scholarly journals Coating Integrity Survey Using DC Voltage Gradient Technique at Korea Gas Corporation

1996 ◽  
Author(s):  
Y. B. Cho ◽  
K. W. Park ◽  
K. S. Jeon ◽  
H. S. Song ◽  
D. S. Won ◽  
...  
Keyword(s):  
Cathodic Polarization ◽  
Field Survey ◽  
Gradient Methods ◽  
Field Method ◽  
Voltage Gradient ◽  
Dc Voltage ◽  
Field Techniques ◽  
Close Interval ◽  
Gradient Technique ◽  
Coating Defect

The reliablity and applicability of various coating defect detecting techniques are investigated utilizing mock pipe. It is shown that both close interval potential survey and dc voltage gradient methods are impertinent as field techniques: They require considerable cathodic polarization in order to effectively locate the coating defects. DC voltage gradient with current interruption technique is recommended as a viable field method in that it is able to precisely locate the defects irrespective of CP condition. Utilizing this method field survey was undertaken for the KGC’s pipeline of 120 km and 106 assumed defects were located.

Quantitative Evaluation of Indirect Inspection Reliability and Pipeline Reliability Based on Statistical Methods

2004 ◽  
Author(s):  
James N. Mihell ◽  
David Coleman ◽  
Ryan Sporns
Keyword(s):  
Statistical Analysis ◽  
Voltage Gradient ◽  
Direct Examination ◽  
Factors Affecting ◽  
Incidence Data ◽  
Natural Gas Pipeline ◽  
Close Interval ◽  
Order Of Magnitude ◽  
External Corrosion ◽  
The Impact

To support an External Corrosion Direct Assessment (ECDA), Indirect Inspections were performed on a 44 km section of NPS 6 extruded polyethylene coated natural gas pipeline. Based on previous investigations of the pipeline, external corrosion defects were known to have occurred at coating holidays. Such holidays can often be detected using current voltage gradient surveys and close interval surveys. Two successive ACVG surveys over the pipeline were preformed. In addition, Close Interval Survey data were considered in order to complete the Indirect Inspection dataset. Statistical analysis methods were developed and employed against the data generated from these surveys so that the following objectives could be met: 1. Assess the reliability of the Indirect Inspection technique in terms of its ability to locate coating holidays and hence, its ability to locate potential corrosion features; and, 2. Assess, in quantitative terms, the reliability of the pipeline in terms of its potential for failure, and quantitatively establish the impact that the Indirect Inspection and dig program had in improving that reliability. In completing the first objective, duplicate survey results were compared with Direct Examination results. The statistical analysis provided a means of estimating technique reliability, which was conservatively estimated at 96%. Subsequent evaluation of factors affecting technique reliability indicated that the density of indications and consistency of applying the Indirect Inspection technique had a bearing on the overall reliability. The second objective was completed by applying the results of the Indirect Inspection reliability study to a statistical analysis of corrosion incidence data and corrosion size distributions that were derived from the Direct Examination data. Pipeline reliability was quantitatively expressed as a function of year of operation and the reliability of the Indirect Inspection technique. For the case examined, the Indirect Inspection techniques that were applied were found to increase pipeline reliability by approximately an order of magnitude.

Evaluation of Wireless Tools for Determining Contact Status Between a Casing and the Carrier Pipe

2012 ◽  
Author(s):  
Fengmei Song ◽  
John McFarland ◽  
Xihua He
Keyword(s):  
Oil And Gas ◽  
Voltage Gradient ◽  
Property Damage ◽  
Steel Pipes ◽  
Close Interval ◽  
Ac Current ◽  
External Corrosion

For more than half a century, cased crossings have been used to support oil and gas steel pipes for crossing highways, railways, or rivers. Leaks or ruptures of cased crossings have occurred that resulted in casualties and property damage. Unlike uncased pipes buried in soils, which can be assessed for external corrosion directly and indirectly, the presence of a steel casing wall makes it challenging, even if possible, to conduct these assessments. The effect of the casing wall on the external corrosion of the carrier pipe inside the annulus is not well understood; it is unclear what tools can be used to effectively inspect the cased pipes. Empirical experience from the pipeline industry has shown that a few tools can be used to detect the contact status between a casing and the carrier pipe, which can help assess the severity of the carrier pipe external corrosion. Unfortunately, the criteria used to detect a contact status vary by user for the same tool and thus, the effectiveness of these criteria is uncertain. This paper reports results from a recent study aimed at evaluating the effectiveness of AC current attenuation, AC voltage gradient, and close interval (potential) survey as tools for detecting the contact status between a casing and the carrier pipe.

