Assessment of Operational Degradation of Pipeline Steels

This paper summarizes a series of the authors’ research in the field of assessing the operational degradation of oil and gas transit pipeline steels. Both mechanical and electrochemical properties of steels are deteriorated after operation, as is their resistance to environmentally-assisted cracking. The characteristics of resistance to brittle fracture and stress corrosion cracking decrease most intensively, which is associated with a development of in-bulk dissipated microdamages of the material. The most sensitive indicators of changes in the material’s state caused by degradation are impact toughness and fracture toughness by the J-integral method. The degradation degree of pipeline steels can also be evaluated nondestructively based on in-service changes in their polarization resistance and potential of the fracture surface. Attention is drawn to hydrogenation of a pipe wall from inside as a result of the electrochemical interaction of pipe metal with condensed moisture, which facilitates operational degradation of steel due to the combined action of operating stresses and hydrogen. The development of microdamages along steel texture was evidenced metallographically as a trend to the selective etching of boundaries between adjacent bands of ferrite and pearlite and fractographically by revealing brittle fracture elements on the fracture surfaces, namely delamination and cleavage, indicating the sites of cohesion weakening between ferrite and pearlite bands. The state of the X52 steel in its initial state and after use for 30 years was assessed based on the numerical simulation method.

Estimation of the resource of pipes of the main circulation pipeline of a NPP by the criterion of crack resistance with account of operational degradation of properties

The results of an experimental determination of the characteristics of cyclic crack growth resistance of specimens made of stainless steel 08Kh18N12T are given. Compact samples 20 mm thick cut from Du 550–30 pipes of the primary circuit of the main circulation pipeline (MCР) were studied under eccentric tension in the initial state and after 100 thousand hours of operation in the conditions of the Novo-Voronezh NPP. Using a new engineering approach based on measuring the specimen tightening and constructing a cyclic elastoplastic fracture diagram for a specimen with a crack in the coordinates “tightening – the stress intensity factor, calculated taking into account the plasticity correction”, a calculated life estimation is given for the pipe of Du 550–30 MCР NPP, made of 08Kh18N12T steel, according to the criterion of cyclic crack growth resistance, taking into account operational degradation of properties caused by the running time of 100 thousand hours. The life (survivability), expressed in a number of cycles of change in internal pressure, for a pipe with the most dangerous defects (surface semi-elliptical crack and combined defect “pitting + crack”) is determined. An analysis of the influence of the level of initial damage and the type of hazardous defect on the survivability of the pipes is made. The results can be used to analyze damage and predict the life of pipes made of ductile metals and alloys, in cooling systems of reactors, as well as main pipelines of hydrocarbon transport.

Operational Degradation of Engine Oil in Agricultural Technology

Proposed paper is focused on description and observation of operational degradation of engine oil in agricultural technology. Engine oil is one of the most important liquids used in combustion engines. Correct function of any machine is based on the appropriate selection of lubricants; moreover, it is also important to care for the entire lubrication system. Determining the condition of the oil used in operational conditions is very important for potential further oil use. Previously, engine oil had to be changed after expiration of legally valid intervals regardless of its actual performance parameters. However, its usage may be extended if engine oil parameters meet the legal requirements. This can be achieved by removing engine oil samples from machines on a regular basis. By examining the samples taken, it is possible to determine the actual oil state. In such manner, it is possible to prolong interchange periods and save both the financial resources and environment.

Operational Degradation of Spheroidal Graphite Cast Iron EN GJS SiMo

The specifics of low-alloyed cast irons after EN 16124 standard of type GJS SiMo for high temperature applications of exhaust tracts of internal combustion piston engines. Boundary exposition temperature. Structure failure of cast iron by temperature overloading. Metalography, SEM, XRD of overexposed exhaust pipelines. Failure reason hypothesis of useful properties by exceeding of critical temperature.

Rolling-Contact Hardening Evaluated by Indentation

The operational degradation of surface layers due to a rolling contact process was simulated for Hadfield steel by a special testing rig. A specific limited state based on cumulative depletion of plasticity was achieved.Precise evaluation of the surface layer's mechanical parameters is necessary for a service life prediction. Very low depth of localized dislocation hardening process doesn ́t allow the standard mechanical testing. The comparative instrumented indentation tests using Vickers and cylindrical indenter were used for evaluation of defined stage of surface degradation process. The intensity and reach of deformation hardening are partially limiting for particular methodology. The yield stress of surface layers was estimated according to an analytical model of uniaxial vs. indentation plastic flow ratio.