The Ultimate Load Bearing Capacity And Life Prediction Research For The Slurry Pipeline

The slurry pipeline project of Baotou Iron&Steel (Group) Co. Ltd., is a key projectof Inner Mongolia,and the third pulp pipeline in china,with highest pressure, maximumcaliber, farthest transportation distance, received extensive attention worldwide. Aftersix years of construction, the project brings economic benefits of12billion yuan RMBevery year, and very significant social benefits and environmental benefits. A19kilometer seamless tube of start was smelted, rolled and constructed by our companyown. Risk evaluation and life prediction is greatest importance to the safety.First, this paper systematically analyzed the buried pipeline under various loadcalculated pipe pressure, soil pressure, longitudinal thrust, bending, seismic load andwater hammer effect, horizontal thrust, blasting pressure load, etc. Identified in all kindsof conditions in the pipeline, high pressure pipeline pressure is the decisive factor, farbigger than other load effect.On the base of system analysis about force acting on the pipe, such as mechanicalproperties of material, parameters of defect, failure modes of line pipe. In this article,we’ll introducing Yu’s Unified Strength Theory, studied the stress state of pipelines andthe ultimate load bearing capacity, Find out the elastic limit solutions and the plasticlimit solutions by an analytical method, reveals the relationship between the geometrydimension, defect size, and the yield limit of material. Determining the stress state ofdifferent variables of the pipeline, including defect depth and width, defect length anddefects of wall thickness error, loss of roundness etc, analyzed the influence of pipestress.Under extremely slurry pipeline internal pressure, the feature of failure is rapidlyblowout, after a brief period of plastic development stage, failure mode should avoid brittle fracture and elastoplastic torn damage. Therefore according to the strength of themodel and the life failure model, and the allowable stress criterion and the residualstrength coefficient criterion, established the limit state equation and pipeline failurecriterion,Considering the fuzzy stochastic characteristics of the defect size and strength ofmaterials, we review a number of related experimental data, and the measurement datafrom the construction site, The data through statistical analysis show that defect size,development rate, material strength assessment parameter matching different probabilitydistribution, and has the characteristics of fuzzy random.Test and the measured data are subject to some limitations. Need for parameterestimation, by the least squares method estimating the mean value and expectation,variance and coefficient of variation of Gumbel distribution, normal distribution,uniform distribution. Using the Monte-Carlo simulation method, generates largesample random data, the most critical defect size can be obtained according to thefunction of Gumbel distributions, then the limited data expanded into large samplesimulation data, a fuzzy random probability data space was established.Defect rate of development is another important data, we obtained according towear corrosion test experimental data of42hours,in order to predict defects added valueof any time, adopt the gray system theory, the experimental data combine the originalseries, use accumulation generation, also the least square method to determine thevector, solving gray gray-scale parameters, establishes the time response function, thuspredict the rate values of defect development year-to-year.Adding the initial value with the added value of defect size, can put the fuzzyrandom probability data space expands to any time. According to the Yu’s UnifiedStrength Theory,checking elastic limit solution and the plastic limit solution,checkinganalysis the capacity of data space in each data,and determine their meets the limit stateand the failure mode, then calculate failure probability and recovery time, eventuallymapped the lifetime curves of pipelines.Through the analysis of life curve, to determine the safety of baotou slurry pipelineservice deadline, divided the safe operation of pipeline into the seven stages across60years, such as safety operation period, monitoring operation period, limited safety period, extended deploying, speeding up stage, failure destruction period, give allperiods of failure probability,the defects in the pipeline development process, answeredabout residual strength, residual life and overterm service three basic problems. Providescientific decision-making basis for the safety operation of Baotou iron and steel Group.This paper studies to unified strength theory as the core content to test andmeasurement data for background and based on analysis of stress as the basis, theGumbel distribution and grey system as the key method, solve the problems of lifeprediction. Research involving the mining, oil&gas storage and transportation,metallurgy, chemical, machinery, corrosion protection and etc, apply the fuzzy randomprobability theory and reliability theory, the gray system theory, extreme valuedistribution parameter estimation, chemical corrosion and abrasion theory, introducethe latest research results of the fluid mechanics, soil mechanics, structural mechanics,fracture mechanics, damage mechanics, elastic-plastic mechanics, mechanics ofmaterials, and so on.The analytical solution of the unified strength theory is derived out.The result of this paper can be applied directly to slurry pipeline, oil and gaspipelines, chemical pipeline, municipal pipeline, coal slurry pipeline projects,for allkinds of media pipes, the bearing capacity of the limit state, failure probability and lifeprediction has important guiding significance and practical value. and our method canresolve the problem more effectively.