Reliability-Based Evaluation of Pipelines Using Above Ground Inspection Methods for External Corrosion

2004 ◽  
Author(s):  
Mark K. Fuglem ◽  
Mark J. Stephens
Keyword(s):  
Size Distribution ◽  
Special Consideration ◽  
Voltage Gradient ◽  
Direct Voltage ◽  
Close Interval ◽  
Ac Current ◽  
External Corrosion

Above ground inspection methods such as Close Interval, AC Current Attenuation, Direct Voltage Gradient and Pearson surveys are often employed to examine pipelines for external corrosion, especially when in-line inspection and hydrotesting are not feasible. Compared to in-line inspection, these methods can be superior in identifying general areas of corrosion, however, they generally have a higher probability of missing significant defects. This paper examines the use of quantitative reliability-based methods for assessing the integrity of pipelines that have been inspected using above ground methods where these inspections are followed up by a selective excavation and defect sizing process. Special consideration is given to the inference of the size distribution of undetected defects when the number of detected defects is small.

The Responses of Mammalian Spinal Axons to an Applied DC Voltage Gradient

1997 ◽  
Vol 145 (2) ◽  
pp. 376-389 ◽  
Author(s):  
Richard B. Borgens ◽  
Debra M. Bohnert
Keyword(s):  
Voltage Gradient ◽  
Dc Voltage

scholarly journals Efecto de las fallas de recubrimiento mecánico en los potenciales de protección catódica en ductos enterrados

2019 ◽  
Vol 7 (Especial-2) ◽  
pp. 39-47
Author(s):  
Luis Miguel González ◽  
Lesly sabina Villaseñor Cerón ◽  
María Isabel Reyes Valderrama ◽  
Juan Hernández Ávila ◽  
Ventura Rodriguez Lugo
Keyword(s):  
Direct Current ◽  
Voltage Gradient ◽  
Current Voltage ◽  
Close Interval ◽  
Direct Current Voltage

El presente trabajo se enfoca en evaluar el efecto de las fallas de recubrimiento mecánico en los potenciales de protección catódica en ductos enterrados. Los estudios se llevaron a cabo en un ducto en sureste del país, con el objetivo de realizar un programa de mantenimiento preventivo y correctivo, alargando la vida útil de las instalaciones, manteniendo la seguridad y la confiabilidad de las mismas. Dado que la corrosión externa es una de las mayores causas de fugas en ductos subterráneos, las tuberías son protegidas contra estos efectos mediante una combinación de recubrimientos mecánicos y sistemas de protección catódica. Actualmente en la industria es la combinación más efectiva para controlar los efectos de corrosión externa en tuberías subterráneas. La técnica CIPS (Close Interval Potential Survey), se basa en la inspección para el análisis de los niveles de protección catódica en ductos enterrados. La técnica DCVG (Direct Current Voltage Gradient), es un sistema desarrollado para el análisis de defectos de recubrimiento en tuberías enterradas. El control de la corrosión depende de un equilibrio entre el estado del recubrimiento y los niveles de protección catódica. Para obtener niveles efectivos de protección catódica, los potenciales tubo-suelo deben ser mantenidos entre –850 mV “instant off” (subprotección) y –1250 mV “instant off” (sobreprotección). Esta meta solo puede ser alcanzada si existe un decaimiento controlado en el perfil de potencial en la tubería desde los puntos de máximo potencial (los rectificadores) a los puntos de mínimo potencial (las áreas más remotas de los rectificadores). El ritmo de decaimiento de potencial depende principalmente de la condición del recubrimiento de los ductos que se considera como el factor crítico para el correcto funcionamiento de los sistemas de protección catódica.

scholarly journals Maximum voltage gradient technique for optimization of ablation for typical atrial flutter with zero-fluoroscopy approach

