Full-scale Pipe Tests Research Articles

The Master S-N Curve Approach to Fatigue of Piping and Vessel Welds

In support of the new revision of ASME Div 2 Codes, a unified master S-N curve approach has been developed using a recently developed mesh-insensitive structural stress procedure. The effectiveness of the new master S-N curve approach has been documented in a number of earlier publications for many joint types and loading conditions, including pipe and vessel welds. In this paper, additional S-N data for pipe and vessel girth welds are analysed using the mesh-insensitive structural stress procedure and the master S-N curve approach. The new data include a large series of full-scale pipe tests for applications in deepwater riser recently completed. A series of full-scale vessel and pipe tests under pressure pulsation have also been analysed. It is particularly worth noting that some of the vessel tests were used to support ASME Sec. III related applications, in which some tests incorporated welds with artificially machined flaws and one test was a stainless steel pipe removed from an actual reactor. Regardless of the drastically different joint geometries and loading modes, an excellent correlation among all the S-N data analysed have been achieved by using the master S-N curve approach. Furthermore, it seems that all these pipe and vessel test results can also be correlated with all plate joint data collected thus far.

원주방향 노치형 감육부를 가진 배관의 손상거동 평가

In order to evaluate a failure behavior of pipe with notch-type wall thinning, the present study performed full-scale pipe tests using the 102mm, Schedule 80 pipe specimen simulated notch- and circular-type thinning defects. The pipe tests were conducted under the conditions of both monotonic and cyclic bending moment at a constant internal pressure of 10 MPa. From the results. of experiment, the failure mode, load carrying capacity, deformation ability, and fatigue life of a notch-type wall thinned pipe were investigated, and they were compared with those of a circular-type wall thinned pipe. The failure mode of notched pipe was similar to that of circular-type thinned pipe under the monotonic bending load. Under the cyclic bending load, however, the mode was clearly distinguished with variation in the shape of wall thinning. The load carrying capacity of a pipe containing notch-type wall thinning was about the same or slightly lower than that of a pipe containing circular-type wall thinning when the thinning area was subjected to tensile stress, whereas it was higher than that of a pipe containing circular-type thinning defect when the thinning area was subjected to compressive stress. On the other hand, the deformation ability and fatigue life of a notch-type wall thinned pipe was lower than those of a circular-type wall thinned pipe.

감육형상 및 내압이 원자력 감육배관의 파단에 미치는 영향 -내압과 굽힘모멘트가 동시에 작용하는 경우-

Failure of a pipeline due to local wall thinning is getting more attention in the nuclear power plant industry.br/ Although guidelines such as ANSI/ ASME B31 G and ASME Code Case N597 are still useful for assessing the integrity of a wall thinned pipeline. there are some limitations in these guidelines. For instance, these guidelines consider only pressure loading and thus neglect bending loading. However, most pipelines in nuclear power plants are subjected to internal pressure and bending moment due to dead-weight loads and seismic loads. Therefore, an assessment procedure for locally wall thinned pipeline subjected to combined loading is needed. In this paper, three-dimensional finite element(FE) analyses were performed to simulate full-scale pipe tests conducted for various shapes of wall thinned area under internal pressure and bending moment. Maximum moments based on true ultimate stress(σｎ,₁) were obtained from FE results to predict the failure of the pipe. These results were compared with test results, which showed good agreement. Additional finite element analyses were performed to investigate the effect of key parameters, such as wall thinned depth, wall thinned angle and wall thinned length; on maximum moment. Also, the effect of internal pressure on maximum moment was investigated. Change of internal pressure did not show significant effect on the maximum moment.br/

Assessment of Local Wall Thinned Pipeline Under Combined Bending and Pressure

Failure of a pipeline due to local wall thinning is getting more attention in the nuclear power plant industry. Although guidelines such as ANSI/ASME B31G are still useful for assessing the integrity of a wall thinned pipeline, there are some limitations in these guidelines. For instance, these guidelines consider only pressure loading and thus neglect bending loading. However, most pipelines in nuclear power plants are subjected to internal pressure and bending moment due to dead-weight loads and seismic loads. Therefore, an assessment procedure for locally wall thinned pipeline subjected to combined loading is needed. In this paper, three-dimensional finite element (FE) analyses were performed to simulate full-scale pipe tests conducted for various shapes of wall thinned area under internal pressure and bending moment. Maximum moments based on true ultimate stress (σu,t) were obtain from FE results to predict the failure of the pipe. These results were compared with test results, which showed good agreement. Additional finite element analyses were performed to investigate the effect of key parameters, such as wall thinned depth, wall thinned angle and wall thinned length, on maximum moment. Also, the effect of internal pressure on maximum moment was investigated. Change of internal pressure did not show significant effect on the maximum moment.

Development of a Piping Integrity Evaluation Simulator Based on the Hardware-in-the-Loop Simulation

In order to verify the analytical methods predicting failure behavior of cracked piping, full-scale pipe tests are crucial in nuclear power plant piping. For this reason, series of international test programs have been conducted. However, full-scale pipe tests require expensive testing equipment and long period of testing time. The objective of this paper is to develop a test system which can economically simulate the full-scale pipe test regarding the integrity evaluation. This system provides the failure behavior of cracked pipe by testing a wide-plate specimen. The system provides the failure behavior of cracked pipe by testing a wide-plate specimen. The system was developed for the integrity evaluation of nuclear piping based on the methodology of hardware-in-the-loop (HiL) simulation. Using this simulator, the piping integrity can be evaluated based on the elastic-plastic behavior of full-scale pipe, and the high cost full-scale pipe test may be replaced with this economical system.

