Experimental design to study corrosion under insulation in harsh marine environments

Corrosion under insulation (CUI) is a serious issue in harsh marine environments. Corrosion damage can have catastrophic effects on health and safety, asset integrity, the environment, and productivity if it is not detected and managed early. Limited information is available for CUI in marine environments. To overcome this issue, three types of corrosion tests are proposed: Determination of the effect of environmental factors on CUI using laboratory simulation, field testing, and accelerated marine atmosphere testing for CUI. This paper describes the methodology for developing statistically significant data to evaluate CUI in harsh marine field conditions, develop an accelerated laboratory test procedure to simulate CUI, develop a model of CUI rate, and develop risk-based remaining life assessment model for assets under CUI attack.     

Modelling of pitting corrosion in marine and offshore steel structures – A technical review

Corrosion is a major cause of structural deterioration in marine and offshore structures. It affects the life of process equipment and pipelines, and can result in structural failure, leakage, product loss, environmental pollution and the loss of life. Pitting corrosion is regarded as one of the most hazardous forms of corrosion for marine and offshore structures. The total loss of the structure might be very small, but local rate of attack can be very large and can lead to early catastrophic failure. Pitting corrosion is a localized accelerated dissolution of metal that occurs as a result of a breakdown in the protective passive film on the metal surface. It has been studied for many years; however, the structural failure due to pit characteristics is still not fully understood. Accurate pit depth measurements, precise strength assessment techniques, risk analysis due to pitting, and the mathematical relationship of the environmental factors that causes pitting failure are also factors, which need further understanding. Hence this paper focuses on these issues. It reviews and analyses the current understanding of the pitting corrosion mechanism and investigates all possible factors that can cause pitting corrosion. Furthermore, different techniques employed by scientists and researchers to identify and model the pitting corrosion are also reviewed and analysed. Future work should involve an in-depth scientific study of the corrosion mechanism and an engineering predictive model is recommended in order to assess failure, and thereby attempt to increase the remaining life of offshore assets.     

Development of HGAPSO-SVR corrosion prediction approach for offshore oil and gas pipelines

Managing the oil and gas pipelines against corrosion is one of the major challenges of the oil and gas sector because of the complexities associated with the initiation, stabilization, and growth of the corrosion defects. The present research attempts to develop a model for predicting the maximum depth of pitting corrosion in oil and gas pipelines using SVM algorithm. In order to improve the SVM performance, Hybrid PSO and GA was utilized. Monte Carlo simulation was used to determine the time lapse for the pit depth growth. In order to implement the above modeling approaches and to prove their efficiency and accuracy against a large database, a total of 340 data samples for corrosion depth and rate are retrieved from the Iranian Oilfields. The performance of the new algorithm shows that it has higher stability and accuracy. In addition, the forecasting results of the new algorithm are compared with the 11 intelligent optimization algorithms, it shows that the novel hybrid algorithm has higher accuracy, better generalization ability, and stronger robustness. The coefficient of determination (R²) value in the testing phase for SVM-HGAPSO was estimated by 0.99. Proposed hybrid model and Monte-Carlo simulations pitting corrosion based on Poisson square wave process have been used to predict the time evolution of the mean value of the pit depth distribution for different categories of maximum pitting rates (low, moderate, high and sever). The models was validated with 4 field data for each of the pitting corrosion categories and the results agreed well. The pipelines under severe pitting corrosion rate were, more conservatively predicted by HGAPSO-SVR than those under low, moderate and high pitting corrosion rates. The results obtained demonstrate the potentials of this technique for the integrity management of corroded aged pipelines.     

Offshore safety case approach and formal safety assessment of ships

PROBLEM: Tragic marine and offshore accidents have caused serious consequences including loss of lives, loss of property, and damage of the environment. METHOD: A proactive, risk-based "goal setting" regime is introduced to the marine and offshore industries to increase the level of safety. DISCUSSION: To maximize marine and offshore safety, risks need to be modeled and safety-based decisions need to be made in a logical and confident way. Risk modeling and decision-making tools need to be developed and applied in a practical environment. SUMMARY: This paper describes both the offshore safety case approach and formal safety assessment of ships in detail with particular reference to the design aspects. The current practices and the latest development in safety assessment in both the marine and offshore industries are described. The relationship between the offshore safety case approach and formal ship safety assessment is described and discussed. Three examples are used to demonstrate both the offshore safety case approach and formal ship safety assessment. The study of risk criteria in marine and offshore safety assessment is carried out. The recommendations on further work required are given. IMPACT ON INDUSTRY: This paper gives safety engineers in the marine and offshore industries an overview of the offshore safety case approach and formal ship safety assessment. The significance of moving toward a risk-based "goal setting" regime is given.     

