某连续催化重整装置加热炉炉管开裂原因分析

某连续催化重整装置中反应器上游加热炉的炉管,在服役11a后产生裂纹引发开裂和泄漏.通过对该炉管的化学成分、室温拉伸性能、高温拉伸性能、金相组织、硬度、断口形貌和腐蚀产物的分析查找开裂原因.结果 表明:该炉管的失效为尘化腐蚀所致,炉管内壁渗碳,外壁发生氧化,高温力学性能降低较为明显.     

制氢转化炉管材HP40Nb的失效分析

某石化公司制氢转化炉炉管在运行不到40 000 h后突然破裂起火,宏观检测、表面探伤,力学性能测试,能谱、金相、电镜、X射线、应力等分析表明:炉管材料晶界碳化物过多以及疏松空洞的存在削弱了韧性,产生了较多的微观裂纹,加上管外保温材料中存在较多的Na ,Cl,K ,Mg2 ,Ca2 ,导致下猪尾管到下支耳之间应力较大部位发生应力腐蚀开裂,58号炉管首先开裂泄漏起火,其他炉管在外部火焰烘烤下短时高温损伤、变形鼓包直至开裂.针对失效原因提出了今后使用过程中应采取的防护措施.     

制氢转化炉炉管下法兰失效分析

工程停修后制氢转化炉炉管下法兰开工试车时发生开裂泄漏.就此,对下法兰进行了裂纹宏观分析、化学成分分析、金相分析、断口形貌观察及腐蚀产物分析.结果表明,下法兰焊缝、热影响区及母材均发生了一定程度的敏化.下法兰的开裂属于敏化状态下的连多硫酸应力腐蚀开裂,这种开裂,除工作条件、环境因素外,还与材料不符合标准有关,建议选用双相不锈钢或耐热不锈钢加以避免.     

某电厂316L不锈钢输氨管腐蚀开裂原因

某电厂316L不锈钢输氨管道在运行过程中发生开裂现象。采用宏观观察、化学成分分析、金相检验、扫描电镜及能谱分析等方法分析了管道开裂的原因。结果表明：管道裂纹由内壁向外壁扩展,呈穿晶开裂特征,裂纹呈树枝状形貌,符合应力腐蚀开裂特征;腐蚀产物中存在Cl元素,在拘束拉应力和腐蚀介质的共同作用下,管道发生了应力腐蚀开裂。     

球罐应力腐蚀开裂研究与安全性分析

对球罐应力腐蚀开裂的原因和主要影响因素进行了分析.针对16MnR和SPV50Q球罐用钢,在分析湿硫化氢环境下应力腐蚀开裂形式的基础上,通过改进的WOL预裂纹试样的应力腐蚀开裂试验,对不同球罐用钢、不同硫化氢浓度、不同焊接状态条件下的应力腐蚀开裂进行了研究,并对设备的安全性能进行了分析,进而提出了防止应力腐蚀开裂的对策.     

安全阀配对法兰焊口裂纹产生原因分析

某集气装置原料气放空安全阀配对法兰焊口处出现裂纹,通过宏观以及微观检验、化学成分分析、力学性能测试等方法对裂纹产生的原因进行了分析。结果表明：该裂纹为硫化物应力腐蚀开裂所致,焊接工艺不当或焊后冷却速度过快导致焊接接头区域出现硫化物应力腐蚀开裂敏感性组织是该焊口产生裂纹的主要原因。     

弹壳开裂失效分析

对某型H68黄铜弹壳进行检查时发现大量弹壳存在裂纹。通过对弹壳进行宏观和微观观察、能谱分析、金相检验和残余应力测定等,分析了弹壳开裂的原因。结果表明:弹壳的开裂性质为应力腐蚀开裂,其原因是由于收口位置存在一定的残余拉应力,且该位置的晶粒尺寸较大,在外界介质的协同作用下产生了应力腐蚀裂纹。     

