Failure analysis of carbon steel components in a water bath heater and the influence of ethylene glycol concentration

Water bath heaters are designed to heat the gas prior to pressure reduction. In this paper, corrosion failure of coil tubes, fire tubes and inner surface of the shell from a large water bath heater is described and the effect of ethylene glycol concentration has been investigated. In order to study the main cause of failure, non-destructive and destructive tests, including evaluation of mechanical properties, X-ray diffraction, scanning electron microscopy, EDS (energy dispersive spectroscopy), microanalysis of corrosion products and chemical analysis of water used in the heater were carried out on specimens prepared from coil tubes. The results indicated that insufficient control of water level in the tank resulted in oxygen concentration corrosion. After evaporation of water content, a residue remained on the surface leading to under deposit corrosion and, through that, a blister-like damage took place on the shell roof. After detachment, corrosion products and scales, fell down and remained on the upper surface of the components, leading to scale corrosion of carbon steel coil and fire tubes. Results of laboratory corrosion tests revealed that water containing 10–40% ethylene glycol had the lowest corrosion rate, whereas with concentrations < 10%, the corrosion rate was high.     

污水池水压及水封爆破拆除

利用控制爆破拆除了大型污水沉淀池和曝气池。根据池底和池壁的钢筋混凝土厚度,池底采用炮泥和水混合封填的水封爆破,池壁采取了水压爆破。从爆后的效果看,池底的双层双向钢筋已与混凝土完全脱离,池壁爆破后钢筋已基本完全暴露,加以机械配合就可彻底拆除。利用这种爆破方法很好地解决了拆除钢筋混凝土结构中的飞石问题,节约施工成本,加快了工程进度,取得了理想的爆破效果。     

污水池水压及水封爆破拆除

利用控制爆破拆除了大型污水沉淀池和曝气池。根据池底和池壁的钢筋混凝土厚度,池底采用炮泥和水混合封填的水封爆破,池壁采取了水压爆破。从爆后的效果看,池底的双层双向钢筋已与混凝土完全脱离,池壁爆破后钢筋已基本完全暴露,加以机械配合就可彻底拆除。利用这种爆破方法很好地解决了拆除钢筋混凝土结构中的飞石问题,节约施工成本,加快了工程进度,取得了理想的爆破效果。     

原油储罐底板腐蚀的原因及其防护措施

针对原油储罐底板腐蚀严重的问题,分析了产生腐蚀的原因,提出了罐底板采用涂料与牺牲阳极联合保护、支柱对应处底板增焊不锈钢板等防护措施,取得了良好的应用效果.     

Q235B钢原油储罐底板腐蚀穿孔原因

某Q235B钢储罐底板发生腐蚀穿孔泄漏事故。通过宏观分析、微观分析、化学成分分析、力学性能试验、金相检验等方法,对储罐底板腐蚀穿孔原因进行了分析。结果表明:储罐底板的涂层因质量较差发生鼓包后破损,在破损点发生了氧腐蚀,进而导致储罐底板腐蚀穿孔。     

Unexpected Corrosion Problems by Organic Fat Charged in Loading Tanks of a Cargo Ship

A failure analysis has been conducted on board a cargo ship to assess the extent of corrosion damage. The damage was classified as unusual by the ship owner since the material, an organic fat (namely tallow), was usually loaded into stainless steels on board tanks without any noticeable corrosion problems. The corrosion phenomenon was classified, by the technical crew, as pitting on the bottom of two tanks, particularly the 6p (port tank) and the 6s (starboard tank). The pitting was defined as anomalous since only two tanks were affected and a total of five tanks were made of same stainless steels and loaded with same organic fat mixture. Corrosion pits were found during final inspection by the captain, following load discharge and tanks cleaning operations. The initial inspection was carried out while the cargo ship was harboured at Algeciras (Spain). Because of the observations, the ship remained in harbour for 3 days awaiting inspection by qualified technicians to evaluate the possibility of resuming navigation. The cargo ship was then inspected by one of the authors in collaboration with two metallurgists acting as consultants to the ship owner. The purpose of the inspection was to investigate on damage phenomena, to evaluate the integrity of cargo structures and to decide on two possible options: resuming navigation or immediately ordering a very expensive stop for urgent maintenance. This paper was structured to show documentation (some details have been omitted for propriety reasons) and visual inspection results used to establish failure mechanisms and probable failure-root causes. These results enabled a decision for the cargo ship to resume travel to next dockyard for maintenance operations.

