Experimental Investigation On The Safety Assessment Of LDPE Tubular Reactor

LDPE ultra pressure tubular reactor is the key equipment in ultrahigh pressure polyethylence production system, which is autofrettaged to enhance elastic loading capabilities and extend fatigue life before long-operation. But in practice, the beneficial residual stress will relax due to production conditions and external environment, which leads to the drop in fatigue life and safety performance of the tubular reactor, and the consequence of leakage and explosion is tragedy.Therefore the safety assessment of LDPE tubular reactor is very important for the safety production and reduction of economic losses It has great significance in scientific research and engineering project.In this paper, the conclusions were obtained by taking the LDPE tubular reactor as a research object. The assessment of the tubular reactor under static load and cyclic load, based on the mechanical property test, X-Ray diffraction stress test, autofrettage and burst test are conducted.(1) The test results of mechanical property shown that the material performances meet the requirements of standards, then compared elastic area and plastic area, found that with the increase of the degree of plastic, the material toughness drops.(2) The burst test conducted for the LDPE tubular reactor, obtained the stress-strain curve and burst safety factor, and the result was compared with the results of Finite element analysis.Then we analyzed the relations about burst safety factor and diameter ratio:0.40455 1.58 bn = - +K( 2≤K≤3).(3) By taking the reverse yielding analysis before the autofrettage test, the critical diameter ratio that determined the autofrettage pressure range was calculated(Kc=2.16). Through the autofrettage process for the tubular reactor test, the change of the yield stress and safety factor after autofrettage process were analysed by using analytic method and finite element method.(4) The fatigue life which were obtained by the Shigley method and Fatigue module, found the largest relative error of the results were 9.35%.Then compared to 630 MPa and 691 MPa autofrettage treatment effect on fatigue life.