Study on Failure Possibility of Full Containment LNG Storage Tanks with API 581 Risk-based Inspection

The total storage of full containment LNG storage tanks is very huge. Once the tank rupture or leakage,the consequence will be unimaginable. Therefore it is necessary to perform the risk-based inspection( RBI) and evaluation on LNG storage tanks,and the analysis on LNG storage tanks failure possibility is especially important in the RBI. Recently,Risk-based inspection( RBI) technology based on API 581 is gradually adopted and has become a new technology to determine economic feasibility and safety of equipment in petrochemical plants.However,there are limitations of applying API 581 to LNG equipment because of the unique structure of LNG storage tank( the metal inner tank and concrete outer tank). Therefore,a failure probability calculation model suitable for full containment LNG storage tanks is proposed. The domestic inner tank is usually made of 9% Ni,and its failure possibility can be calculate based on API581; the outer tank is usually made of pre-stressed concrete,and the failure possibility of structure durability can be calculated by the method of fuzzy mathematics;Then the failure possibility of the inner tank and the outer tank will be comprehensive considered by using cellulose model. Finally,by citing a real example,it also detailedly introduces the application of this proposed calculation model in the failure possibility analysis of full containment LNG storage tanks. This study provides a new approach for the evaluation of failure possibility on full containment LNG storage tanks.     

常压储罐腐蚀的风险分析

介绍了采用基于风险的检验（RBI）评价技术对常压储罐腐蚀进行风险分析的方法，通过对常压储罐的腐蚀进行风险分析，可以科学地对常压储罐的腐蚀状况进行预测，得出储罐腐蚀的风险等级。并依据风险分析的结果合理地制定储罐的检验策略，并对有较高风险的储罐进行有重点、有针对性的风险管理，从而提高储罐的运营效益及安全性。     

Optimal maintenance decisions under imperfect inspection

The process industry is increasingly making use of Risk Based Inspection (RBI) techniques to develop cost and/or safety optimal inspection plans. This paper proposes an adaptive Bayesian decision model to determine these optimal inspection plans under uncertain deterioration. It uses the gamma stochastic process to model the corrosion damage mechanism and Bayes’ theorem to update prior knowledge over the corrosion rate with imperfect wall thickness measurements. This is very important in the process industry as current non-destructive inspection techniques are not capable of measuring the exact material thickness, nor can these inspections cover the total surface area of the component. The decision model finds a periodic inspection and replacement policy, which minimizes the expected average costs per year. The failure condition is assumed to be random and depends on uncertain operation conditions and material properties. The combined deterioration and decision model is illustrated by an example using actual plant data of a pressurized steel vessel.     

Monitoring multivariate aviation safety data by data depth: control charts and threshold systems

Aviation safety analysis is increasingly needed in regulating air traffic and safety, in light of the rapid growth in air traffic density. With the recent advances in computer technology, large amounts of multivariate aviation safety data are now routinely collected in databases. Many existing analysis methods prescribed in those databases and corresponding safety indictors are based on classical statistical analysis, and their applicability are considerably restricted by the requirement of normality. An alternative nonparametric methodology based on data depth is pursued in this paper. For a given multivariate sample, a data depth can be used to measure their depth or outlyingness with respect to the underlying distribution. The measure of depth leads to a center-outward ordering of the sample points. Derived from this ordering, Liu (1995) introduced a simple, yet effective, control chart for monitoring multivariate observations. The control chart is combined here with properly chosen false alarm rates to develop meaningful threshold systems for multivariate aviation safety data for both regulating and monitoring purposes. The developed procedure is applied to the aviation inspection results collected by the Federal Aviation Administration (FAA) inspection system. The threshold system serves as a standard for evaluating the performance of aircraft operators, and provides clear guidelines for identifying unexpected performances and for assigning appropriate corrective actions.     

Evaluation of Aluminium Alloys Degradation in Aging Aircraft

The specimens of D16ATHB and B95T1 aluminum alloys (like 2024T3 and 7075T6 alloys, respectively) cut out from lower and upper wing skins of AN-12 aircraft after 40 years exploitation are investigated. The dependencies between mechanical characteristics and electrical conductivity obtained for long-term exploited alloys show a radically different trend in comparison with known for alloys in as-received state after various heat treatments. Such data are explained by results of materials fine structure study. Nondestructive eddy current (EC) method and instrument for aluminum alloys degradation monitoring in aging aircraft are analyzed.     

