Strength Analysis Of Elbow With Defects And Life Prediction Of Pipeline In Typical Refining Unit

This paper mainly studies the pipeline of atmospheric and vacuum unit. First, It assesses the risk of the pipeline and analyses the corrosion.Then it has conducted a research of two aspects that are about the limit load of bend with the local thinning defects and the remaining life of the pipeline. In the case of the residual strength of the elbow, the allowable ultimate load value of the inner wall of the outer arch is locally thinned.The allowable limit load values of the inner wall with the same degree of local thinning are compared. In the case of residual life, a method based on Monte-Carlo method using Matlab software program is proposed.Concrete research content is as follows:(1) Based on the RBI method, The PCMS software was used to analyze the risk of 48 pipes (86 measuring points) of the atmospheric and vacuum distillation unit; Draw the result of risk level of every pipeline.(2) The results of field corrosion test of a conventional decompression device are analyzed and summarized, the anti-corrosion measures have been given according to the test results. After adopt the proposed measures according to the actual situation, the corrosion of the device slows down. That proof of the effectiveness of on-site corrosion inspection and anti-corrosion measures.(3) In the field of corrosion inspection work, the second bend of the top pipeline is found to be locally thinned. As the weak link in the pipeline system, the role of the elbow is essential, so the limit load analysis of the elbow has been proposed based on Ansys Workbench.Under certain conditions, the limit load value is 17.15MPa when the defect at the inner wall of the elbow outside the arch, larger than the ultimate load value of 15.84MPa when the same size defects at the inner wall of the same size elbow inner arch. It is proved that the defect position for the value of the limit load of elbows have certain effect.(4) Using the Access software to develop the device pipeline thickness information management database. Facts have proved that, this database for the improvement of pipeline management, rapid inquiry device pipeline information and timely control of the corrosion of the pipeline has a certain help.(5) On the basis of Matlab software application, using the Monte-Carlo method, the residual life prediction of the pipeline has ben proposed based on the concept of uniform corrosion rate. The corresponding annual corrosion rates have been calculated according to the pipe year thickness measurement data. Fit this set of data in the Matlab using a certain method, found that it conforms to the law of normal distribution. After fitting the normal distribution curve, get the parameters (expected and variance); and then randomly generated 9000000 random corrosion rate in the use of Matlab function according to this normal distribution model. According to the random corrosion rate,calculate the remaining wall thickness after a certain age, compared with the measured wall thickness, error is less. The corrosion failure probability corresponding to the useful life is then calculated based on this set of corrosion rates(according to engineering experience, uniform corrosion thinner wall thickness is less than 3 as a failure). Finally,according to reliability 0.9, determine the duration of the pipeline can continue to serve, get the result of its remaining life.