A comparison of the simplified probabilistic method in R6 with the partial safety factor approach

Probabilistic assessments are a useful aid to decision making in areas such as safety analysis, design studies and the deployment of resources on maintenance, inspection and repair. In principle, a full probabilistic assessment requires a complete knowledge of the relevant failure models and the distributions for each of the input quantities. However, in practice, these requirements cannot normally be met in full and it is necessary to employ various simplifying assumptions and approximations in order to make the analysis tractable. The partial factor method and the simplified approach in R6 provide two relatively simple and independent methods of assessing failure probabilities using R6.The two methods have been applied to a set of test cases and the results compared. In the case of the partial safety factor method target reliabilities in the range 10⁻³–10⁻⁵ were considered. Sets of partial safety factors for load, defect size, fracture toughness and yield stress were taken from BS 7910 and used for assessments covering different regions on the R6 failure assessment diagram. A calculation of the assessed failure probability was also carried out for each of these sets of conditions using a simplified probabilistic approach developed for the R6 procedure.The assessed failure probabilities were compared with the corresponding target reliability assumed for the partial safety factor calculation. It was found that the partial safety factor assessments were generally conservative compared to the simplified approach. However, in many instances the assessed probabilities were several orders of magnitude smaller than the target reliabilities suggesting that the recommended values of partial safety factors in BS7910 were excessively conservative for some of these conditions.     

Plastic collapse load prediction and failure assessment diagram analysis of cracked circular hollow section T‐joint and Y‐joint

This paper concerns the validation of standard safety assessment procedure given in BS 7910 for cracked circular hollow section T‐joint and Y‐joint, using the finite element (FE) results. A robust and efficient FE mesh generator is developed to produce the 3D models of the cracked joints and to calculate the elastic J‐integral (J_e) and elastic–plastic J‐integral (J_ep) values of the crack respectively. In order to verify its accuracy and convergence, the plastic collapse loads (P_c) obtained from experimental tests and FE predictions are compared; they agree very well with each other. It is also found from experimental tests that the plastic collapse loads (P_c) predicted using the BS 7910 reduction factor (F_AR) are safe and conservative. Subsequently, the failure assessment diagrams (FADs) of five cracked T‐joints and three cracked Y‐joints are constructed using the FE results, following the J‐integral method, which is classified as Level 3C in BS 7910. Thereafter, a comparison between the constructed FAD curves and the standard Level 2A curve is carried out, and it is observed that the safety assessment results using the standard Level 2A curve might be unsafe because some parts of the constructed FAD curves fall inside of the standard one. A penalty factor of 1.15 working on both the elastic–plastic J‐integral and plastic collapse load (P_c) is proposed to move all the constructed FAD curves just outside of the standard Level 2A curve.     

Fracture mechanics in fatigue calculations as the assistance in structural design. Case study

A case study originated from a request to perform fatigue calculations on a partial penetration weld in a steel casting on a new heavy lift ship. The ship has a special lifting system for lifting and transporting topsides of offshore oil/gas platforms. There are many sizes of offshore platforms so the lift system is designed to move along the vessel on rails, which are part of the main deck of the ship hull. The loads passing into the rails during lift operations are large, and massive steel castings of complex shapes are used to distribute these loads into the hull. The castings are very thick so it is difficult to achieve full penetration welds, and therefore the initial design proposed partial penetration welds. In order to decide if the partial penetration welds were adequate, a fatigue assessment was carried out using a fracture mechanics approach based on BS7910. Different possibilities of the bevelling of castings edges in preparation for welding were considered in the stress analysis and in the crack growth estimations. In the areas of the ship hull which experienced high dynamic stress ranges none of the different possibilities showed acceptable fatigue life, and would demand re-design. The stress intensity factors obtained through the extensive finite element analysis were compared with the analytical solutions available in literature. Both results showed good correspondence.     

Modelling and assessment of dependent performance shaping factors through Analytic Network Process

Despite continuous progresses in research and applications, one of the major weaknesses of current HRA methods dwells in their limited capability of modelling the mutual influences between performance shaping factors (PSFs). Indeed at least two types of dependencies between PSFs can be defined: (i) dependency between the states of the PSFs; (ii) dependency between the influences (impacts) of the PSFs on the human performance. This paper introduces a method, based on Analytic Network Process (ANP), for the quantification of the latter, where the overall contribution of each PSF (weight) to the human error probability (HEP) is eventually returned. The core of the method is the modelling process, articulated into two steps: firstly, a qualitative network of dependencies between PSFs is identified, then, the importance of each PSF is quantitatively assessed using ANP. The model allows to distinguish two components of the PSF influence: direct influence that is the influence that the considered PSF is able to express by itself, notwithstanding the presence of other PSFs and indirect influence that is the incremental influence of the considered PSF through its influence on other PSFs. A case study in Air Traffic Control is presented where the proposed approach is integrated into the cognitive simulator PROCOS. The results demonstrated a significant modification of the influence of PSFs over the operator performance when dependencies are taken into account, underlining the importance of considering not only the possible correlation between the states of PSFs but also their mutual dependency in affecting human performance in complex systems.     

