From measurement collection to remaining useful life estimation : defining a diagnostic-prognostic frame for optimal maintenance scheduling of choke valves undergoing erosion
Condition Based Maintenance (CBM) aims at regulating maintenance scheduling based on data analyses and system condition monitoring. Clear advantages of optimizing maintenance scheduling include relevant cost savings and improved safety and plant availability. A critical aspect is the integration of CBM strategies with condition monitoring technologies for handling a wide range of information sources and eventually making optimal decisions on when and what to repair. In this work, a practical case study concerning maintenance of choke valves in offshore oil platforms has been investigated. Choke valves used in offshore oil platforms undergo erosion caused by the sand grains transported by the oil-water-gas mixture extracted from the well. Erosion is a critical problem which can affect the correct functioning of the valves, result in revenue losses and cause environmental hazards. In this respect, this work proposes a diagnostic-prognostic scheme for assessing the actual health state of a choke va lv and eventually estimating its Remaining Useful Life (RUL). In particular, the focus has been on th e identification of those parameters which contribute to the actual erosion of the choke valve, the development of a model-based approach for calculating a reliable indicator of the choke valve health state, the actual estimation of the choke RU L based on that indicator using statistical approache s and, finally, the investigation of methods to reduc e the uncertainty of the RUL estimation by adding highly meaningful knowledge on the erosion state of the choke valve .
Sand erosion of wear-resistant materials : erosion in choke valves
Abstract Sand particles from oil and gas production may cause considerable erosion damage in critical parts of transport and processing equipment such as valves and chokes. Increased longevity of such components will lead to significant savings as offshore oil and gas production move subsea, and it can be achieved in two ways; through selection of erosion-resistant materials or through design optimization. A total of 28 different materials including standard steel grades, solid tungsten carbide materials, coatings and ceramics have been tested under various impact angles and velocities of sand particles, and examined for erosion characteristics. The test results have been used to determine empirical model equations and to determine the relative erosion resistance for the materials. The results show that a longevity gain factor of up to more 102 is possible to achieve by selection of proper material. Optimization of choke design for a needle choke has shown that additional savings with a factor of more than 102 is obtainable.
Overproduction of a truncated poly (vinyl alcohol) dehydrogenase in recombinant Pichia pastoris by low-temperature induction strategy and related mechanism analysis
Based on the N-terminal sequencing of poly (vinyl alcohol) dehydrogenase (PVADH), a 1,644-bp gene encoding a truncated PVADH (tPVADH) was amplified using the synthetic gene (GenBank accession No. JQ235753) as a template, and was further transformed into Pichia pastoris GS115 with the vector pPIC9K. The maximal tPVADH activity reached 546 U/mL in shake flask. The influence of methanol concentration and induction temperature on tPVADH production was further investigated in 3-L bioreactor. When the methanol concentration and induction temperature were controlled at 15 g/L and 22 °C, respectively, the maximal tPVADH activity reached 8,464 U/mL, which was nearly 10 times that of mature PVADH expressed under the same condition and was the highest level ever reported. The reason responsible for the significant improvement of tPVADH production at low induction temperature was explored in terms of cell viability, extracellular proteases activity, and alcohol oxidase activity.