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.

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.

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.

A New Technique for Locating Coating Faults on Buried Metallic Pipelines

2008 ◽  
Vol 38 ◽  
pp. 113-120 ◽  
Author(s):  
Lucio Di Biase ◽  
Ranieri Cigna ◽  
Osvaldo Fumei
Keyword(s):  
Direct Current ◽  
Fault Location ◽  
New Technique ◽  
Research Centre ◽  
Voltage Gradient ◽  
Unique Method ◽  
Training And Research ◽  
Direct Current Voltage ◽  
A New Technique ◽  
External Corrosion

Among the specialized electrical surveys to search for coating faults, assess possible external corrosion conditions and verify Cathodic Protection effectiveness, DCVG (Direct Current Voltage Gradient) survey, and in particular the Transverse DCVG is usually considered the most effective technique for finding coating faults on transport pipelines for oil, gas, and water. In this paper some preliminary results are reported that show that using a.c. current instead of direct current the localization of the coating faults can be much more precise and simple to be performed at the same time. Compared with the DCVG, the ACVG has many advantages among which: it does not need ON/OFF cycles since the OFF conditions are almost constant in the absence of alternating stray currents, it can be carried out with economic and simple instrument, the use of unpolarizable reference electrodes (SCE) is not necessary and furthermore, it locates the faults and quantifies their importance with much more accuracy. Besides, the method needs shorter times and less manpower: one only operator is sufficient to perform the survey and it is therefore cheaper than performing DCVG. The results of the experiments carried out at the Training and Research Centre of Riyadh by comparing the results of the two methods using the same current densities, clearly show the different behaviour of the two techniques, in the presence of simulated / calibrated coating faults. Further researches are in course with this quite new technique as the localisation of coating faults is being made in terms of impedance rather than in terms of resistance. This has quite a huge implication when corrosion conditions of real coating faults are concerned. In case of a.c. interference (e.g. due to a.c. fed railways or electricity power lines) this could be a unique method able to locate corroding coating faults on a buried, interfered metallic pipeline. The method is being patented not only as a new technique for coating fault location, but also for its promising further developments still under investigation, as capable of finding corroding faults in case of a.c. interference.

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.

A Robust Approach to Pipeline Integrity Management Using Direct Assessment Based on Structural Reliability Analysis

2004 ◽  
Author(s):  
Marcus McCallum ◽  
Andrew Francis ◽  
Tim Illson ◽  
Mark McQueen ◽  
Mike Scott ◽  
...  
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Voltage Gradient ◽  
Pipeline System ◽  
Pipe Failure ◽  
Internal Corrosion ◽  
Direct Assessment ◽  
Structural Reliability Analysis ◽  
Integrity Management ◽  
External Corrosion

Approximately 1450 km (900 miles) of a 4020-km (2500 mile) natural gas pipeline system operated by Crosstex Energy Service L.P in Texas are subject to the Texas Railroad Commission’s (TRRC) integrity management rules. Consequently, in preparation for the construction of an extensive and robust integrity management program, Crosstex commissioned Advantica to assist in the development and application of a pilot study on a 13.4 km (8.3 mile) section of a 14” pipeline. The purpose of the study, which is based on Structural Reliability Analysis (SRA), was to compare the level of integrity that could be inferred from the use of Direct Assessment (DA) techniques with the level that could be inferred from ILI results. Based on a preliminary assessment of available data, the study identified both external and internal corrosion as potential threats to integrity. SRA was used in conjunction with ‘Bayesian Updating’ to determine the probability of pipe failure due to external corrosion, taking account of results from above-ground measurements and a number of bell-hole excavations. The above-ground survey techniques utilized included Close Interval Survey (CIS) and Direct Current Voltage Gradient (DCVG). A similar approach was adopted to address the threat due to internal corrosion, but hydraulic modelling was substituted for the above-ground measurements. A third study based on SRA was used to determine the combined probability of failure due to both internal and external corrosion taking account of ILI results. The outcome of the analyses demonstrated that the level of integrity that could be inferred from the use of Crosstex’ DA methodology was similar to that which could be inferred from the use of ILI. The results were presented to the TRRC for review and approval. This paper gives a detailed description of the SRA based methodology that was employed by Crosstex and presents the results that clearly demonstrate the comparability of ILI and DA for the purpose of integrity management.

