A. Valor

Predictive Model for Pitting Corrosion in Buried Oil and Gas Pipelines

Abstract A predictive model for pitting corrosion in buried pipelines is proposed. The model takes into consideration the chemical and physical properties of the soil and pipe to predict the time dependence of pitting depth and rate. Maximum pit depths were collected together with soil and pipe data at more than 250 excavation sites over a three-year period. The time dependence of the maximum pit depth was modeled as dmax = κ(t − t0)ν, where t is the exposure time, t0 is the pit initiation time, and κ and ν are the pitting proportionality and exponent parameters, respectively. A multivariate regression analysis was conducted with dmax as the dependent variable and the pipeline age, and the soil and pipe properties as the independent variables. The dependence of κ and ν on the predictor variables was found for the three soil textural classes identified in this study: clay, clay loam, and sandy clay loam. The proportionality parameter κ was found to be primarily influenced by the redox potential, pH value, ...

Markov Chain Models for the Stochastic Modeling of Pitting Corrosion

The stochastic nature of pitting corrosion of metallic structures has been widely recognized. It is assumed that this kind of deterioration retains no memory of the past, so only the current state of the damage influences its future development. This characteristic allows pitting corrosion to be categorized as a Markov process. In this paper, two different models of pitting corrosion, developed using Markov chains, are presented. Firstly, a continuous-time, nonhomogeneous linear growth (pure birth) Markov process is used to model external pitting corrosion in underground pipelines. A closed-form solution of the system of Kolmogorovs forward equations is used to describe the transition probability function in a discrete pit depth space. The transition probability function is identified by correlating the stochastic pit depth mean with the empirical deterministic mean. In the second model, the distribution of maximum pit depths in a pitting experiment is successfully modeled after the combination of two stochastic processes: pit initiation and pit growth. Pit generation is modeled as a nonhomogeneous Poisson process, in which induction time is simulated as the realization of a Weibull process. Pit growth is simulated using a nonhomogeneous Markov process. An analytical solution of Kolmogorovs system of equations is also found for the transition probabilities from the first Markov state. Extreme value statistics is employed to find the distribution of maximum pit depths.

Statistical Analysis of Pitting Corrosion Field Data and Their Use for Realistic Reliability Estimations in Non-Piggable Pipeline Systems

The reliability and risk of non-piggable, corroding oil and gas pipelines can be estimated from historical failure data and through reliability models based on the assumed or measured number of corrosion defects and defect size distribution. In this work, an extensive field survey carried out in an upstream gathering pipeline system in Southern Mexico is presented. It has helped determine realistic values for the number of corrosion defects per kilometer (defect density) and obtain a better description of the corrosion defect size distributions in this system. To illustrate the impact that these new corrosion data can have on pipeline risk management, a reliability study is also presented where the field-gathered corrosion data have been used as input to a reliability framework for the estimation of the failure index of non-piggable pipelines and pipeline systems when different amounts of corrosion data are available.

Structural and thermal study of calcium undecanoate

In the present work, an X-ray diffraction (XRD) and thermal study of calcium undecanoate is presented. The measured highresolution XRD powder pattern of the synthesized salt at room temperature, using synchrotron radiation, showed that the salt is a mixture of monohydrated and anhydrous calcium undecanoate. Calcium undecanoate monohydrate proved to have a monoclinic cell with a symmetry described by the P21=a space group. The structure dehydrates at about 1001C. After dehydration, the salt undergoes a phase transformation which results in a thermotropic mesophase. Further heating of the salt leads to decomposition and melting. Ketones are the probable products of decomposition at 4001C. r 2003 Elsevier Science (USA). All rights reserved.

Technical Note: Field Study—Pitting Corrosion of Underground Pipelines Related to Local Soil and Pipe Characteristics

Abstract Recently, the authors proposed a new predictive model for pitting corrosion in underground pipelines. The model is based on field measurements of maximum pitting corrosion depth together with local soil and pipeline characteristics. The pitting corrosion data collection was conducted over a three-year period, for onshore buried pipelines operating in southern Mexico. This technical note contains a detailed description of the results of the field measurements, indicating the data entries classified as outlier observations and the textural soil class ascribed to each data entry.

