Centrifugal pumps are widely used in the industry, especially in the oil and gas sector for fluids transport. Classically, these are designed to transfer single phase fluids (e.g., water) at high flow rates and relatively low pressures when compared with other pump types. As part of their constructive feature, centrifugal pumps rely on seals to prevent air entrapment into the rotor during its normal operation. Although this is a constructive feature, water should pass through the pump inlet even when the inlet manifold is damaged. Modern pumps are integrated in pumping units which consist of a drive (normally electric motor), a transmission (when needed), an electronic package (for monitoring and control), and the pump itself. The unit also has intake and outlet manifolds equipped with valves. Modern systems also include electronic components to measure and monitor pump working parameters such as pressure, temperature, etc. Equipment monitoring devices (vibration sensors, microphones) are installed on modern pumping units to help users evaluate the state of the machinery and detect deviations from the normal working condition. This paper addresses the influence of air-water two-phase mixture on the characteristic curve of a centrifugal pump; pump vibration in operation at various flow rates under these conditions; the possibilities of using the results of experimental investigations in the numerical simulations for design and training purposes, and the possibility of using vibration and sound analysis to detect changes in the equipment working condition. Conclusions show that vibration analysis provides accurate information about the pump's functional state and the pumping process. Moreover, the acoustic emission also enables the evaluation of the pump status, but needs further improvements to better capture and isolate the usable sounds from the environment.Processes 2018, 6, 18 2 of 15 refers to the difficulty of finding a general analytical model that explains the changes of the pump characteristic curve [3,6].The development in materials and pump construction have led to an increased life time and better reliability of the products. The pump application may limit the access of personnel for a thorough visual pump inspection, so that under these conditions, the use of non-intrusive sensors can replace humans for detecting pump failure. Sometimes, air entrapment does not necessarily lead to a major failure, hence the pump may work under two-phase flow until a replacement/solution is found. However, as the pump characteristic is changing, the control system needs to know how to adjust the pumping parameters accordingly, so that the pump runs under safe conditions. This paper shows the concept of how the pump characteristic curves transform from the normal state to the conditions of circulating a two-phase mixture. Several papers have shown and demonstrated the ability of vibrations measurement as an effective solution to identify improper machine state (such as valve opening or pump vibrations) [8][9][10][11][12...

No abstract

The methods of assessment of the limit state of failure of the pipelines from transport systems are characterized by high safety factors. The current trend is that by more accurate calculation methods, structured on several levels and based on the information about the factors involved in the evaluation process (material characteristics, pipeline thickness, operating pressure and their range of variation, the precision of the used investigation method, the security class of pipeline) these safety factors may be reduced. The mentioned aspects can be found in many papers and in the recent versions of standards DNV RP 579 and API 101. The paper shows the importance of considering the defect position to reduce the level of conservatism of the method of evaluation. This is possible in the modern methods of inspection which indicates the position of the defect. Based on the results of an inspection we can calculate the probability of failure of a pipeline and it can be an indicator of pipeline safety instead of the actual indicator expressed by the number of defects per km established by the operator or by the third parties. Any inspection of a pipeline has to be followed by a maintenance program based on available information. In this case, even if we have to emit certain assumptions and approximations (such as neglecting the interaction between the defects), the repairs of a pipeline may be indicated at the right time to maintain the safety in the operation.

Pipe corrosion is a frequent phenomenon, and if repairs are delayed it could lead to environmental damage. Drilling activities can expand only when sufficient surface transportation capacity for the produced fluids exists and thus good maintenance of the transportation system is important. Furthermore, the technology presented herein can be easily upgraded as a repair solution for surface casing section below the casing head, which have been repeatedly reported as being highly corroded for older wells. This paper presents the results of the research work carried out by the authors in order to evaluate the design methods of the modern composite material systems used to repair steel pipes carrying hydrocarbons upon which local metal loss defects (generated by corrosion and/or erosion processes) have been detected. The pipe repair technologies consisting of the application of composite material wraps (made of a polymeric matrix and reinforcing fabric) are perceived as being advantageous alternative solutions for substituting the conventional technologies, which require welding operations to be performed in the corroded pipe areas. The performance and the design methods of the composite repair systems have been investigated by evaluating the reinforcement effects (the restoration level of the damaged pipe mechanical strength) generated by the applied composite wraps as a function of their geometry and mechanical properties. To that purpose, numerical models based on finite elements (previously developed by the authors and certified by comparing them with the results of several experimental programs performed within our university) have been used. The calculation methods proposed in literature (among which a method previously proposed by the authors) to define the composite wrap dimensions (thickness and length) for a given pipe have been compared to the numerical results in order to select the most adequate solution for the design of the composite repair system. The influence in the design process of the defect orientation and of its width has also been investigated.

This paper presents the results of a theoretical-experimental study on the influence of FDM parameters (height of the deposited layer at one pass Hs and percentage of filling Pu) on the dimensions of cylindrical spur gears made of PLA (shaft diameter d and bore diameter D). In this context, we designed the 3D model of a cylindrical gear with module m= 1 and z= 60 spur teeth, which we used for FDM 3D printing of 27 PLA parts with different values of coating height deposited at a pitch Hs of 0.10, 0.15, 0.20mm and different values 50, 75, and 100% of filling percentage Pu. The 324 values obtained from measuring the diameters d and D of 27 cylindrical spur gears made of PLA and the calculated values of statistical indicators (arithmetic mean, standard deviation, dispersion) were used to determine the dimensional accuracy of the analyzed parts. The study results show that the percentage of filling has a greater influence than the shaft diameter on the dimensional accuracy of cylindrical spur gears made of PLA.