Water Hammer Likely Cause of Large Oil Spill in North Sea

On December 12, 2007, the second largest oil spill in the history of Norwegian oil exploration occurred on StatoilHydro’s Statfjord Alpha platform. The spill was caused by a snapped 20″ oil off-loading hose. Thorough investigations by StatoilHydro [1] and by the Norwegian authorities [2] revealed the chain of events that led to this incident. One of the links in this chain was the unintended fast closure of the shuttle tanker’s bow loading valve during off-loading. This closure initiated a pressure surge in the oil off-loading system. As part of the internal investigation by StatoilHydro, TNO carried out a water hammer analysis of the entire oil off-loading system, including the off-loading hoses to the seabed and further subsea piping up to the platform. These simulations revealed that high pressures could occur in the oil off-loading system due to fast closure of the bow loading valve followed by multiple reflections at diameter changes. The maximum pressures were more than 100 bar above the normal operating pressure of 10 bar. The diameter changes were introduced into the oil off-loading system to maximize the off-loading capacity. The results of the water hammer analysis provided the missing link between the fast closure of the valve and the damaged hose and also showed that this damage most likely occurred within 0.5 second after the closure of the valve. Based on the results of this analysis, also other oil off-loading systems are being reinvestigated to prevent a similar incident to occur in the future.

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Analysis of Oil Spill Risk in DP Shuttle Tanker Direct Offloading Operations

Volume 2: Structures, Safety and Reliability ◽

10.1115/omae2011-50344 ◽

2011 ◽

Author(s):

Haibo Chen ◽

Torgeir Moan ◽

Arve Lerstad ◽

Ka˚re Breivik

Keyword(s):

Oil Spill ◽

Weak Link ◽

Base Case ◽

Frequency Model ◽

Offshore Installations ◽

Study Results ◽

Loading System ◽

Oil Export ◽

History Of ◽

Risk Reduction Measures

DP shuttle tankers performing offloading directly from fixed or geostationary floating offshore installations is addressed in this paper. It is important to ensure that disconnection of offloading hose can be achieved in time given shuttle tanker DP failure and position loss. The accident scenario is the hose fail-to-disconnect while shuttle tanker has an excessive position excursion. The consequence can be oil spill combined with the damage the offloading system. The spill amount can be as much as the crude oil volume in the hose, or over 1000 m3 if isolation and shutdown of oil export pump on the installation are not achieved timely. Various barriers to prevent oil spill have been developed over the past 30 years’ history of shuttle tanker offshore loading. However, the direct offloading is a new operational context to the traditional offloading. A quantitative frequency model for oil spill initiated by DP shuttle tanker position loss in direct offloading is presented in this paper. Case study results show that in the base case where only traditional barriers are used, the frequency for large oil spill up to 1000 m3 or more may reach 2.48E−03 per year, given 20 hours offloading cargo transfer time and 52 times offloadings per year. This frequency is not negligible, and risk reduction measures are viewed necessary. Novel safety barriers, i.e. Automatic Shutdown and Release (ASDR), as well as the HPR (Hydroacoustic Position Reference) and BLS (Bow Loading System) weak link mode, are analyzed as sensitivity cases. Results show that the frequency of large oil spill can then be reduced to 3.81E−05 per year, i.e. 1.5% of the base case value, and this is well within 1.0E−04 per year level. Recommendations to minimize oil spill risk during DP shuttle tanker direct offloading operations are proposed in this paper.

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Temperature, seasonality and salinity history of the early Eocene North Sea Basin inferred from fish otoliths and mollusks

Rendiconti online della Società Geologica Italiana ◽

10.3301/rol.2014.129 ◽

2014 ◽

Vol 31 ◽

pp. 217-218

Author(s):

Daan Vanhove

Keyword(s):

North Sea ◽

Early Eocene ◽

History Of ◽

Temperature Seasonality ◽

Fish Otoliths

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Pipeline Instrumentation: The British Gas National Transmission System

Measurement and Control ◽

10.1177/002029408702000103 ◽

1987 ◽

Vol 20 (1) ◽

pp. 18-25

Author(s):

P Gilbert

Keyword(s):