我国与印尼民用爆炸物品储存库标准对比分析

民用爆炸物品使用属于特殊行业的行为,涉及爆炸物品的购买、运输、储存和操作等环节,是构成本质安全和社会公共安全的重要因素。为比较我国与印尼民用爆炸物品储存库标准的不同,更好地指导工程实践,以我国和印尼合作的某铅锌矿项目民用爆炸物品储存库建设工程为背景,通过对比分析两国民用爆炸物品储存库相关标准,发现在储存库标准体系、分类方法以及安全距离设置等方面均存在不同之处。相较印尼标准,我国标准体系更为健全完善,分类方法更为合理实用,技术指标更为科学严谨。其对比分析结论,有助于项目部积极采用我国民用爆炸物品储存库标准,提高工程本质安全和社会公共安全水平,并助力我国矿山企业"走出去",我国标准"走出去",进一步提升我国在国际合作中的话语权。     

The fracture behaviour of a welded tubular joint--an ESIS TC1-3 round robin on failure assessment methods: Part III-UK BS7910 methodology

The basic principles of assessment of defects in the new BS7910:1999 procedures as applied to offshore structure tubular joints are briefly described. Based on the author's experience with a series of research investigations into ultimate strength of cracked tubular joints, analyses are carried out to give safe estimates of the expected tearing behaviour and ultimate strength for the model tubular joints used for the ESIS TC1-3 round robin programme.     

Base material fatigue data for low alloy forged steels used in the subsea industry. Part 2: Effect of cathodic protection

In air S–N fatigue data for forged low alloy steels as used in the subsea industry are presented in Part 1 of this paper. The test scope in Part 1 included testing to quantify the effect of the surface roughness, mean stress and material strength on the high cycle fatigue strength of low alloy steels with a tensile strength in the range of 600–800 MPa. A method for estimating the in air S–N curve from the tensile strength (material grade), surface roughness (machining) and mean stress (such as residual stresses, pressure testing, pre-load and external loads) is presented in Part 1. In this Part 2, fatigue test results for low alloy steels and one carbon steel tested in seawater with cathodic protection with a potential of −1050 mV versus an Ag/AgCl reference electrode are presented. The fatigue testing has been performed using smooth specimens. The tested smooth specimens have (actual) tensile strengths in the range from 627 to 790 MPa. Penalty factors for the tested smooth specimens in seawater with cathodic protection with respect to in air performance (Part 1) are presented and compared with penalty factors used in fatigue design codes such as DNVGL-RP-0005 (former DNV-RP-C203) and BS 7608. The obtained environmental reduction factors are found to be in accordance with the penalty factors used in BS 7608 provided that the maximum stress in the cycle is less than 94% of the yield stress for the material. The penalty factors used for forged steels in DNVGL-RP-0005 are non-conservative compared to the test outcome for the steel tested in an artificial 3.5% NaCl seawater solution. For higher stress levels, larger penalty factors than used in BS 7608 are required. It is found that the obtained S–N based environmental reduction factors are of similar magnitude as BS 7910 fatigue crack growth based reduction factors for CP.     

The SINTAP fracture toughness estimation procedure

The maximum likelihood (MML) procedure for the analysis of fracture toughness data generated at a single temperature that was developed for the SINTAP flaw assessment procedure is described. The procedure involves a series of steps to ensure that a Weibull toughness distribution fitted to experimental data is conservative. Validation is provided by experimental data from weld metal, heat affected zone and parent plate. Results are compared with those from assessments carried out to existing methods described in BSI PD6493:1991 and BS 7910:1999. It is concluded that for small data sets, the MML procedure provides a greater level of consistency and reduces selection of potentially non-conservative fracture toughness values.     