A spatial-temporal approach for corrosion prediction in time-varying marine environment

Corrosion in seawater is simultaneously influenced by multiple environmental factors including dissolved oxygen (DO), temperature, salinity, pH, and so on. These factors vary along with time and are different in different locations. The spatial-temporal variation of the actual marine environment cannot be ignored in corrosion prediction models. This paper proposes a new method for corrosion prediction in the actual time-varying marine environment which includes the design of experiments, calibration of acceleration models, and the modeling of marine environment. Acceleration models capture the effects of environmental factors and acts as the link between the environment and the corrosion process. The marine environment is described with the Kriging spatial-temporal model. Then the proposed method is used to give corrosion predictions for metals in different locations and vessels travel in different waters. This method could be helpful for corrosion resistance evaluation and environment corrosivity assessment.     

Risk-based inspection (RBI) of a gas pressure reduction station

One of the principles of corrosion management is proper inspection methodology, and in particular the risk-based inspection (RBI). Occasionally a large percentage of the total risk of a unit is concentrated in a small part of the equipment, which can be reduced by using risk management techniques. In this study, a semi-quantitative risk-based inspection method has been performed in a gas station with for its components (pipelines, filters, etc.), to identify the existing damage mechanisms and also to rank its equipment in terms of inspection intervals. In this regard, RBI was performed for the gas station which consisted of phases (Phase A & Phase B) with Class 300 and Class 600 equipment. According to documented conditions and reviewed records the main damage mechanism for the investigated components in the gas station was identified as wall thinning due to erosion corrosion and external corrosion. In terms of inspection, results showed that most of the equipment studied had medium risk level and a few had medium to high level of risk. In this regard, the corrosion rates of Class 300 and Class 600 equipment were also studied and compared, and it was indicated that the corrosion rates were higher at locations for Class 300 equipment where more pressure drop had occurred. Overall, based on the obtained corrosion rates and obtained risk matrixes, it was concluded that wall thinning (erosion-corrosion) was the determining risk factor for equipment inspected in the gas pressure reduction station.     

A risk-based approach to design warning system for processing facilities

Alarm flooding is a major safety issue in today's processing facilities. Important recommendations are available for alarm management; however, they are often violated in practice, especially in the alarm systems implemented through the distributed control system. An effective process alarm prioritization and management system is desired for a safe and effective operation of a process facility.In present work, authors address two main issues related to an alarm system – the reliability and the prioritization of the alarms. The main objective is to deal with the alarm-flooding problem in process facilities. A multi alert voting system based on sensor redundancy approach is proposed to improve the reliability. A quantitative risk-based alarm management approach is proposed to address the flooding issue. In the risk-based approach, an integrated model consisting of the probability (P), the impact (I) of the potential hazards, and the process safety time is proposed to prioritize these raised alarms.The proposed approach is further explained by a reactor system with pressure and temperature variable monitoring and controls, where the hazards associated with two alerts caused by over high pressure and over high temperature are analyzed and integrated with response time for alarms generation and prioritization.     

基于改进K-means和CNN的储罐罐底点蚀诊断模型*

为解决储罐罐底点蚀问题,提出基于改进K-means和CNN的储罐罐底点蚀诊断模型,在传统聚类基础上引入肘部法则,保证k值选取3的准确性,将原始声发射信号特征参数和聚类后的类别信息输入模型进行训练,系统预测准确率高达99%。研究结果表明:该模型能够及时发现点蚀现象,指导管理者确定储罐开罐检查时间顺序,避免点蚀穿孔造成的人力、物力损失,降低储罐运行风险,保障储罐运行安全,研究结果可为罐底点蚀诊断提供技术支撑。     

塔河油田站间伴生气管线腐蚀风险评价

塔河油田某站间伴生气管线输送气体H2S含量较高,若管线发生腐蚀,导致伴生气泄漏会污染环境,造成人员伤害,因此对该管线的腐蚀风险进行了评估。评估结果认为该管线在目前的运行工况和腐蚀环境下,使用GB 6479—2000的20#钢适用于SSC2酸性环境,不会发生硫化物应力腐蚀开裂;预测腐蚀速率为0.51 mm/a,以H2S为主的腐蚀可能产生严重的局部腐蚀或点蚀,需定期进行腐蚀监测。     

