Stress corrosion cracking in 316L stainless steel bellows of a pressure safety valve

There were three consecutive occurrences of bellows failure in a particular pressure safety valve (PSV) of a petroleum refinery within a time span of one week. The bellows were made of 316L grade austenitic stainless steel, and the PSV was mounted on one of the vessels of vacuum gas oil service in a hydrocracker unit. Metallurgical analysis of the failed bellows revealed that the failure had occurred by stress corrosion cracking (SCC). It was found that the SCC was promoted in the bellows due to the presence of high amount of chloride ions in the operating environment. Studies confirmed that SCC had initiated from the outer surface of the bellows and propagated inwards, resulting in leakage of hydrocarbon from the PSV. The source of chlorine in the environment was identified. It was discovered that SCC in the bellows was caused due to a previous failure in the heavy polynuclear aromatics (HPNA) absorption bed located upstream the process flow line. This failure was due to the presence of high concentrations of chlorine in the granulated activated carbon that was used in the HPNA absorption bed. During the repair of the HPNA bed, there was deposition of carbon soot on the body of the PSV. This carbon soot was the source of chloride ions for SCC to occur in the bellows. Generally, in chloride SCC, crack propagation in 316L SS takes place by transgranular mode. In the present case, however, the crack propagation was predominantly by intergranular mode. The metallurgical factors responsible for this change in micro-mechanism of crack propagation during SCC have been discussed.     

Adaptive variable universe of discourse fuzzy control for a class of nonlinear systems with unknown dead zones

In this paper, based on an adaptive nonbackstepping design algorithm, we proposed a novel variable universe of discourse fuzzy control (VUDFC) approach for a class of single‐input–single‐output strict‐feedback nonlinear systems with unknown dead‐zone inputs. Firstly, we convert the form of system into a normal form on the basis of some new state variables and coordinate transformation; at the same time, state‐feedback control is changed to output‐feedback control. Secondly, we design observers to estimate the new unmeasurable states. Then, different from considering the traditional backstepping‐based fuzzy control scheme, we introduce a direct VUDFC scheme, which is mainly based on changing of contraction‐expansion factors to modify the universe of discourse online, and fuzzy rules can automatically reproduce to develop the control performance; thus, the size of initial rule base is greatly reduced. This new algorithm can alleviate tracking error, improve the accuracy of the system, and strengthen robustness. Lastly, according to Lyapunov theorem analysis, we prove that all the signals in the closed‐loop system can be guaranteed to be stable, and the output can track the reference signal very well. Simulation results illustrated the effectiveness of the proposed VUDFC approach.     

热风炉冷风放风阀带压更换

分析了热风炉冷风放风阀更换情况,利用冷风放风阀工作特性实现带压更换,效果良好.     

含至多四个参与者的量子秘密共享方案的最优信息率

信息率是衡量量子秘密共享方案性能的一个重要指标.在本文中,我们利用超图的相关理论刻画了量子存取结构.然后,利用超图和量子存取结构间的关系给出了参与者人数至多为4的所有13个量子存取结构,并基于量子信息论研究了其最优信息率及所对应的完善的量子秘密共享方案.对其中的5种存取结构的最优信息率的准确值进行了计算,并讨论了达到此信息率的方案的具体构造;对余下的8种存取结构的最优信息率的上界进行了计算.     

某型发动机高温转速不足分析

文章分析了某型发动机在外场点火试车试验中,发动机到达一定的转速后,发动机转速增加缓慢,伺服阀可能产生的原因.重点从系统油压波动、油液温度、液流流态等方面对伺服阀进行了分析.     

谈雨淋系统

通过分析雨淋系统流量的确定方法和防护区的划分,给出了设计雨淋系统的一些思路,同时提出了适合设计雨淋系统的建筑类型,为雨淋系统流量的确定、防护分区的划分以及适用建筑的类型研究提供了依据。     

Microbubble generator excited by fluidic oscillator's third harmonic frequency

Efficient generation of sub-millimetre microbubbles was recently made possible by pulsating the flow of gas supplied into a parallel-exits aerator, using a fluidic oscillator for the purpose. Without moving parts, it can generate oscillation at high frequency, an important factor due to bubble natural frequency rapidly increasing with the desirable decrease of their size. This paper discusses development of an unusual oscillator – a part of an integral oscillator/aerator unit – capable of generating a particularly high driving frequency, in the kilohertz range, in a layout that promotes a strong third harmonic frequency of the basic oscillation.     

核电用大口径闸阀关闭件发生热粘连的可能性分析

介绍了核电站用闸阀在高温条件下防止产生热粘连的结构要素,及其防止产生热粘连的理论分析。     

层次分析法在铁路T梁架设方案比选中的应用

为从贵广铁路DK775+300~DK803+700段T梁架设工程备选方案中比选获得最优方案,采用层次分析法辅助进行决策分析,经求解得出了组合权重,确定了最优方案,该方案经实践检验正确,满足了建设要求,值得推广应用。