基于平均频谱的储油罐罐底腐蚀声发射特征分析

针对声发射(AE)罐底检测过程中传统分析方法无法准确判断储油罐罐底腐蚀区域腐蚀程度的问题,提出了基于平均频谱的储油罐罐底腐蚀声发射特征分析方法,用于判断储油罐罐底板腐蚀类型.该方法利用平均值原理,分别求出罐底板不同腐蚀区域的平均频谱,再通过傅里叶逆变换得到该区域的平均波形,以此来表征腐蚀区域占主导地位的声发射信号特征.为了验证分析方法的有效性,进行了现场储油罐检测实验,实验过程中应用护卫传感器屏蔽罐内噪声干扰.实验结果表明,护卫传感器可以有效屏蔽大量罐内噪声信号,使定位结果更加准确.应用护卫传感器所得到的定位结果与开罐检测结果基本一致.在获得准确的声发射定位结果的前提下,应用基于平均频谱的分析方法,可以有效识别不同腐蚀类型,进而准确判断出罐底腐蚀程度.     

Analysis of pitting corrosion failure of copper tubes in an apartment fire sprinkler system

Microscopical and structural analyses as well as visual inspection of copper tubes were used to investigate the cause of pitting corrosion failure of copper tubes in the wet pipe sprinkler system. Chemical analysis of the water in the copper tubing and XRF/XRD analysis of its sediments were also used to obtain hints on what was happening in the copper tubing during the progress of the pitting corrosion. It was found from the failed copper tube that a significant amount of pressurized air was present over the water in the copper tubing during operation and a series of corrosion pits were aligned adjacent to the water/air line. The waterline localized corrosion, a type of differential oxygen concentration cell corrosion, induced by pressurized air over the water in the copper tubing was identified as the cause of the pitting corrosion failure. A state of a very low oxygen concentration was maintained under the envelope of a dense layer of malachite, the corrosion byproduct, which was evidenced by the formation of Cu₂O crystalline particles inside the corrosion pit. CuO particles observed on the inside surface of the copper tube do not seem to help prevent local as well as general corrosion. Accelerated pitting corrosion of the copper tube in the wet fire sprinkler system was simulated using a differential aeration cell. Finally, measures for stopping or delaying the pitting corrosion of the copper tube in the wet sprinkler system are suggested.     

钢筋混凝土煤气柜的水压爆破拆除

利用水压爆破拆除了处于复杂环境下的一个大型钢筋混凝土煤气柜。为了控制柜壁的坍塌方向和范围 ,采取了一系列的技术措施 ,这些措施包括增加底层布药量、降低药包整体布置高度、减少总药量、靠近壁体分散布置药包以及控制不同方向炸高等。文中分析了工程难点 ,介绍了爆破方案设计、爆破参数选择以及安全措施等 ,并简述了爆破效果     

钢筋混凝土煤气柜的水压爆破拆除

利用水压爆破拆除了处于复杂环境下的一个大型钢筋混凝土煤气柜。为了控制柜壁的坍塌方向和范围 ,采取了一系列的技术措施 ,这些措施包括增加底层布药量、降低药包整体布置高度、减少总药量、靠近壁体分散布置药包以及控制不同方向炸高等。文中分析了工程难点 ,介绍了爆破方案设计、爆破参数选择以及安全措施等 ,并简述了爆破效果     

薄壁钢筋混凝土烟囱和水塔定向爆破拆除

结合某薄壁钢筋混凝土烟囱和水塔的定向爆破拆除,提出了确保定向爆破安全、成功的几条重要技术措施:①爆破切口圆心角可减小到208°;②在后支撑中心点加钢斜腿支撑,既增大了抵抗烟囱的下坐支撑力,又克服了烟囱的后坐力;③采用“<”形锐角定向窗切口,使定向窗端部受力更均匀;④首次试用快干水泥堵塞炮孔,有效防止了浅眼爆破的冲炮;⑤采用砂包墙埂作飞石防护屏障,既彻底阻挡了飞石,又屏蔽了爆破声响。最终爆破效果相当完美。     

Corrosion and stress-corrosion cracking of exploited storage tank steel

We study the corrosion resistance of St3S steel under loading and its susceptibility to corrosion and hydrogen-induced cracking in bottom water. Sections of a tank are distinguished according to the character of the media interacting with the metal of the inner surface in the process of operation. It is shown that bottom water is characterized by high levels of corrosion activity and that the degrees of in-service degradation of different sections of the tank are different. The worst corrosion and stress-corrosion resistance are exhibited by steel operating in contact with bottom water. Significant levels of plastic strains intensify the process of corrosion in steel and make the rates of corrosion in different sections of the tank closer to each other. The in-service degradation of steel can not only intensify the process of corrosion of the inner surface of the tank but also promote the brittle fracture of the material characterized by the elevated susceptibility to hydrogen-induced cracking.Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 113–117, May–June, 2004.     

Water chemistry and processing effects on the corrosion degradation of copper tubing in cooling water systems

Specimens of copper tubing from an industrial scale chiller were subjected to a complete corrosion failure analysis. Nondestructive inspection of the tubing indicated substantial corrosion damage and provided the impetus for the corrosion analysis. By application of the typical methods encountered in metallurgical failure investigations, as well as additional chemical analysis techniques, the most probable cause of failure was identified to be a change in the water chemistry during the service life of the tubes. Additional items that may have contributed to the failure include the geometric design of the tube and the post-manufacture cleaning process prior to service. Recommendations were made regarding water treatment and the requirements for any replacement tubes. In addition to discussion of the specific failure(s) investigated, notes regarding the general procedures for corrosion failure analysis are also presented.     

