The Design and Installation of the LEOS Leak Detection and Location System for the Northstar Project

The Northstar project is the first crude oil production facility constructed offshore in the Beaufort Sea. Produced crude oil is transferred via a buried subsea pipeline to shore and overland to the Trans Alaska Pipeline Pump Station PS1 facility. During the permitting process, concern was expressed that a very small chronic leak in the subsea oil line would remain undetected during the winter months of continuous ice cover. Therefore, the US Army Corps of Engineers stipulated that a prototype leak detection system be installed that would capable of detecting a threshold leak less than 32 BOPD. This paper addresses the efforts to develop and install the LEOS leak detection system for arctic operations. The system is based on the well-established LEOS leak detection technology (manufactured by Framatome ANP, formerly by Siemens AG). The system comprises a perforated plastic tube with a thin water impermeable acetate outer sheath that allows hydrocarbon molecules to diffuse into the air filled tube. The air inside the tube is replaced periodically (every 24 hours) and is passed through a hydrocarbon-sensing module. The module contains resistors sensitive to the presence of very small concentrations of hydrocarbon molecules. The presence and location of a leak is determined by measuring the time taken for the localized concentration of hydrocarbon molecules associated with a leak to reach the end of the tube. LEOS components and materials were engineered to survive installation during arctic winter conditions. It was also necessary to protect the plastic LEOS sensor tube as it was lowered through the ice, attached to the pipeline, into a pre-excavated trench and then backfilled. The 10km long LEOS tube was delivered to site in 31-coiled 300m (1000-ft) bundles that were transported from Germany to Alaska. The LEOS sensing tube was preinstalled in a protective outer polyethylene tube which was unreeled through a reverse bending jig. Crude oil production started at the Northstar production facility in October 2001 and the LEOS system has been operational since then and is providing the highest degree of assurance that no oil is escaping from the pipeline.

Feedback and Mapping Control of Natural Gas Engines

Automatic controls have been used on all types of machinery since the first complicated machines became popular in the 19th century. Controls are used to maintain pressures, temperatures, operating speeds, flows and many other operating parameters. Natural gas engines have used a variety of controls for various purposes since the first natural gas engines were produced. This paper will discuss the history of mechanical controls used on natural gas engines and the introduction and application of electronic controls. The paper will discuss open loop (mapping) and closed loop (feedback) type controls and common applications of each. Mechanical control systems such as governors, fuel regulators, fuel mixing valves, thermostats, and turbocharger wastegates will be discussed and classified as open or closed loop controls. Electronic control systems such as governors, air/fuel ratio controls, detonation controls, and turbocharger controls will also be discussed and classified. This paper will also discuss state of the art controls which perform numerous functions to get desired performance, and can be communicated with remotely.

Basis of the New Criteria in ASME B31.8 for Prioritization and Repair of Mechanical Damage

Mechanical damage in the form of dents has emerged as a key safety concern for pipelines. In response, ASME B31.8, with assistance from GTI, undertook a detailed review of industry research and operating experience with respect to various forms of mechanical damage. Revised criteria for prioritizing and effectively repairing damage in natural gas pipelines were developed based on the findings. The criteria address plain dents, third-party type damage, dents that affect weldments, dents affected by corrosion, and strain levels associated with deformation of the pipe section. This paper discusses the generalities of the scientific findings and basis for the changes to the Code.

A Justification for Designing and Operating Pipelines Up to Stresses of 80% SMYS

Oil and gas majors are interested in several projects worldwide involving large diameter, long distance gas pipelines that pass through remote locations. Consequently, the majors are investigating the feasibility of operating pipelines of this type at stress levels up to and including 80% of the specified minimum yield strength (SMYS) of the pipe material. This paper summarises a study to investigate the impact upon safety, reliability and integrity of designing and operating pipelines to stresses up to 80% SMYS.

Reducing Compressor Station Ambient Noise Level by Controlling Compressor Internal Noise Source

Dresser-Rand single stage pipeline booster compressors have been popular for gas transmission applications due to their high efficiency. As more compressors are installed in natural gas compressor stations close to populated areas, the noise level emitted from the compressor stations becomes a concern. To address the potential community noise concerns, Dresser-Rand recently developed a very effective noise control device — the Duct Resonator array or DR array, to attenuate the internal noise of the compressor, which is typically a major noise source of a compressor station. This technology has been validated by extensive in-house experimental study to be acoustically effective and yet have no measurable adverse effect on aerodynamic performance. This paper discusses the application of DR arrays in two compressors that are in-service at a Williams Gas Pipeline compressor station. Note: the DR arrays are now included in the third unit addition. A successful collaboration among the compressor manufacturer, the compressor user, and a third party acoustics expert was coordinated to take acoustic measurements independently to evaluate the noise reduction provided by the DR arrays. The comprehensive acoustic data acquisition included sound pressure level and sound intensity level measurements around each of the two compressors and several noise level surveys both inside and outside of the compressor building. Noise testing was first performed on each of the two compressors prior to the installation of the DR arrays and was repeated after the compressor hardware modification with DR arrays. A comparison of the noise data recorded before and after the installation of the DR arrays confirmed that the compressor noise level inside the compressor building and the noise level outside of the building were reduced significantly. The DR array has proved to be an efficient and effective device for reducing noise and vibration levels of both existing and new centrifugal compressors and associated piping.