Medicine ◽  
2017 ◽  
Vol 96 (25) ◽  
pp. e6939 ◽  
Author(s):  
Karol Deutsch ◽  
Janusz Śledź ◽  
Mariusz Mazij ◽  
Bartosz Ludwik ◽  
Michał Labus ◽  
...  
Keyword(s):  
Atrial Flutter ◽  
Voltage Gradient ◽  
Typical Atrial Flutter ◽  
Gradient Technique ◽  
Maximum Voltage ◽  
Zero Fluoroscopy

Analysis of Efficient Interval Field Techniques for Random Field Analysis With Uncertain Correlation Length

2011 ◽  
Author(s):  
Wim Verhaeghe ◽  
Wim Desmet ◽  
Dirk Vandepitte ◽  
David Moens
Keyword(s):  
Random Field ◽  
Correlation Length ◽  
Probabilistic Approach ◽  
Field Method ◽  
Field Analysis ◽  
Field Representation ◽  
Field Techniques ◽  
Spatially Distributed ◽  
Base Vector ◽  
First Time

The representation of uncertainties that give rise to a spatially distributed influence is still a topic of research in the non-probabilistic approach. The authors have developed an interval field framework to deal with multiple dependent uncertainties. Recently, the interval field method was developed to deal with random field expansions with an uncertain correlation length. The base vectors of this interval field come from a number of exact expansions of the random field in the correlation length space (e.g., Karhunen-Loe`ve expansion). The scaling interval factors are essentially a function of the correlation length. The present paper studies for the first time the convergence of an uncertain FE output (i.e. the interval on the FE output) with respect to the dimension of the base vector space, which is determined by the number of eigenvectors retained in one exact random field expansion and the number of exact random field expansions used to build the interval field representation.

Evaluation of the dark field method for large association of spread DNA

1978 ◽  
Vol 36 (2) ◽  
pp. 190-191
Author(s):  
Douglas C. Barker
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Mitochondrial Dna ◽  
Extraction Method ◽  
Field Method ◽  
Dark Field ◽  
Kinetoplast Dna ◽  
Field Electron ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A number of satisfactory methods are available for the electron microscopy of nicleic acids. These methods concentrated on fragments of nuclear, viral and mitochondrial DNA less than 50 megadaltons, on denaturation and heteroduplex mapping (Davies et al 1971) or on the interaction between proteins and DNA (Brack and Delain 1975). Less attention has been paid to the experimental criteria necessary for spreading and visualisation by dark field electron microscopy of large intact issociations of DNA. This communication will report on those criteria in relation to the ultrastructure of the (approx. 1 x 10-14g) DNA component of the kinetoplast from Trypanosomes. An extraction method has been developed to eliminate native endonucleases and nuclear contamination and to isolate the kinetoplast DNA (KDNA) as a compact network of high molecular weight. In collaboration with Dr. Ch. Brack (Basel [nstitute of Immunology), we studied the conditions necessary to prepare this KDNA Tor dark field electron microscopy using the microdrop spreading technique.

A Many-Beam Technique for Enhanced Resolution of Partial Dislocations

1972 ◽  
Vol 30 ◽  
pp. 646-647
Author(s):  
J. M. Oblak ◽  
B. H. Kear
Keyword(s):  
Phase Shift ◽  
Field Method ◽  
Dark Field ◽  
Bright Field ◽  
Field Technique ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Enhanced Resolution ◽  
Nickel Base ◽  
Beam Technique

The “weak-beam” and systematic many-beam techniques are the currently available methods for resolution of closely spaced dislocations or other inhomogeneities imaged through strain contrast. The former is a dark field technique and image intensities are usually very weak. The latter is a bright field technique, but generally use of a high voltage instrument is required. In what follows a bright field method for obtaining enhanced resolution of partial dislocations at 100 KV accelerating potential will be described.A brief discussion of an application will first be given. A study of intermediate temperature creep processes in commercial nickel-base alloys strengthened by the Ll2 Ni3 Al γ precipitate has suggested that partial dislocations such as those labelled 1 and 2 in Fig. 1(a) are in reality composed of two closely spaced a/6 <112> Shockley partials. Stacking fault contrast, when present, tends to obscure resolution of the partials; thus, conditions for resolution must be chosen such that the phase shift at the fault is 0 or a multiple of 2π.

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