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Selman C.,Wood Group Integrity Management
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

Depending upon the location and source of the estimate, corrosion accounts for between 20% and 50% of oil and gas pipeline failures. Modelling of external corrosion and the liquid phase during design is relatively robust, and design risks are relatively low. Corrosion in the vapour phase is, however, extremely difficult to model accurately for fundamental physical, chemical and practical reasons, and is not readily amenable to operational mitigation. The design process is challenging and has resulted in many cases of unexpected pipeline damage or failure. This paper describes the most common form of vapour phase corrosion, the origins of the uncertainty in prediction, then discusses strategies developed by experience for determining the appropriate corrosion design for wet gas pipelines. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

Collins S.,SANTOS Ltd | Mills A.,Wood Group Integrity Management
Annual Conference of the Australasian Corrosion Association 2014: Corrosion and Prevention 2014 | Year: 2014

Since 2012, Santos have been in the process of implementing an extensive update to their static pressure equipment inspection and integrity management programs, following formal API RP 581 Risk Based Inspection (RBI) principles. This is a significant multi-year project, covering the majority of Santos' Eastern Australian Business Unit surface assets and equipment, and requiring a substantial commitment in resources. Risk Based Inspection of ageing equipment places a high demand on the integrity of the underlying data, including collating, interpretation and analysis of results. Supported by Wood Group Integrity Management (WGIM), Santos have been able to implement a fully quantitative RBI program across multiple sites with speed and confidence, delivering significant risk and cost reductions to Santos. Whereas normal industry practice has been to use an area based risk approach, Santos elected to use a full financial RBI approach to manage all of their Static Pressure Equipment, including vessels, tanks, piping and PSVs. A fully financial quantitative risk assessment approach allows informed inspection and integrity management decisions to be taken, considering all of the potential risk impacts (safety, environmental and production and equipment costs). The RBI process is only one part of the integrity management approach used by Santos. Through the RBI process, Santos also enhanced their Integrity Management Plans (IMPs) and the definition of Integrity Operating Windows (IOWs), updated Business Processes and the associated Guidelines and Procedures including Training and Support for Staff and Contractors involved in the RBI process. This paper addresses the business processes, software selection process, management of technical challenges (especially management of deficiencies in the API RP 581 RBI approach and software), data collection & validation, output review through workshops & specialist input, and the transferring of risk results into 'on the ground' execution. Specifically, the paper outlines the benefits and challenges of implementing a fully quantitative financial risk model, in comparison to a simpler qualitative approach. The findings are applicable to any oil & gas operator wishing to optimise their inspection programs and best manage their operational risks.

Barker R.,University of Leeds | Hu X.,Wood Group Integrity Management | Neville A.,University of Leeds | Cushnaghan S.,Royal Dutch Shell
SPE Journal | Year: 2014

Various sections of carbon-steel pipework removed from an offshore facility were found to have experienced severe degradation, partly attributed to an insufficient inhibitor dose rate, as discussed in a previous case study (Hu et al. 2011b). An investigation was conducted to compare the predictive capability of an empirical model generated with data from a submerged-impinging-jet laboratory apparatus. The model was assessed in its ability to determine the rate of thickness loss for carbon-steel pipework subjected to a CO 2-containing erosion-corrosion environment, reviewing to what extent the prediction agrees with inspection data. The investigation considers whether the developed tool could have predicted pipework failures on the facility, comparing it with the degradation rate calculated from a leak that occurred within the past 2 years. The program of experiments set out to create a means of prediction with the material-loss data from submerged-impinging-jet tests over a range of conditions replicating those within the line. Information pertaining to the temperature, production rate, and sand loading was collated for the offshore facility. These data were used along with mass-loss results to predict the degradation rate on the asset as a function of time over a 5-year period. This in turn was used to predict the total thickness loss of the pipework wall as a function of time. Consideration was also given to the current use of inhibition (10 ppm Inhibitor A) as well as the predicted thickness losses as a function of time had a candidate inhibitor been used instead (50 ppm Inhibitor B). Limitations of the model are presented, along with suggestions for ways to develop the model further. Copyright © 2014 Society of Petroleum Engineers.

Ahmed T.M.,Wood Group Integrity Management
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

Fatigue performance is a serious concern for welded joints of risers and subsea flowlines used for deepwater oil and gas developments. Today's design requirements for some flowlines are becoming increasingly more complex because of high pressures/high-temperature requirements or high plastic strain during installation and service. The impact of such design requirements on fatigue performance has not been fully understood. The paper examines the influence of operating temperature and plastic deformation on the fatigue crack growth behavior of metals. Attempts were made to review the fatigue literature and rationalize the influence of high operating temperature and plastic deformation on fatigue through the strong correlation between the material elastic modulus and fatigue crack growth curves in air. The paper emphasizes the importance of the elastic modulus which has been shown in the fatigue literature to have a significant role on fatigue behavior of metallic materials tested in air at high load ratios. The findings are relevant when carrying out fatigue life assessments for projects related to high temperature applications or where pipelines experience high plastic strain during installation or service. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

Ifezue D.,Wood Group Integrity Management | Tobins F.,University Of Abuja
Journal of Failure Analysis and Prevention | Year: 2013

During preparation for a hydrotest on a 6-in. liquid discharge line of an onshore gas terminal, water was observed to be dripping from the gland packing on the isolation gate valve. On closer inspection, it was found that the gland eyebolt on the valve was fractured. The fractured sample was sent for metallurgical examination to determine the cause of the fracture. Results of this investigation suggest that the brittle fracture of the eyebolt was caused by hydrogen embrittlement (HE). The eyebolt was supplied with the wrong composition and hardness, thereby producing increased sensitivity to HE. This article illustrates the typical procedure for a metallurgical failure investigation and presents the results of the investigation, lessons to be learnt and remedies to be applied to prevent re-occurrence. The main recommendations are to; review the valve supplier's quality assurance procedures and to ensure that new valves are supplied in the specified composition and hardness; carry out positive material identification tests on all existing stock of Class 600 gate valves and consider using tempered plated bolting for the high risk (hydrogen-rich environment) environment. © 2013 ASM International.

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