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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. [ABSTRACT FROM AUTHOR]

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.

Special work involves hot work, confined space, blinding‐pipeline operation with stop plate, work at height, lifting work, temporary electricity, excavation work, work for road breaking, and other work, which may cause harm or damage to the operators themselves, surrounding buildings, equipment, and facilities. In this article, we conducted a statistical investigation on 154 large and above hazardous chemical accidents that occurred between 2008 and 2021 in China, and found that there were 58 accidents that occurred in special work alone, accounting for 37.7% of the total number of accidents. However, at present, no statistical analysis has been conducted on the characteristics of special work accidents in China. Therefore, this paper analyzes the special work accidents in terms of six aspects: categories of special work, industry distribution, enterprise scales, provincial location distribution, time‐volatility characteristics, and accident causes. Moreover, this article puts forward countermeasures and suggestions, aiming to provide useful information for the prevention of special work accidents in China. [ABSTRACT FROM AUTHOR]

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.

Hot work, work involving electric or gas welding, cutting, brazing, or similar flame or spark‐producing operations, is a major industrial hazard. Many countries have formulated relevant regulations and standards for hot work to regulate their management procedures and operational requirements. This article compares and analyses the safety‐related regulations and standards for hot work in China and the United States. The article puts forward relevant suggestions for the revision and improvement of China's hot work regulations and standards in comparison with the US regulations and standards. In terms of details, the US regulations and standards are more scientific, stringent, and guiding. China's standards are more closely related to China's national conditions, but some provisions lack scientific basis and are poorly operable. Further enhancement of the scientific, guidance, and operationality of China's hot work‐related regulations and standards is recommended. [ABSTRACT FROM AUTHOR]

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.

Additive manufacturing (AM) brings the possibility to produce tools with a complex design of the cooling channels to achieve desired properties in the working piece. However, AM of tool steels can be challenging due to the residual stresses and crack formation which may be mitigated by optimizing process parameters. In this study, process parameters development in the laser powder bed fusion (L-PBF) of a martensitic hot work tool steel was under investigation. Having power, scanning speed and hatch distance as variables, a design of experiment was performed to map a process window to produce dense components. In addition, the same sets of process parameters were applied at different preheating temperatures to study and discuss the effect of three preheating temperatures on the porosity, microstructure and hardness of the manufactured components. The characterization of the parts was done using optical and scanning electron microscopy, x-ray diffraction and micro-hardness test. The results showed that the martensitic hot work tool steel can be manufactured with L-PBF with high densities above 99.95%. [ABSTRACT FROM AUTHOR]

Purpose: reasons for writing the paper is to present, the optimal procedure to manage specific critical job as hot work on board sea going vessels. Design/methodology/approach: an analysis of various shipping companies safety management systems and requirements demanded to perform hot works. Findings: found that safety management systems and demands to perform hot works are varied between shipping companies. Research limitations/implications: management of specific high risk job as hot work to be unified. Practical implications: suggestion is given to unify procedures of hot work management Social implications: reduction of risk to happen undesired events and mitigations of hazards associated with hot work. Originality/value: recommendation to shipping companies for modification of safety management system where is necessary to improve safety on board. [ABSTRACT FROM AUTHOR]

In industry, thermally shocked components lead to early failures and unexpected breakdowns during production resulting in huge losses in profit. Thus, the present study investigates the as-received, hardened and hardened and nitrogen treated H13 tool steels subjected to a thermal shock gradient similar to the actual industrial applications. The thermal shock gradients were created by using an in-house-built thermal shock fatigue cyclic treatment machine. The effect of thermal shock fatigue cyclic treatments at 1000 and 2000 thermal shock cycles in hot and molten metal chambers was noticed. All the thermal shock fatigue cyclic-treated samples were analysed by hardness, X-ray diffraction, microscopy and magnetic tests. The interesting changes in hardness, distorted crystal structure and crack initiation were found to be different for differently treated H13 tool steel specimens. The molten aluminium was more prone to stick to the surface of as-received as well as hardened and nitrogen treated steel compared to the hardened H13 steel specimens, which would delay the crack initiation. The wear resistance properties of the hardened H13 steel specimens were found to be higher than as-received and hardened and nitrogen treated H13 steel specimens after thermal shock fatigue cyclic treatment. The loss in magnetic properties was significant for the hardened and hardened and nitrogen treated samples compared to as-received H13 tool steel specimens. Therefore, the present 1000 and 2000 thermal fatigue cycles for 30 s at 670 °C would be worthy to predict the proper heat treatment method to design the parameters as well as the life of die-casting components and to help in the economical production of casting. [ABSTRACT FROM AUTHOR]

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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.