氯乙烯储罐注水堵漏腐蚀风险的预测方法研究*

为更好地解决氯乙烯储罐注水堵漏可能导致储罐发生腐蚀泄漏的实际问题,提出1种基于ASPEN和神经网络的氯乙烯储罐注水堵漏腐蚀风险的预测方法。运用ASPEN流程模拟软件,对氯乙烯储罐注水堵漏工艺进行模拟,得到不同泄漏孔径下注水速率和HCl浓度的关系;以HCl浓度作为导致腐蚀的主要影响因素,对不同种钢材进行挂片腐蚀实验;结合神经网络分析,得出HCl浓度与腐蚀速率之间的拟合式,预测储罐腐蚀情况。结果表明:神经网络预测结果平均相对误差7.63%,随注水速率的提高,HCl浓度变化呈下降趋势,腐蚀速率变化呈下降趋势;在等效泄漏孔径24 mm、注水速率0.87 m/s时,Q345R腐蚀速率13.93 mm/a,20#腐蚀速率10.48 mm/a,201不锈钢腐蚀速率7.09 mm/a为3者中最低,但此工况下,201不锈钢有点蚀倾向,储罐易发生穿孔,故201不锈钢不宜用作氯乙烯储罐母材,并提出对《石油化工企业设计防火标准(2018年版)》的修订建议。     

Fuzzy dynamic risk-based maintenance investment optimization for offshore process facilities

A methodology for maintenance planning is developed which helps in improving the reliability of the components and safety performance in process facilities. This methodology helps design an optimum safety maintenance investment plan by integrating the optimization techniques and a fuzzy dynamic risk-based method. Intuitionistic Fuzzy Analytic Hierarchy Process (IFAHP) is applied to deal with uncertain data. The proposed approach employs multi-experts’ knowledge which helps to optimize the maintenance investments. A separator system in an offshore process facility platform is selected as a case study to demonstrate the application of the proposed methodology. A practical example in the separator system is surveyed and potential failures and Basic Events (BEs) are identified. Finally, a risk-based maintenance plan is provided for future safety investment analysis. The results indicate that the developed methodology estimates the risk more accurately, which enhances the reliability of future process operations.     

锅炉省煤器H型鳍片管局部泄漏机理研究

本文以某电厂的#1机组锅炉炉省煤器H型鳍片管为研究对象,设计对比试验,从宏观分析和微观分析两方面,对鳍片管局部泄漏的原因进行了深入研究,最终推断发生泄漏是局部点蚀所致。在锅炉运行过程中,沟槽内灰分沉积致使S、CI元素在沟槽底部富集而发生点蚀,减薄管壁,直至局部区域管壁不足以承压而发生泄漏。本文研究贴近工程实际,具有实际的工业应用价值,为以后相关问题提供解决思路。     

复合板压力容器点腐蚀缺陷运行适应性评价

为准确反映含点腐蚀缺陷复合板压力容器的安全状态,在复合结构弹性力学分析的基础上,通过工程实例,采用运行适应性(FFS)评价方法对其进行安全评定与剩余寿命评估。结果表明:复合板压力容器安全评定时应考虑覆材的影响,依据提出的力学模型分别对覆材厚度计入和不计入强度设计2种情况进行应力校核,同时结合蚀孔的分布特征,对其特征尺寸进行统计学平均后计算剩余强度。在剩余寿命预测中,已考虑蚀孔直径和深度随时间变化对剩余强度的影响。通过计算最大工作压力(MAWP)参量,已对某一压力容器进行寿命评估。     

Security Risk Assessment Methodology for the petroleum and petrochemical industries

The American National Standards Institute (ANSI)/American Petroleum Institute (API) Standard 780 Security Risk Assessment (SRA) Methodology was published in June 2013 as a U. S. standard for security risk assessments on petroleum and petrochemical facilities. The standard represents a model standard for evaluating all security risks of petroleum and petrochemical infrastructure and operations and assists industries in more thoroughly and consistently conducting SRAs. The 2013 Standard is an update from the previous API/NPRA SRA Methodology (2004) and focuses on expanding functional utility without changing the basic methodology.The methodology can be applied to a wide range of assets even beyond the typical operating facilities of the industry. This includes refining and petrochemical manufacturing operations, pipelines, and transportation operations including truck, marine, and rail, as well as worker and executive security, housing compounds, and remote operational sites. The new standard describes the most efficient and thorough approach for assessing security risks widely applicable to the types of facilities operated by the industry and the security issues they face. It is voluntary but has been adopted by the Kingdom of Saudi Arabia Ministry of Interior High Commission for Industrial Security as the mandatory security risk assessment methodology for industrial facilities.This paper examines the key elements of the ANSI/API SRA process and discusses how forward thinking organizations may use risk-based performance metrics to systematically analyze facility security postures and identify appropriately scaled and fiscally responsible countermeasures based on current and projected threats. The AcuTech Consulting Group developed the methodology under contract to the API, and the author was the project manager for the project.     

