启动循环泵溢流管泄漏原因分析

通过宏观分析、金相检验、扫描电镜及X射线能谱分析、维氏硬度试验等方法,对某电厂启动循环泵溢流管的泄露原因进行了分析。结果表明：该溢流管失效的性质是氯离子导致的不锈钢应力腐蚀开裂;溢流管失效是材料、应力和介质三方面问题联合作用的结果,主要原因是氯化物在溢流管异种钢焊接接头外表面附着和富集。     

Korrosionsverhalten der Legierung Al-Li-Cu-Mg

Corrosion Behaviour of the Al-Li-Cu-Mg Alloy The localized corrosion behaviour of the Al-Li-Cu-Mg alloy 8090-T651 (25 mm thick plate) was investigated using salt spray tests, EXCO tests and tests according to the MIL-H-6088F specification. These accelerated laboratory tests indicate that the material is susceptible to intergranular and exfoliation corrosion. The stress corrosion cracking behaviour was studied under constant load, constant deformation and slow strain rate conditions. The material was found to be resistant against stress corrosion cracking in the long transverse direction. In the short transverse direction a threshold stress below 50 MPa was determined. The same values were measured for the conventional alloys 2014-T351 and 2024-T351. The fracture surfaces of specimens failed due to stress corrosion cracking were examined using a scanning electron microscope. Fractographic features attributed to corrosion were discussed.     

Failure Analysis for the Welded Elbow at the Bottom of the Rectifying Tower in the Alcohol Evaporation System

Cracking was found on the welded elbow at the bottom of rectifying tower in an alcohol evaporation system. In order to determine the cause of failure, a detailed analysis was conducted. The analysis included macroscopic observation for the failed tube and optical microscopy for the morphology of cracks. The characterization of fracture was analyzed by scanning electron microscopy, and the components subjected to the cracks were analyzed using energy-dispersive x-ray spectroscopy. Results revealed that the welded elbow had suffered damage from external chloride stress corrosion cracking (ECSCC). The environmental factor responsible for ECSCC is the chloride present in the dampish insulation. The stress factor is the result of the welding residual stress induced in the material which was used to fabricate the elbow.     

Stress corrosion studies of ion implanted austenitic steel

Stress corrosion studies of 50 Mn18Cr4 austenitic steel implanted with 120 keV N⁺, 100 keV Cr⁺, 200keV and 400 keV Er⁺ ions were carried out by constant strain method in the nitrate solution. Surface composition and depth profiles of the implanted material were measured by AES sputter etching technique. The results exhibit that nitrogen implantation has no significant affection to the stress corrosion, but the chromium and erbium implantation has prolonged the incubation period of the stress corrosion cracking.     

D210塔简体泄漏原因分析

采用化学成分分析、金相检验和断口分析等方法,对304L钢D210塔筒体泄漏原因进行了分析。结果表明：D210塔筒体泄漏原因是由于氯离子的存在而产生应力腐蚀开裂所致。由于敏感材料、应力腐蚀环境及应力三个条件共同存在,在一定温度下使其产生应力腐蚀裂纹,裂纹起始于筒体外壁角焊缝处,而后向内壁扩展,最终穿透筒壁,致使该塔筒体在角焊缝处产生破裂泄漏。     

Failure investigation of a convection line elbow

Failure investigation was carried out on a cracked 5″ 304L stainless steel elbow tube for the convection line of an ethylene furnace. The crack was observed in the heat-affected zone (HAZ) at the end leading to the elbow parent material. The crack was along the circumference and was about 12″ in length. The crack started from the toe of the weld to the parent metal on the elbow side. The failure investigation revealed that the HAZ of the elbow tube suffered from stress corrosion cracking and mild grain boundary carbide precipitation during welding. The carbide precipitation was possibly due to improper welding practices such as high heat input and/or extended welding time. The tube thickness, which is relatively thick, was a contributing factor in making proper welding more difficult.     

疲劳损伤对波纹管耐连多硫酸腐蚀性能的影响

针对催化裂化装置用波纹管使用中所面临的连多硫酸应力腐蚀问题,采用热态连多硫酸腐蚀模拟装置,试验研究了固溶态Incoloy825波纹管的耐连多硫酸应力腐蚀性能,并利用金相显微镜、SEM、EDX等手段分析了腐蚀波纹管的表面形貌和断口特征,探讨了设计疲劳寿命及累积疲劳损伤对波纹管连多硫酸应力腐蚀敏感性的影响规律。结果表明,在60℃的H2SxO6溶液中,设计疲劳寿命及累积疲劳损伤对固溶态Incoloy825波纹管的腐蚀敏感性影响显著。设计疲劳寿命越低、累积疲劳损伤越大,则越易形成应力腐蚀裂纹。     