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.

The extinction time of a general birth and death process with catastrophes

1986 ◽  
Vol 23 (04) ◽  
pp. 851-858 ◽  
Author(s):  
P. J. Brockwell
Keyword(s):  
Laplace Transform ◽  
Size Distribution ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Death Process ◽  
Extinction Time ◽  
Birth And Death Process ◽  
Different Types ◽  
The Laplace Transform ◽  
Necessary And Sufficient

The Laplace transform of the extinction time is determined for a general birth and death process with arbitrary catastrophe rate and catastrophe size distribution. It is assumed only that the birth rates satisfyλ0= 0,λj> 0 for eachj> 0, and. Necessary and sufficient conditions for certain extinction of the population are derived. The results are applied to the linear birth and death process (λj=jλ, µj=jμ) with catastrophes of several different types.

Macrostructure and microphysics of Saturn's E-ring

1984 ◽  
Vol 75 ◽  
pp. 607-613 ◽  
Author(s):  
Kevin D. Pang ◽  
Charles C. Voge ◽  
Jack W. Rhoads
Keyword(s):  
Size Distribution ◽  
Spherical Shape ◽  
Mie Scattering ◽  
Narrow Size Distribution ◽  
Electrostatic Levitation ◽  
Volcanic Origin ◽  
Micron Diameter

Abstract.All observed optical and infrared properties of Saturn's E-ring can be explained in terms of Mie scattering by a narrow size distribution of ice spheres of 2 - 2.5 micron diameter. The spherical shape of the ring particles and their narrow size distribution imply a molten (possibly volcanic) origin on Enceladus. The E-ring consists of many layers, possibly stratified by electrostatic levitation.

Grain Refinement in Titanium-Erbium Alloys

1974 ◽  
Vol 32 ◽  
pp. 522-523
Author(s):  
B. B. Rath ◽  
J. E. O'Neal ◽  
R. J. Lederich
Keyword(s):  
Electron Microscopy ◽  
Size Distribution ◽  
Grain Refinement ◽  
Grain Growth ◽  
Volume Fraction ◽  
Pure Titanium ◽  
Systematic Investigation ◽  
Second Phase ◽  
Titanium Matrix ◽  
Average Size

Addition of small amounts of erbium has a profound effect on recrystallization and grain growth in titanium. Erbium, because of its negligible solubility in titanium, precipitates in the titanium matrix as a finely dispersed second phase. The presence of this phase, depending on its average size, distribution, and volume fraction in titanium, strongly inhibits the migration of grain boundaries during recrystallization and grain growth, and thus produces ultimate grains of sub-micrometer dimensions. A systematic investigation has been conducted to study the isothermal grain growth in electrolytically pure titanium and titanium-erbium alloys (Er concentration ranging from 0-0.3 at.%) over the temperature range of 450 to 850°C by electron microscopy.

Formation and Structure of Casein Micelles in Lactating Mammary Tissue

1970 ◽  
Vol 28 ◽  
pp. 150-151
Author(s):  
Robert J. Carroll ◽  
Marvin P. Thompson ◽  
Harold M. Farrell
Keyword(s):  
Size Distribution ◽  
G Protein ◽  
Milk Proteins ◽  
Mammary Tissue ◽  
Colloidal System ◽  
Casein Micelles ◽  
The Stability

Milk is an unusually stable colloidal system; the stability of this system is due primarily to the formation of micelles by the major milk proteins, the caseins. Numerous models for the structure of casein micelles have been proposed; these models have been formulated on the basis of in vitro studies. Synthetic casein micelles (i.e., those formed by mixing the purified αsl- and k-caseins with Ca2+ in appropriate ratios) are dissimilar to those from freshly-drawn milks in (i) size distribution, (ii) ratio of Ca/P, and (iii) solvation (g. water/g. protein). Evidently, in vivo organization of the caseins into the micellar form occurs in-a manner which is not identical to the in vitro mode of formation.

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