Quality and statistical classification of Brazilian vegetable oils using mid-infrared and Raman spectroscopy

Palm oil, soy oil, sunflower oil, corn oil, castor oil, and rapeseed oil were analyzed with Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. The quality of different oils was evaluated and statistically classified by principal component analysis (PCA) and a partial least squares (PLS) regression model. First, a calibration set of spectra was selected from one sampling batch. The qualitative variations in spectra are discussed with a prediction of oil composition (saturated, mono- and polyunsaturated fatty acids) from mid-infrared analysis and iodine value from FT-Raman analysis, based on ratioing the intensity of bands at given wavenumbers. A more robust and convincing oil classification is obtained from two-parameter statistical models. The statistical analysis of FT-Raman spectra favorably distinguishes according to the iodine value, while the mid-infrared spectra are most sensitive to hydroxyl moieties. Second, the models are validated with a set of spectra from another sampling batch, including the same oil types as-received and after different aging times together with a hydrogenated castor oil and high-oleic sunflower oil. There is very good agreement between the model predictions and the Raman measurements, but the statistical significance is lower for mid-infrared spectra. In the future, this calibration model will be used to check vegetable oil qualities before using them in polymerization processes.     

Risk-Based Inspection of a Crude Oil Import/Export Line: The Corrosion Engineer’s Role

This paper uses the case study of a line used to import and export stabilized crude oil to illustrate the steps, the benefits and the role of a corrosion engineer for a typical semi-quantitative Risk-Based Inspection (RBI) process. The line was originally designed for dry service, but currently receives a significant amount of produced water which accumulates in deadlegs with resultant deterioration. Historically, this line also experienced a number of high profile failures attributed to microbial activity, preferential weld decay and corrosion under insulation. Consequently the HSE issued an improvement notice which included a requirement for an RBI study to mitigate these threats and to provide operational integrity assurance. The scope of the RBI review considered in this paper covers only the corrosion circuit, which is from the tank isolation valve to the storage tanks. On the basis of the identified threats and the associated risks, the following inspection, monitoring, and repair (IMR) actions were recommended by the RBI team: (1) an intermediate, non-invasive, rolling inspection at a 12-monthly frequency. This includes a 100% ultrasonic testing (UT) or saturated low frequency eddy current (SLOFEC) scan of all susceptible deadlegs and a USFD (using time of flight diffraction, ToFD) of all welds on the deadlegs; (2) a thorough, non-invasive inspection at a 36-monthly frequency. This includes a full line walk and general visual inspection; a 100% UT scan or SLOFEC on all deadlegs; inspection of small bore branches for fatigue cracks with magnetic particle inspection (MPI) or eddy current (EC) Inspection and visual examination of all accessible supports; (3) a survey to identify corrosion monitoring locations for probes, coupons and sampling points; and (4) Identification and deletion of all unnecessary deadlegs during the next turn around (TAR) maintenance. These actions have since been implemented and provide the largest single contribution to the significant reduction in the number of failures/anomalies experienced on this line. The primary role of the corrosion engineer in this process is to ensure that all the credible threats for this circuit (generic and from inspection history) are identified, risk assessed, and appropriate inspection/monitoring techniques and frequencies identified, and assigned in order to mitigate the high risk threats.     

Magnetoresistance enhancement of amorphous CoNbZr-buffered magnetoresistive multilayers

Amorphous CoNbZr alloys are thermally stable and thus have been intensively studied as soft layers of a pseudo-spin-valve (PSV). By depositing a wedge-shaped Co inset layer (IL) between the CoNbZr and Cu layer, we were able to simultaneously fabricate CoNbZr(t_CNZ)/Co(0-3 nm)/Cu/Co PSVs with various CoNbZr and Co IL thicknesses. We have investigated the dependence of magnetic properties, giant magnetoresistance (GMR) effect, and microstructure on the thickness of the amorphous CoNbZr buffer layer. The GMR enhancement behaviour of the PSVs with different CoNbZr thickness was also studied along the inset Co wedge. By optimizing the thickness of CoNbZr and Co IL, a maximum GMR ratio of 7% was obtained in the stack of CoNbZr(4 nm)/Co(1.2 nm)/Cu(2.2 nm)/Co(4 nm).     

