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Stress-Corrosion Cracking of a Type 304 Stainless Steel Pipe Caused by Residual Welding Stresses 焊接残余应力引起的304型不锈钢管应力腐蚀开裂
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c0091528
A 150 mm (6 in.) schedule 80S type 304 stainless steel pipe (11 mm, or 0.432 in., wall thickness), which had served as an equalizer line in the primary loop of a pressurized-water reactor, was found to contain several circumferential cracks 50 to 100 mm (2 to 4 in.) long. Two of these cracks, which had penetrated the pipe wall, were responsible for leaks detected in a hydrostatic test performed during a general inspection after seven years of service. Investigation (visual inspection, visual and ultrasonic weld examination, water analysis, and chemical analysis) supported the conclusion that the failure was caused by SCC due to stress, sensitization, and environment. Recommendations included replacing all pipe sections and installing them using low-heat-input, multiple-pass welding procedures.
150毫米(6英寸)80S 304型不锈钢管(11毫米,或0.432英寸)。在压水堆主回路中用作平衡线的管道,被发现含有几个50至100毫米(2至4英寸)长的周长裂缝。其中两个裂缝已经穿透了管壁,在服役七年后的一次常规检查中进行的水压测试中发现了泄漏。调查(目视检查、目视和超声焊缝检查、水分析和化学分析)支持了由于应力、敏化和环境导致的SCC失效的结论。建议包括更换所有管道部分,并使用低热量输入、多道焊接程序进行安装。
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引用次数: 0
“On-Load Corrosion” in Tubes of High Pressure Boilers 高压锅炉管道的“有载腐蚀”
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001396
The phenomenon of on-load corrosion is directly associated with the production of magnetite on the water-side surface of boiler tubes. On-load corrosion may first be manifested by the sudden, violent rupture of a boiler tube, such failures being found to occur predominantly on the fire-side surface of tubes situated in zones exposed to radiant heat where high rates of heat transfer pertain. In most instances, a large number of adjacent tubes are found to have suffered, the affected zone frequently extending in a horizontal band across the boiler. In some instances, pronounced local attack has taken place at butt welds in water-wall tubes, particularly those situated in zones of high heat flux. To prevent on-load corrosion an adequate flow of water must occur within the tubes in the susceptible regions of a boiler. Corrosion products and suspended matter from the pre-boiler equipment should be prevented from entering the boiler itself. Also, it is good practice to reduce as far as possible the intrusion of weld flash and other impedances to smooth flow within the boiler tubes.
有载腐蚀现象与锅炉管水侧表面产生磁铁矿有直接关系。负载腐蚀首先表现为锅炉管的突然剧烈破裂,这种故障主要发生在辐射热区的管的火侧表面,因为热传导率高。在大多数情况下,发现大量相邻的管道受到影响,受影响的区域经常以水平带的形式延伸到整个锅炉。在某些情况下,在水壁管的对接焊缝处,特别是那些位于高热流区的对接焊缝处,发生了明显的局部冲击。为了防止有载腐蚀,在锅炉的易受腐蚀区域的管道内必须有足够的水流。应防止锅炉前设备的腐蚀产物和悬浮物进入锅炉本身。此外,最好的做法是尽可能减少焊接闪光和其他阻抗对锅炉管内流动的干扰。
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引用次数: 0
Stress-Corrosion Cracking Failure of a Sensitized Valve Stem 敏化阀杆的应力腐蚀开裂失效
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c0091640
A valve stem made of 17-4 PH (AISI type 630) stainless steel, which was used for operating a gate valve in a steam power plant, failed after approximately four months of service, during which it had been exposed to high-purity water at approximately 175 deg C (350 deg F) and 11 MPa (1600 psi). The valve stem was reported to have been solution heat treated at 1040 +/-14 deg C (1900 +/-25 deg F) for 30 min and either air quenched or oil quenched to room temperature. The stem was then reportedly aged at 550 to 595 deg C (1025 to 1100 deg F) for four hours. Investigation (visual inspection, 0.7x/50x images, hardness testing, reheat treatment, and metallographic examination) supported the conclusion that failure was by progressive SCC that originated at a stress concentration. Also, the solution heat treatment had been either omitted or performed at too high of a temperature, and the aging treatment had been at too low of a temperature. Recommendations included the following heat treatments: after forging, solution heat treat at 1040 deg C (1900 deg F) for one hour, then oil quench; to avoid susceptibility to SCC, age at 595 deg C (1100 deg F) for four hours, then air cool.