Synthesis and X-ray diffraction study of calcium salts of some carboxylic acids

An experimental X-ray diffraction ~XRD! study of calcium salts of four carboxylic acids is presented. Calcium salts of propionic, butyric, valeric, and caproic acids were synthesized mixing in a mortar Ca~OH!2 with the liquid acids. Measuring the thermogravimetric analysis curves it was determined that the salts were actually monohydrates. The densities of the synthesized samples were measured using a density gradient column. The measured values for the densities were as follows: Dm(propionate)51.38 g/cm3, Dm(butyrate)51.30 g/cm3, Dm(valerate)51.26 g/cm3, Dm(caproate) 51.22 g/cm3. The XRD analysis revealed that these compounds have monoclinic cells with symmetry described by the P21 /a space group. Calcium propionate hydrate has cell parameters: a52.437 51(5) nm, b50.681 24(1) nm, c50.591 43(1) nm, b595.320(2)°. For calcium butyrate hydrate the cell parameters are: a52.966 84(8) nm, b50.680 74(2) nm, c50.589 29(2) nm, b 595.442(3)°. The cell parameters for calcium valerate hydrate are: a53.566 36(4) nm, b 50.682 49(1) nm, c50.592 77(1) nm, b5107.280(1)° and for calcium caproate hydrate a 54.180 30(5) nm, b50.682 61(1) nm, c50.592 13(1) nm, b5110.230(1)°. The calculated density values from the XRD results, taking into account that the number of chemical formulas in the unit cell equals four, agree very well with the measured ones. It was established that the unit cell parameter a grows with the increase of the number of carbon atoms in the aliphatic chain, while parameters b and c remain almost constant. This is an indication of the stacking layer character of the structure as has been suggested for calcium stearate monohydrate. This fact points to the possibility of the refinement of the crystalline structures taking as the starting point the reported structure for calcium stearate monohydrate.

Discussion: Statistical Characterization of Pitting Corrosion—Part 1: Data Analysis and Part 2: Probabilistic Modeling for Maximum Pit Depth

Abstract A. Valor, et al., discuss “Statistical Characterization of Pitting Corrosion—Part 1: Data Analysis” and “Statistical Characterization of Pitting Corrosion—Part 2: Probabilistic Modeling for Maximum Pit Depth,” by R.E. Melchers, which were published in Corrosion 61, 7 (2005), p. 655–664 and Corrosion 61, 8 (2005), p. 766–777, respectively. A reply from R.E. Melchers follows.

Detection of Counterfeit Tequila by Fluorescence Spectroscopy

An ultraviolet (UV) light induced fluorescence study to discriminate fake tequila from genuine ones is presented. A portable homemade system based on four light emitting diodes (LEDs) from 255 to 405 nm and a miniature spectrometer was used. It has been shown that unlike fake and silver tequila, which produce weak fluorescence signal, genuine mixed, rested, and aged tequilas show high fluorescence emission in the range from 400 to 750 nm. The fluorescence intensity grows with aging in 100% agave tequila. Such fluorescence differences can even be observed with naked eyes. The presented results demonstrate that the fluorescence measurement could be a good method to detect counterfeit tequila.

STATISTICAL MODELING OF PITTING CORROSION IN BURIED PIPELINES TAKING INTO ACCOUNT SOIL PROPERTIES

Small leaks caused by external pitting corrosion are the leading cause of failure in oil and gas pipelines in many regions of Mexico. Because of this, the need for realistic and reliable pitting corrosion growth models that are capable of accounting for the chemical and physical properties of soils and pipeline coatings is especially great. In this work, maximum pit depths and soil and coating data that were gathered at excavation sites across southern Mexico are used to investigate the impact of soil and pipe characteristics on pitting corrosion in buried pipelines. Soil field-measurements included resistivity, pH, pipe-to-soil potential, humidity, chloride, bicarbonate and sulphate levels, redox potential, soil texture and coating type. Together with the local physical chemistry of the soil and the coating characteristics, the maximum pit depth and pipeline’s age were recorded at more than 250 dig sites. The time dependence of the maximum pit depth was modeled as ymax = β(t−t0 )α , with β and α being positive constants, t being the pipe’s age and t0 the pit initiation time. A multivariate regression analysis was conducted with ymax as the dependent variable, while the pipeline’ age and the soil and pipe properties were used as the independent variables. The optimal dependence of β and α on these variables was found and predictive models were proposed to describe the time dependence of the average maximum pit depth and growth rate on soil and pipe properties. Besides the creation of a generic model fitted to all the gathered data, a model was proposed for each one of the three soil types identified in this study: clay, clay-loam and sandy-clay-loam. It is shown that the application of the proposed model allows for prediction of corrosion pit growth more accurately than previous models and that this improvement positively impacts on integrity management plans that address the threat posed by external pitting corrosion.Copyright

On the interactions of potassium bromide with alkali fluorides

Abstract The interactions of alkali fluorides (LiF, NaF, KF, CsF) with potassium bromide (KBr) by milling and by crystallization from water solutions have been studied by X-ray diffraction and IR techniques. KBr reacts with CsF according to CsF+KBr→KF+CsBr. With LiF and NaF, KBr does not react. With KF, KBr forms a very hygroscopic solid in which KF partially dissolves in the water of hydration and also forms the crystalline phase KF·2H 2 O.