Alfred E. Crouch

Conformable Eddy Current Array for Mapping External Pipeline Corrosion

In a new project sponsored by the U.S. Department of Energy’s National Energy Technology Laboratory, feasibility is being determined for a convenient, affordable method to map corrosion on the outside surface of pipelines. The goal of the project is a system that can produce a contour map of a corroded area and be easily deployed in the field by pipeline maintenance personnel. The collected data will support assessment algorithms such as B31G and RSTRENG (Remaining Strength), which rely on three-dimensional corrosion sizing. The array will be made up of multiple eddy current sensors, scanned electronically to collect data that represent local wall-loss measurements. The work is being performed at Southwest Research Institute and is building upon the results of an earlier project concerned with graphitic corrosion in cast iron pipe. Technical assistance is being provided by Clock Spring Company, who is cofunding the project and planning to commercialize the system if it proves feasible. This paper presents the basic measuring technology, results of laboratory testing of breadboard coils and a description of the proposed field operating procedure.Copyright

REALTIME MONITORING OF PIPELINES FOR THIRD-PARTY CONTACT

Third-party contact with pipelines (typically caused by contact with a digging or drilling device) can result in mechanical damage to the pipe, in addition to coating damage that can initiate corrosion. Because this type of damage often goes unreported and can lead to eventual catastrophic failure of the pipe, a reliable, cost-effective method is needed for monitoring and reporting third-party contact events. The impressed alternating cycle current (IACC) pipeline monitoring method consists of impressing electrical signals on the pipe by generating a time-varying voltage between the pipe and the soil at periodic locations where pipeline access is available. The signal voltage between the pipe and ground is monitored continuously at receiving stations located some distance away. Third-party contact to the pipe that breaks through the coating changes the signal received at the receiving stations. In this project, the IACC monitoring method is being developed, tested, and demonstrated. Work performed to date includes (1) a technology assessment, (2) development of an IACC model to predict performance and assist with selection of signal operating parameters, (3) investigation of potential interactions with cathodic protection systems, and (4) experimental measurements on operating pipelines. Based on information recently found in published studies, it is believed that the operation of IACC on a pipeline will cause no interference with CP systems. Initial results on operating pipelines showed that IACC signals could be successfully propagated over a distance of 3.5 miles, and that simulated contact can be detected up to a distance of 1.4 miles, depending on the pipeline and soil conditions.

IN-LINE STRESS MEASUREMENT BY THE CONTINUOUS BARKHAUSEN METHOD

This paper describes a novel concept for measuring pipe wall stress. Southwest Research Institute® (SwRI® ) pioneered the use of the Barkhausen effect for stress measurement in the 1960s, and the method is still in use today. University researchers in Canada are using the technique for determining stress magnitude and direction by making measurements at quite high resolution. Their technique, which follows from the early SwRI work, requires an alternating magnetic excitation field and an inductive sensor that responds to the Barkhausen magnetic transitions. In contrast, the Continuous Barkhausen concept does not require an alternating excitation field, relying instead on the field transition already present as a magnetic flux leakage (MFL) pig moves through a pipeline. All MFL pigs in use today create Barkhausen noise as they move through the pipeline. The only requirement for using those signals to reveal information about the pipe is to provide suitable sensors and amplifiers to develop a data interpretation procedure. This paper reports on work sponsored by the U.S. Department of Transportation in which SwRI and their commercializing partner, H. ROSEN Engineering, performed laboratory and pull-test experiments to validate the technique using MFL pig hardware in a test line having artificially induced stress anomalies. Details of the technique, laboratory experimental results, and pull-test results are presented, along with recommendations for the application of the method to operating pipelines.Copyright

Nonlinear Harmonic Monitoring of Gouged Dents in Pipeline Specimens Under Cyclic Loading

The only in-line inspection technology commercially available for quantitative evaluation of gouged dents is the geometry pig which cannot discriminate between gouged and smooth dents and has no sensitivity to re-rounded dents. Southwest Research Institute® (SwRI®), has been funded by the US Pipeline and Hazardous Materials Safety Administration (PHMSA) and the Gas Research Institute (GRI) through the Pipeline Research Council International (PRCI), to determine the capability of the nonlinear harmonic (NLH) method to characterize the severity of gouged dents, including those that have been re-rounded by internal pressure. This paper describes the NLH method and presents a summary of results from previous work involving burst tests of gouged dents in 24” pipe as a precursor to the current work that involves experiments with four pressure chambers made from 12-inch line pipe under cyclic pressure changes. In each case, internal scanner hardware, driven from outside the pipe, deployed NLH probes against the pipe inner surface, the gouges being on the outer surface. Analysis of the mapped NLH signals on the inner pipe surface revealed residual strain patterns in the pipe and the strain anomalies produced by gouging. The strain anomalies clearly indicated the presence of the gouges on the outside surface, even when they had re-rounded. The signal maps also indicated the length and width of the gouges whereas the signal strength indicated the residual depth. Data are presented showing that the NLH method is capable of ranking the severity of pipeline gouged dents and their propensity for failure under cyclic loading.© 2006 ASME

DEFECT ASSESSMENT USING CONFORMABLE ARRAY DATA

This report covers the design and fabrication of a conformable eddy current array useful for the mapping and measurement of external corrosion on a transmission pipeline. The feasibility of the basic measuring approach was demonstrated and the general guidelines for sensor design were disclosed in a previous project. This project was concerned with design of a practical array, development of interface electronics, and design of the operation and analysis software. A prototype system was constructed, checked out, and demonstrated on natural corrosion in a field environment.

Using MFL Corrosion Signals to Determine Biaxial Stress in Operating Pipelines

Previous work has shown that a corrosion assessment more accurate than B31.G or RSTRENG can be made if pipeline stresses are considered. A shell analysis can be carried out if both the corrosion profile and local pipe wall stresses are known. The corrosion profile can be approximated from analysis of magnetic flux leakage (MFL) signals acquired by an inline inspection tool (smart pig), but a measure of pipe wall stress has not been available. Approximations have been made based on pipe curvature, but a more direct measurement is desirable.Recent work has produced data that show a correlation between multi-level MFL signals from metal-loss defects and the stress in the pipe wall at the defect location. This paper presents the results of MFL scans of simulated corrosion defects in pipe specimens subjected to simultaneous internal pressure and four-point bending. MFL data were acquired at two different magnetic excitations using an internal scanner. The scanner’s sensor array measured axial, radial and circumferential magnetic flux components on the inner pipe surface adjacent to the defect. Comparison of the signals at high and low magnetization yields an estimate of the difference between axial and hoop stresses. If internal pressure is known, the hoop component can be determined, leaving data proportional to axial stress.Copyright