Pipe Wall Thinning Research Articles

Experimental Evaluation of Novel Hybrid Microwave/Ultrasonic Technique to Locate and Characterize Pipe Wall Thinning

Research using microwaves (MWs) to detect pipe wall thinning (PWT) distinguishes the presence of wall thinning, but does not accurately locate the discontinuities. Ultrasonic testing (UT) is capable of accurately locating the PWT defect, but cannot do so without time-consuming linear scanning. This novel work combines the MW technique as a way to predict the location of a series of PWT specimens, and the UT technique as a way to characterize the PWT specimens in terms of location, depth, and profile shape. The UT probe is guided to the predicted location derived from the Phase One MW results, generating the Phase Two results to determine accurate location, depth measurement, and profile shape detection. The work uses the previously successful experimental setup for testing of an aluminum pipe with 154.051 mm inner diameter (ID) and 1 m length. A vector network analyzer (VNA) generates a MW sweeping frequency range of 1.4–2.3 GHz. This signal is propagated within reference pipes with both open end and short-circuit configurations for calibration of the system. The calibrated system is used to detect the presence and location of six PWT specimens, with two profile shapes, at three depths of thinning and three locations along the pipe. The predicted locations from Phase One are then used to guide a calibrated, manually guided straight beam UT probe to the predicted position. From that point, the UT probe is used in order to accurately localize and determine the depth and shape profile of the specimens.

Mathematical modeling of orifice downstream flow under flow-accelerated corrosion

The main objective of this paper is to establish an analytical model to evaluate the rate of corrosion in a horizontal pipe downstream of an orifice under flow-accelerated corrosion (FAC). FAC is a major issue causing the wall thinning of carbon steel piping in power plants. In this work, the dimensional analysis was employed using the method of repeating variables and the Buckingham Pi Theorem. It was found that the Sherwood number and the relative distance from orifice are the main dimensionless parameters influencing FAC downstream of an orifice. Concerning the available experimental data, two different cases considered; orifice ratio (OR) of 0.25 and 0.5. The result of mathematical modeling agreed with the experimental data. The maximum value of the FAC rate could be well-predicted for the OR of 0.25, while the location of the maximum FAC rate could be well predicted for the OR of 0.5. It was found that the maximum value of FAC rate increases with decreasing orifice ratio and also the maximum value will be located between 1 and 4dp downstream of the orifice in both cases. This work could be useful for professionals in industry and researchers in the field and could be the starting point for a new way of evaluating the FAC rate downstream of a flow’s singularity.

A flexible film type EMAT for inspection of small diameter pipe

Pipe structures are widely applied in industries, and different kinds of defects may occur in the structures during their long-time service. For non-destructive testing of defects in pipes of small diameter, it has to be conducted from the inner side of the pipe when there is no space for detection from the outside or the geometry of the outside tube surface is too complicated. In this work, a flexible film type Electromagnetic acoustic transducer (EMAT) probe with a dual coil configuration is developed. The new probe is flexible and can be inserted into the pipe for inspection. First, the feasibility of the new probe was studied through numerical simulation. Then the feasibility of the proposed flexible EMAT for detection of wall thinning in small diameter pipe was verified experimentally. It was found that the new EMAT method is suitable for the detection of wall thinning defects for small pipes.

A Feasibility Study of Noncontact Ultrasonic Sensor for Nuclear Power Plant Inspection

A pipe-wall thinning measurement is a key inspection to ensure the integrity of the piping system in nuclear power plants. To monitor the integrity of the piping system, a number of ultrasonic thickness measurements are manually performed during the outage of the nuclear power plant. Since most of the pipes are covered with an insulator, removing the insulator is necessary for the ultrasonic thickness measurement. Noncontact ultrasonic sensors enable ultrasonic thickness inspection without removing the insulator. This leads to reduction of the inspection time and reduced radiation exposure of the inspector. The inductively-coupled transducer system (ICTS) is a noncontact ultrasonic sensor system which uses electromagnetic induction between coils to drive an installed transducer. In this study, we investigated the applicability of an innovative ICTS developed at the University of Bristol to nuclear power plant inspection, particularly pipe-wall thinning inspection. The following experiments were performed using ICTS: thickness measurement performance, the effect of the coil separation, the effect of the insulator, the effect of different inspection materials, the radiation tolerance, and the measurement accuracy of wastage defects. These initial experimental results showed that the ICTS has the possibility to enable wall-thinning inspection in nuclear power plants without removing the insulator. Future work will address the issue of measuring wall-thinning in more complex pipework geometries and at elevated temperatures.