汽轮机低压转子1Cr12Ni3Mo2VN不锈钢叶片的开裂原因分析

对某火力发电厂2号汽轮机组末级开裂叶片进行宏观检查、化学成分分析、金相组织以及断口扫描和元素成分能谱分析。结果表明：该叶片裂纹形成属于腐蚀疲劳失效,蒸汽中存在氯、硫等腐蚀介质引起叶片发生电化学腐蚀,在离心拉应力作用下发生沿晶应力腐蚀开裂,形成裂纹源。在腐蚀介质、拉应力和激振力综合作用下,腐蚀疲劳裂纹加速扩展,并最终发生瞬时断裂。     

缓冲蓄压器端盖开裂失效分析

通过宏观检验、化学成分分析、金相检验、断口分析以及能谱分析等方法,并结合零件实际情况综合分析的方法,对某型飞机缓冲蓄压器端盖开裂失效的原因进行了分析。结果表明:该端盖开裂属性为应力腐蚀开裂,而锻件表面微裂纹和氯元素沉积引起的腐蚀是造成端盖应力腐蚀开裂的主要原因。     

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显,主要呈拉长状,横向试样的裂纹沿纵向扩展,裂纹一旦形成,沿着拉长晶界迅速扩展,裂纹平直,开裂时间短;型材横向截面晶粒呈等轴状,纵向试样的裂纹沿横向扩展,裂纹扩展过程中会沿着晶界发生偏折,开裂时间长。7055型材应力腐蚀机理为氢脆和电化学理论的共同作用。      

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。     

Sensitization induced stress corrosion failure of AISI 347 stainless steel fractionator furnace tubes

Austenitic stainless steel tubes are used as furnace tubes in petrochemical industries mainly because of their corrosion resistance and mechanical strength. AISI 347 grade stainless steel is used as furnace heater tubes in the fractionator of hydrocracker unit. Even though this stainless steel is stabilized with the addition of niobium thus preventing sensitization related corrosion failures, operational and maintenance errors may result in premature failures if conditions prevail. The present work reports the premature failure of AISI 347 grade fractionator furnace tubes after nearly 8 years of service. The failure occurred after shutdown. Carbonaceous deposits were found on the inner walls of the tube and circumferential cracks were found beneath the deposit. The service exposed 347 SS alloy tube was in the sensitized condition as confirmed by microstructure and double loop electrochemical potentiodynamic reactivation test. The tube material got sensitized possibly by localized overheating at the carbon layer deposited site. During shutdown of hydrocracker unit polythionic acid formation occurred possibly due to errors in shutdown procedures. Sensitized alloy 347 tube undergone polythionic acid induced intergranular stress corrosion cracking (PASCC).     

Origins of tensile stress-induced circumferential cracking of waterwall tubes in boilers

Abstract

The leakage and rupture of boiler tubes in power plants is a serious problem that can lead to unscheduled and costly outages. The predominant failure location of current concern is circumferential cracking on the fireside of waterwall tubes in the furnace waterwall section of a boiler. Although there is basic agreement that cracking results from a combination of thermal fatigue and corrosion, a complete explanation of the basic phenomena needed to establish the root causes of this problem is lacking. The purpose of the present study was to analyse the sources of the tensile stress responsible for initiating circumferential cracking and to identify the key parameters controlling this tensile stress. The results of analytical modelling suggested that a combination of increasing tube wall temperature with increasing thickness of internal oxide layers, and temperature spiking due to deslagging events eventually may result in tensile stresses sufficient to crack the fireside oxide and initiate the development of circumferential cracks. This scenario also led to suggestions for reducing tensile stresses in waterwall tubes which, in turn, would be expected to delay/avoid circumferential cracking and improve the reliability of waterwall tubes.     