Stress corrosion of Ni-based superalloys

Abstract

The development of gas turbines to increase fuel efficiency is resulting in progressively higher operating temperatures in the under platform regions of the blades. These regions have traditionally been considered low risk areas. However, higher metal temperatures combined with stresses and the deposition of contaminants from the cooling air system may result in complex degradation mechanisms. Static stress corrosion testing has been conducted on C-ring specimens at a range of stresses in a hot corrosion environment. Cracks were observed in C-rings after exposure times greater than 100 h. Scanning electron microscopy (SEM) systems were used to image cracks and characterise deposits to improve understanding of the mechanism. Finite element analysis (FEA) has been used to model the stress intensity under test conditions. CMSX-4 specimens subject to static stresses combined with hot corrosion demonstrated significant material degradation (crack initiation and propagation) suggesting a combined stress corrosion mechanism resulting in cracking.     

The main mechanisms of stress corrosion cracking in natural gas trunk lines

Stress corrosion cracking in a pipe material presents a most critical hazard to natural gas trunk lines. The paper addresses the causes (mechanism) of crack formation and growth. Understanding of these issues will enable a proper implementation of methods for early identification, diagnostic, and prediction of this type of failure. A most comprehensive explanation of a joint influence of internal and external factors on the corrosion cracking can be provided by means of the probabilistic local electrochemical corrosion theory. It is based on the probabilistic nature of initiation of a local corrosion damage. A probabilistic approach is used to develop a concept of stress corrosion cracking. The factors responsible for the formation of local damage nuclei have been determined. The pipe manufacturing operations are shown to have a certain effect on the pipeline susceptibility to stress corrosion cracking. Modeling has been performed for the corrosion processes that may occur in a gas trunk line section subjected to a stress corrosion cracking hazard.     

燃料气换热器管束鼓包开裂分析

某燃料气换热器在运行过程中发现其换热管束出现多处鼓包开裂现象,为查明鼓包开裂原因,对换热管束进行了宏观和微观检验、化学成分分析、金相检验和扫描电镜分析。结果表明:换热管内存在压力波动、换热管壁厚不均匀、壳程介质H2S含量较高以及换热管材料中存在,夹杂物都是导致其鼓包开裂的原因;换热管壁厚较薄处容易形成应力集中,使该处硫化氢腐蚀严重,壁厚进一步减薄,当壁厚减薄达到一定值时,在管内压力波动作用下形成鼓包,随着腐蚀的加剧和压力波动的继续作用,最终导致换热管于鼓包处产生裂纹,进而发生泄漏。     

7055铝合金T型型材的应力腐蚀行为研究

通过拉伸性能测试、C环应力腐蚀试验、金相分析、扫描电镜和透射电镜观察等研究了7055铝合金T型型材的应力腐蚀开裂(SCC)行为.结果表明:7055铝合金T型型材纵向试样的抗拉强度、屈服强度、伸长率及断面收缩率均大于横向试样的;在间浸腐蚀和恒温恒湿环境下,纵向C环试样的开裂时间均长于横向试样的.型材纵向截面晶粒变形特征明...     

矩形脉动真空灭菌器内腔开裂原因

某医院矩形脉动真空灭菌器内腔发生开裂事故,通过宏观分析、金相检验和光谱分析等方法,结合工作介质,对内腔开裂的原因进行了分析。结果表明:灭菌器内腔与加强筋不连续焊接处存在焊接残余应力,且靠近内腔弯折处存在局部应力集中现象;灭菌器内腔的工作介质中含有氯离子,而氯离子水溶液是300系列不锈钢发生应力腐蚀开裂的敏感介质。灭菌器内腔在焊接残余应力、含氯离子介质等因素的综合作用下发生起始于靠近内腔弯折的焊接起始处的应力腐蚀开裂。     

Effect of sulfide ions on the stress corrosion behaviour of Al-brass and Cu10Ni alloys in salt water

The stress corrosion cracking (SCC) behavior of Al-brass and Cu10Ni alloys was investigated in 3.5% NaCl solution in absence and in presence of different concentrations of Na₂S under open-circuit potentials using the constant slow strain rate technique. The results indicated that the Cu10Ni alloy is more susceptible to stress corrosion cracking than as-received Al-brass at strain rate of 3.5 × 10^–6 s^–1 in 3.5% NaCl in presence of high concentration of sulfide ions (1000 ppm). The sulfide ions (up to 500 ppm) has no effect on the stress corrosion cracking of the annealed Al-brass in 3.5% NaCl at two strain rates of 7.4 × 10^–6 and 3.5 × 10^–6 s^–1. The results support film rupture for Al-brass and sulfide stress corrosion cracking assisted with pitting corrosion for Cu10Ni at slip steps as the operating mechanisms.     