원주 방향 두께가 불균일한 배관의 진동 모드 특성을 이용한 배관 감육 검사 기법 연구

현재의 초음파 두께 측정에 기반한 배관 감육 검사 속도를 개선하기 위해 배관 쉘 진동 모드의 고유 진동수 변화를 이용한 감육 검사 기법을 제안하였다. 감육이 발생한 부위의 축방향 수직 단면의 두께는 원주 방향을 따라 불균일하게 변화하는데, 두께가 균일한 경우에 비해 쉘 모드의 고유 진동수가 감소하거나 두 개 이상으로 분기됨을 확인하였다. 배관의 고유 진동수는 한 번의 측정으로도 평가할 수 있으므로, 제안한 방법을 이용하면 축방향 수직 단면의 평균 두께 변화를 빠르게 확인할 수 있어 초음파 두께 측정 방식에 비해 신속한 감육 검사가 가능하다. 본 논문에서는 제안 기법의 원리를 설명하고, 2차원과 3차원 감육 배관 모델 및 시편을 이용한 전산 해석과 실험을 통해 제안한 기법의 적용성을 검증하였다. This work proposes an alternative pipe wall-thinning inspection method based on change of eigenfrequencies of shell vibration modes in wall-thinned pipes. It takes much time to detect wall-thinning of pipes using ultrasonic thickness gauge and only a limited number of pipes are under regular inspection. In a pipe with locally decreased thickness, stiffness varies along circumferential direction and natural frequencies of shell vibration modes of the pipe change or frequencies of same modes bifurcate into two different values. Therefore, one can monitor pipe wall-thinning by measuring change of natural frequencies or estimate wall-thinning shape qualitatively. The feasibility of the proposed method was studied by FE vibration analysis for wall-thinned pipes. Modal testing was also carried out for the pipes with artificial wall-thinned section to verify the working performance of the suggested technique.

Failure analysis and erosion prediction of tee junction in fracturing operation

Erosion wear in piping is an unavoidable degradation process in the oil and gas industry that causes pipe wall thinning and leads to economic losses and potentially produce personal injuries. The mechanism of pipe erosion remains poorly understood. This study focused on predicting the erosion of a tee junction (T) under various flow types during fracturing operation. The failure analysis of tee junction was determined from its macroscopic features and scanning electron microscope (SEM) images and allowed definition of the failure mode and failure mechanism were defined, which appeared to be significantly different from what has been considered to be traditional. The failure analysis and fluid mechanics theory were used to build a computational fluid dynamics (CFD) simulation method to predict the erosion of the tee junction. The model of two-phase flow in a tee junction indicated that the solid-phase flow is determined by combined effects of the main tube flow, the flow inertia, and the turbulent flow. The distribution of the erosion in the tee was significantly different for various flow types and the simulation results were consistent with the results of the failure analysis. This model of predicted local distribution of erosion wear can assist the monitoring of pipe walls to prevent accidents and reduce maintenance labor.

Impedance Based Health Monitoring Technique with Probabilistic Neural Network for Possible Wall Thinning Detection of Metal Structures

Corrosion of structures and wall thinning of pipes can severely affect the mechanical strength as wall thickness is reduced. Thus a cost effective structural health monitoring technique plays an important role when managing a structure. The electromechanical impedance (EMI) method is a local method that has limited sensing range, resulting in a high cost when covering large areas. In this study, a reattachable EMI method is investigated using a stack of multiple metal plates to conduct an experiment involving thickness reduction. In addition, the main problem of the impedance signatures changing subjected to reattaching the piezoelectric transducer is solved by using the probabilistic neural network algorithm presented for the study. The proposed approach successfully identifies the thickness of two different structures with high accuracy.

Thinning pipe wall detection using coupled oscillation between cylindrical shell and attached sub-structure.

In this paper, we discussed the thinning pipe wall detection using coupled oscillation between cylindrical shell and attached sub-strcture. At first, the resonance frequencies of the in-plane bending deformation mode are compared between numerical and analytical model. Thereby, it is confirmed that the resonance frequency is changed at the pipe wall thinning by both models. The dependency of sensitivity of the resonance frequency to the mass of the attached sub-structure is evaluated.

Influence of Measurement Noise on Nondestructive Identification of Location and Thickness of Pipe Wall Thinning by Inverse Analysis of Electromagnetic Field

Influence of Measurement Noise on Nondestructive Identification of Location and Thickness of Pipe Wall Thinning by Inverse Analysis of Electromagnetic Field

配管減肉管理規格に対する予測手法導入に関する検討

In JSME, research committee for the improvement of pipe wall thinning management had been held for 6 years in three phases since FY2008. In this committee, research and surveillance have been conducted on concerned technical area. Succeedingly, the 4th phase started from FY2015 and under this committee, new working group called “Management Rule Revision WG” was set up to review practical application and standardization of the developed relevant technique, especially prediction method. In this WG, implementation of prediction method to the management rule is mainly being discussed. So far in its activities, concept of adding new “Chapter D” providing option of utilizing prediction method to PWR/BWR technical rule has been proposed.

