Experimental Investigation of Rheological Behaviors and Flow Improving by Chemical for Waxy Crude Oils

It has been proved that the flow improver makes the transportation of waxy crude oils in pipeline much more economic and safe, but so far an universal flow improver for various waxy crude oils has not been found because of inadequately understanding the action mechanism of the flow improvers. Therefore it is necessary for the mechanism to be studied further. A series of synthetic waxy oils (SWOs) with or without flow improver GY1, a long chain alkyl acrylate polymer based chemical, are prepared from 25# transformer oil, 50#, 60# (macrocrystalline) and 80# (microcrystalline) wax, single or mixed, and in some cases 60# road asphalt by mixing the ingredients at 100°C for 1 hour. Characteristic temperatures, viscosity-temperature properties and rheological behaviors are studied by using rheological techniques, and microstructures of wax crystals grown from SWOs at 20 °C are analyzed by using a polarization microscopy. Some abnormal viscosity-temperature properties of SWOs are found, which mainly results from wax crystallization and network structure formed by wax crystals. The mechanisms involved in the structure formation and fluidity improved by chemical for SWOs are discussed here. Studies show that the structure formation is followed by the formation of crystal nuclei, growth and interconnection or bridging of the wax crystal particles, which is closely relevant to wax molecular dimension and content, crystalline particle size, shape, concentration and surface characteristics. GY1 added into the SWOs lowers their cloud points by 0–2.0 °C and enhances the amounts of wax precipitated at 30 °C by 10–35wt%, which might not be involved in the mechanisms of the fluidity improving under this study. The extent of pour point depression by GY1 increases with increasing the wax molecular size and decreasing the wax content in the SWOs. As long as the SWO treated by GY1 has a greater yield stress reduction at the temperature closed to its pour point, its viscosity and pour point reduction will be more obvious. The common shortcut of pour point depression and viscosity reduction is to inhibit or desintegrate the formation of paraffin crystal network. The mechanisms involved in fluidity improvement of waxy crude oils by chemicals include modifying surface properties of waxy crystals and promoting crystal particle growth with higher symmetry.

Testing to Determine Whether a PetroSleeve Can be Used for an Electrical Connection to a Pipe for AC Mitigation

The use of a mechanical electrical connection to a pipeline is tested to determine its’ viability. Historically, the installation of a cadweld on pipelines has been the method generally accepted for attaching an electrical connection to pipe. Cadwelds are usually serviceable. In the case of accommodating up to 800 amperes of current, up to 3 CAD welds have been used. In addition, there is a general feeling in the pipeline industry to avoid cadwelds, if possible, because they can create a heat affected zone and the possibility of cracking. Where pipelines traverse or parallel high voltage transmission lines, there exists the possibility of voltage and current induction when phase imbalance occurs. These current flows can approach 800 amps. If a cadweld is the main conduct at the pipe surface, burns, high heat, or connection malfunction can occur. This paper describes the testing undertaken to determine if a PetroSleeve installation could be used as a mechanical electrical connection suitable for conducting up to 800 amperes of current. Following the initial testing, three sleeves were installed on operating pipelines for AC Mitigation.

Validation of Sleeve Weld Integrity and Workmanship Level Development

Full encirclement repair sleeves with fillet-welded ends are often used as permanent repairs on pipelines to reinforce areas with defects, such as cracks or corrosion. In-service failures have occurred at reinforcing sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks and undercut at the fillet welds, inadequate weld size, and sleeve longitudinal seam ruptures. This work was undertaken to support the development of tools for sleeve design and for conducting an engineering assessment to determine the tolerable dimensions of flaw indications at full encirclement repair sleeves. In particular, the project was intended to validate the stresses estimated using finite element analysis (FEA) models against actual in-service loading conditions experienced at reinforcing sleeves. The experimental work focused on the collection of full-scale experimental data describing pipe and sleeve strains for the following field and laboratory conditions: • Strains induced by sleeve welding, • Strains induced by pressurization of the sleeved pipe, • Strains induced by pressurization of the sleeved pipe and the annulus between the pipe and sleeve. Finite element models of the field and laboratory sleeved pipe segments were developed and subjected to the same applied loading conditions as the full-scale sleeved pipe segments. Comparisons of the measured strains against those estimated using FEA were completed to determine the ability of the models to predict the behaviour of the sleeved pipe segments. Comparisons were made to illustrate the relative strain levels and deformation trends, the accuracies of the strain predictions and trends in changes with pressure, the differences in behaviours between tight and loose fitting sleeves, and the effects of pressurizing the annulus between the pipe wall and sleeve. The analysis of the field data and FEA modeling predictions led to several conclusions regarding to use of numerical models for predicting sleeved pipe behaviour and weld flaw acceptance: • FEA results demonstrated behaviours that were consistent with full scale data, • Trends in the FEA predicted strains agreed with the full-scale data, • FEA models describing the effects of gaps between the pipe and sleeve and annulus pressurization agreed with field experience and engineering judgment, • Evaluation of the significance of root and toe flaws can be completed by extending the models validated in this work.