用于操作蒸汽发电厂闸阀的17-4 PH (AISI 630型)不锈钢阀杆,在暴露于175摄氏度(350华氏度)和11兆帕(1600 psi)的高纯净水中大约四个月后失效。据报道,阀杆在1040 +/-14摄氏度(1900 +/-25华氏度)下进行了30分钟的固溶热处理,空气淬火或油淬火至室温。然后据报道,茎在550到595摄氏度(1025到1100华氏度)下老化4小时。调查(目视检查,0.7x/50x图像,硬度测试,再热处理和金相检查)支持了失效是由应力集中引起的渐进SCC引起的结论。此外,固溶热处理或被省略或在过高的温度下进行,而时效处理在过低的温度下进行。建议包括以下热处理方法:锻造后,在1040℃(1900°F)下固溶热处理1小时,然后油淬火;为了避免对SCC的易感,在595摄氏度(1100华氏度)下放置4小时,然后风冷。
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引用次数: 0
Damage in a Gas Turbine Hot Gas Casing 燃气轮机热燃气机匣损坏
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001737
T. D. da Silveira, I. Le May
The hot gas casing of a gas turbine used for peak load power production had developed extensive cracking during operation. The operating time was 18,000 h, and it had been subjected to 1,600 operating cycles. The gas temperature on the hot side was 985 deg C, on the cold side 204 deg C, the material being AISI 321 stainless steel. The purpose of the present study was to determine optimum repair welding procedures on the premise that the material was basically sound and undamaged by creep. The cracking was the result of thermal fatigue, and such cracks can propagate at elevated temperature, with damage ahead of the crack tip occurring by means of very local processes of creep. Metallographic examination disclosed heavy surface layers of carbides, such that the material was extremely brittle when subjected to bending. Accordingly, although it was demonstrated that the casing could be welded successfully, it was suggested that the remaining useful life was effectively exhausted and that it should be replaced. Thermal stresses produced during operation would rapidly result in additional cracks.
某调峰发电用燃气轮机热燃气机壳在运行过程中出现大面积开裂。运行时间18000 h,运行周期1600次。热侧气体温度985℃,冷侧气体温度204℃,材料为AISI 321不锈钢。本研究的目的是在材料基本完好且未受蠕变损伤的前提下,确定最佳的修复焊接工艺。裂纹是热疲劳的结果,这种裂纹可以在高温下扩展,裂纹尖端之前的损伤通过非常局部的蠕变过程发生。金相检查发现表面有很重的碳化物层,因此材料在弯曲时非常脆。因此,尽管证明了套管可以成功焊接,但有人建议,剩余的使用寿命实际上已经耗尽,应该更换套管。在运行过程中产生的热应力会迅速导致额外的裂纹。
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引用次数: 0
Stress-Corrosion Cracking and Galvanic Corrosion of Admiralty Brass 海军黄铜的应力腐蚀开裂和电偶腐蚀
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001651
P. J. Kenny
Some of the admiralty brass tubes were failing in a heat exchanger. The heat exchanger cooled air by passing river water through the inside of the tubes. The wall thickness of all tubes ranged between 1.19 to 1.27 mm (0.047 to 0.050 in.). General intergranular corrosion occurred at the inside surfaces of the tubes. Transgranular stress-corrosion cracking, probably the result of sulphates under basic conditions, and dezincification occurred also as the result of galvanic corrosion under the deposits in the tubes. Recommendations were to use a closed-loop water system to eliminate sulphates, ammonia, etc., and to run trials on one unit with tubes of other alloys such as 80-20 Cu-Ni or 70-30 Cu-Ni to evaluate their performance prior to any large scale retubing operations.