• Cause and consequence analysis for industrial hot work is conducted. • The ABT model and PN are integrated to analyze hot work accident evolution. • An improved regional center method is developed to obtain crisp evaluation value. • Data fitting is performed for probability calculation. Hot work poses great hazards to industrial operation site. Although regulatory and guidance exist, accidents caused by hot work continue to occur. Risk assessment has proved to be an effective method for risk control. However, current studies paid less attention to the evolution process of industrial hot work accidents and the quantitative risk assessment seems to be insufficient. In this context, we aimed to perform comprehensive risk evolution analysis and quantitative risk assessment of hot work using adaptive bow tie (ABT) and Petri nets (PNs). The ABT model is improved to analyze deep causes, consequences, and their relationships. PNs are employed to conduct quantitative risk assessment. To address uncertainties, the triangular membership function and improved regional center method are proposed to calculate the confidences of all places and transitions in the PNs. The probabilities are finally obtained by data fitting method. The study found that the most likely consequence of hot work accident is near miss. The results also indicate that hot work accident prevention measures should emphasize on the isolation of workplace, combustible gases test, removal of combustible substances, job organization, and job training. Besides, emergency devices maintenance and emergency drilling are critical to prevent accidents from expanding. [Display omitted] [ABSTRACT FROM AUTHOR]

The temperature, velocity, and size of hot metal sparks are essential to understanding their ability to ignite flammable materials. However, existing measurement methods have limitations to achieve detailed, in situ measurements of these parameters. This paper describes a methodology that combines color-ratio pyrometry and particle streak tracing velocimetry, together with digital image processing to obtain non-intrusive measurements of the temperature, velocity, and size of multiple sparks in a spray. Furthermore, these measurements can be performed using a properly calibrated commercially available color digital camera. The principle of the measurement is firstly introduced, and the repeatability and accuracy of the method are validated via a designed experiment. Then the method is performed to measure the temperature and velocity of metal (steel) sparks in sprays generated by abrasive cutting. Measurements of initial spark temperatures and velocities are reported, as well as the evolution of the temperature and velocity along the flight path of the sparks. Observed initial spark temperature in this work mostly ranged within 1500°C to 1700°C. Results show evidence of both melting and oxidation of the sparks. Different blade speeds are used to understand their effect on spark velocity and temperature. The results of this study can be used as input parameters for spark oxidation and transport models, which in turn can be used to assess the hazards of spark sprays in wildland spot fires, ignition, explosions of flammable gaseous mixtures and dust clouds, and for monitoring and optimizing the material processes such as thermal-spray coating. [ABSTRACT FROM AUTHOR]

The ignition of combustible material by contact with hot metal particles is an important pathway by which wildland and urban spot fires are started. This work examines how fuel characteristics such as density, morphology and chemical composition effect the ability of the fuel to be ignited by a hot metal particle. Fuels were prepared out of three materials: alpha-cellulose, a barley/wheat/oat grass blend, and pine needles. Each material was prepared as a powder and as larger, long pieces: strips of cellulose paper, loose grass, and pine needles. These fuels are representative of thermal insulation (cellulose strips), dry grasses (grass blend), forest litter (pine needles) and duff (powders). Aluminum particles ranging from 2 mm to 8 mm in diameter heated to temperatures between 575°C and 1100°C were dropped onto these fuels. The particle temperature required for ignition becomes higher as the particle size decreased. The results show that the required temperatures for ignition of powders were lower, with this trend particularly pronounced for the alpha-cellulose fuels. The biomass fuels required higher temperature particles to ignite, indicating that the presence of other ligno-cellulosic materials make ignition more difficult. [ABSTRACT FROM AUTHOR]

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.

Background Monitoring core body temperature to identify heat strain in workers engaged in hot work in heat stress environments is intrusive and expensive. Nonintrusive, inexpensive methods are needed to calculate individual Physiological Strain Index (PSI). Objective Thermal imaging and heart rate monitoring were used in this study to calculate Physiological Strain Index (PSI) from thermal imaging temperatures of human subjects wearing thermal protective garments during recovery from hot work. Methods Ten male subjects were evaluated for physiological strain while participating in hot work. Thermal images of the head and neck were captured with a high-resolution thermal imaging camera concomitant with measures of gastrointestinal and skin temperature. Lin's concordance correlation coefficient (rho_c), Pearson's coefficient (r) and bias correction factor (C-b) were calculated to compare thermal imaging based temperatures to gastrointestinal temperatures. Calculations of PSI based thermal imaging recorded temperatures were compared to gastrointestinal based PSI. Results Participants reached a peak PSI of 5.2, indicating moderate heat strain. Sagittal measurements showed low correlation (rho_c=0.133), moderate precision (r=0.496) and low accuracy (C_b=0.269) with gastrointestinal temperature. Bland-Altman plots of imaging measurements showed increasing agreement as gastrointestinal temperature rose; however, the Limits of Agreement (LoA) fell outside the ±0.25 C range of clinical significance. Bland-Altman plots of PSI calculated from imaging measurements showed increasing agreement as gastrointestinal temperature rose; however, the LoA fell outside the ±0.5 range of clinical significance. Conclusion Results of this study confirmed previous research showing thermal imagery is not highly correlated to body core temperature during recovery from moderate heat strain in mild ambient conditions. Measurements display a trend toward increasing correlation at higher body core temperatures. Accuracy was not sufficient at mild to moderate heat strain to allow calculation of individual physiological stress. [ABSTRACT FROM AUTHOR]