有限元分析不同形状腐蚀坑水冷壁管的剩余强度

基于ANSYS有限元软件,对含不同形状腐蚀坑水冷壁管剩余强度进行了研究。研究表明,将管壁上腐蚀坑简化为柱状,当腐蚀坑直径和腐蚀深度组合达到?5 mm-80%壁厚、?8 mm-70%壁厚、?12 mm-60%壁厚3种情况时,腐蚀坑直径和腐蚀深度增加则可认为腐蚀区失效;将腐蚀坑简化为球形,当腐蚀坑直径和腐蚀深度达到10H-70%壁厚(H为腐蚀深度)时,腐蚀坑直径或深度增加则可认为腐蚀区域失效;将腐蚀坑简化为矩形,当腐蚀坑尺寸和腐蚀深度达到6H-60%壁厚时,腐蚀深度和尺寸增加会造成腐蚀区域失效。相同尺寸和腐蚀深度的柱形坑、球形坑和矩形坑,球形坑最安全,柱形腐蚀坑最容易失效。     

基于风险的工业管道在线检测技术研究

化工装置工业管道面临焊接和腐蚀两大问题,装置的长期运行与管道定期检验的矛盾日益突出.通过对数字射线、脉冲涡流、超声导波三种管道在线检测技术的对比分析,结合基于风险的检验(RBI)理念,探索出一套适用于工业管道在线检验的技术,对节约企业成本、保障管道安全具有重要意义.     

发酵罐不锈钢换热盘管泄漏失效分析

通过失效现场情况了解、宏观检查、材质分析、金相检验、电镜观察、能谱分析及冲击断面分析等研究06Cr19Ni10发酵罐盘管失效原因。结果显示由于发酵罐盘管材质熔炼工艺不恰当,固溶处理不当,冷却循环水中Cl^-含量超标,焊缝热影响区、管材母材区大面积发生不同程度晶间腐蚀,局部点蚀穿孔。建议对用于设备重要部位或对生产工艺有重大影响的,且服役环境存在晶间腐蚀倾向的不锈钢,增加耐晶间腐蚀检测。快速识别伪劣不锈钢检测手段亟待增强。     

丁二烯装置基于风险的检验技术应用

采用RBI技术对丁二烯装置进行风险评估,经分析装置存在的主要损伤机理有碱应力腐蚀开裂、有机酸腐蚀、冷却水腐蚀、冲刷腐蚀和丁二烯自聚等,装置的风险由失效后果主导,失效可能性较高的评估.单元集中在脱重冷凝系统和薄壁小直径管道。根据基于风险的检验策略对装置实施检验,检验过程中发现装置存在脱重冷凝系统设备应力腐蚀开裂、一萃塔系统换热器点蚀、接管角焊缝开裂和压力管道腐蚀減薄等主要问题,检验检测结果与风险评估过程中识别的损伤机理和薄弱环节保持一致。     

20 Years on lessons learned from Piper Alpha. The evolution of concurrent and inherently safe design

It has now been well over 20 years since the North Sea Piper Alpha disaster in 1988. There have been many lessons learned; some documented others just etched in memory. The event chronicled many significant changes in the offshore industry. The emanating point for most sweeping changes has been the Cullen Report and the UK North Sea industry. This paper reviews some of the critical lessons and identifies many ‘secondary’ finer points that constitute important learnings. The paper looks at major changes instigated by step changes in safety criticality. It is argued that the ‘second tier’ modes of failure such as corrosion, materials degradation, environmental cracking, erosion, plant ergonomics, etc. need to be better examined. These mechanisms are dangerous threats to the integrity of deep subsea assets, and it is noted that such root causes of failure as witnessed or predicted have yet to be fully appraised. The authors’ use wide experiences and case histories to highlight such concerns, offering rational fit-for-purpose solutions. The industry disconnections between, urgency to build, knowledge transfer, and management of change, are refocused. Powerful advances in risk-based mechanical, process, materials, and corrosion engineering are emphasized and the use of key performance indicators (KPIs) are reasoned for best life-cycle integrity. To keep up with the pace of growth in the deepwater sector, methods of concurrent and inherently safe design have evolved in a world where the practicalities and costs of modification, repair and retrofit are extremely difficult. Hence getting it right at the outset is paramount. Thus the drive for purposeful investment, at design is more justifiable, than the traditional practice of postponing costs (and problems) to operations. In this way the ominous ‘gray’ zone between the two cost centers is better bridged for reasons of safety and commercial advantage.     

基于风险的检验技术在苯加氢装置管道的应用

简述基于风险的压力管道检验技术基本理念,讨论压力管道的危害风险和失效模式,介绍了风险评估方法及其适用场合、风险评估程序。对某苯加氢装置的管道系统进行风险检验评价,对该管道的各种危险因素进行分析,并对其基础数据和检验检测结果进行了研究和探讨,近而采用5×5风险矩阵法和定性分析,对苯加氢装置管道系统进行风险评估,根据该评估结论,提出了科学制定检修计划的建议和控制风险措施。研究结果表明:基于风险的检验技术,既能节约大量的停机和检验维修费用,又能有效地提高重点设备的安全性和管理水平。