海军的一些黄铜管在热交换器中失效了。热交换器通过让河水通过管道内部来冷却空气。所有管的壁厚在1.19到1.27毫米(0.047到0.050英寸)之间。一般晶间腐蚀发生在管的内表面。穿晶应力腐蚀开裂,可能是硫酸盐在基本条件下的结果,脱锌也可能是由于管中沉积物下的电偶腐蚀的结果。建议使用闭环水系统来去除硫酸盐、氨等,并在一个单元上用其他合金(如80-20 Cu-Ni或70-30 Cu-Ni)的管子进行试验,以评估其性能,然后再进行任何大规模的重新管道操作。
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引用次数: 0
Failure Analysis of Boiler Water Wall-Tubes at a Power Generation Plant 某电厂锅炉水冷壁管失效分析
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001709
A. El-Batahgy, W. Metwally
Several waterwall tubes in a power station boiler failed after ten years of service. The boiler is a suspension type equipped with 30 IK boxes where retractable soot blowers are inserted to clean the inside of the boiler using high-pressure steam. The tubes, which operate at 693 deg F (367 deg C) and 2935 psi (20.5 MPa), failed near the IK boxes as a result of thermal fatigue. Thermal fatigue damage was accelerated by repetitive exposure to water droplets from the soot blower and the associated rapid cooling.
某电站锅炉的几根水冷壁管在使用十年后失效。该锅炉为悬吊式,装有30个IK箱体,插入可伸缩的吹灰器,利用高压蒸汽对锅炉内部进行清洗。由于热疲劳,这些管道在693华氏度(367摄氏度)和2935 psi (20.5 MPa)下工作,在IK盒附近失效。反复暴露于吹灰器的水滴和相关的快速冷却会加速热疲劳损伤。
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引用次数: 0
The Disruption of a Turbo-Alternator Gearbox 涡轮发电机变速箱的故障
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001473
A combination of adverse factors was present in the disruption of a turbo-alternator gearbox. The major cause was the imposition of a gross overload far in excess of that for which the gearbox was designed. The contributory factors were a rim material (EN9 steel) that was inherently notch-sensitive and liable to rupture in a brittle manner. Discontinuities were present in the rims formed by the drain holes drilled in their abutting faces, and possibly enhanced by the stress-raising effect of microcracks in the smeared metal at their surfaces It is probable that the load reached a value in excess of the yield point within the delay time of the material so when the fracture was initiated, it was preceded by several microcracks giving rise to the propagation of a brittle fracture.
在涡轮发电机变速箱的破坏中存在不利因素的组合。主要原因是强加的总过载远远超过了齿轮箱的设计。造成这种情况的因素是一种边缘材料(EN9钢),它本身对缺口敏感,容易脆性断裂。在相邻面上钻出的漏孔所形成的边缘上存在不连续,并且可能由于涂覆金属表面的微裂纹的应力提升效应而增强。在材料的延迟时间内,载荷可能达到超过屈服点的值,因此当断裂开始时,在其之前会有几个微裂纹引起脆性断裂的扩展。
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引用次数: 0
Failure of Copper-Zinc Alloy Cooling-Tower Hardware 铜锌合金冷却塔硬件故障
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c0046737
After 14 months of service, cracks were discovered in castings and bolts used to fasten together braces, posts, and other structural members of a cooling tower, where they were subjected to externally applied stresses. The castings were made of copper alloys C86200 and C86300 (manganese bronze). The bolts and nuts were made of copper alloy C46400 (naval brass, uninhibited). The water that was circulated through the tower had high concentrations of oxygen, carbon dioxide, and chloramines. Analysis (visual inspection, bend tests, fractographs, 50x unetched micrographs, 100x micrographs etched with H4OH, and 500x micrographs) supported the conclusions that the castings and bolts failed by SCC caused by the combined effects of dezincification damage and applied stresses. Recommendations included replacing the castings with copper alloy C87200 (cast silicon bronze) castings. Replacement bolts and nuts should be made from copper alloy C65100 or C65500 (wrought silicon bronze).