600MW机组汽轮机低压缸腐蚀原因分析与预防措施

某600 MW机组在大修检查时发现汽轮机低压缸普遍锈蚀。低压缸转子经喷砂清除锈蚀产物后,底部暴露出明显坑蚀。通过扫描电镜(SEM)、能谱仪(EDS)、电感耦合等离子质谱(ICP)和离子色谱(IC)等对低压缸和其他部位(高压缸、中压缸)进行检查分析,查明腐蚀原因。经过检测分析认为,低压缸转子叶片的锈蚀主要是在停机期间形成的原位停机氧腐蚀,积盐中氯离子参与形成的含氧电化学腐蚀。停机中防锈蚀措施不当,自然冷却,真空破坏后空气侵入,湿度饱和,形成停机腐蚀条件。     

Failure analysis of 316L stainless steel tubing of the high-pressure still condenser

Sherritt International Corporation experienced corrosion failures with the 316L stainless steel tubing in a high-pressure still condenser employed for ammonia recovery. A detailed failure analysis was conducted on the condenser tubing to determine the mode and the root cause of the failure. The analysis included both optical and scanning electron microscopy (SEM) of the inner and outer surfaces of the tube as well as characterization of the corrosion products using energy-dispersive X-ray spectroscopy (EDX). Results revealed that the corrosion attack was confined to the first ～100 mm of the tubing at the inlet where the tube was connected to the top tubesheet. The tube suffered both external stress-corrosion cracking (SCC) and crevice corrosion from the shell side (water side), and wall thinning of the inner surface (the tube side) due to erosion corrosion. It was evident that failure of one of the tubes occurred due to SCC that penetrated the whole wall thickness and resulted in a leak failure. Some prevention measures are proposed to avoid this type of corrosion attack in the future.     

隧道全断面开挖光面爆破设计

介绍了军都山隧道开挖施工中所采用的全断面光面爆破快速施工技术。根据隧道围岩硬度大、节理裂隙发育等地质情况,在施工现场进行了掏槽孔不同深度的装药试验,对隧道开挖的爆破参数、炮孔布置、装药结构和起爆网路进行了分析和设计,提出了保证隧道开挖成型质量和提高循环进尺的施工方案与措施,确保了军都山隧道全断面开挖爆破取得圆满成功,可供类似工程参考。     

Failure analysis of the wall tubes of a water-tube boiler

An industrial case history of the failure of the evaporator (water wall) tubes of a water-tube boiler is presented in this study. After two years in service, a leak was detected in one of the tubes over its bent section with pitting corrosion on its internal surface. Later on, the same symptoms were discovered in other tubes of the same boiler, and several tubes were extracted for failure analysis. On the basis of visual inspection, chemical analysis, microstructural examination, hardness measurements, and residual stress measurements via X-ray diffraction (XRD), the failure mechanism of the tubes was identified as stress corrosion cracking (SCC). In this paper, the results obtained from the experimental analysis are summarized, and finite element (FE) models are used to predict the residual stress due to the bending of the tube and the operational stress at the moment of failure. It was found that tensile residual stress from an inadequate stress relief treatment prior to service and high concentration of dissolved oxygen in the feed water were the main reasons for the premature failure of the boiler tubes by SCC.     

Flow enhanced corrosion of water injection pipelines

A pipe spool from the subsea water injection piping network for oil operations at Eastern Desert was retrieved and internal corrosion and grooving were observed at the 6 O’clock position, in one section of the pipe, and not in the other. Two cuts from the sited piping were received for analysis to establish an overview of whether the failure is related to materials aspects or operating conditions. Results of visual inspection, chemical analysis, metallographic examination, SEM/EDX analysis, and mechanical testing showed that the corrosion resistance against flow for the quenched and tempered structure of the first cut was better than that of the cold rolled structure of the second cut. This is largely due to the uniform distributed polygonal ferrite and the small volume fraction of pearlite. Continuous removal of the loose adhered scales by electrochemical dissolution and mass transfer resulted in creation of fresh surfaces for further corrosive attack. This reduced the pipe wall below the critical thickness required to support the operating pressure and resulted in ductile failure of the pipe. Such mechanism of failure is known as the flow enhanced corrosion (FEC) mechanism. Failure in such mechanism is a catastrophic one that usually results in serious damage and injuries if not detected before undergoing.     

定向爆破拆除框架式水塔

高 2 7m的水塔建于 193 4年 ,其顶部水罐由 12根钢筋混凝土柱支撑。在倒向侧 7根立柱上形成不同高度的爆破切口 ,背向侧倾倒中心线上的一根立柱上形成小爆破切口 ,其余 4根立柱底部打贯通孔 ,使水塔准确定向倾倒。文中讨论了立柱切口高度的计算 ,爆破参数的确定 ,并介绍了所采用的安全措施。