Degradation of the Tubing Metal in Hydrogen-Sulfide Environments

We analyze damages in tubing metal of domestic (D steel) and foreign (C-95 steel) production and also determine the coefficients of degradation of the metal after long-term exploitation. It is shown that the tubing metal of C-95 steel is subject to general corrosion, hydrogen-induced cracking, and hydrogen-sulfide stress corrosion cracking even under the conditions of inhibition. Tubing metal of D steel was not subject to hydrogen-sulfide stress corrosion cracking even after eleven years of exploitation. It is established that degradation of D steel is lower than that of C-95 steel.     

Influence of retrogression and re-aging treatment on corrosion behaviour of an Al–Zn–Mg–Cu alloy

Influence of retrogression and re-aging treatment on the microstructure, strength, exfoliation corrosion, inter-granular corrosion and stress corrosion cracking of an Al–Zn–Mg–Cu alloy has been investigated by means of optical microscope (OM), transmission electron microscope (TEM) and electrochemical impedance spectroscopy (EIS). The results show that retrogression and re-aging treatment can increase the size and the distribution discontinuity of the grain boundary precipitates, and lead to the increase of the corrosion resistance without the loss of strength and ductility. In addition, the analysis of electrochemical impedance spectroscopy shows that retrogression and re-aging treatment can enhance the resistance to exfoliation corrosion.     

Stress corrosion cracking of stainless steel pipes for Methyl-Methacrylate process plants

In a Methyl Methacrylate (MMA) plant, tree-like transgranular cracks were found near the weld of a pipe that had been used for transferring MMA material at 110 °C and 0.77 kg/cm². The pipe was made of ASTM A312 TP304 stainless steel.In this study, it was shown that the failure was due to the stress corrosion cracking (SCC) caused by the chloride that remained in the pipe. Corrosion pitting occurred on the inside surface of the pipe. The stress corrosion cracking started from the pits and grew out through the thickness. Concentrated chloride was found in the deposit stuck to the pipe in addition to the pre-process MMA materials. Many work-hardened grains were observed in the area of SCC, providing the evidence of high residual stress due to welding, which could serve as the driving force for the SCC. Recommendations are made for preventing further failure due to SCC in such cases.     

A study on axial cracking failure of drill pipe body

Frequently happening drill pipe failure accidents in oil and gas wells not only affect drilling speed, but cause enormous economic losses and many safety issues. Most of these accidents are transverse cracking of drill pipe body and pin thread or axial cracking of box thread. Based on the axial cracking failures of drill pipe body in an ultra-deep well in China, this paper give a systematic analysis of axial cracking failure in consideration of service condition, material quality and stress corrosion mechanism. Measurement and inspection are performed on macroscopic and microscopic morphology of crack surface, corrosion products and circumferential residual stress. Then stress corrosion cracking experiments against hydrogen sulfide is conducted. Finally, the critical stress value for sulfide stress corrosion cracking of the drill pipe material is obtained, and the mechanisms of axial cracking failure and corresponding preventive measures are proposed.     

Zusammenwirken von Spannungsrißkorrosion und Ermüdung bei der Schwingungsrißkorrosion eines hochfesten Stahles

Conjoint Action of Stress Corrosion Cracking and Fatigue on Corrosion Fatigue of a High Strength Steel The corrosion fatigue characteristics of a high strength, martensitic steel in 0.5 n NaCl solution is investigated with regard to the fatigue and stress corrosion cracking behaviour of the material. Test parameters are stress ratio and frequency, testing is carried out with fracture mechanics methods, the crack surfaces are examined fractographically. An analysis of the results reveals that corrosion fatigue in high strength steel is caused by fatigue or by stress corrosion cracking, depending on the kinetics of the two processes. Fatigue and stress corrosion cracking do not act cumulative or additive. Instead, the kinetically faster process causes crack advance. The crack growth characteristics are interpreted with respect to the fractographic appearance of the crack surfaces. Corrosion fatigue cracks propagate either intergranular relative to the prior austenite grain boundaries as stress corrosion cracks do or transgranular like fatigue cracks, depending on the crack growth rates of the two processes. Fatigue and stress corrosion cracking do not interact, at least in a measurable degree, because of the different crack path of the two fracture processes. Results can be assessed quantitatively with the “process competition model”.     

1Cr5Mo钢弯管开裂原因分析

采用化学成分分析、力学性能测试、金相分析、断口形貌观察和断口波谱成分分析等方法对1Cr5Mo钢工艺管线弯头开裂原因进行了分析,并用有限元法计算分析了管线弯头的应力分布。结果表明,弯管材料成分中含碳量偏高,导致其塑性较差。在介质腐蚀下,弯管的上弯头内壁出现裂纹,在较高应力作用下裂纹不断扩展,最终形成穿透性裂纹,是典型的应力腐蚀开裂。     

Influence of retrogression and reaging on microstructure and properties of 8090 Al–Li alloy

Abstract

An investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T₂ phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.

MST/1670