Structural integrity and life assessment of oil drilling rig pipes using analytical method

Structural integrity and life assessment of oil rig pipes using analytical method is presented and applied to an oil drilling rig pipe. The new concept based on risk evaluation according to probability and consequence of failure is used. Analytical expressions for surface cracks, provided by Raju and Newman, are used to calculate stress intensity factors for different crack geometries. Furthermore, the rig welded pipe failure probability is estimated by simple application of the Failure Assessment Diagram (FAD) and used together with potential consequences to evaluate the risk level by application of risk matrix. The same logic is employed in the case of cyclic loading, i.e. fatigue crack growth, by using Paris law to calculate crack length depending on the number of cycles. Simple numerical integration is applied to take into account the change of the geometry parameter Y due to increasing depth of a surface crack

Structural integrity and life assessment of oil drilling rig pipes using analytical method

Structural integrity and life assessment of oil rig pipes using analytical method is presented and applied to an oil drilling rig pipe. The new concept based on risk evaluation according to probability and consequence of failure is used. Analytical expressions for surface cracks, provided by Raju and Newman, are used to calculate stress intensity factors for different crack geometries. Furthermore, the rig welded pipe failure probability is estimated by simple application of the Failure Assessment Diagram (FAD) and used together with potential consequences to evaluate the risk level by application of risk matrix. The same logic is employed in the case of cyclic loading, i.e. fatigue crack growth, by using Paris law to calculate crack length depending on the number of cycles. Simple numerical integration is applied to take into account the change of the geometry parameter Y due to increasing depth of a surface crack

Assessment of the integrity of welded pipes

Predmet rada je analiza integriteta zavarenih cevi izrađenih od čelika API J55 visokofrekventnim kontaktnim zavarivanjem (VF). Eksperimentalna ispitivanja mehaničkih osobina osnovnog materijala su izvršena na cevima povučenim iz ekspolatacije posle 70 000 sati rada. Uticaj oštećenja tipa površinske prsline na integritet cevi ispitan je hidrostatičkim pritiskom cevi sa aksijalnom površinskom prslinom u osnovnom materijalu. Ponašanje pri lomu je ispitivano korištenjem modifikovanih kompaktnih epruveta za zatezanje (CT), s početnom prslinom u osnovnom materijalu, zavarenom spoju i zoni uticaja toplote (ZUT). Kritična vrednost faktora intenziteta napona KIc određena je na osnovu kritične vrednosti J integrala JIc. Osim eksperimentalnog istraživanja, na osnovu dobijenih vrednosti za Kr i Sr primenom dijagrama analize loma (FAD) izvršena je procena integriteta zavarenih cevi sa aksijalnom površinskom prslinom na spoljašnjoj površini.The subject of the paper is analysis of the integrity of welded pipes made of API J55 steel by high frequency contact welding (HF). Experimental research on the mechanical properties of the base material was conducted on pipes withdrawn from exploatation after 70 000 hours at service. Defect influence of the surface crack on the integrity of pipes was tested using hydrostatic pressure of pipes with axial surface crack in the base material. Fracture behaviour was tested using modified compact specimen (CT), with the initial crack in the base material, welded joint and heat affected zone (HAZ). Critical value of the tensile strength factors KIc was determined based on the critical value J of the integral JIc. Apart from the experimental research, based on the derived values of Kr and Sr and by applying fracture analysis diagram (FAD) an assessment of the integrity of welded pipes with axial surface crack on the outer surface area was conducted

Determination of damage and repair methodology for the runner manhole of Kaplan turbine at the hydro power plant 'Djerdap 1'

Results of non-destructive testing of the Kaplan turbine runner manhole welded structure are presented, on the basis of which the repair methodology is defined. During repair, the welding technology for elements of the manhole is modified along with the proposal given for the modification of its structural design, because the finite element method calculation proved that the rectangular welded structure of the manhole was significantly better than round welded structure when it comes to integrity and service life

Determination of damage and repair methodology for the runner manhole of Kaplan turbine at the hydro power plant 'Djerdap 1'

Results of non-destructive testing of the Kaplan turbine runner manhole welded structure are presented, on the basis of which the repair methodology is defined. During repair, the welding technology for elements of the manhole is modified along with the proposal given for the modification of its structural design, because the finite element method calculation proved that the rectangular welded structure of the manhole was significantly better than round welded structure when it comes to integrity and service life

Damage Level Estimate of API J55 Steel for Welded Seam Casing Pipes

The subject of this paper is investigation of the damage level of API J55 steel, used for manufacturing casing pipes by high frequency (HF) contact welding. The analysed pipe was withdrawn after about 70 000 hours of service in an oil drilling rig. Experimental analysis included determining the mechanical properties of the base material and welded joint, in particular the tensile and impact toughness testing. Fracture behaviour is examined by testing the modified compact tension (CT) specimens machined with a pre-crack in the base metal, weld metal and heat affected zone (HAZ). The critical value of the stress intensity factor KIc is determined using the critical value of the J integral JIc. Fatigue crack growth rate and fatigue threshold stress intensity factor range are determined by three point bending tests of the Charpy specimens with a V-notch. The investigation conducted on specimens cut from the exploited pipe and the new pipe of the same grade revealed that material properties were not seriously altered during the analysed period of service