The Design, Development and Validation of an Innovative High Strength, Self Monitoring, Composite Pipe Liner for the Restoration of Energy Transmission Pipelines

The research described in this paper centers on a composite of thermoplastic materials that can be inserted in a degraded steel pipe to completely restore its strength. Through the use of fabrics consisting of ultra high strength fibers that are co-helically wrapped over a thin walled thermoplastic cylindrical tube that serves as a core, arbitrarily high pressures can be achieved. This paper first outlines the design, manufacturing and installation procedures developed for this unique material to provide a context for the engineering research. Based on this outline, the technological basis that has been developed for assuring the strength and long term durability of this concept during its insertion, and in its very long term service as a liner in energy transmission pipelines, is presented in detail. The research that is described includes burst testing of the material in stand alone pipe form, load/elongation testing of ultra high strength fabrics, and linear and nonlinear elastic and viscoelastic analysis models. This body of work indicates that the concept is fundamentally feasible for restoring a wide range of large diameter natural gas and liquid transmission pipelines to be able to carry arbitrarily high pressures over very long lifetimes. It also indicates that liners can be safely installed in long lengths even in lines with severe bends in a continuous manner. With further research the concept has the potential for eliminating hydro testing and smart pigging during service, and could possibly be installed in some lines that are currently unpiggable.

Determination of Safe Pumping Temperature for Waxy Crude Pipelines

Flow risk of a hot waxy crude pipeline mainly comes from restart failure, i.e. oil gelation resulted from prolonged pipeline shutdown, and unstable operation at low flow rate. Once the unstable operation happens, the friction loss of the pipeline increases with decreasing flow rate and finally flow may cease if treated improperly. To avoid these flow risks, the pumping temperature of the crude is generally required to be kept above a minimum allowable temperature, and conventionally the pour point temperature is taken. This practice is effective but quite rough. Obviously, to control the inlet temperature of a heating station at the pour point temperature implies different safety margin for winter and summer operation. For large throughput hot oil pipelines, reduction of the heating temperature even by a little bit may save a great amount of fuel. Therefore, how to save fuel while ensuring safe operation has been a valuable topic for long time. On the other hand, many factors impacting the flow safety are stochastic and with uncertainty, so analysis without considering this feature can hardly yield convincible results, though this has been the common case for many years. In this paper, by taking the stochastic feature into account, a Stable Operation Index (SOI) and a Pipeline Restartability Index (PRI) were proposed to assess the flow safety of a pipeline concerning the low-flowrate stable operation and restartability after shutdown. Combining these two indexes, a Pipeline Flow Safety Index (PFSI) was adopted to assess the flow risks of hot waxy crude pipelines. On this basis a new approach to quantitatively determining the safe pumping temperature was developed and illustrated by a case study. Encouraging results show that this new approach has the potential to replace the simple rule of pour point as a guide to determining the safe pumping temperature of waxy crude pipelines.

A Central Database Improves Pipeline Projects

Pipeline projects see enormous benefit from using geospatial information systems since a pipeline will commonly cover large geographic distances. In doing so, terabytes of engineering, geotechnical, and environmental data can be generated for engineering and regulatory needs. A central database allows the project to organize this information and provide a single source of truth. In fact, the central database is as much a philosophy as it is computer infrastructure. This level of organization allows a project to properly manage change, thus ensuring data integrity and security. When data is reliable and secure, its full value can be realized during the pipeline planning stage and even further leveraged through construction and operation.

Hydraulic Characteristics of Pipelines Transporting Hot Waxy Crudes

Waxy crudes are generally pipelined by means of heating. In general, the friction loss of a pipeline decreases with decreasing flow rate. This is the case of isothermal pipeline. However, a hot oil pipeline operated at low flow rate might show a contrary case, i.e. friction-loss increases with decreasing flow rate. This is an unstable operation state and may result in disastrous consequence of flow ceasing if tackled improperly. For a waxy crude pipeline, this may also be exaggerated by the non-Newtonian flow characteristics at temperatures near the pour point. That is to say, there may exist a critical flow rate for pipelines transporting heated waxy crude, and in order to ensure safe operation, the flow rate of a pipeline transporting hot oil should be no less than this critical flow rate. Based on theoretical analysis and can study, the hydraulic characteristics of pipelines transporting hot waxy crudes was investigated, and an empirical model was developed correlating the critical flow rate QC and the pipelining parameters, such as the average overall heat transfer coefficient, the ground temperature, the heating temperature, etc. Another relationship was found between TZC, the outlet temperature of the pipeline corresponding to the critical flow rate, and the critical flow rate. This TZC is also the lowest pipeline outlet temperature that ensures the normal pipelining operation state. Case study on a 720mm O.D. pipeline transporting heated Daqing waxy crude with a pour point of 36 °C showed that the TZC was in a range of 31∼34.2°C.

