Subsea services

Thoroughly investigate subsea services in the vicinity of the construction site from historical records and through the use of geophysical techniques such as... 

Crown Estates hold records of all permitted subsea services, although the exact position may not be defined the records will give an indication of the presence of subsea services in the vicinity. 

Pre-accident test procedures were incapable of revealing these failures, because the design of the BOP control system did not allow independent functional testing of the redundant systems, neither while the BOP was on the rig nor while it was in subsea service. Withont snch independent functional testing, latent failures had caused three of the four channels to fail. (Appendix 2B of the CSB report.)... 

Subsea production systems provide for large savings in manpower as they are unmanned facilities. However, these systems can be subject to very high opex from the well servicing and subsea intervention point of view as expensive vessels have to be mobilised to perform the work. As subsea systems become more reliable this opex will be reduced. 

Corrosion resistance in subsea environments is of prime importance, as FPSO s are constructed in open water to facilitate mooring tankers at offshore oil and gas exploration stations without jetties and breakwaters. Unlike bronze components, which can develop severe galvanic corrosion, PEEK bearings and thrust washers provide longterm corrosion resistance and superior wear resistance. PEEK compoimd requires no external lubrication, another key advantage in this application. Bronze bearings and thrust washers are subject to premature wear and reduced service life should they run dry. (Victrex pic, Victrex Tech. Ctr., Hillhouse Int L, Thornton Cleveleys, Lancashire FY5 4QD, UK Phone +44—1253-897700 URL www. victrex.com). 

It is also possible to carry out a probabilistic analysis for subsea pipelines in relation to the requirements of fitness for service or life extension. This approach is supported by Hopkins et al. (2001) where the uncertainty values in relation to the inspection data, material strength, and so forth are accounted for The statistics of the input parameters and the engineering models then determine, by probabilistic analysis, the failure probability for each failure mode or mechanism and the variation of the failure probability over time. Once the uncertainty of each input value has been described statistically, a Monte Carlo simulation can be used to predict the growth rate of known defects over time. 

Corrosion in oil and gas service can be classified into two categories internal corrosion and external corrosion. Internal corrosion is primarily due to the corrosive components present in the fluids handled by the particular oil and gas asset. External corrosion, on the other hand, occurs when the asset interacts with its surrounding environment. For example, in a subsea pipeline, internal corrosion is attributed to the corrosive fluids transported by the pipeline, whereas external corrosion occurs when the pipeline is attacked by the surrounding seawater. The nature and extent of damage caused by internal and external factors are highly dependent upon the chemical and physical attributes of the operating conditions. Chemical attributes are described by the various contaminants in the... 

In between these extremes there are numerous examples of floating devices that have more or less in common with ordinary shipping. One group comprises vessels specifically designed for standby, supply services, anchor handling, seismic or geological exploration, subsea work and so forth. These vessels may both look like... 

A subsea production system is usually tailor-made for a specific application and for a specified service life. The service life is determined from the reservoir properties and the production plans and may, for example, be io = 10 years. Experience has shown that the initial service life estimates have been too short. Improved technology, new methods for enhanced oil recovery and tie-in of neighboring wells often lead to an actual service hfe that is significantly longer than the initially planned service life. 

The following situation is typical At some time t < to, the operator has to decide whether to tie-in a neighboring well to the existing subsea production system or to install a new system. The tied-in well and possibly enhanced oil production from the old wells will increase the planned, total service life to 2. The question is then Can we, at time /], trust that the existing subsea production system will survive and function satisfactorily till time /2 Or, should the current system be discarded and replaced by a new system either now (at time ij) or in the near future (i.e., around time to)7... 

Assume that we want to make a decision related to life extension of a subsea system at time h, where t < to, the initially planned service life of the system. 

Marine Structures (0951-8339). This journal aims to provide a medium for presentation and discussion of the latest developments in research, design, fabrication, and in-service experience relating to marine structures, i.e., all structures of steel, concrete, light alloy or composite construction having an interface with the sea, including ships, fixed and mobile offshore platforms, snhmarine and submersibles, pipelines, subsea systans for shallow and deep ocean operations, and coastal structures such as piers. 

Janoff, Vicic, and Cain [11] used accelerated life test methods to select the best material to use for lip seals used in water/glycol fluids contained in subsea oil-field hydraulic systems. The required seal life was 20 years at 93°C sustained temperature at 20.7 MPa pressure with 100 mechanical operations. Finite Element Analysis was used to determine the actual seal temperature in the installed component to establish the service temperature rating. Polyurethane and thermoplastic alloy seals were tested in water/glycol and hydrocarbon hydraulic fluids at 3—5 elevated temperatures at 20.7 MPa constant pressure. Failure was defined as seal leakage at pressure. Test results were analyzed using Least Squares regression in an equation like that used by KenneUey et al. The correlation coefficients exceeded 0.95 and show excellent fit to the model. Table 16B.1 shows the results of the study. 

The subsea part of the system will be connected with the damaged well and wiU have the capabiUty of totally capturing the leak, even if the wellhead is damaged. An initial subsea response system was put into service in February 2011. 

Figures 12.14—12.17 show applications of the ProAssure products. It can be seen that overwrap repairs can be successfully applied on the platform, in the splash zone as well as in the sea. Obviously the complexity increases as repairs move from dry to wet and subsea environments. This is not only restricted to application of the composite laminate but also to related activities such as removal of existing coatings and surface preparation, as well as additional requirements such as the need for scaffolding, absailers and/or a service barge. A similar scenario applies to the clamp repair solution, which is generally advantageous over the overwrap repair method in cases of deeper...

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