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A method was developed and tested for measuring and subsequently removing telluric Mathematical techniques for separating the telluric current signal from the cathodic curr~nt effects from continuous pipe-to-elec-protection signal are described. The net trolyte potential profile measurements on submerged pipelines located in geomagnetifrom the electric field sites is correlated vessel moving at approximately six' (6) knots.with the potential profile values recorded at The pipe-to-electrolyte potential is recorded the same time.

The Arctic imposes unique challenges for design of cathodic protection (CP) systems for offshore structures. These include alternative structure designs, and environmental factors such as pack ice, high water resistivity, extreme tidal velocities and amplitudes, and severe weather. Traditional approaches to CP design for offshore structures are typically not suitable for service in Arctic conditions. Adaptations include almost exclusive use of impressed current or hybrid CP systems, versus traditional sacrificial anode designs, specialized anode deployment and cabling systems, and design of CP monitoring equipment suitable for Arctic conditions.The effect of Arctic conditions on CP current requirement, anode current output, anode material selection, anode configuration, cabling systems and power supplies is discussed. Case histories of specialized CP designs for offshore structures in the Russian Arctic and Cook Inlet are presented. These case histories include relevant CP design, construction, installation and operating details.

Flexible risers are regularly used to produce oil and gas in subsea production systems and by nature interconnect the subsea production system to the floating or fixed host facilities. Unbonded flexible pipes are made of a combination of metallic and non-metallic layers, each layer being individually terminated at each extremity by complex end fittings. Mostly submerged in seawater, the metallic parts require careful material selection and cathodic protection (CP) to survive the expected service life. Design engineers must determine whether the flexible pipe risers should be electrically connected to the host in order to receive cathodic protection current or be electrically isolated. If the host structure is equipped with a sacrificial anode system, then electrical continuity between the riser and the host structure is generally preferred. The exception is often when the riser and host structure are operated by separate organizations, in which case electrical isolation may be preferred simply to provide delineation of ownership between the two CP systems. The paper discusses these interface issues between hull and subsea where the hull is equipped with an impressed current cathodic protection (ICCP) system, and provides guidance for addressing them during flexible pipe CP design, operation, and monitoring. Specifically, CP design philosophies for flexible risers will be addressed with respect to manufacturing, installation and interface with the host structure’s Impressed Current Cathodic Protection (ICCP) system. The discussion will emphasize the importance of early coordination between the host structure ICCP system designers and the subsea SACP system designers, and will include recommendations for CP system computer modeling, CP system design operation and CP system monitoring. One of the challenges is to understand what to consider for the exposed surfaces in the flexible pipes and its multiple layers, and also the evaluation of the linear resistance of each riser segment. The linear resistance of the riser is a major determinant with respect to potential attenuation, which in turn largely determines the extent of current drain between the subsea sacrificial anode system and the hull ICCP system. To model the flexible riser CP system behavior for self-protection, linear resistance may be maximized, however the use of a realistic linear resistance is recommended for evaluation of the interaction between the host structure and subsea system. Realistic flexible linear resistance would also reduce conservatism in the CP design, potentially save time during the offshore campaign by reducing anode quantities, and also providing correct evaluation of drain current and stray currents.