Leading Practices for the Prevention of Mechanical Damage

Practices that are used by pipeline operators to prevent mechanical damage are examined in this paper. A set of practices specific to pipeline operations is presented. The practices were initially developed by a group of subject matter experts working under the auspices of the American Petroleum Institute and the Association of Oil Pipelines (API/AOPL) Performance Excellence Team. The practices drew upon the work started within the Common Ground Initiative in the late 1990s and continued by the Common Ground Alliance. The practices presented were reviewed again in preparation of this report. The practices build upon practices defined by Common Ground Alliance (CGA), largely by providing greater specificity and ensuring completeness and follow through in communication and documentation. A subset of these practices became the foundation of the standard, API 1166 Excavation Monitoring and Observation. The paper also provides an overview of historical safety performance for the period 1995 through 2003; with a specific focus on mechanical damage related incidents including the additional detail available in the recent change in Pipeline and Hazardous Materials Safety Administration (PHMSA, US-DOT) Incident Reporting. This period was selected because it represented the time period where there was a heightened interest in preventing damage to pipelines as described above. The large majority of mechanical damage related incidents result in an immediate impact; a small portion occur at some later point in time. Data for the nine-year period indicate that approximately 90 percent of the incidents result in an immediate impact. This is significant in that it underscores the importance of prevention of damage. The experience of hazardous liquid pipelines has shown a continuing decrease in numbers of annual incidents. The experience of natural gas pipelines has not shown a decreasing trend; in fact, it is relatively flat for the period of study. While the heightened awareness and strong commitment to dedication are known to have had an impact on damage prevention through numerous stories and vast experience shared by a variety of stakeholders, it is prudent to be concerned that the performance may be reaching a “plateau”.

Data Management as the Foundation of Integrity Management

Worldwide, regulatory bodies are applying increasing pressure on pipeline operators to manage their pipeline systems in a safe and reliable manner. To respond to these escalating requirements, operators are developing comprehensive integrity management systems. Integrity management begins with developing strong data management capabilities to host and integrate numerous sources of physical data. A key issue in today’s integrity data management system development is integration of all pipeline data from multiple levels of the organization to one central location for easy and effective utilization of the information. Data are often scattered throughout the organization, which often tends towards data duplication, poor decisions, errors, and inefficiencies. The lack of an effective data management process leads to time and resource constrains. In the long run; development of a comprehensive integrated system has proven to be worth the investment. The primary objective of the data model is to account for a common/standard linear referencing of all pipeline features occurring along the pipeline route, and/or within the pipeline right of way. This paper describes the key factors to consider when developing a full data management system and provides some insights into how these integrated data are used to address the need for integrity management.

Development of a Supersonic Ejector for Capturing Very Low-Pressure Vent Gases and Re-Injection Into a High-Pressure Gas Stream

The purpose of the ejector device is to capture the gas leakage from a dry-gas seal at low pressure, and re-inject it into the fuel gas line to the gas generator (without the use of compressors or rotating elements), hence providing a means to utilize the gas that would otherwise be vented to atmosphere. Implementation of this device will also have the benefit of reducing greenhouse gas emissions to the atmosphere. The primary challenge to achieve the above goal lies in the fact that the leakage gas pressure is in the range of 70–340 kPag, while the minimum pressure required upstream of the fuel gas regulator is in the range of 2400–3300 kPag. The device consists of a two-stage supersonic ejector. The first stage is highly supersonic (nozzle exit Mach number ≃ 2.54), while the second stage is moderately supersonic (nozzle exit Mach number ≃ 1.72). Several tests where conducted on various configurations of the two stages on natural gas in order to arrive at the optimum design and operating parameters. The optimum design gave an expansion pressure ratio (motive/suction) of the order of 14.0 and compression pressure ratio (discharge/suction) of around 8.1. These ratios would meet the requirement of the minimum suction and discharge pressure mentioned above. This paper presents the optimum configuration arrived at after several iterations of different geometries of the supersonic nozzles, particularly for the first stage ejector, and presents the performance test results of the integrated system. The results indicate that the device would meet the requirements of capturing the low pressure, low flow dry gas seal leakage and re-inject it into the fuel gas stream with an overall ejector efficiency (based on thermodynamic availability) of 80%.