磁気センサを用いた配管減肉部の位置および肉厚の非破壊同定法の検証実験

磁気センサを用いた配管減肉部の位置および肉厚の非破壊同定法の検証実験

実験モード解析によるステンレス配管の一様減肉の非破壊評価

In this study, experimental modal analysis system for evaluating modal characteristics of piping has been constructed by combining experimental setup and MATLAB programming. The experimental setup could monitor piping vibration produced by hammering. The MATLAB programming could identify such modal characteristics as natural frequency and modal damping ratio from the vibration data obtained by the experimental setup. The constructed experimental modal analysis system was applied to stainless steel pipes with different wall thickness, and the modal characteristics available for the evaluation of uniform wall thinning of the pipes were discussed by comparing the relationship between the pipe wall thickness and the modal characteristics. It was found that the modal damping ratio of mode 1 was promising parameter for the evaluation of the pipe wall thinning.

Numerical study on non-axisymmetric wall thinning in pipelines with swirling flow

In order to understand the mechanisms of non-axisymmetric pipe-wall thinning in the Mihama nuclear power plant accident of 2004, a numerical simulation of pipe-wall thinning in an elbow-orifice pipeline with swirling flow was carried out based on mass and momentum transfer equations with a standard k-ε model of turbulence at a Reynolds number of 5.8×106. The pipe-wall thinning was evaluated on the basis of the mass transfer coefficient using the diffusion coefficient of ferrous iron in bulk water flow. The numerical simulation revealed that swirling flow with a certain level of swirl intensity generates a spiral motion downstream of the elbow and sustains a longer distance than expected from an elbow flow without swirl. This type of non-axisymmetrical flow triggers strongly biased flow at the orifice, which results in non-axisymmetric pipe-wall thinning downstream of the orifice.

원전 2차계통수 모사 환경에서 용접배관 감육 특성에 미치는 재료 및 유속의 영향

The pipelines and equipments are degraded by flow-accelerated corrosion (FAC), and a large-scale test facility was constructed for simulate the FAC phenomena in secondary coolant environment of PWR type nuclear power plants. Using this facility, FAC test was performed on weld pipe (carbon steel and low alloy steel) at the conditions of high velocity flow (> 10 m/s). Wall thickness was measured by high temperature ultrasonic monitoring systems (four-channel buffer rod type and waveguide type) during test period and room temperature manual ultrasonic method before and after test period. This work deals with the complex effects of flow velocity on the wall thinning in weld pipe and the test results showed that the higher flow velocity induced different increasement of wall thinning rate for the carbon steel and low alloy steel pipe.

Cause Analysis of Flow Accelerated Corrosion and Erosion-Corrosion Cases in Korea Nuclear Power Plants

Significant piping wall thinning caused by Flow-Accelerated Corrosion (FAC) and Erosion Corrosion (EC) continues to occur, even after the Mihama Power Station unit 3 secondary pipe rupture in 2004, in which workers were seriously injured or died. Nuclear power plants in many countries have experienced FAC and EC-related cases in steam cycle piping systems. Korea has also experienced piping wall thinning cases including thinning in the downstream straight pipe of a check valve in a feedwater pump line, the downstream elbow of a control valve in a feedwater flow control line, and failure of the straight pipe downstream of an orifice in an auxiliary steam return line. Cause analyses were performed by reviewing thickness data using Ultrasonic Techniques (UT) and, Scanning Electron Microscope (SEM) images for the failed pipe, and numerical simulation results for FAC and EC cases in Korea Nuclear Power Plants. It was concluded that the main cause of wall thinning for the downstream pipe of a check valve is FAC caused by water vortex flow due to the internal flow shape of a check valve, the main cause of wall thinning for the downstream elbow of a control valve is FAC caused by a thickness difference with the upstream pipe, and the main cause of wall thinning for the downstream pipe of an orifice is FAC and EC caused by liquid droplets and vortex flow. In order to investigate more cases, additional analyses were performed with the review of a lot of thickness data for inspected pipes. The results showed that pipe wall thinning was also affected by the operating condition of upstream equipment. Management of FAC and EC based on these cases will focus on the downstream piping of abnormal or unusual operated equipment.

Thin-Plate-Type Embedded Ultrasonic Transducer Based on Magnetostriction for the Thickness Monitoring of the Secondary Piping System of a Nuclear Power Plant

Pipe wall thinning in the secondary piping system of a nuclear power plant is currently a major problem that typically affects the safety and reliability of the nuclear power plant directly. Regular in-service inspections are carried out to manage the piping system only during the overhaul. Online thickness monitoring is necessary to avoid abrupt breakage due to wall thinning. To this end, a transducer that can withstand a high-temperature environment and should be installed under the insulation layer. We propose a thin plate type of embedded ultrasonic transducer based on magnetostriction. The transducer was designed and fabricated to measure the thickness of a pipe under a high-temperature condition. A number of experimental results confirmed the validity of the present transducer.