Application of the European flaw assessment procedure SINTAP to pipes

The recently developed European flaw assessment procedure SINTAP is applied to a total of 97 full-scale pipe tests with through-wall and surface cracks subjected to internal pressure and four point bending. Based on the experimental data various analysis levels of SINTAP are discussed with respect to their potential for predicting the failure loads and the margins of conservatism.

J-R Curves From Circumferentially Through-Wall-Cracked Pipe Tests Subjected to Combined Bending and Tension—Part I: Theory and Numerical Simulation

One of the key aspects in leak-before-break analyses is to predict the maximum load-carrying capacity of a circumferentially cracked pipe. Such analyses require the fracture resistance of the material using the J-integral parameter, typically using small-scale laboratory specimens, such as compact tension, C(T), or three-point bend specimens. To evaluate the similitude between the laboratory specimens and a circumferentially through-wall-cracked pipe, the toughness can be evaluated directly from the pipe using an analysis typically called an η-factor approach. The fracture resistance from the pipe tests can then be compared to laboratory specimen toughness values to assess similitude issues. Additionally, several analysis methods (i.e., LBB.NRC, LBB.ENG, LBB.GE, etc.) that predict maximum load capability of through-wall-cracked pipes have η-factor analyses embedded in them. Hence, the evaluation of the J-R curve accuracy or consistency with small-scale specimens is a verification of one step in such predictive analyses. This paper presents extensions to the earlier η-factor solutions for circumferentially through-wall-cracked pipes where the previous analyses were for cracks in pipes under either pure bending or pure tension. The improvements investigated account for loading under combined bending and tension due to internal pressure. The application of these methods to full-scale pipe tests is presented in Part II (Miura and Wilkowski, 1998) of this paper.

J-R Curves From Circumferentially Through-Wall-Cracked Pipe Tests Subjected to Combined Bending and Tension—Part II: Experimental and Analytical Validation

In Part I (Miura and Wilkowski, 1998) of this paper, the theory of the two η-factor solutions for circumferentially through-wall-cracked pipes subjected to combined bending and tension due to internal pressure was presented. These solutions seemed to give reasonable predictions by comparing with the existing simplified J-estimation scheme. It was also ascertained that the J would be underestimated if the effect of the internal pressure was not properly considered. Consequently, this paper presents the application of these solutions to full-scale pipe tests. The tests were performed at 288°C (550°F) under combined bending and internal pressure. The materials used for the tests were both carbon steel and stainless steel. The effect of combined loading on the J-R curves was determined and compared to C(T) specimen J-R curves. The solutions were then verified by using three-dimensional finite element analysis.

Numerical Simulations of Full-Scale Corroded Pipe Tests With Combined Loading

The ANSI/ASME B31G guideline has been useful to pipeline operators in assessing the integrity of corroded line pipe. Because large safety margins have had to be incorporated, the guidelines can be excessively conservative, which in turn can force costly repairs and replacements that may not actually be necessary. On the other hand, because the current guidelines consider only pressure loading and neglect bending and axial compression, they could give nonconservative failure predictions when combined loading exists. Therefore, a study was initiated to develop a theoretically sound methodology for assessing the integrity of corroded line pipe subjected to combined loading. A key step in the successful application of this methodology is the development of a sophisticated three-dimensional finite element procedure that can accurately simulate full-scale pipe tests under conditions of combined loading. This paper describes thirteen full-scale failure tests on artificially corroded pipes subjected to simultaneous internal pressure, bending, and longitudinal compression and presents a detailed account of the finite element analysis procedure that was developed to simulate these tests numerically. Additional finite element analyses that were conducted to investigate the effect of key parameters on failure, and to expand the corroded pipe failure database, are also discussed.

Finite volume method and multigrid acceleration in modelling of rapid crack propagation in full-scale pipe test

Rapid Crack Propagation (RCP) along pressurised plastic pipes is by far the most dangerous pipe failure mode. Despite the economic benefits offered by increasing pipe size and operating pressure, both strategies increase the risk and the potential consequences of RCP. It is therefore extremely important to account for RCP in establishing the safe operational conditions. Combined experimental-numerical study is the only reliable approach of addressing the problem, and extensive research is undertaken by various fracture groups (e.g. Southwest Research Institute --- USA, Imperial College --- UK). This paper presents numerical results from finite volume modelling of full-scale test on medium density polyethylene gas pressurised pipes. The crack speed and pressure profile are prescribed in the analysis. Both steady-state and transient RCPs are considered, and the comparison between the two shown. The steady-state results are efficiently achieved employing a full multigrid acceleration technique, where sets of progressively finer grids are used in V-cycles. Also, the effect of inelastic behaviour of polyethylene on RCP results is demonstrated.

Allowable defect sizes in a sour crude oil pipeline for corrosion fatigue conditions

Abstract A fracture mechanics treatment of corrosion fatigue crack growth rates is used to estimate corrosion fatigue life and allowable defect depths for specified lives of sour crude oil pipelines. The present study is based on a case history of a major Canadian crude oil pipeline that experienced five fatigue failures during its first 10 years of operation. Characteristic pressure fluctuation spectra have been derived from pump stations' pressure records. Fatigue crack growth rates for various crack configurations and orientations, and the effects of environment (crude oil with hydrogen sulphide content from zero to saturation) on these have been measured in the laboratory. Calculated fatigue lives have been verified by full-scale pipe tests pressurized with crude oil containing 100 ppm of hydrogen sulphide, using the characteristic pressure spectrum simulating operating conditions.