经过14个月的使用,在冷却塔的支架、柱子和其他结构部件的铸件和螺栓上发现了裂缝,在那里它们受到外部施加的应力。铸件由铜合金C86200和C86300(锰青铜)制成。螺栓和螺母由铜合金C46400(海军黄铜,不受限制)制成。在塔内循环的水含有高浓度的氧气、二氧化碳和氯胺。分析(目视检查、弯曲试验、断口形貌、50倍未蚀刻显微照片、100倍H4OH蚀刻显微照片和500倍显微照片)支持以下结论:脱锌损伤和外加应力共同作用导致铸件和螺栓发生SCC破坏。建议包括用铜合金C87200(铸造硅青铜)铸件代替铸件。更换螺栓和螺母应采用铜合金C65100或C65500(锻造硅青铜)。
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引用次数: 0
Cracking at a Superheater Header Connection 过热器接头开裂
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001001
T. D. da Silveira, I. Le May
Examination of the header of the third superheater of a boiler producing 150 t/h of steam at 525 deg C and 118 kPa, disclosed extensive internal cracking at the connection to the tube joining this to a safety valve. Cracking was observed within the tube and in the thickness of the shell wall itself. The boiler had been in operation for approximately 160,000 h and was shut down for inspection when the cracking was detected. The material involved was 2.25 Cr, 1 Mo steel, and the unit had been subjected to 115 shutdowns. Initiation of the cracks was attributed to thermal shock, caused by the periodic return of condensate along the long connecting line (some 9 m long). Propagation of the cracks was due to thermal cycling, together with periodic pressure cycles, producing growth by low cycle fatigue. This was aided by corrosion within the cracks and by the wedging action caused by corrosion deposits at their tips. The failure suggests control of dissolved solids in the boiler feedwater may have been inadequate.
某锅炉第三个过热器的集箱在525℃和118 kPa下产生150 t/h的蒸汽,在连接安全阀的管道连接处发现了广泛的内部裂缝。在管内和壳壁本身的厚度中观察到开裂。该锅炉已经运行了大约160,000小时,当检测到裂缝时,被关闭进行检查。涉及的材料为2.25 Cr, 1 Mo钢,该机组已停产115次。裂缝的产生是由于热冲击造成的,热冲击是由沿长连接线(约9米长)的冷凝水周期性返回引起的。裂纹的扩展是由于热循环和周期性压力循环,通过低周疲劳产生扩展。这是由于裂缝内的腐蚀和尖端腐蚀沉积引起的楔入作用。这次故障表明,对锅炉给水中溶解固体的控制可能不够。
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引用次数: 0
Multiple Cracking of 234 In. Thick Boiler Drum From Thermal Shock 多重裂纹234英寸。厚锅炉汽包热冲击
Pub Date : 2019-06-01 DOI: 10.31399/asm.fach.power.c9001477
During the routine hydraulic pressure test of a boiler following modification, failure by leakage from the drum took place and was traced to a region where extensive multiple cracking had occurred. Catastrophic rupture or fragmentation of the vessel fortunately did not take place. Prior to the test, cracking was present already, extending up to 90% of the wall thickness. Analyses of brownish deposit material did not reveal the presence of any substances likely to cause stress-corrosion cracking of a Ni-Cu-Mo low-alloy steel.
在锅炉改造后的常规水压试验中,由于汽包泄漏而发生故障,并追溯到发生大面积多重裂缝的区域。幸运的是,没有发生灾难性的破裂或破裂。在测试之前,裂缝已经存在,延伸到壁厚的90%。对棕色沉积物材料的分析没有发现任何可能导致Ni-Cu-Mo低合金钢应力腐蚀开裂的物质的存在。
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引用次数: 0
期刊
ASM Failure Analysis Case Histories: Power Generating Equipment
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