Influence of intermittent flow sub-patterns on erosion-corrosion in horizontal pipe

Thinning of pipe wall due to erosion and corrosion has resulted in many catastrophic failures and huge economic losses in petroleum refineries (Wood et al., 2013) and nuclear power stations (Ahmed, 2012). The intermittent structure of two-phase flow through pipe (intermittent flow regime) is an important factor responsible for such erosion and corrosion. The present research is an effort to develop a regime map showing possible erosion and corrosion phenomena due to intermittent flows in pipe. In this direction, flow visualization experiments are carried out for three distinct sub-regimes of intermittent flow namely, plug flow with or without bubble rim, less aerated slug flow and highly aerated slug flow. Images captured at a rate of 1600 frames per second at 288 diameter downstream of inlet are utilised for analysing the dynamics of intermittent flow structure in terms of expansion, contraction, breaking, coalescence, collapse, and collision of bubbles. Quantitative measurements of intermittent flow characteristics (including plug/slug frequency, plug/slug velocity and length of liquid plug/slug) and their influence on erosion-corrosion phenomena in the pipe are reported in detail. Based on these qualitative and quantitative analysis, a regime map for prediction of erosion-corrosion phenomena in pipes is established as a function of inlet flow conditions for both the phases. Transition boundaries for four distinct erosion-corrosion phenomena: shear stress induced erosion, cavitation erosion, liquid impact induced erosion and flow accelerated corrosion are represented in the map and eight distinct regimes of erosion-corrosion are illustrated. The regime map is represented in terms of non-dimensional superficial Reynolds numbers of both the phases to account for pipe diameter, flow rate and fluid viscosity. This erosion-corrosion regime map developed in this research will immensely aid to the effective design of piping systems and optimization of operating conditions for safer operation of petroleum refineries and nuclear power stations.

Pressurized line pipe wall thinning detection using a distributed fiber-optic sensing system

Wall thinning defects in steel pipes are usually localized and are difficult to detect using traditional sensors that have a small coverage and limited measuring range. A distributed fiber sensor, based on the Brillouin backscattering sensing system, has been demonstrated to be able to measure the strain and detect the defect in a pipe accurately. A 1.8 m pipe segment that contains artificial thinning from 13 to 60% of wall thickness at various positions was subjected to an internal pressure of 350 kgf/cm2. Hoop strain distribution along the whole pipe segment was monitored by a single optical fiber. The measured strains compared favorably with strain gauge results. The method proposed in this study shows promising results for the detection of the existence and location of wall thinning defects in long distance pressurized pipe.

Detection of Corrosion and Wall Thinning in Carbon Steel Pipe Covered With Insulation Using Pulsed Eddy Current

Non Destructive Testing (NDT) methods that are capable of detecting the wall thinning and defects through insulation and cladding sheets are necessary. In this study we developed a Pulsed Eddy Current (PEC) system to detect wall thinning of ferro magnetic steel pipes covered with 95 ㎜ thick fiber glass thermal insulator and shielded with aluminum plate of thickness 0.4 ㎜. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and a search coil sensor were used as a detecting element. In both the cases, the experimental data indicates a considerable change in the detected pulse corresponding to the change in sample thickness. The thickness of the tube was made to change such as 2.5 ㎜, 5 ㎜ and 8 ㎜ from the inner surface to simulate wall thinning. Fast Fourier Transform (FFT) was calculated using window approach and the results were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra.

Development of Wall-Thinning Evaluation Procedure for Nuclear Power Plant Piping—Part 1: Quantification of Thickness Measurement Deviation

Pipe wall thinning by flow-accelerated corrosion and various types of erosion is a significant and costly damage phenomenon in secondary piping systems of nuclear power plants (NPPs). Most NPPs have management programs to ensure pipe integrity due to wall thinning that includes periodic measurements for pipe wall thicknesses using nondestructive evaluation techniques. Numerous measurements using ultrasonic tests (UTs; one of the nondestructive evaluation technologies) have been performed during scheduled outages in NPPs. Using the thickness measurement data, wall thinning rates of each component are determined conservatively according to several evaluation methods developed by the United States Electric Power Research Institute. However, little is known about the conservativeness or reliability of the evaluation methods because of a lack of understanding of the measurement error. In this study, quantitative models for UT thickness measurement deviations of nuclear pipes and fittings were developed as the first step for establishing an optimized thinning evaluation procedure considering measurement error. In order to understand the characteristics of UT thickness measurement errors of nuclear pipes and fittings, round robin test results, which were obtained by previous researchers under laboratory conditions, were analyzed. Then, based on a large dataset of actual plant data from four NPPs, a quantitative model for UT thickness measurement deviation is proposed for plant conditions.