压力容器设计压力的可靠性探讨

国家标准GB 150.1—2011规定的安全阀整定压力为工作压力的1.05～1.10倍,这样虽能保证安全性,但如何保证系统工作的可靠性是个值得探讨的问题。通过分析总结国家标准及国外规范ASME/API中有关安全阀整定压力与回座压力和密封试验压力的关系,认为装有安全阀的压力容器的设计压力应当按相应安全阀标准调整最高工作压力,并给出了相应的计算公式,以保证系统的安全性、可靠性及经济性。     

Cyclic loading and marine environment effects on the properties of HDPE umbilical cables

This work presents a study of the effects of cyclic loading and marine environment on the mechanical properties of high-density polyethylene (HDPE) used in the external layer of submarine cables. Two different types of samples were tested. The first type was tested in the as-received condition whereas the second one was taken from the cyclic-loaded material. The cyclic-load test was carried out in a device, according to the API 17E standard (API 17E-98, Specification for sub sea production control umbilicas). These samples were submitted to a process of artificial aging. All the specimens were submitted to tensile test and the analysis and comparison of the results showed that HDPE suffered alterations in its mechanical behavior, especially the material submitted to cyclic loading. Both aged and as-received samples were observed by using scanning electron microscopy and their hardness was also measured. The results showed that the cyclic loading, the seawater and the ultraviolet radiations accelerated the degradation process of HDPE.     

A methodology for risk-based inspection planning of oil and gas pipes based on fuzzy logic framework

In an efficient and effective pipe integrity management programme, maintenance engineers often use the risk-based inspection (RBI) and maintenance strategy. Unfortunately, the calculation of risk is a daunting task because in order to calculate the risk of failure, a maintenance engineer needs to predict the rate of growth of a defect, the effect of the defect on the integrity of the structure and the consequence of failure. Unfortunately precise calculation for either of these parts is quite difficult.Fuzzy logic is a mathematical tool suitable for handling imprecise information in the real world. The benefit of this approach lies in its ability to include personal experiences along with acceptable deterministic models in the calculation. The structure of the model also allows easy calibration of the model to suit a particular plant condition. This approach can thus help to reduce the dependence upon the precise data, allow modelling even when a phenomenon is incompletely understood, and reduce the difficulties arising due to the complex computation required by more traditional methods.This paper presents a proposed methodology, based on fuzzy logic framework, for the establishment of an RBI programme for pipes. The paper also presents in detail a section of the methodology that can be used for calculating the estimated rate of CO₂ corrosion in carbon steel pipes. In this technique the plant operating parameters (temperature, gas and liquid flow rates, total pressure, CO₂ partial pressure and pH) are taken as fuzzy variables and used to calculate the Predicted Rate of Corrosion. The inspected rate of corrosion and the efficiency of inspection are also considered as fuzzy variables and are used to calculate Trust in Inspection Results and Trust in Predicted Results. By combining all the modules an estimated rate of corrosion is calculated. This estimated rate of corrosion can then be used for developing the risk-based inspection programme.     

Statistical analysis of the effects of prior load on fracture

Collated fracture data for three steels, A533B, A508 and BS1501, and an Aluminium alloy, 2650, were examined to assess the statistical significance of the effect of prior loading on subsequent fracture. Weibull statistical and probabilistic analysis was used throughout. Two prior loading conditions were examined; one associated with warm pre-stress, and a second using pre-compression. For the former, prior loading resulted in an increase in the mean toughness together with an increase in the shape parameter and a decrease in variability compared to the as-received material. In contrast, when prior loading involved out-of-plane compressive loading (or side-punching) statistical evidence revealed that there was a reduction in toughness together with a decrease in the shape parameter and an increase in variability. Two numerical models were applied to steel data and were able to predict the overall trends obtained from the experiments, but could not reproduce accurately the experimental statistical distributions.     

