TransAlaska Pipeline System Linewide Slackline Investigations for Potential Pipe Vibrations

During the summer of 1996, the TransAlaska Pipeline System (TAPS) experienced pipe vibrations near Thompson Pass, which is located 25 miles north of the Valdez Marine Terminal (VMT). The VMT is the southern terminus of the 48-inch oil pipeline transporting Alaska North Slope Crude for further shipment to market via marine tankers. The pipeline is designed to operate in a slackline mode as it flows over the 2,810 ft. elevation of Thompson Pass. As a result of the slackline experience gained at Thompson Pass, Alyeska evaluated other areas along TAPS where continuous slackline operation either existed in the past or could exist in the future with declining pipeline throughputs. A study determined that other locations along the pipeline could operate in a continuous slackline mode and should be investigated for potential slackline operating problems. This paper describes the slackline testing and evaluation and methods developed by Alyeska to control problems caused by slackline operation. General evaluations and observations of the slackline dynamics phenomena that can cause pipe vibrations along with guidelines and recommendations for the control or elimination of slackline vibration problems are presented.

Hydrogen Facilitated Anodic Dissolution Type Stress Corrosion Cracking of Pipeline Steels in Coating Disbondment Chemistry

The stress corrosion cracking (SCC) of pipeline steels in coating disbondment chemistry (near neutral pH solution) was studied by using slow strain rate tests (SSRT), polarization techniques, SEM and SIMS (secondary ion mass spectroscope). It was found that SCC susceptibility increased as the applied electrochemical potential and strain rates decreased. Hydrogen (H) precharging or addition of CO2 facilitated the process of SCC, suggesting that dissolution and hydrogen ingress are involved in the cracking process. SIMS analysis showed that hydrogen could diffuse into steels around the crack tip during the SCC process, which would facilitate the dissolution rate of the steel and increase SCC susceptibility. A mechanism was proposed which shows that hydrogen enhances anodic dissolution type of SCC in dilute aqueous solution. A thermodynamic analysis of the SCC process was carried out, and was found to be consistent with the experimental results.

Dual-Purpose Fibre Optic System Providing Simultaneous, Real-Time Communications and Distributed Vibration Sensing for Pipeline Applications

A proprietary fibre optic sensing technology has been developed and is capable of simultaneously utilising an existing fibre optic communication cable as an integrity-testing sensing cable, thus providing continuous, real-time monitoring of the fibre cable and any structure near the cable (ie., ground, tunnels, ducts, pipes, buildings, equipment, vessels, etc.). With this system, simultaneous fibre optic communications and real-time vibration monitoring was demonstrated using a wavelength multiplexed fibre system for a channel bandwidth of 500 MHz over 18 km of standard singlemode fibre. Real-time vibration monitoring was also demonstrated using standard singlemode and multimode fibre over lengths of 28 km and 53 km, respectively. Trials of the system are currently underway in Australia and the first commercial field installation with this capability is to be completed in mid-1998 in Indonesia. This paper highlights the benefits and potential of this dual-capacity system and details results obtained to-date.

Route Selection for Project Success: Addressing “Feeling/Perception” Issues

Selecting a route for a pipeline right-of-way (ROW) generally consists of engineering (technical and economic), socioeconomic and biophysical components. To effectively select a route, simultaneous consideration must be given to all the components from the initiation of a project to the integration of all aspects of each throughout the route selection process. To successfully select a route which creates a win-win situation for all the stakeholders of a pipeline project, political/governmental issues, community and land owner views, public perceptions and other similar controlling factors (such as Safety, Health, Environment and Risk (SHER)) must be carefully analyzed and integrated into the process. It is the consideration of all these issues that will lead to a ROW which will provide a technically acceptable solution, which is at the same time the least expensive, economically viable and acceptable to the community it traverses. This paper will provide an overview of route selection techniques (including new technologies) used and the process generally practiced by pipeline designers, highlighting controlling issues and optimization methods that need to be utilized in order to achieve a cost effective route selection. It provides details on significant “Feeling/Perception” issues that can either thwart or, by careful consideration of these issues, lead to a successful pipeline project. An example of such a route selection process will be provided on a project located in rough and mountainous terrain, that has significant regulatory/governmental, land, environmental, indigenous and geological issues.