In September 2009, a fatal incident occurred in a cryogenic gas processing plant. The investigation of the incident indicated a number of potential issues that may have contributed to or caused the event. These issues include hot work procedures, electrostatic discharge, electrical conduit sealing, convective 'breathing' due to multiple vents, equipment age, maintenance, and worker training. The investigation concluded that the fuel for this event was provided by small leaks from the product pipes inside of the cold box; the oxygen was provided by convective 'breathing' that occurred due to the presence of two vents from the cold box and the erosion of the flapper valves that were intended to seal these vents; and ignition occurred due to stray currents that resulted from poor hot work procedures, and locating the return lead far from the work location. This article provides an overview of the process and facility, a timeline of events, a summary of the investigative process, and a discussion of the lessons learned from this event. © 2015 American Institute of Chemical Engineers Process Saf Prog 35: 143-148, 2016 [ABSTRACT FROM AUTHOR]

Gas purging processes in pipeline safety maintenance were studied using the Computational Fluid Dynamics (CFD) methods. A new model (model 1) closer to actual working conditions and another two-side injection model were investigated. The simulation results showed that the relative purging efficiency of model 1 decreases compared to the ideal model (model 0), and two-sided injection model increases the efficiency relative to the single sided purging model. In addition, the models with different intake methods, outlet positions, outlet sizes and outlet pressures were simulated. If the outlet is opened after delaying some time, purging efficiency is improved. Furthermore if "relay purging" method is adopted, the efficiency is increased by 18% with two gas inlets and by 11% with a single inlet. The outlet position affects the average velocity in the last purging time. If the outlet diameter is equal or larger than that of the inlet, the purging efficiency is much higher. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cost-effective partially damaged pipeline repair method is proposed and verified. • The temporary plugging material is composed of hydrogel and composite clay. • Adjusting the pipeline internal pressure achieved the shift from plugging to dredging. • The hydrogel material recovered at the filtration can be reused, reducing the cost. The traditional maintenance method for locally damaged long-distance oil pipeline involves hot work. Tedious technological processes are required to prevent the explosion of oil and gas due to the existence of combustible oil and gas in the pipeline. This study presents and verifies an economical and efficient replacement method for partially damaged oil pipelines. The core of the new method is to inject temporary plugging material to isolate the locally damaged pipeline and then carry out hot work. The temporary plugging material is composed of hydrogel and composite clay. The main function of hydrogel is to push away the residual oil to form an isolated oil and gas area. When the plugging length was 3 m, the hydrogel can resist the maximum pipeline pressure of 29.46 kPa. The composite clay increased the plugging capacity, thereby achieving plugging with pressure. When the plugging length was 2 m, the maximum resistance pressure of the composite clay was 0.49 MPa. The use ratio of the two materials can be flexibly adjusted in accordance with the actual plugging pressure. When the pipeline pressure was greater than the maximum plugging pressure, the plugging area was damaged, and the pipeline resumed transportation. In addition, hydrogels possess excellent heat absorption ability, which can reduce heat transfer during hot work to ensure safety. The hydrogels can be collected from the filtration station after the operation completion and can be recycled after simple treatment to reduce construction costs. The new replacement method of locally damaged oil pipeline has evident advantages compared with the traditional method. [ABSTRACT FROM AUTHOR]

Hot work on oil pipelines is a dangerous but essential operation. Traditional process has a large amount of energy waste and inert gas consumption during the operation. This study prepared a tough composite hydrogel that can temporarily block local oil pipelines and then carry out hot work. As a filling material, montmorillonite (MMT) can effectively improve the compressive strength of hydrogels. The composite hydrogel can push the residual oil to both ends of the pipeline to form a safe isolated oil and gas area. The product with a plugging length of 4.5 m withstood the pipeline pressure of 0.67 MPa. In temporary plugging, the plugged pipeline changed to the dredging state when the pipeline pressure exceeded the maximum plugging pressure, simplifying the complex operation process. The flame resistance performance indicated that the composite hydrogel absorbed the heat generated by hot work and ensured the safety of the operation. The prepared plugging material provided obvious advantages such as reducing energy waste and saving time and cost when applied to hot work of oil pipelines. [Display omitted] • The filling material effectively improve the compressive strength of hydrogel. • The plugging area formed by composite hydrogel can isolate oil and gas. • The materials possesses excellent flame retardant then hot work can be carried out. • The plugged area can be shifted to a dredging state by changing pipeline pressure. [ABSTRACT FROM AUTHOR]

Conditioned clothing for alleviating the effects of heat and cold has found use mainly in military applications. There are a few circumstances in industry where the provision of such clothing could be an economic proposition. Very often, however, there are other factors that militate against its adoption, e.g. the need for protection against hazards other than heat and cold, problems of wearer acceptance and interference with the work. Clearly the solution of these problems requires close co-operation between industry and clothing manufacturers as has been achieved in the nuclear industry. [ABSTRACT FROM PUBLISHER]