Alexis M. Fraser

Bio: Alexis M. Fraser is an academic researcher from National Institute of Standards and Technology. The author has contributed to research in topics: Computer science & Pipeline (software). The author has an hindex of 1, co-authored 1 publications receiving 207 citations.

Probabilistic Corrosion Assessment for Natural Gas Storage Wells

Abstract: Regulations for gas storage wells require that operators perform initial and subsequent mechanical integrity evaluations as determined using risk assessment [1], incorporated by reference in 49 CFR 192.12 for U.S. operators [2]. As a well ages, metal loss on the casing can grow, increasing the probability of a failure from corrosion. Inspection and repair programs manage this probability by reducing uncertainty in the casing condition and repairing significant metal loss anomalies. However, performing a casing inspection involves a considerable amount of risk, which can vary depending on the well configuration [3]. The benefit of inspection and repair needs to be balanced with the inspection risk to determine the interval that minimizes the overall risk. This paper demonstrates that if detailed information about a well’s configuration, loading, and existing corrosion population is considered, a probabilistic corrosion analysis can be completed to determine a reinspection date that minimizes the overall risk of a release. A probabilistic implementation of the Level II analysis found in API 579 Fitness-For-Service is described and recommended for these assessments [4]. The deterministic version of this model is the most accurate for predicting burst pressures of casings with metal loss under a wide range of loading conditions [5]. The measurement error of inspection tools and their reporting thresholds relative to typical corrosion rates presents many challenges in calculating corrosion rates deterministically. Calculating unrealistically high growth rates and apparent negative growth rates using inspection data is common. Using the tool measurement error and the distribution of calculated growth rates across several wells, a Bayesian updating approach is described, grouping anomalies in similar environments to develop credible growth rate distributions specific to each joint on a well. This paper provides several assessments of realistic storage well configurations and corrosion populations to demonstrate how the probabilistic corrosion assessment can determine an inspection interval that minimizes the overall risk and ultimately inform integrity maintenance plans on a well-by-well basis. The examples span a wide range of well conditions to illustrate that the optimal inspection and repair program depends on each well’s configuration, loading, and existing corrosion population. The effect of a corrosion anomaly’s depth in the well and the cement quality on the expected release rate and the resulting risk is also examined.

Modelling Accidental Impact Threats to Natural Gas Storage Wells

Abstract: API RP 1171, which was recently incorporated by reference in US regulation 49 CFR 192.12, and the recent changes to the California Code of Regulations have mandated risk assessments be performed for underground storage wells. A quantitative risk assessment framework has been developed for SoCalGas’s underground gas storage sites in California. This framework includes quantitative models for accidental impact threats to the wellhead and lateral piping, including damage from excavations, vehicle collisions, lifting operations, and aircraft crashes (for first, second, and third-parties). In an industry survey of underground storage operators conducted by the Gas Research Institute in 2004, 15% of the recorded significant release incidents were due to accidental impact threats. Additionally, since there are likely individuals in the immediate vicinity when the incidents occur, releases due to accidental impact threats may carry more significant consequences. In this work, models were adapted from existing industry models for pipelines, nuclear facilities, and aboveground piping stations by updating the inputs to reflect an underground gas storage context and calibrating the overall results to match historical underground gas storage incident data. The models incorporate well-specific attributes and measurements as well as subject matter expert (SME) experience and judgement, with key variables for each model including: • Excavation damage: excavation frequency (estimated from site-specific one-call data), material and operational properties of buried lateral piping, depth of cover • Vehicle collisions: vehicle traffic near the well (estimated from modelling the site road network and all site activities involving vehicles), presence of any barriers, the layout of any aboveground lateral piping • Lifting operations: lifting operation frequency near the well (estimated from modelling the future workover activities at all nearby wells), material and operational properties of the wellhead, and any aboveground lateral piping • Aircraft crashes: proximity and orientation relative to nearby airports, amount and type of traffic at the nearby airports, the layout of the lateral piping This paper illustrates the results for field-wide assessments of these accidental impact threats, showing how the risk is differentiated by the specific well context. In contrast to using a single historical incident rate, the models capture the differences in risk between wells within and across fields and can help estimate the effect of performing mitigation activities on specific wells.

Estimating Measurement Performance With Truncated Data Sets

Abstract: In September 2021, the API released the third edition of the 1163 Standard “In-line Inspection Systems Qualification”. This edition brought many improvements over previous versions, including more detail in Section 8 “System Results Validation”, which defines the methodologies used to validate ILI run tolerances. The standard describes three levels of validation, with ‘Level 3’ requiring the operator calculate ILI tool measurement performance with real-world data measured in validation spools and excavation sites. Real-world, inspection data sets have some characteristics that make them difficult to use to accurately estimate measurement performance, one of which is ‘truncation’, that is data with a lower- or upper-bound threshold above which no data is reported. For example, most UTCD ILI tools have a lower truncation level, such as 1 mm for crack height, which represents a signal threshold below which measurements are either not reliable, or not reported. Although small features below the reporting threshold exist on the pipeline, they are not normally reported by the ILI tool. This paper describes a model to estimate ILI tool performance using API 1163 Level 3 methods when the data set has a lower-truncation threshold. The model is tested with simulation data to show how it responds over a wide range of feature population characteristics, and then applied to two real field data sets. Comparisons are made between the truncation algorithm and the standard non-truncated version of the algorithm, to show where the new algorithm performs best and is most useful to implement pipeline integrity mitigations. The model used in this study is consistent with the example documented in API 1163 - Appendix C, the Bayesian inference method. The results of the model produce measurement performance specifications that can be used as inputs in a pipeline risk or reliability analysis. The influence of truncated data sets is common in the field of inspection and NDE (including thickness measurements), as it reflects the reality that there are features below reporting threshold. The steps required to format the results for use, and achieve more accurate measurement performance results (e.g., unity charts), are described in this paper.

Calcium Orthophosphates in Nature, Biology and Medicine

Abstract: The present overview is intended to point the readers’ attention to the important subject of calcium orthophosphates. These materials are of the special significance because they represent the inorganic part of major normal (bones, teeth and dear antlers) and pathological ( i.e. those appearing due to various diseases) calcified tissues of mammals. Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium ortho-phosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and as tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, technical grade calcium orthophosphates are very popular mineral fertilizers. Thus ere calcium orthophosphates are of great significance for humankind and, in this paper, an overview on the current knowledge on this subject is provided.

Review: mineralization of synthetic polymer scaffolds for bone tissue engineering.

Abstract: It has repeatedly been shown that demineralization improves the ability of bone auto- and allografts to regenerate natural bone tissue. Conversely, much work in the field of bone tissue engineering has used composite materials consisting of a mineralized phase or materials designed to mineralize rapidly in situ. In this review, we seek to examine these disparate roles of mineralization and the underlying factors that cause this discordance and to examine methods and principles of the mineralization of synthetic polymer scaffolds. Biomimetic approaches to mineralization and phosphorus-containing materials are highlighted, and a brief section focusing on drug-delivery strategies using mineralized scaffolds is included.