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The complex coupling relationship between liquid sodium and concrete materials affects both the sodium fire characteristics and concrete properties through heat and chemical erosion. In this study, experiments on direct and indirect (separated by a steel plate) contact of the columnar sodium fire with the concrete surface were performed. It was found that the combustion efficiency of liquid sodium in direct contact with concrete was significantly enhanced and accompanied by intermittent explosions and splashing of small concrete fragments. The sodium fire on the surface of the concrete considerably increased the internal temperature, pore size, and distribution density of the concrete. In addition, the depth of influence on the loosening of the concrete structure was also greatly extended. The contact of liquid sodium with the concrete substantially affected its permeability resistance. The water absorption of the concrete surface was increased by more than 70% when liquid sodium directly impacted the bare concrete surface. However, the change in water absorption in the centre of the concrete was primarily affected by the duration of the external heat.

Deck machinery that is driven by the hydraulic motor is a key part for ship exploration in the polar area. In this paper, the hydraulic vane motor in deck machinery was taken as the research object. The material of motor shields was QT350-22L, which was used as the plate valve, and the rotor material was LC2-1. The rotor slides relative to the plate valve under the pressure of the high-pressure oil, and the surfaces worn damage. Wear tests were performed using a pin-on-disk structure under six different temperatures (room temperature (25 °C), 0 °C, −10 °C, −20 °C, −30 °C and −40 °C), two kinds of hydraulic oil(15# and 10# aviation hydraulic oil) and the two normal loads(150 N and 300 N)respectively. In order to analyze the wear mechanism of the friction test specimen under different condition, the surface morphology of the friction test was carried out by scanning electron microscope(SEM) and laser interference profilometer. As the temperature decreased, the coefficient of friction did not change linearly. At the temperature of −20 °C, the coefficient of friction was the smallest, and when the temperature was lower, the coefficient of friction increased slowly and finally stable. Moreover, typical wear and tear modes were different at different test temperatures. The factors were the mechanical properties of the material and the lubrication medium changed in the low temperature. Changes in oil properties affected oil film thickness and distribution and abrasive grain removal ability between friction pairs. According to the experimental results, the paper summarizes the failure mechanism of the hydraulic motor, which can not only optimize the design of the hydraulic motor but also provide reference data for the establishment of online intelligent fault diagnosis system of the marine hydraulic system.

Deck machinery that is driven by hydraulic motor is a key part for ship exploration in polar area. The reliability of hydraulic motor which works as the key power source of deck machinery is concerned by manufacturers, especially under very low temperature. The low temperature friction characteristics is one of the important factors that influence the reliability of the motor. In this paper, the hydraulic vane motor in deck machinery was taken as the research object. The friction test of the vane head which was made of polyimide (SP21, E.I.Du Pont Company) and the stator, which is made of nodular cast iron(brand is QT350-22L, ISO 1083:2004), was carried out by using the low-temperature tribology tester. Wear tests were performed using a pin-on-disc structure under five different temperatures (−10 °C,-20 °C,-30 °C,-40 °C and −50 °C) and three different loads (300N, 450N and 600N) respectively. In order to analyze the wear mechanism of the friction test specimen under different condition, the surface morphology figures of specimen were got by digital microscope system (DMS). The experiment results showed temperature and load have a great influence to the friction coefficient. With temperature decreasing, the friction coefficient does not change linearly, because the mechanical properties of specimen material and the lubrication medium varied significantly in low temperature. Moreover, typical wear and tear patterns are different in different working temperatures. Therefore, the failure mechanism of the hydraulic motor was summarized. The research can not only optimize the design of hydraulic motor, but also provide reference data for the establishment of online intelligent fault diagnosis system of marine deck machinery.

Liquid sodium, as a special form of metal has unique combustion characteristics and is difficult to extinguish quickly. To obtain a deeper understanding of the combustion and suppression characteristics of a columnar sodium fire affected by fire extinguishing powder in a confined space, investigative experiments were conducted in a cylindrical test chamber. The temperature of the space and the bottom surface were measured and analysed, and the effects on the suppression of combustion and the spatial heat flow field when different amounts of Class D fire extinguishing powder were sprayed into the space in the early and late combustion stages were compared. A local high temperature easily formed near the columnar sodium flow zone, because the sodium is more likely to adhere to the sensor at that measurement point. For a space heat flow field formed by a sodium fire in a confined space, the lateral temperature distribution at each height of the space is approximately linear. The overall temperature distribution at the upper space is relatively uniform, and the temperature near the fire source in the lower part of the space varies exponentially along the height. Compared with the spraying of fire extinguishing powder in the late stage of a sodium fire, spraying at the initial stage is more effective in suppressing the combustion of liquid sodium, the flow of liquid sodium and the disturbance of the space heat flow field. Further, the reignition hazard that may occur when spraying fire extinguishing powder to suppress a sodium fire should be given sufficient attention.