深水大管径厚壁海底管道ECA评估

根据英国BS7910标准2B级断裂评定准则,对某深水海底管线焊接接头进行了ECA评定,得到了最大铺设应力和最大错边的情况下焊接接头表面和埋藏裂纹的临界尺寸,为海底管线铺设中AU聃佥验提供了验收标准,有效的降低了焊接返修率,保证了施工速度,节约了成本。     

The task demands‐resources method: A new approach to human reliability analysis from a psychological perspective

This study proposes a new approach to human reliability analysis (HRA) by introducing the occupational stress model in human resources management. Most existing HRA methods are restricted to a given set of risk factors in the task context, which are often called performance shaping factors (PSFs), and they are built on the causal relationship between PSFs and human performance, with little concern for the psychological factors that drive human behavior. We argue that a well‐developed occupational stress model that incorporates comprehensive working conditions and focuses on psychological factors offers us a new perspective to evaluate human reliability. The proposed approach, namely, the task demands‐resources (TD‐R) method, considers that the PSFs, in the task context, can be categorized into two different groups: task demands and task resources. These two PSF groups can both motivate and stress the operators during the task, thereby influencing their performances. Based on the theoretical framework of the TD‐R method, we also designed a probabilistic model linking motivational intensity to human error probability (HEP) under different stress levels. A human reliability experiment has been conducted to validate the effectiveness and flexibility of the TD‐R method. The experiment results showed that the TD‐R method could produce a meaningful explanation for the operators' performances and provide a quantification result for HEP.     

Engineering critical assessment for offshore pipelines with 3-D elliptical embedded cracks

Offshore pipelines are usually constructed by girth welding method, while weldments may naturally contain surface or embedded defects. Most existing fracture assessment procedures based on the load-controlled method are not explicitly designed for situations with large plastic strain. In this paper, the nonlinear elastic plastic fracture response of pipeline girth weld with embedded cracks is investigated through 3-D finite element analysis combined with submodeling technique. Strain-based estimation formulas for crack tip opening displacement are proposed for the pure bending load as well as the bending combined with the internal pressure. Furthermore, comparisons of fracture assessment between BS7910 and finite element analysis in the current study are made for various crack sizes.     

Palmgren–Miner’s rule and fracture mechanics-based inspection planning

A Palmgren–Miner’s rule and fracture mechanics (FM) based approach coupled with Bayesian updating in order to establish inspection plans for marine structures is proposed. A FM formulation based upon the British Standard (BS) 7910 is calibrated by S–N curves and Palmgren–Miner’s rule. A model is developed taking account of the uncertainties associated with S–N curves and Palmgren–Miner’s rule to quantify the random growth of a flaw predicted by the calibrated FM formulation. The long-term stress range acting on a structural component is fitted to a two-parameter Weibull distribution, according to the rules of the American Bureau of Shipping (ABS). The reliability after inspection is updated by the Bayesian approach accounting for the probability of detection (POD) and inspection results. An inspection plan is then set up on the basis of the comparison between the updated reliability and a target reliability index. Typical fatigue–prone structural details from a tanker are utilized for demonstration of the capabilities of the approach proposed.     

R-CODE software for the support of calculations required by the R5 and R6 procedures

The R6 Procedure and the ‘Assessment procedure for the high temperature response of structures’, R5, are well known and continue to be developed by Nuclear Electric Ltd in the UK. This paper looks at the software that has been developed to help undertake the calculations required by these assessment procedures. R-CODE version 3.00 computerises creep crack growth and incorporates simplified creep-fatigue crack growth calculations. The program may also be used to perform assessments according to PD6539 and PD6493 or BS7910. Full allowance can be made for incubation and redistribution periods. Continuum damage may be evaluated in terms of life fraction or ductility exhaustion methods. The program covers all the Categories, Options and Failure Assessment Diagrams of R6, for defining stability under short-term loadings when used for low temperature assessments.     

婴儿学步车中、美、欧安全技术标准比较分析

本文对婴儿学步车中、美、欧安全技术标准进行了分析研究,比较了这三类标准之间的主要差异,为童车产品出口企业和检测机构提供借鉴。     

中国和欧盟婴幼儿食品接触用产品监管标准研究

目的 针对婴幼儿食品接触产品,分析中国与欧盟标准的异同,为国内产品标准的提升提供依据.方法 综述中国和欧盟婴幼儿食品接触产品标准状况,结合中国婴童用品使用中存在的现实问题,分析国内标准存在的不足,展望未来标准化工作的重点方向.结果 中国和欧盟均高度重视奶瓶、奶嘴质量安全,对关注度高的物质限量严格;由于标准架构不同,因此欧盟标准要求得更全面、更严格;我国食品安全国家标准体系对"婴幼儿"定义模糊不清,哺喂工具类、饮水壶、杯等强制性产品类的国家标准缺失.结论 虽然我国婴童用食品接触产品标准卫生安全要求严格,但产品标准有待健全,涵盖卫生性能、产品结构设计和物理力学性能的产品类国家标准亟需制定.     