Fracture behaviour of hybrid glass matrix composites: thermal ageing effects

The thermal aging of a glass matrix composite reinforced by short carbon fibres as well as by ZrO₂ particles (hybrid composite) was investigated at temperatures in the range 500–700 °C for exposure durations of 24 h in air. The mechanical properties of as-received and aged samples were evaluated at room temperature by using the three-point flexure chevron notch technique. The fracture toughness values of as-received specimens were in the range 2.6–6.4 MPa m^1/2. Fracture toughness was affected by the thermal aging conditions. For thermal aging at temperatures <700 °C, degradation of fibre–matrix interfaces occurred and therefore the apparent fracture toughness and flaw tolerant resistance decreased. For the most severe ageing conditions tested (700 °C/24 h), fracture toughness values dropped to 0.4 MPa m^1/2. Significant degradation of the material was detected for this aging condition, mainly characterised by porosity formation in the matrix as a result of softening of the glass and oxidation of the carbon fibres.     

Accelerated thermo-oxidative aging for carbon fiber reinforced polycyanate under high pressure atmosphere

The aim of this study is to accelerate thermo-oxidative aging in carbon fiber reinforced plastics (CFRP) submitted to high temperature atmospheric pressure. In this study, long-term thermo-oxidative aging test was conducted to examine the effect of high pressure atmospheric environment on the weight and mechanical properties of CFRP to accelerate the rate of thermo-oxidative degradation. The effect of thermo-oxidative environment under high atmospheric pressure on the change in weight, strength, and shrinkage behavior of a CFRP with polycyanate (FSD-M-08178) was investigated. The aging test was conducted at 180 °C up to 8,000 h under atmospheric pressure and the test result was used as a reference data. Other aging tests were also conducted under elevated pressure conditions (0.3 and 0.5 MPa) at the same exposure temperature up to 2,000 h and the test results were treated as the accelerated aging test data. Unidirectional laminates [0]₈ and [90]₈ for tensile specimens and angle ply laminates [±45]_2S for off-axis tensile specimens were aged in oven, and then mechanical tests were carried out on them. The results indicated that elevated pressure would cause faster and larger weight gain in earlier aging period. The outcomes of these experiments were changes in weight, strength, and local shrinkage deformation were changed quickly under elevated atmospheric pressure environment. Same micro damage onset and extension irrespective of pressure during thermo-oxidative aging and subsequent loading test were observed. The test results indicate that the change in weight, strength, and local shrinkage deformation could be accelerated by elevated pressure without change in thermo-oxidative degradation mechanism. Therefore, the elevated pressure testing would be a better method to accelerate thermo-oxidative degradation. On the other hand, the change in strength under elevated pressure conditions is faster than local shrinkage deformation. Equivalent acceleration rate of degradation could not be obtained.     

An evaluation of costs and benefits of a vehicle periodic inspection scheme with six-monthly inspections compared to annual inspections

Although previous research suggests that safety benefits accrue from periodic vehicle inspection programmes, little consideration has been given to whether the benefits are sufficient to justify the often considerable costs of such schemes. Methodological barriers impede many attempts to evaluate the overall safety benefits of periodic vehicle inspection schemes, including this study, which did not attempt to evaluate the New Zealand warrant of fitness scheme as a whole. Instead, this study evaluated one aspect of the scheme: the effects of doubling the inspection frequency, from annual to biannual, when the vehicle reaches six years of age. In particular, reductions in safety-related vehicle faults were estimated together with the value of the safety benefits compared to the costs. When merged crash data, licensing data and roadworthiness inspection data were analysed, there were estimated to be improvements in injury crash involvement rates and prevalence of safety-related faults of respectively 8% (95% CI 0.4–15%) and 13.5% (95% CI 12.8–14.2%) associated with the increase from annual to 6-monthly inspections. The wide confidence interval for the drop in crash rate shows considerably statistical uncertainty about the precise size of the drop. Even assuming that this proportion of vehicle faults prevented by doubling the inspection frequency could be maintained over the vehicle age range 7–20 years, the safety benefits are very unlikely to exceed the additional costs of the 6-monthly inspections to the motorists, valued at $NZ 500 million annually excluding the overall costs of administering the scheme. The New Zealand warrant of fitness scheme as a whole cannot be robustly evaluated using the analysis approach used here, but the safety benefits would need to be substantial – yielding an unlikely 12% reduction in injury crashes – for benefits to equal costs.     

