A surge control system for a natural gas centrifugal compressor station has been modified in order to reduce shutdowns caused by high discharge temperature and provide a more robust and stable operation. The process consists of a compressor driven by a 14 MW gas turbine and recycle piping, a 16” recycle valve, a PLC based surge control algorithm, a flow measurement element, and a compressor differential pressure transmitter. The control objective is to manipulate the recycle valve to maintain flow through the compressor to a setpoint determined from the differential pressure across the compressor. Field tests were conducted to measure the open loop process dynamics of the valve, piping, compressor and transmitters. From the test data, the relevant process dynamics were determined enabling the development of a first order plus dead time model of the system. The process dynamics are complex due to the gas dynamic effects of the station piping and tend to exhibit inverse and time delayed behavior. Large variations in process gain also create problems with obtaining a consistent flow response under different operating conditions. A stability analysis was completed and the control system was redesigned with several enhancements including derivative control, flow signal filtering, process linearization, and improved controller programming techniques. The results of the modifications are the compressor does not shut down when subjected to transients from other units, the compressor can be started against high head conditions, and the closed loop response time is ten times faster than the previous system. The new system has been in operation since May 1997.

Recent advances in PLC, SCADA and leak detection system technologies lead to the development of a highly integrated control system. Interconnected with fiber optic communication speeds (OC-1), this level of integration moves away from the historic model of stand-alone field controllers connected over low speed communication links to a centralized control center which, in turn, exchanges data from the host system to stand-alone leak detection processors. A new system design approach utilized familiar pipeline control elements such as PLC controllers and MODBUS communication protocols in combination with elements more typically associated with an office environment such as Windows NT servers, PC compatible computers, and Ethernet TCP/IP communications networks. These open-architecture components were used to fully develop, debug and test the SCADA system prior to system startup. The pipeline simulator is used as the centerpiece for this process to perform thorough operational validation of the system long before initial linefill. Once the various components were fully tested they were exported to the physical system in an operational state. The result is nearly seamless control systems supported by high data rates, high model speeds, common databases, and multi-channel communications. The increased level of integration has had dramatic impacts in leak detection, system safety, engineering development, operator training, and overall reliability of the control systems. The following paper presents a narrative overview of these new developments in the context of an implementation on Pacific Pipeline System (PPS). PPS is a recently constructed and commissioned 209 km (130 mile), 50.8 cm (20″) diameter, hot crude oil pipeline between the southern portion of California’s San Joaquin Valley and refineries in the Los Angeles basin. Following the Interstate 5 corridor over the “Grapevine”, Tejon Pass, Angeles National Forest and through heavily populated areas, this pipeline traverses some of the most environmentally and safety sensitive regions in the United States. The joint federal and state Environmental Impact Report / Environmental Impact Statement (EIR/EIS) set high hurdles for leak detection and control system performance. The historic control architecture and technologies were not adequate. This paper provides an overview of the environmental and physical constraints of the Pacific Pipeline System alignment, hydraulics, pumping and metering equipment, and block valve locations. It also discusses their impact on the design, programming and commissioning of a SCADA system meeting the requirements of the EIR/EIS. The paper then describes in more detail the fiber-optic communication system, control system architecture, SCADA system, leak detection models, simulator models and implementation methods, along with the engineering decisions leading to a comprehensive solution for the SCADA and leak detection requirements.

Motor and pump units can start either directly across the line (utility) or through a VFD. If the power system is weak (high impedance and relatively low available MVA), the result will be limitations on the maximum size of motor that may be started directly across the line. Currently some available power systems are not capable of starting large motors across the line and therefore VFD systems are required. A VFD can be used for starting purposes or to operate a motor/pump unit (unit) continuously. Liquids pipelines have been using VFDs for unit starting purposes and for pressure control while either one of the units connected to the VFD or while there is a dedicated VFD per unit. One VFD can be used to operate all the units. The VFD starts the motor, ramps it up, and synchronizes it with the utility to switch the motor from VFD operation to utility operation. The VFD follows the same sequence with the next unit. The VFD also switches the motor from utility operation to VFD operation. With pumps in series, one unit can remain connected to the VFD for pressure control in liquids pipelines. Each unit can also be controlled by a dedicated VFD, allowing independent control of each unit for start-up and speed control. Both single VFD or dedicated VFD per unit offer advantages. Benefits of using a single VFD for all units are cost savings for some applications, a backup start across the line when allowed by the power system, and station pressure control. The benefits of a dedicated VFD per unit application include more flexibility in flow and pressure control, ease of expansion without interrupting existing operations for an extended period, energy efficiency, and redundancy. Motor protection schemes for the above two VFD applications are discussed and compared in this paper. In order to maintain a safe and reliable pipeline system, comprehensive motor protection functions are provided to the pump unit. Although the principles are the same, there are some differences between the two motor protection applications. For a dedicated VFD per unit application, the VFD protection/control circuitry normally provides motor protection because the motor is always connected to the VFD. RTDs over-temperature protection is not typically a standard feature of VFDs, however, it can be provided by proper PLC programming or the VFD incoming feeder protection relay.

Since 1999 PEMEX Gas (PGPB) has adopted a risk management scheme as common practice to support maintenance programming in a pipeline network of more than 11,000 kilometres. The risk management approach has been extensively used in the 14 working sites that comprise the pipeline division. Taking into account that over the past four years the pipeline incident rate has been significantly reduced and has thus lessened the consequence of failure cost in terms of reduced service interruption, property damage and safety, PGPB decided to re-evaluate and upgrade its risk management programme by enhancing the risk assessment tool to better reflect increased awareness and experience with the evaluation of the pipeline network risks. Decisions to implement risk–reduction activities derived from the results of the risk assessment phase are addressed in terms of “Dollars of Risk” by a quantitative risk model. Development of Tolerable Risk Criteria (Ref. 2) indicated the amount of risk that PGPB is willing to maintain in its pipeline facilities. This paper shows a case study of a risk management application, describing the benefits of having a methodology available to support maintenance planning and investment in pipeline systems.