Distribution System ◽

Transmission System ◽

Process Conditions ◽

Pipeline System ◽

Operating Pressure ◽

Distribution Grid ◽

History Of Development ◽

History Of ◽

Instrument Engineer ◽

Transmission And Distribution

The transmission and distribution system operated by British Gas plc is the largest integrated pipeline system in Europe. The whole system comprises a national transmission system which carries gas from five terminals to the twelve gas regions. Each region in turn carries the gas through a regional transmission system into a distribution grid and thence onto its customers. The national, regional and distribution system all present the instrument engineer with different technical challenges because of the way in which they have been built and are operated, however, it is simplest to characterise them by their process conditions. The operating pressure is highest in the national transmission system being up to 75 bar, in the regional transmission system the pressure is usually less than 37 bar, and in the distribution grid it is less than 7 bar. In general, the pipe diameters decrease from the national system downwards, and the measured flowrates are lowest in the distribution grids. This paper is concerned only with instrumentation on the national transmission system. The discussion will cover current technology which is typical of that being installed at present, and concentrates on the more commonly found instrumentation. The paper begins with a brief history of development of the national transmission system and a description of how it is operated. This is followed by a discussion on the application of computers to the control of unmanned installations. A section concerning the measurement of pressure and its application to the control of the system comes next. The main part of the paper contains an analysis of high accuracy flowmetering and the paper concludes with some comments on developments in instrumentation and their application to changing operation of the national transmission system.

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Second Paper: Deep Drawing and Free Forming Using a Water Hammer Technique

Proceedings of the Institution of Mechanical Engineers ◽

10.1243/pime_proc_1964_179_019_02 ◽

1964 ◽

Vol 179 (1) ◽

pp. 222-233 ◽

Cited By ~ 3

Author(s):

A. P. Vafiadakis ◽

W. Johnson ◽

I. S. Donaldson

Keyword(s):

Deep Drawing ◽

Time History ◽

Water Hammer ◽

High Rate ◽

Pressure Time ◽

Order Of Magnitude ◽

History Of ◽

Overall Efficiency ◽

Initial Movement ◽

Better Than

Earlier work on a water-hammer technique for high-rate forming of sheet metal has been extended to include work on deep drawing using lead plugs. A study of the pressure-time history of a deforming blank during its initial movement is reported. An assessment of the overall efficiency of the process has been made and is found to be about 50 per cent; this is an order of magnitude better than that found with comparable electro-hydraulic and explosive methods.

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Numerical simulations of non-spherical bubble collapse

Journal of Fluid Mechanics ◽

10.1017/s0022112009006351 ◽

2009 ◽

Vol 629 ◽

pp. 231-262 ◽

Cited By ~ 151

Author(s):

ERIC JOHNSEN ◽

TIM COLONIUS

Keyword(s):

Bubble Dynamics ◽

High Pressures ◽

Pressure Ratio ◽

Free Field ◽

Water Hammer ◽

Incident Shock ◽

Bubble Collapse ◽

Shock Propagation ◽

Potential Damage ◽

Very High

A high-order accurate shock- and interface-capturing scheme is used to simulate the collapse of a gas bubble in water. In order to better understand the damage caused by collapsing bubbles, the dynamics of the shock-induced and Rayleigh collapse of a bubble near a planar rigid surface and in a free field are analysed. Collapse times, bubble displacements, interfacial velocities and surface pressures are quantified as a function of the pressure ratio driving the collapse and of the initial bubble stand-off distance from the wall; these quantities are compared to the available theory and experiments and show good agreement with the data for both the bubble dynamics and the propagation of the shock emitted upon the collapse. Non-spherical collapse involves the formation of a re-entrant jet directed towards the wall or in the direction of propagation of the incoming shock. In shock-induced collapse, very high jet velocities can be achieved, and the finite time for shock propagation through the bubble may be non-negligible compared to the collapse time for the pressure ratios of interest. Several types of shock waves are generated during the collapse, including precursor and water-hammer shocks that arise from the re-entrant jet formation and its impact upon the distal side of the bubble, respectively. The water-hammer shock can generate very high pressures on the wall, far exceeding those from the incident shock. The potential damage to the neighbouring surface is quantified by measuring the wall pressure. The range of stand-off distances and the surface area for which amplification of the incident shock due to bubble collapse occurs is determined.

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