有机玻璃在典型环境下的老化性能

在热空气（50℃）、湿热（50℃,85%R.H.）、紫外光（50℃,131 nm）、自来水（50℃）和盐水（3%NaCl,50℃）五种条件下对有机玻璃做了70d（天）左右的人工加速老化试验,然后对不同环境和不同老化时间的有机玻璃试样进行了力学性能测试,并进一步利用凝胶渗透色谱法（GPC）、示差扫描量热法（DSC）等手段,分析了老化前后有机玻璃试样的结构和组成差异,结合老化前后有机玻璃力学性能的变化,揭示了有机玻璃在五种条件下的老化规律和老化机理。     

在用氨制冷装置压力管道检验分析与研究

介绍了氨制冷装置压力管道特点,研究发现压力管道检验过程中存在诸多安全隐患,且安全状况达不到要求,难以按照现行管道检验规程进行安全状况等级评定,给定期检验工作造成很大困难。分析了氨制冷装置使用过程中普遍存在的问题、管理缺陷及在用氨制冷系统事故的起因及特征。提出了压力管道为氨制冷装置中事故率较高的部位,给出了对当前氨制冷装置压力管道的检验与使用管理的建议,对规范涉氨压力管道的定期检验、减少事故的发生及提高设备的使用效率起到重要指导作用。     

Giant magnetoresistance, microstructure, and application characteristics of amorphous CoNbZr-based pseudo-spin valves

We have fabricated pseudo-spin-valve (PSV) multilayers with amorphous CoNbZr alloy as a soft magnetic layer and a buffer layer by magnetron sputtering. We investigated the multilayers' giant magnetoresistance (GMR), microstructure,thermal annealing effects, and application characteristics. Our results show that the film microstructure, consequently the magnetostatic coupling effect and the magnetization reversal process, strongly depends on the CoNbZr thickness. We observed antiparallel magnetization alignments in the samples with a 2-4nm CoNbZr layer and a measured maximum GMR ratio of 6.5%. The PSV with 4 nm CoNbZr has a superior thermal stability to 400 /spl deg/C as a result of the dense and homogeneous Cu spacer. After patterning with a 6 /spl mu/m/spl times/1 /spl mu/m elliptic stripe, the structure forms a single domain. The dynamic GMR behavior under a 10 kHz sinusoidal magnetic field indicates the patterned stripe has a linear and stable GMR response. We therefore believe that PSVs with amorphous CoNbZr have good potential for spintronic devices.     

球形装药海底裸爆压力测试与分析

介绍了单个球形装药海底裸爆试验方法及测试技术,包括试验条件、试验设计、试验测试、波形分析及试验数据统计处理等;对海底爆炸冲击波的特性和传播规律进行了试验研究,重点论述了前驱波、冲击波、反射波、二次波的波形分析与峰值压力测试和计算,总结出部分相关结论。     

Microcrack growth and fatigue behavior of a duplex stainless steel

The kinetics of microcrack growth during cycling has been studied in a S32205 duplex stainless steel in the as-received and aged (100 h at 475 °C) conditions. Cylindrical specimens with a shallow notch were subjected to a constant plastic strain range of 0.3% in both thermal conditions. The characteristic features of surface damage and crack growth showed striking differences in microcrack density, nucleation location and propagation rate between the two thermal conditions even though the fatigue lives are comparable. In the as-received material, microcrack density is low and they nucleate mainly at grain and phase boundaries or second-phase particles. In the aged condition, slip markings first appear in the ferritic phase and they are the preferred site for microcrack nucleation. Crack propagation takes place along slip markings in adjacent grains for crack lengths less than 100 μm. A comparison between fatigue life and the relevant parameters of a microcrack growth law was made.