Strain-Based Failure Criteria for Sharp Part-Wall Defects in Pipelines

Failure criteria in current engineering critical assessment procedures for defects in pipelines and welds are stress-based. For example, failure is presumed to occur when the net section average stress reaches some arbitrary flow stress. These approaches are unrealistic for defects of limited length where loading of the net section (ligament) is essentially strain controlled. In order to improve upon this, the authors developed a strain-based failure criterion for part wall pipe defects in terms of the maximum ligament plastic extension. While this criterion[l] provided a basis for assessing the criticality of blunt defects, with respect to plastic collapse, it did not address sharp or planar defects which promote fracture. As a defect becomes sharper, failure is determined more by local strain at the defect tip which is typically characterized by the crack tip opening displacement (CTOD). This paper describes the development of a sharp/planar defect strain-based failure criterion which relates the maximum ligament extension to the critical CTOD of the material. Two and three dimensional non-linear finite element analyses are used to determine local root extensions of circumferential defects which can be related to the loading, defect and pipe dimensions. The root extensions are calibrated to standard CTOD measurements through non-linear finite element analysis. The failure criterion development process considers various defect lengths, material work hardening rates and material models. The failure criterion is compared with analytical and experimental data to demonstrate its predictive capability. The end result of this work is the development of an alternative acceptance criterion for sharp weld defects permitting more effective repair decisions to be made based on a more uniform level of reliability.

Colombian Crude Export System Begins Full Operation

Shipments began in October 1997 along Oleoducto Central S.A (OCENSA), the 837 km oil export system, consisting of 406, 762 and 914 mm (16”, 30” and 36”) diameter pipe, from eastern Colombia to the country’s north coast on the Carribean Sea. Start-up follows the completion of a phased construction program which began in 1993–94 and ended in September 1997. The system transports production from the Cusiana / Cupiagua oilfields, and several adjacent smaller production fields in the eastern foothills of the Andes to an offshore terminal loading unit 11 km offshore. The authors provide an operating overview of this system designed to handle some 88,410 m3/d (556 kbd) and some of its operating challenges.

The Canadian Energy Pipeline Association Stress Corrosion Cracking Database

The SCC (stress corrosion cracking) database was initiated by the CEPA (Canadian Energy Pipeline Association) SCC Working. The current generation of the database has a broad scope, containing detailed data for each and every colony and its associated environmental conditions. The database also includes corrosion and dents amongst other integrity concerns to identify any correlation with SCC and provide a common industry data format to investigate these other integrity issues. The intent of the current version of the database is to provide for the most detailed data entry that one could typically capture at an investigative dig. With the wide acceptance of the current version the CEPA database it is evolving into the industry standard for investigative excavation data. The initial trending results are based on the dataset generated by CEPA member companies, which represents over a thousand investigative excavations. The trend results should only be interpreted broadly at this time, although they do generally support industry’s understanding of SCC. The development and implementation of the CEPA SCC database is premised on the belief, developed through extensive field investigations and laboratory research, that SCC is not a random development, but it initiates and grows at specific locations susceptible to SCC. It is further premised on the belief that such susceptible sites can be generally located by appropriate prioritization techniques. Thus, the objective of the database is to explore correlation among the various operational and environmental variables to improve the current understanding of how to locate SCC, and in particular ‘significant’ SCC, in order that measures can be taken to prevent operational failures and enhance the safety of Canadian pipelines. The need for an industry database regarding SCC was identified by the CEPA SCC working group shortly after its formation 1994. It was apparent that the various companies were collecting the field data from investigative excavations in significantly different formats, only some of which were electronic. The need for a common data structure and data repository to facilitate trending was reinforced numerous times at the Banff Conferences and by the NEB during its inquiry into SCC in 1995/96.

Pipeline Repair Based on Diagnostic Inspection – Investment Return

After the review and analysis of a 6000 km (3750 miles) pipeline system’s failure cases, we asked a theoretical question: what would this data show if we didn’t implement any in-line inspection or the consequential repairs and interventions? The amount of data considered is large enough to analyse how we could effect the undesirable changes. The results clearly indicate that ILI and its associated interventions can measurably reduce the number of failures on a pipeline system. However, the extent of reduction is somewhat dependant on the vintage of the pipeline system. If such interventions repair near critical defects only, the number of future failures decrease, but the trend remain unchanged. However, if the intervention is comprehensive, the failure trend will also decrease, indicatings, that in-line inspection of pipelines is a profitable investment.

An Instrumented Field Corrosion Test Loop

A multi-purpose instrumented loop in line with an oil producing well is described. The loop has several ports for coupons which were replaced periodically. Some of the coupons were used for electrochemical monitoring in addition to weight loss and visual inspection. Weight loss, pit rate and all the electrochemical methods used gave corrosion rates that were dependent on the positions of the coupons inside the loop. The corrosion rate of the coupons increased from top to bottom. This order reflected the media and flow to which the coupons were exposed in a multi-phase producing well.

Risk Management at TransCanada Pipelines

This Paper presents the method TransCanada PipeLines uses to assess the integrity risks with respect to operating its high pressure natural gas pipelines. TransCanada PipeLines’ experiences, results and successes gained through the implementation of its risk program, TRPRAM (TransCanada Pipelines Risk Assessment Model) are highlighted.