粉尘比电阻不同测试标准的对比分析

为了准确测定粉尘比电阻,为静电除尘设计、静电防护设计和判定粉尘静电点燃提供重要参数,根据粉尘比电阻的测定普遍采用的3个标准IEC 1241-2-2、BS 5958-1和ASME PTC28 4.05,开发3种不同的比电阻测定装置,并对典型粉尘的比电阻进行测试。结果表明,粉尘比电阻的测试结果与测试方法有关,不同方法的测定结果有较大偏差;粉尘样品的密实度和其上的加载电压是影响测定结果的重要因素,密实度越大,电压值越大,测得的比电阻值越小;对于不同的工程应用目的,应采用不同的测试方法,IEC标准和BS标准通常用于静电防护设计,而ASME标准通常用于静电除尘设计。     

Novel Approach to Energy Management via Performance Shaping Factors inPower Plants

The literature that a lack of integration between the performance shaping factors (PSFs) and the energy management performance (EMP) is one of the critical problems that prevent performance improvement and reduces the power plant’s efficiency. To solve this problem, this article aims to achieve two main objectives: (1) Systematically investigate and identify the critical success factors (CSFs) for integration with PSFs and EMP; (2) Develop a novel modelling approach to predict the performance of power plants based on innovative integrated strategies. The research methodology is grounded on the theoretical and practical approach to improving performance. The Newcastle Ottawa Scale (NOS) was used to assess the quality of the literature that met the criteria. To ensure the reliability and accuracy of the proposed model, the researchers developed a hypothesis and evaluated the CSFs via a case study in the Iraqi power plants. The findings of this study succeeded in developing a novel modeling approach to predict the performance by integrating the CSFs of both the PSFs and EMP to increase the positive interaction and energy efficiency of power plants. The results confirmed the validity of the selected hypotheses and verified the positive and important relationship with the success and improvement of the performance in power plants. However, the lack of consistency and balance in the current studies indicates that the performance strategy in power plants did not receive sufficient attention and needs further investigations.     

Incorporation of residual stresses into the SINTAP defect assessment procedure

Residual stresses are an important consideration in the structural integrity assessment of welded joints and reliable predictions of structural integrity therefore require that the residual stress distribution is adequately accounted for. However, distributions are dependent on the weld geometry and, in the absence of comprehensive information for welded joints, it is usually necessary to make conservative assumptions. This can result in unrealistic predictions, and consequently, further information on the nature and behaviour of residual stress distributions is required to enable the provision of improved guidance on this subject.The further development of the BS 7910 and R6 procedures for the assessment of residual stress effects was a principal task in the EC funded project named structural integrity assessment procedures for European industry, SINTAP, and an extensive investigation of this subject was performed. It entailed an extensive literature review of distributions in the principal weld geometries (including plate butt, pipe butt, pipe to plate, T-butt and tubular welded joints), experimental and numerical investigations and the development and validation of procedures.     

MLEM deconvolution of protein X-ray diffraction images based on a multiple-PSF model

In this paper we analyze the degradation of protein X-ray diffraction images by diffuse light distortion (DLD). In order to correct the degradation, a new multiple point spread function (PSF) model is introduced and used to restore X-ray diffraction image data (XRD). Raw PSFs are collected from isolated spots in high-resolution areas on the diffraction patterns which represent the orientation of DLDs. An adaptive ridge regression (ARR) technique is used to remove noise from the raw PSF data. A target Gaussian function is used to model the raw PSFs. A maximum likelihood expectation maximization (MLEM) algorithm combined with a multi-PSF model is employed to restore high intensity, asymmetrical protein X-ray diffraction data. Experimental results using a single and multiple PSFs are presented and discussed. We show that using a multiple PSF model in the deconvolution algorithm improved the quality of the XRD and as a result the spot integration error (/spl chi//sup 2/) and corresponding electron density map are improved.     

Latency and mode of error detection in a process industry

Licensee event reports (LERs) from an industry provide important information feedback about safety to the industry itself, the regulators and to the public. LERs from four nuclear power reactors were analyzed to find out about detection times, mode of detection and qualitative differences in reports from different reactors. The reliability of the codings was satisfactory and measured as the covariance between the ratings from two independent judges. The results showed differences in detection time across the reactors. On the average about 10% of the errors remained undetected for 100 weeks or more, but the great majority of errors were detected soon after their first appearance in the plant. On the average 40% of the errors were detected in regular tests and 40% through alarms. Operators found about 16% of the errors through noticing something abnormal in the plant. The remaining errors were detected in other ways. There were qualitative differences between the LERs from the different reactors reflecting the different conditions in the plants. The number of reports differed by a magnitude 1:2 between the different plants. However, a greater number of LERs can indicate both higher safety standards (e.g. a greater willingness to report all possible events to be able to learn from them) and lower safety standards (e.g. reporting as few events as possible to make a good impression). It was pointed out that LERs are indispensable in order to maintain safety of an industry and that the differences between plants found in the analyses of this study indicate how error reports can be used to initiate further investigations for improved safety.