This paper addresses the problem of developing an optimization structure to aid the operational decision-making in a real-world pipeline scenario. The pipeline connects an inland refinery to a harbor, conveying different types of products (gasoline, diesel, kerosene, alcohol, liquefied petroleum gas, jet fuel, etc). The scheduling of activities has to be specified in advance by a specialist, who must provide low cost operational procedures. The specialist has to take into account issues concerning product availability, tankage constraints, pumping sequencing, flow rate determination, and a series of operational requirements. Thus, the decision-making process is hard and error-prone due to the diversity of aspects to be considered. Nevertheless, the developed optimization structure can aid the specialist in solving the pipeline scheduling task with improved efficiency. Such optimization structure has its core in a novel mathematical approach, which uses Constraint Logic Programming (CLP) and Mixed Integer Linear Programming (MILP) technologies in an integrated CLP-MILP model. In particular, the integration of CLP and MILP technologies has been recognized as an emerging discipline for achieving the best that CLP and MILP can contribute to solve scheduling problems [1]. The scheme used for integrating CLP and MILP is double modeling [1], and the combined CLP-MILP model is implemented and solved by using a commercial tool [2]. Illustrative instances demonstrate that the optimization structure is able to define new operational points to the pipeline system, providing significant cost saving.

This paper will present the context, objectives, challenges and innovative software development and project management techniques that enabled the building of a comprehensive oil accounting (OA) system. A major stage in the continuing development of OA components, completed in 2002, replaced an aging legacy system and added considerable functionality. Components are added to the OA system on a continuous basis The target result is an automated crude oil balancing and revenue accounting system that interfaces with other pipeline-management software systems. The challenge was to custom build and implement an OA system that: • Significantly reduces dependence on IS resource’s specialized skills. • Automates data validation between pipeline operations and management software systems. • Reduces turn-around time of the monthly invoice cycle. • Dramatically increases customer’s information availability and enhances information dissemination to customers. • Accommodates new business rules with minimal reconfiguration effort. The project management approach was to compress system development and delivery into predictable and controllable segments. These segments deliver complete components into the production environment at established milestones rather than as a whole system at a single “big-bang” event. The segmented delivery approach is known as SCRUM in the IT industry. It enabled the team to react effectively to changing business requirements throughout development. Additional techniques known as XP (Extreme Programming) were also utilized to greatly enhance the quality and predictability of system delivery. XP stresses very strong and committed client project involvement. This paper will outline the oil accounting system components and the SCRUM and XP techniques the project delivery team believes have significantly enhanced the success of the project. Due to the proven success of these techniques they are currently being used in several other IS projects including additions to the OA system. In summary, the project management and software system development approach, and stakeholder involvement secured the success of the OA system delivery. These approaches embody the philosophy of continuous improvement and superior quality in information system delivery.

Geographic Information System (GIS) software has evolved to the point where it is extremely valuable to the planning, construction and operation of pipelines across a range of industries. Recently, GIS software of high quality has become freely available for use and modification under open source licensing schemes. This paper evaluates the utility of a geographic information system prepared using open source software for shared departmental use. Analysis includes areas such as functionality of the software, setup time, and total cost of ownership. The departmental focus is at a level concerned with pipeline planning and cost estimating. The full GIS package used for the analysis consists of a database, spatial data management software, and a web server providing web-based access to geomatic data suitable for a pipeline construction department. The utility of application programming interfaces provided through the GIS with open source software development tools is analysed in the form of a what-if economic comparison tool for pipeline route selection. The ability of the GIS to integrate data from other departmental systems is also examined. Final conclusions serve to aid pipeline GIS teams in determining if open source solutions are ready for widespread use.

Two-phase flow pipelines are utilized in simultaneous transferring of liquid and gas from reservoir fields to production units and refineries. In order to obtain the hydraulic design of pipelines, pressure drop and liquid holdup were calculated following pipeline flow regime determination. Two semi-empirical and mechanistical models were used. Empirical models e.g. Beggs & Brill, 1973, are only applicable in certain situations were pipeline conditions are adaptable to the model; therefore we used the Taitel & Dukler, 1976, Baker et al., 1988, Petalas & Aziz, 1998, and Gomez et al., 1999, mechanistical models which are practical in more extensive conditions. The FLOPAT code was designed and utilized which is capable of the determining the physical properties of the fluid by either compositional or non-compositional (black oil) fluid models. It was challenged in various pipeline positions e. g. horizontal, vertical and inclined. Specification of the flow regime and also pressure drop and liquid holdup could precisely be calculated by mechanistical models. The flow regimes considered in the pipeline were: stratified, wavy & annular (Segregated Flow), plug & slug (Intermittent Flow) and bubble & mist (Distributive Flow). We also compared output results against the Stanford Multiphase Flow Database which were used by Petalas & Aziz, 1998, and the effect of the flow rate, pipeline diameter, inclination, temperature and pressure on the flow regime, liquid holdup and pressure drop were studied. The outputs (flow regime, pressure drop and liquid holdup) were comparable with the existing pipeline data. Moreover, by this comparison one may possibly suggest the more suitable model for usage in a certain pipeline.