Regenerating the NC code in order to improve the surface quality

U okviru ovog rada prikazani su rezultati ispitivanja utjecaja promjenljivih parametara obrade: koraka i broja okretaja na površinsku hrapavost legure aluminija 6005A-T6, pri CNC istosmjernoj i suprotnosmjernoj obradi glodanjem s alatima različitih dimenzija i od različitih materijala (Ø6 HSS, Ø6 VHM i Ø10 VHM). Navedene su karakteristike i klasifikacija aluminijuskih legura. Dana je definicija hrapavosti površine kod završnog glodanja (end milling) i navedeni parametri koji na nju utječu. Zaključeno je da je korak najutjecajniji parametar na hrapavost, dok je najmanja hrapavost postignuta glodanjem (up milling). Jednadžbe korelacije dale su dobro predviđanje površinske hrapavosti u slučaju obrade VHM glodalom Ø10. Rezultati eksperimenta poslužit će kao ulaz u model za upravljanje ulaznim parametrima procesa obrade putem regeneriranja NC koda u cilju poboljšanja kvalitete obrađene površine.The paper presents the research results of the impact of variable machining parameters: feed and spindle speed on surface roughness of Aluminium alloy 6005-T6, at CNC in the up and down milling with tools of different dimensions and different materials (Ø6 HSS, Ø6 VHM and Ø10 VHM). The properties and classification of Aluminium alloys are cited. The definition of surface roughness at end milling is given and parameters that affect it are specified. It was concluded that the feed is the parameter that has the most influence on surface roughens, while the lowest roughness is achieved by up milling. Correlation equations have provided good prediction of surface roughness in the case of machining of VHM by cutter Ø10. The results of the experiment will serve as an input into the model for control of input parameters of the machining process by regeneration of NC code for the purpose of quality improvement of machined surface

Evaluation of Agricultural Machinery Using Multi-Criteria Analysis Methods

To achieve the highest possible agricultural production, it is necessary to procure the appropriate agricultural machinery. A tractor is the most useful machine in agriculture that performs various functions. Therefore, the selection of a tractor is one of the key decisions in the agriculture production process. This study aims to evaluate heavy tractors for agricultural production in Bosnia and Herzegovina. Since this is a selection between different tractors, which are evaluated using several criteria, the methods of multi-criteria analysis (MCDA) were used in this study. Five different methods were used to determine the weight of the criteria, of which a modified standard-deviation method is a new method used in practice, while the tractor ranking was performed using the CRADIS (compromise ranking of alternatives from distance to ideal solution) method. The results showed that the best-ranked tractor is A4, while the most deviations from the ranking occur when the entropy method is used. The contribution of this study is in the systematization of the methods for the objective determination of the criteria weights and the development of new methods to facilitate decision-making in agriculture and other industries

Structural life assessment of oil rig pipes made of API J55 steel by high frequency welding

Predmet rada je analiza integriteta i procjena preostalog vijeka zaštitnih zavarenih cijevi izrađenih od čelika API J55 visokofrekventnim kontaktnim zavarivanjem (VF). Eksperimentalna ispitivanja mehaničkih svojstava osnovnog materijala i ispitivanja na zamor izvršena su na cijevima povučenim iz naftne bušotine nakon 70 000 sati rada. Ispitivanje brzine rasta zamorne pukotine da/dN i opsega faktora intenzivnosti naprezanja na pragu zamora, ∆Kth, izvedeno je na standardnim Charpy epruvetama sa zarezom. Broj ciklusa do loma je izračunat na osnovi početne i krajnje kritične duljine pukotine. Na osnovi broja ciklusa do loma i broja ciklusa opterećenja određen je preostali vijek cijevi s vanjskom aksijalnom površinskom pukotinom. Pokazano je da je preostali vijek osjetljiviji na promjenu opsega opterećenja nego na početnu dubinu pukotine.Structural life of welded pipes made of API J55 steel by high-frequency (HF) welding has been evaluated. Experimental tests of base metal mechanical properties, including fatigue properties, were conducted on pipes after 70 000 hours of service in an oil drilling rig. The fatigue crack growth rate and fatigue threshold is obtained using the pre-cracked Charpy specimens. The number of cycles to the final fracture is then calculated using initial and critical crack depths. Based on the number of cycles to the final fracture and the remaining fatigue lifetime of pipes with axial outer surface crack are determined. It was shown that the remaining fatigue lifetime is more sensitive to the changes in the stress range than to the initial crack depth

Prediction of Laser Formed Shaped Surface Characteristics Using Computational Intelligence Techniques

The main purpose of this study was to establish a prediction model for parameters of shaped surface based on laser forming process. Shape modelling from a flat sheet by lasers forming process needs numerous irradiations along surface paths with different heating parameters. Since the prediction of the parameters of shape modelling could be very complex task, computational intelligence techniques could be used for the prediction process. In this article support vector regression (SVR) was applied for the shaped surface parameters prediction. The SVR model was compared with other computational intelligence models like artificial neural network (ANN) and genetic programming (GP) techniques as benchmark models. Laser power, laser scan speed and spot diameter were used as inputs. The crucial aim of the study was to predict favourable and unfavourable shape forms according to the machining parameters. By the way one should make optimal machining conditions in order to avoid unfavourable shape forms. Based on the results, SVR model outperformed ANN and GP models for the shaped surface parameters prediction