Soil-Structure Interaction of Heated Pipeline Buried in Soft Clay

Heated pipelines buried in soft clay can develop a very challenging behavior. The thermal expansion of the pipelines normally induces buckles, which will be supported by the passive soil reaction. The buckles of the pipelines in soft clay can generate a non-linear inelastic behavior that is an unstable situation named “snap through”. In such situation the pipeline can jump from a configuration of a few centimeters displacement to another of meters displacement. Once the snap through situation has developed, there is the possibility of a local pipeline buckling, causing the pipeline rupture and as a consequence an oil spill. This paper presents the results obtained during the analysis of the rupture of a buried heated pipeline in the Guanabara Bay of Rio de Janeiro, Brazil. A very sophisticated procedure including a simulation of the thermal mechanical interactions between the soil and the pipeline structure was developed for back analysis of the thermal inelastic pipeline buckling. Computer modeling was carried out using the finite element method considering of the non-linear material behavior of the soil and pipeline, and nonlinear geometrical behavior of the pipeline. A cyclic thermal-mechanical soil-pipeline structure interaction model was the challenging aspect of the simulation, that explains the trigger mechanism of the snap through behavior of heated pipelines, which was responsible for the rupture of the pipeline in Guanabara Bay.

Pipeline Inspection Operations With Geometric Pigs: Campos Basin Main Results

The increasing use of geometric pigs in the last five years has significantly contributed to the quality of pipelines in construction, as well as to geometric defect detection, assessment and identification, improving pipeline maintenance and overall quality. Geometric pigs with advanced built-in electronics allow precise defect sizing, helping pipeline integrity analysis. This paper presents actual anomalies detected by geometric pigs through comprehensive assessment and anomaly identification.

Probability of Exceedance (POE) Methodology for Developing Integrity Programs Based on Pipeline Operator-Specific Technical and Economic Factors

With the availability of in-line inspection data, pipeline operators have additional information to develop the technical and economic justification for integrity verification programs (i.e. Fitness-for-Purpose) across an entire pipeline system. The Probability of Exceedance (POE) methodology described herein provides a defensible decision making process for addressing immediate corrosion threats identified through metal loss in-line inspection (ILI) and the use of sub-critical in-line inspection data to develop a long term integrity management program. In addition, this paper describes the process used to develop a Corrosion In-line Inspection POE-based Assessment for one of the systems operated by TransGas Limited (Saskatchewan, Canada). In 2001, TransGas Limited and CC Technologies undertook an integrity verification program of the Loomis to Herbert gas pipeline system to develop an appropriate scope and schedule maintenance activities along this pipeline system. This methodology customizes Probability of Exceedance (POE) results with a deterministic corrosion growth model to determine pipeline specific excavation/repair and re-inspection interval alternatives. Consequently, feature repairs can be scheduled based on severity, operational and financial conditions while maintaining safety as first priority. The merging of deterministic and probabilistic models identified the Loomis to Herbert pipeline system’s worst predicted metal loss depth and the lowest safety factor per each repair/reinspection interval alternative, which when combined with the cost/benefit analysis provided a simplified and safe decision-making process.

Pipeline Dent Management Program

Enbridge Pipelines Inc. operates the world’s longest and most complex liquids pipeline network. As part of Enbridge’s Integrity Management Program In-Line Inspections have been and will continue to be conducted on more than 15,000 km of pipeline. The Inspection Programs have included using the most technologically advanced geometry tools in the world to detect geometrical discontinuities such as ovality, dents, and buckles. During the past number of years, Enbridge Pipelines Inc. has been involved in developing a method of evaluating the suitability of dents in pipelines for continued service. The majority of the work involved the development of a method of modeling the stresses within a dent using Finite Element Analysis (FEA). The development and validation of this model was completed by Fleet Technology Limited (FTL) through several projects sponsored by Enbridge, which included field trials and comparisons to previously published data. This model combined with proven fracture mechanics theory provides a method of determining a predicted life of a dent based on either the past or future operating conditions of the pipeline. CSA Standard Z662 – Oil and Gas Pipeline Systems provides criteria for the acceptability of dents for continued service. There have been occurrences, however, where dents that meet the CSA acceptability criteria have experienced failure. The dent model is being used to help define shape characteristics in addition to dent depth, the only shape factor considered by CSA, which contribute to dent failure. The dent model has also been utilized to validate the accuracy of current In-Line Inspection techniques. Typically a dent will lose some of its shape as the overburden is lifted from the pipeline and after the indentor is removed. Often there can be a dramatic “re-rounding” that will occur. The work included comparing the re-rounded dent shapes from a Finite Element model simulating the removal of the constraint on the pipe to the measured dent profile from a mold of the dent taken in the field after it has been excavated. This provided a measure of the accuracy of the tool. This paper will provide an overview of Enbridge’s dent management program, a description of the dent selection process for the excavation program, and a detailed review of the ILI validation work.

The Role of a Geographic Information System (GIS) in the Sustainability of Export Pipeline Projects

Sustainable development in the energy industry is rapidly expanding beyond the conceptual stage. Policies addressing the three principles of Sustainable Development (economic growth, environmental protection, and social progress) are being established and strategies to execute these policies are being developed and implemented in the field. Export pipeline projects provide a wide variety of applications for the three elements of sustainable development. Properly designed, installed and operated pipeline systems enable the energy industry to deliver hydrocarbon products to the market place in a way that delivers economic rewards while preserving the integrity of the environment and surrounding communities and their ways of life. Conoco is developing a strong corporate culture around sustainable development; and, pipeline systems play a vital role in delivering the triple bottom line results for our stakeholders. This paper will present some of the key focal points used by Conoco Inc. in pipeline project development. It proposes GIS technology to make pipeline projects a contributor to sustainable growth success.