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Abstract A risk assessment method for hot work based on G1-EWM and unascertained measurement theory was proposed to prevent hot work accidents in underground mines. Firstly, based on the risk influencing factors and classification criteria for underground hot work operations in mines, a single indicator measurement matrix was constructed using unascertained measurement theory; Secondly, a risk assessment index system for mine underground hot work operations was established. The combination weight coefficient of each index was determined using the order relationship analysis method (G1) and entropy weight method (EWM) and coupled with the single index measurement evaluation vector to calculate the multi-index comprehensive evaluation vector of the evaluation object; Finally, the model was validated and examined using engineering examples, and the evaluation level was determined using confidence identification criteria. The results showed that the proposed method, when used to evaluate the risk of hot work operations in tunnels and vertical shafts in metal mines, produces risk levels that are in line with reality III (Moderate Risk) for the vertical shaft and IV (High Risk) for the tunnels. The evaluation model results are consistent with the risk evaluation results the whole process of on-site hot work, which verifies the model feasibility. A unique strategy and method for risk management in hot work operations in underground mines is provided by the combination of weighting and unascertained measure models, which has theoretical and practical value. Future research could focus on refineing this model by exploring the applicability in diverse mining environments and integrating advanced analytical techniques to enhance the predictive accuracy and operational efficiency.

Additive manufacturing techniques employing laser-based metal melting have garnered significant attention within the scientific community. Despite a decade of comprehensive research on the fundamentals of these techniques, there still remain unexplored facets related to heat flux impact on metallic alloys’ properties. Particularly, the effects of point-by-point laser operation on melt pool formation in metallic materials still remain unclear. Thus, this study focuses on the implications of laser metal melting, particularly investigating a point-by-point laser mode operation’s influence on melt pool formation and its geometry in the phase-transformation-sensitive material H11 hot work tool steel. To examine the melt pool, singular laser tracks with various laser parameters were scanned across H11 sheet metal, which allowed for the elimination of layer-by-layer heat cycles’ influence on the melt pool’s microstructure. Samples were examined by means of metallography, revealing significant differences in the melt pool’s depth, influenced mostly by exposure time rather than volumetric energy density. Heat-affected zone effects were found to have a limited range and thus potentially marginal effects in layer-by-layer manufacturing conditions. At the same time, retained austenite concentrations near fusion lines have been found within melt pools, suggesting potential micro-segregation of the alloying additions. The results present guidelines towards laser melting processes optimization.

A new quantitative risk assessment method for hot work is proposed based on the analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE). It can help pipeline companies realize the risk management of hot work and further ensure the safe operation of oil and gas pipelines. Taking one natural gas pipeline in China as an example, this paper evaluates the risk of a single hot work in the spring of one natural gas pipeline in a high consequence region. First of all, the risk factors are determined with reference to the job safety analysis (JSA), and then experts were invited to fill out a questionnaire to collect their opinions. According to the results of the questionnaire, AHP is used to calculate the weight coefficients of the evaluation indicators, and FCE is used to evaluate the risk level of hot work. After calculation, the comprehensive risk score of hot work is 40.888. It belongs to a ''general risk''. This method can not only quantitatively evaluate the risk levels of hot work, but also reasonably sort the importance of various risk factors. It is helpful for the effective management of hot work and provides suggestions for implementing control measures.

İnsanlar gün içerisindeki faaliyetlerinin büyük bölümünü kapalı alanlarda geçirir. Bu nedenle insanlar için kapalı mahallerde iyi bir havalandırma ve iklimlendirme sistemi tasarlamak son derece kritiktir. İyi bir havalandırma, insanlarda hem vücut sağlığı hem de çalışma verimleri adına önemli bir kıstastır. Sıcaklık maruziyeti, vücudun fizyolojik ve psikolojik dengesini, çalışma verimini önemli ölçüde etkileyen ve çalışma ortamında sıkça karşılaşılan problemlerdendir. Isıl konfor ise, kişinin bulunduğu ortamın sıcaklığı ile uyumun sağlanması ve memnuniyetsizliğin bertaraf edilmesi anlamına gelmektedir. Termal konfor şartlarının tam olarak sağlanamadığı ortamlarda çalışmak zorunda kalan çalışanların verimlerinin düştüğü, güvenli çalışma durumunun zayıfladığı ve buna bağlı olarak iş kazasına maruz kalma sıklıklarının artığı gözlemlenmiştir. Bu yüzden ısıl işlemin zorunlu olduğu, sıcaklık maruziyetinin kaynağında yok edilemediği durumlarda çalışan kişilerin termal konfor şartlarının iyileştirilmeleri öncelikle çalışanların sağlığına sonrasında ise üretim verimine olumlu katkılar sağlayacaktır. Bu çalışmada, ısıl konforu belirleyen parametreler üzerine incelemeler yapılmış olup, örnek mahal olan sıcak şekillendirme prosesi kullanılarak sac şekillendirme yapan hatta çalışan işçilerin ısıl konfor için çalışma koşulları gözlenmiştir. Isıl konforu sağlamak adına soğuk yelek üretilmiş ve ısı transferi dikkate alınarak iyileştirici faaliyetler belirlenmiştir.

Considering that the operation time should be saved as much as possible during the hot work of pipeline in oil and gas station, the time required for nitrogen injection, pipe cutting, welding, NDT and other processes in the hot work of pipeline in station was compared, and it was found that there was much space for time optimization in the nitrogen injection process. For conventional nitrogen injection method, the removal and reassembly of valves, nitrogen injection flanges and other components always result in huge workload and occupy a large amount of hot work time. By referring to the assembling form of flange gasket and changing the internal structure and assembling mode of nitrogen injection device, a fast-assembling type nitrogen injection device for hot work of pipeline in station was developed. With this device, the workload of bolt removal and assembling can be reduced by at least 50% for nitrogen injection, and the time for nitrogen injection process can be saved. Field application shows that, the problems of the nitrogen injection device for the hot work of pipeline in the station, such as inconvenient assembling, time-consuming works and inability to further improve the hot work efficiency, can be effectively handled by using this device, and the device is suggested to be popularized and applied in the hot work construction of pipeline and equipment in the petrochemical industry.

In this study, effect of hot work on microstructure and mechanical properties of nickel based alloy NiAl8Cr8MoZrB (IC-221M) was investigated. For this purpose, four types of hot work processes at 1000 and 1100 °C with various apply strain were done. Also two types of two stage hot work processes were performed. Our results show that low strain rate hot working causes to reduction of eutectic regions in the microstructure and ordering parameter of crystalline structure and increasing high temperature mechanical properties of as-cast alloy. Finally, two stage hot pressing process on the basis of dynamic recrystallization mechanism leads to increasing mechanical properties of alloy at 1000 °C.