Failure analysis of TP304H tubes in the superheated steam section of a reformer furnace

The cracking failure of TP304H tubes in the superheated steam section of a reformer furnace was analyzed. Through the analysis of macro-appearance, micro-appearance of specimens with cracks, metallurgical structure of specimens from an intact pipe section and cracked pipe section, energy spectrum detection of fracture surface, residual stress measurement, and investigation of the service medium, the cracking mode was described as the stress corrosion cracking (SCC) of austenitic stainless steel. In this case, the materials in the heat affected zone were sensitized by inappropriate welding technology. This together with the higher pH value in the steam due to the failure of a gas-liquid separator led to the final cracking of the reformer furnace tube. So the inappropriate welding technology and the failure of the gas-liquid separator were the main factors in this fracture accident.     

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。     

Chloride-induced stress corrosion cracking of furnace burner tubes

The burner tubes (316SS) of an ethylene cracking furnace in a Saudi petrochemical plant experienced repeated premature failures. One failed sample was investigated by chemical and microstructural analytical techniques to find out the failure cause and provide preventive measures. The results indicate that the burner tube failed due to chloride-induced stress corrosion cracking (SCC). Chloride could be due to the contamination coming from the ambient industrial environment. The forming process (bending and drawing) of the tubes prior to installation introduced residual tensile stresses necessary for SCC. It is recommended to stress relieve (or shot peen) the tubes following the forming process, or alternatively apply protective coatings (chloride-free) to prevent contamination. Periodic cleaning of the tube exterior is necessary.     

SCC of Stainless Steel Furnace Tubes in a Heating Furnace

Some furnace tubes made of the austeniticstainless steel 1Cr18Ni9Ti for heating crude oil ex-hibited leakage and were on fire in a refinery.Cor-rosion failure analysis was conducted to explore thecause of failure.Macro-and microexamination in-dicated the failure to be stress corrosion cracking bychloride and sulphide with cracks initiating on theinner surface in weld or heat affected zone.Veri-fying tests demonstrated that the cracks occurredduring operating period.The cause of failure wasrelated to the critical situation of the refinery:lackof desalination equipment,lots of steam with liquidfilm on inside tube walls owing to mixing crude oilwith a great amount of water,increasing decompo-sition of inorganic salts and lowering the tempera-ture in furnace tubes.     

轧钢加热炉炉底管开裂原因分析

采用宏观检验、化学成分分析、力学性能测试、金相检验等方法对轧钢加热炉炉底管产生开裂的原因进行了分析。结果表明：炉底管的开裂是由于原材料本身热处理不当产生魏氏组织和晶粒粗大,降低了钢的韧性和伸长率,在应力的作用下发生开裂。     

高压换热器U形管管口开裂分析

对高压换热器U型管泄漏进行了化学成分分析、力学性能测试、显微组织和断口的宏微观分析。检验结果显示，换热管材料的化学成分和力学性能符合相关标准的要求，显微组织正常；换热器管口开裂为连多硫酸应力腐蚀开裂。     

On the Corrosion Behavior of a ferritic 18 Cr-2 Mo-steel

The investigations carried out with 18 Cr-2 Mo steel were aimed at its behavior under pitting corrosion, crevice corrosion and stress corrosion cracking conditions. This was done in autoclave laboratory experiments and under experimental heat exchanger conditions in Rhine river water with a chloride content of max. 400 ppm. The test temperatures were 80, 100 and 130°C. Model heat exchangers were fabricated and operated to investigate the influence of filler materials and weld joints between the ferritic 18 Cr-2 Mo steel and a standard austenitic steel. The possibilities of fabricating tube sheets by applying a weld overlay and using explosive bonding were explored. 18 Cr-2 Mo steel has been shown to be suited for applications in cooling water systems which have a chloride content of 400 ppm. No stress corrosion cracking occurs under such conditions. Tubes with a wall thichness up to 3 mm have sufficient toughness. Tube sheets can be made of boiler plate protected by an explosive cladding or a weld overlay of 18 Cr-2 Mo. A combination of Type 321 or 304 L and 18 Cr-2 Mo is possible. Provided 18 Cr-2 Mo is sufficiently resistant to the product to be cooled, it is an alternative to austenitic CrNi-(Mo) steels (e.g. AISI 304) when stress corrosion cracking is likely to occur.