect of the stress intensity factor range, but also the effect of crack growth at various stages of loading using a weight average stress intensity factor. It was observed that this new model can represent the fatigue crack growth rate of the SMC at three different load ratios in a single unifying curve.     

Comparison of fast fracture properties of thermoplastics

The fast fracture behavior of polyethylene, polycarbonate and poly(methyl methacrylate) are compared for two different thicknesses of material. The aim was to make fracture measurements under precisely defined steady load conditions after the material has reached a stress relaxed state. It was essential that the experimental technique provided good isolation between crack initiation and crack propagation. This was achieved in small rectangular shaped specimens by adding a tongue to one side extending the intended crack path. A fast crack was initiated in the tongue to propagate into the main section after it had been loaded and allowed to stress relax. When necessary the tongue was embrittled by cooling so a crack can be initiated with minimum force. This new method obtains the threshold load to just maintain crack propagation and also the increase of crack velocity with load above this threshold up to the limiting condition.