Bore Piping Research Articles

Influence of bend geometry on flow accelerated corrosion under neutral pH conditions

Flow accelerated corrosion (FAC) is an unavoidable problem in the integral part of the pipe line systems of Nuclear Power Plants worldwide. This has a significant influence on the thickness loss of the pipe line which affects the operation and maintenance of the plants. During the prolonged operation of the plants, FAC leads to inside wall thinning, rupture and catastrophic failure of the pipeline systems and ultimate shutdown of the reactor system for maintenance. Qualitative coupon based chemical off-line analysis techniques were only followed earlier for the prevention of untoward incidents. With the introduction of ultrasonic nondestructive thickness measurements viz., pre-service, in-service and inspection during shutdowns, the possibility of accidents have been reduced to a maximum extent. However, detailed understanding of FAC and wall thinning of pipes due to different plant operation conditions such as flow velocity, different pH, different temperature and pressure values etc., are not available even today. The present experimental study is aimed to throw light on the parameters that have more impact on FAC. Also it is aimed to identify the vulnerable locations and wall thickness loss along the clock positions. The output of this study will gain currency while dealing with FAC code, and plays a critical role in the establishment of safe and reliable and continuous plant operations. According to existing literature, one of the most important parameters that affect FAC is the piping configuration i.e., geometry of flow path. Hence, the present study is aimed towards the understanding of FAC with respect to the bend angle and bend radius of the carbon steel piping. In this study, carbon steel pipes as per ASTM A106 Gr‘B‘ material with two bend angles viz. 58° and 73° with bend radius 2D and 4D, where D denotes the outer diameter of the pipe, have been chosen. These parameter ranges are available in the existing reactor and hence four different pipe bend specimens have been undertaken. Therefore, the four different pipe specimen holders of ASTM A106 Gr ‘B‘ materials having 15NB (Nominal Bore) pipe bends were designed and fabricated. Under the similar experimental conditions, using the Computational Fluid Dynamics (CFD) studies, the velocity distribution, the wall shear stress and the turbulent kinetic energy were simulated and correlated with the corresponding measured wear rate. Basic parameters like pipe material, bend angle, bend radius, etc. have been used for the simulation studies. Comparison of the simulated flow rate with the experimental values of wall thickness obtained through the ultrasonic measurements indicate that the bend angle and bend radius of the geometry play a crucial role on FAC.

Evaluation for Characteristics of Measured Flow Rate by Clamp-on Type Ultrasonic Flow Meter under Wet Steam in Large Bore Piping

Evaluation for Characteristics of Measured Flow Rate by Clamp-on Type Ultrasonic Flow Meter under Wet Steam in Large Bore Piping

A Study on the Cause Analysis for the Wall Thinning and Leakage in Small Bore Piping Downstream of Orifice

A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed in front of the orifice. This paper deals with UT thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

Experimental and Numerical Evaluation of the Vibration Fatigue of Small Bore Pipe in PWR

The purpose of this paper is to evaluate the vibration of the small bore pipe in nuclear piping under the fatigue loading due to flow fluctuation. The vibration speeds of the pipe-lines were measured to get the effective velocity which is found larger than the allowable value calculated from EDF evaluation method. To perform the piping vibration assessment and construction, the natural shape and the vibration stress at the socket weld position was evaluated by finite element analysis with ABAQUS. From the linear cumulative damage theory, the fatigue life is predicted with the results that lower than the designation level. According to the position of the maximum vibration speed calculated from FEA simulations, the valve is fixed by the rigid support. The natural frequency and the corresponding mode shape are discussed with much lower vibration velocity and vibration stress.

High Level Dynamic Testing and Analytical Correlations for a Small Bore Piping System

High-level dynamic testing of a prototypic insulated small bore diameter pipe system is described. The pipe system was supported by a minimum number of supports, with several combinations of supports and support locations tested. Load input consisted of a dynamic multifrequency time history and sinusoidal loading at increasing acceleration levels until gross deformation of the system occurred. Very high level pipe damping was exhibited when plastic response occurred. Post-test analyses were performed to assess the structural loading and response of the pipe system under the dynamic load input. Several elastic and elasto-plastic analysis failure prediction methods were used, along with simplified inelastic analysis.

Seismic Damping Factors of Small Bore Piping as Influenced by Insulation and Support Elements

Seismic damping tests of a prototypical Liquid Metal Fast Breeder Reactor (LMFBR) small bore piping system is described, and measured transient responses to pulse excitations are reported. The test specimen was representative of a typical LMFBR insulated small bore piping system, and it was supported from a rigid test frame by prototypic dead weight supports, mechanical snubbers, and pipe clamps. Various support configurations were tested to assess the response sensitivity to insulation and other nonlinear support characteristics. Damping factors increased significantly due to the insulation and use of mechanical snubbers. Factors much higher than the magnitudes currently allowed in design by the USNRC Regulatory Guide 1.61, were found. This verified the design values, and it also pointed out the possibility of undue conservatism and costly overdesign resulting from use of the present design values.

Large-Amplitude Pressure Pulse Propagation in Oil Contained in a Narrow Bore Pipe

The velocity and attenuation of sound in an oil contained in a narrow bore thick wall pipe (6.4 mm i.d., 21.4 mm o.d.) have been measured as a function of pressure amplitude. Oscillatory pulses of 15 kc lasting 1 msec were generated with a magnetostrictor. A barium titanate cylinder was used for low level pulses up to 150 kc. Alternatively. pressure step functions were generated by means of an air-driven piston hitting a piston sliding in the oil-filled pipe. Pressure amplitudes were varied by changing the air pressure and the acceleration time of the driving piston. Pressures up to 300 bars having rise times of 20 μsec were obtained readily. Pulses were terminated by limiting the travel of the driven piston either by means of a rigid stop or by the reflection of the pulse from the end of the pipe. Rectangular pulses of 1-msec duration were attenuated 0.6 db/m in oil having a viscosity of 25 centistokes. Velocity increased with pulse amplitude rising from 1365 m/sec to 1400 m/sec for an amplitude increase from 2 to 200 bars. (This research was supported by the International Business Machines Corporation, Endicott, New York.)