Papers by Keyword: Integrity Assessment

Abstract: Corrosion has been the most common type of defects on oil and gas pipelines. For in-service pipelines the corrosion defects are detected through the in-line inspection and evaluated by integrity assessment methods such as ASME B31G. However, the safety factors of these methods have not been carefully studied. In this paper, the Monte Carlo simulation is carried out to estimate the reliability of the corrosion defects of critical sizes with different safety factors. The results show that the reliabilities of the critical defects increase with the increase of the safety factor, but decrease with the increase of the defect length even under the same safety factor. The commonly used safety factor 1.39 can ensure the target reliability is met in the specified case in this paper. But for high consequence cases the selection of safety factor needs further research.

Abstract: Local wall-thinning, which can be found frequently on the surfaces of pipelines, may not only reduce the load-carrying capacities of pipelines, but also cause serious industrial accidents. In this paper, through a large number of computational examples, the effects of axial, circumferential, small area and large area local wall-thinning with different sizes on load-carrying capacities and failure modes of pipelines under both internal pressure and bending moment were investigated and evaluated. By data fitting, an engineering computational formula for plastic limit loads of pipelines with local wall-thinning was presented.

Abstract: The subject of this work is examination of API J55 steel casing pipes manufactured by high frequency (HF) contact welding. Since the pipes were withdrawn after about 70 000 hours of service in an oil drilling rig, the influence of the exploitation conditions on the material properties is determined. Experimental analysis includes tensile, impact toughness and fatigue testing of the specimens cut from the exploited pipe and the new pipe manufactured from the same-grade material. Additionally, pipe with flaws (stress concentrators) is tested by subjecting to internal pressure. The analysed stress concentrators represent defects which are often found in the exploitation: localized corrosion damages (corrosion pits). They were simulated by machining on the external surface of the pipe wall. The behavior of the pipes with these defects is determined by strain measurement and finite element analysis in software package Abaqus. The dimensions of the defects are varied, in order to determine the dependence of load carrying capacity on their depth and length. Several expressions from the literature are applied for estimation of the maximum pressure in damaged pipelines, and the solutions are compared with the predictions of finite element models. Additionally, triaxiality values at the bottom of the defects are compared with those obtained on tensile specimens, having in mind the key role of this parameter in ductile fracture initiation.

Abstract: During the refurbishment of the hydroelectric generating set A6 on HPP Djerdap 1, for the state analysis and assessment of the level and causes of degradation of the structure of the vertical Kaplan turbine runner guide vane apparatus non-destructive tests and inspections, as well as destructive tests of base material and welded joints, have been carried out after 40 years of service. Results of non-destructive tests performed on welded joints are presented in this paper (magnetic particle and ultrasonic inspection), as well as results of destructive tests of the base material and welded joints (testing of tensile properties, impact testing, metallographic analyses of the structure). A large number of crack type line indications were detected by magnetic particle inspections, while the occurrence of partial penetration in roots of welded joints was detected by ultrasonic inspections, as well as lamellar tearing of the base material. Tensile properties of tested samples taken in longitudinal and transverse direction fulfilled the requirements of the standard with certain deviations, which does not stand for samples taken in z-direction with significantly lower values of contraction of the cross-section than minimum prescribed values, which proves that base material is not resistant to the occurrence of lamellar cracks. Metallographic tests performed on specimens taken from the base material in longitudinal and transverse direction showed that the microstructure is stripe-shaped and ferrite-pearlite with non-metallic inclusions of oxide, sulphide, silicate and aluminate type, while metallographic tests performed on specimens taken from welded joints showed that their microstructure is stripe-shaped and ferrite-pearlite with non-metallic inclusions of oxide type. A large number of micro-and macro-cracks were detected in the microstructure as well. Experimental tests enabled the determination of the causes of occurrence of lamellar tearing in base material and crack type defects in welded joints, while analytical calculation that refers to the stress state enabled integrity of welded structure of the upper ring of the turbine runner guide vane apparatus.

Abstract: Recently, the intelligent inspection data of one natural gas transmitting pipeline showed that lots of the blistering was found in the pipe inner surface. In this paper, the method of finite element analysis was carried out to simulate and calculate the effect of blistering to the pipe strength. The results show that the max vonmises stress of the pipe with blistering was close to the yield strength and the max vonmises stress of the pipe increased with the increase of the press in the blistering. The minimum safety factor in the pipe with blistering was 0.99 which was reduced by the blistering. The sulfide stress corrosion (SSCC) and the manufacturing technology of hot rolling compound accelerated the growth of the blistering in the pipe.

Abstract: In the present paper, integrity assessment is made to the defects in weld metal zone of pressure piping of X52 steel using the two basic routes, FAD and CDF, which are provided in the European flaw assessment procedure SINTAP. Based on the experimental data various analysis levels of SINTAP are discussed, including the uncommonly used J-integral level in particular. Furthermore, to meet the need of the reliability assessment of pressure piping containing defects in engineering applications, probabilistic procedures are employed to obtain several probability curves with given survivability on the J-integral level with respect to the great scatter of the tested fracture toughness which is required in the J-integral level analysis.

Abstract: The integrity assessment method for beam-like structures using continuous wavelet transform (CWT) is proposed. CWT is applied to the response acceleration of a structure to decompose the response acceleration correspond to each scale. The curvature difference of the normalized energy for each member caused by structural degradation clearly indicated the location of damaged members in the structure. It is shown that the proposed method can identify damaged members without performing complicated dynamic analyses which usually require significant effort and time.

Abstract: The integrity of major components in nuclear power plant should be maintained during operation. In order to maintain the integrity of these components, complicated assessment procedures are required including fracture mechanics analysis, etc. The integrity assessment of components has been performed by using conventional deterministic approaches whilst there are lots of uncertainties to carry out a rational evaluation. In this respect, probabilistic integrity assessment is considered as an alternative method for nuclear component evaluation. The objectives of this paper are to develop an integrity assessment system based on probabilistic fracture mechanics and to estimate the failure probability of major nuclear components containing a defect. The integrity assessment system consists of three evaluation modules which are first order reliability method, second order reliability method and crude Monte Carlo simulation method. The developed system has been applied to evaluate failure probabilities of nuclear structural components such as steam generator tube and piping. The evaluation results showed a promising applicability of the probabilistic integrity assessment system.

Abstract: Y-branch is often used in connection between a main pipe and two branch pipes, for example, in furnace, quench boiler, nuclear parts and so on. The stress distribution in the Y-branch is very complicated because of complicated shape and complex loads on it. The stresses in the Y-branches cannot be determined by theoretical equations. Finite element method is used to analyze the stresses in the Y-branches. As an example, a Y-branch used in a high temperature furnace is calculated with ANSYS software. The temperature distribution and elastic and elastic-plastic stress fields in the Y-branch under mechanical and thermal loads are calculated. Strength, creep and fatigue of the Y-branch are evaluated based on T-1300, T-1400 of ASME Boiler and Pressure Vessel code Sec Ⅲ Div 1 Subsection NH.