Special Conditions With The Process Piping Failure Analysis And Its Countermeasures

In this thesis,the fundamental theory,testing technique and evaluating analysis method were comprehensively utilized to systematically investigate and solve two failure cases concerned with two types of pipes that applied in special industrial operating conditions and which made respectively from nonmetal and metal materials, which occurred in corporation of industrial production.The composition and structure of two kinds of particle modified polytetrafluoroethylene(PTFE) flexible tubes were studied by XRD,FT-IR and XPS. The thermal conductivity and other thermal properties of two kinds of particle modified polytetrafluoroethylene(PTFE) flexible tubes were analysed by DSC,TG and DTA.The corrosion resistant properties of the tubes were evaluated by immersing them in chemical corrosion medias.The surface morphology of the tubes was observed by 3D-video electricity microscope system.The results show that both domestic and abroad flexible tubes were composite materials consist of PTFE as a matrix and graphite particle as a filling materials,the surface quality of the abroad one is better.The thermal properties of the two types of flexible tubes are almost at the same level.They both can prevent themselves from corrosion attacked by various chemical substances and have little difference with their excellent corrosion resisting properties.The chemical composition and structure of triple outlet jacketed piping of high pressure circulating cooler were inspected by optical-electrical spectrometer(OES) and metallurgical structure inspection.The chemical and element composition of inner surface corrosion substances of jacketed piping were evaluated by x-ray flourescence analysis(XRF),X-ray diffraction(XRD) and thermogravimetric analysis (TGA).The Analysis such as microscopic morphology inspection and chemical composition analysis were studied by scanning electron microscope(SEM) and energy dispersive spectroscope(EDS) on those inner surface corrosion substances systematically.The chemical composition and structure of inner piping of high pressure circulating cooler were inspected by optical-electrical spectrometer and metallurgical structure analysis.The Analysis such as microscopic morphology inspection and chemical composition analysis were studied by SEM and EDS on the bursting crack of inner piping systematically.The chemical and ion composition of circulating cooling water and the chemical composition of its deposits were evaluated by ICP-AES,ion chromatography and FT-IR.The results show that the materials quality of the jacketed and inner piping of the high pressure circulating cooler are qualified according to the quality evaluating criterion.The aggravation of corrosion,the accelerated wall thinning of the inner piping and the so caused bursting crack were caused by the unqualified circulating cooling water which contains certain content of chlorine ion.The aggravation of corrosion and the accelerated wall thinning of the jacketed and inner piping were caused by corrosion under scaling and pitting corrosion due to serious scaling near the cooling water outlet of the jacketed piping and the bend of the inner piping and the so caused local erosive.Another important reason which caused the accelerated wall thinning of the inner piping near the outlet of the jacketed piping is the obstruction of corrosion substances in the bend near the cooling water outlet of the cooler,which creates a dry-wet alternative environment that result in the fast striping of the corrosion substances and the aggravation of local corrosion,and moreover,erosive is also induced by the current direction change due to the striped corrosion substances. The scaling of the circulating cooler is very serious with a large amount,a wide range of distribution and a hard character of the scaling,that is due to the function failure and dosage shortage of the using scaling inhibitor.Finally,based on results from failure analysis performed respectively on two cases of the pipes made from nonmetal and metal materials which are used in special industrial operating conditions,conclusions were made that most of the properties of domestic modified flexible tubes are almost at the same level of those of the abroad counterparts,corresponding countermeasures aim at the failure of high pressure circulating cooler were put forward.These effective suggestions will not only prevent repeating occurrence similar to the analyzed accidents,reduce unnecessary economic loss and avoid possible personnel casualty,but also make the production of corporation more safe,reliable and effective.