论设计安全模式与安全设计模式的相互关系

On the relationship between design safety mode and safety design mode

工程结构是由材料组成的,材料的性能基本决定了结构的安全性。材料失效分析的目的是确定结构失效的根本原因及其预防措施,它对产品研制、质量改进、材料改性、结构优化、事故认定、事件预防等都有重要的工程价值和社会效益。一般而言,常规的"设计安全模式"(Design Safety Mode)是工程结构在设计阶段依据标准、规范、规程及手册进行选型式、选材料和选结构,并通过安全系数的引入提高安全可靠性。然而,工程结构在服役过程中因工况和环境的变化仍会发生意外的失效,这促使人们思考设计安全模式下的结构为何不能保障安全性。对此,本文探讨了工程结构的本质安全问题,并以核电、火电、石化、化工等行业四起典型失效案例进行分析,明确指出设计安全模式下的工程结构并不能绝对保障设计寿命期内的安全,这是因为工程结构安全涉及上游的设计安全、中游的制作安全和下游的服役安全,而中下游变化因素颇多,安全隐患在上游设计阶段有时被忽视。为此,特提出一种"安全设计模式"(Safety Design Mode)新理念。这种安全设计模式是从结构完整性出发,强调全寿命周期内的安全性,考虑设计、材料、制造、安装、检验、运行、维护、环境、运输、贮存等十大因素对安全的影响而采取主动的预防措施,即通过材料失效分析和风险评估,把工程结构在全寿命周期内的安全隐患反馈到上游的设计阶段,在选材和制作时提前预防,从而确保工程结构对工况、环境变化的适应性和耐久性,保障其本质安全。安全设计模式不仅包含了设计安全模式的所有要素,而且综合考虑了工程结构在全寿命周期内的安全性,把材料失效分析与失效模式后果分析、风险评估分析、3P安全保障分析、结构模拟分析及在线监测分析相结合,使工程结构失效的事后分析、事中分析和事前分析统合在闭合环内进行整体的安全分析,通过消除安全隐患,保障其在全寿命周期内的服役安全。因此,安全设计模式这一新理念值得业界进行探讨和研究。

The engineering structure is made of materials, which properties basically determine the structure safety. The purpose of materials failure analysis is to find out the root cause of structure failure and preventive measure. So it has important engineering value and social benefit for product development, quality improvement, material modification, structure optimization, accident identification, incident prevention and so on. Generally speaking, the conventional design safety mode is to select types, materials and structures of the engineering structure in the design stage based on standard, specification, regulation and handbook, and to enhance its safety reliability by introduction of safety factor. However, the engineering structure still encounters unexpected failure due to changes of working condition or environment during its service. This urges people to think about why the engineering structure can’t be secured based on the design safety mode. For this issue,the essential safety of the engineering structure is addressed and four typical failure cases of nuclear power, thermal power, petrochemical and chemical industries are analyzed in this paper. It is clearly pointed out that the engineering structure from the design safety mode can’t absolutely secure the safety of its design life cycle. This is because the structure safety covers upstream design safety, midstream fabrication safety and downstream service safety. There are some variable factors at the midstream and downstream stages and several safety troubles maybe ignored at the upstream design stage. To this end, a new concept called safety design mode is put forward herein. Started from structural integrity, the safety design mode emphasizes the whole-life cycle safety of the engineering structure, and takes active preventive measures by considering the effect of ten factors on safety, such as design, material, manufacture, installation, inspection, operation, maintenance, environment, transportation and storage. That is, through materials failure analysis and risk assessment, the safety troubles of the whole-life cycle of the structure are fed back to the upstream design stage. Therefore the material and fabrication process are suitably chosen in advance, the applicability and durability of the structure to the changes of working conditions and environmental are enhanced, and the essential safety of the structure is fully guaranteed. The safety design mode not only contains all elements of the design safety mode, but also comprehensively considers the whole-life cycle safety of the structure. It combines the materials failure analysis with the failure mode and effect analysis, the risk assessment analysis, the 3P safety guarantee analysis, the structural simulation analysis, and the on-line monitoring analysis. So the post-analysis, in-case analysis and pre-analysis of the structural failure are integrated in a closed loop to carry on the overall safety analysis. By eliminating the potential safety troubles, the service safety of the whole-life cycle of the engineering structure can be ensured. As a result, the proposed new concept of the safety design mode is worthy of discussion and research in industrial circles.