Remaining Useful Life Prediction Method for Multi-Component System Considering Maintenance:Subsea Christmas Tree System as A Case Study

Maintenance is an important technical measure to maintain and restore the performance status of equipment and ensure the safety of the production process in industrial production,and is an indispensable part of prediction and health management.However,most of the existing remaining useful life(RUL)prediction methods assume that there is no maintenance or only perfect maintenance during the whole life cycle;thus,the predicted RUL value of the system is obviously lower than its actual operating value.The complex environment of the system further increases the difficulty of maintenance,and its maintenance nodes and maintenance degree are limited by the construction period and working conditions,which increases the difficulty of RUL prediction.An RUL prediction method for a multi-omponent system based on the Wiener process considering maintenance is proposed.The performance degradation model of components is established by a dynamic Bayesian network as the initial model,which solves the uncertainty of insufficient data problems.Based on the experience of experts,the degree of degradation is divided according to Poisson process simulation random failure,and different maintenance strategies are used to estimate a variety of condition maintenance factors.An example of a subsea tree system is given to verify the effectiveness of the proposed method.

Strength Design Method for Tubing Hanger of Subsea Christmas Tree Against Big Temperature Difference

The tubing hanger is an important component of the subsea Christmas tree, experiencing big temperature difference which will lead to very high thermal stresses. On the basis of API 17D/ISO 13628-4 and ASME VIII-1, and by comprehensively considering the erosion of oil and the gravity load of the tubing, a calculation model is established by regarding design pressure and thermal stress, and the method for designing the tubing hanger of the horizontal Christmas tree under big temperature difference condition is developed from the fourth strength theory. The proposed theory for strength design of the tubing hanger in big temperature difference is verified by numerical results from ABAQUS.

The Christmas Tree

Set high on the great round table stands the lighted Christmas tree.shining its good cheer around the room①. It towers② above the children’sheads as they gaze up at it with admiring eyes. Sitting on the very top ofthe tree is a silver star surrounded by tiny lights. All the branches arehung with silver bells, tinsel and sparkling lights. Around the base

“Father Christmas & Christmas Tree”的由来

“Fatller Christnlas”即“圣诞老人”,又叫“SantaClaus?”,是西方童话故事中的人物。据传他是小亚细亚一位名叫尼古拉的基督教主教的化身。尼古拉为人仁慈,乐善好施。传说有一次他为使邻居家的三个女儿不致被卖还债;在夜里他把三只装满黄金的袜子悄悄地挂在三姐妹的床头,次日一早,她们便看到了袜内黄金,喜出望外,替父亲解了忧,后来她们才得知是尼古拉老人送的。这一天正好是圣诞节,于是便产生了圣诞老人的传说。

Qualitative Assessment of Postharvest Stomata and Chloroplast Degradation in Contrasting Abscission Resistant Balsam Fir (Abies balsamea (L.) Mill.)

Balsam fir is an important Christmas tree species, especially in eastern Canada. The natural Christmas tree industry faces a challenge in postharvest needle abscission. Though there have been many studies describing the physiological triggers and consequences in postharvest balsam fir, there have been no studies describing morphological or ultrastructural changes. Therefore, the objective of this study was to examine changes in stomata and chloroplast of postharvest needles. Branches were collected from low and high needle abscission resistance balsam fir genotypes, placed in water, and displayed in typical household conditions for 11 weeks. Needle abscission, chlorophyll fluorescence, and water uptake were monitored throughout. Needles stomata and chloroplasts were examined under a scanning and transmission electron microscope, respectively, each week. All branches had increased abscission, decreased chlorophyll fluorescence, and decreased water uptake over time. Needle surfaces accumulated fungal hyphae, especially in stomata. Chloroplasts demonstrated some dysfunction within two weeks, with notable decreases in chloroplast starch and increases in plastoglobulins. Within several weeks thylakoid membranes had been dismantled as chloroplasts transformed into gerontoplasts. All biophysical and structural changes were more pronounced in low needle abscission resistant genotypes. This research identifies a potential role for needle fungi in postharvest needle abscission and confirms the postharvest senescence of chloroplasts. Though it was previously speculated that chloroplasts must senesce postharvest, this study identifies how quickly this process occurs and that it occurs at different rates in contrasting genotypes.

深水全电采油树控制系统可靠性评估方法

The subsea all-electric Christmas tree(XT) is a key equipment in subsea production systems.Once it fails,the marine environment will be seriously polluted.Therefore,strict reliability analysis and measures to improve reliability must be performed before a subsea all-electric XT is launched;such measures are crucial to subsea safe production.A fault-tolerant control system was developed in this paper to improve the reliability of XT.A dual-factor degradation model for electrical control system components was proposed to improve the evaluation accuracy,and the reliability of the control system was analyzed based on the Markov model.The influences of the common cause failure and the failure rate in key components on the reliability and availability of the control system were studied.The impacts of mean time to repair and incomplete repair strategy on the availability of the control system were also investigated.Research results show the key factors that affect system reliability,and a specific method to improve the reliability and availability of the control system was given.This reliability analysis method for the control system could be applied to general all-electric subsea control systems to guide their safe production.

Resin Plug Application on Subsea Wells as A Suspension Barrier

A subsea wellhead equipped with obsolete vertical Christmas tree needs to be suspended for subsea tree recovery and subsequently to be permanently abandoned. Due to obsolete Christmas tree design combined with tubing inaccessibility issue,conventional subsea intervention method for setting downhole mechanical plug barriers with a semisubmersible rig or a riserless light well intervention vessel is not feasible to suspend the well. Attempt was made to suspend the well from a riserless light well intervention vessel by setting tubing mechanical plugs in 2017,but the mandrel of the tree running tool (TRT) was sheared off accidently while landing the TRT&subsea intervention lubricator (SIL) on the subsea tree. Due to resin’s superior mechanical and rheological properties,resin was evaluated as a well suspension material to create a suspension barrier. Resin plug was deployed successfully from a dive support vessel (DSV) across the perforations to allow the tree removal at cost effective manner. Resin plugging demonstrates a new approach at well P&A area.