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Exploration • Drilling • Field Services


Cathodic protection of metallic structures D


urability of metallic structures exposed to natural seawater is often linked to the efficiency of protective


systems which consist mainly of cathodic protection. Unsuitable cathodic protection may induce higher


costs of installation and services, loss of performance of the structures, etc. The design of a cathodic protection system involves


many calculations whose results are dependent on the structure (materials, surface area exposed to seawater, etc) and on environmental parameters. These parameters are connected to the properties of the interface metal/ seawater and are specific to the structure (alloy, surface state, coating, biofouling, etc) and the marine environment (salinity, dissolved oxygen, temperature, flow rate, etc). The most common way to select current demand for


a cathodic protection design consists in applying data available in the literature. In case of inaccurate data with regards to actual parameters, it can result in an over/ under-protection of the installation and therefore an over-cost or underestimated lifetime of the cathodic protection.


Bonanza or bust: shale-gas developments


F


rom unbridled enthusiasm to extreme caution, when it comes to tapping shale gas reserves


approaches vary widely. Energy security, export opportunities and environmental activism often combine in unexpected ways. Shale gas represents nothing short of an energy revolution for some countries, while others see the costs and risks of drilling as too great to overcome. In a new report, the Economist Intelligence Unit analyses fledgling shale-gas developments worldwide, focussing on the countries with the largest reserves. Proponents of gas, which burns cleaner than


coal, suggest that it could be part of the answer to climate change. At the same time, even as energy demand surges ahead, the giants of the oil industry are finding it harder than ever to tap new reserves, which is forcing them to look to previously neglected, harder-to-reach hydrocarbons. Among these, hitherto disregarded shale-gas reserves are generating the most enthusiasm. The EIU’s report pulls together recent analysis of


several shale-gas hot spots, in addition to addressing the implications of shale exploration. ●


For more information, visit www.eiu.com/shalegas


28 www.engineerlive.com The French Corrosion Institute carried out a research


work with the objectives of supplying to cathodic protection designers data collected in situ, in the actual environment in which the protected structure is deployed. The experiment was based on the deployment of six


arrays which met CPC sensors from nke electronics and an environmental parameter data logger. A CPC sensor records the coupling current between a


cathode and a sacrificial anode, and the cathode potential versus a pseudo-reference electrode (pure zinc) as a function of time. A resistance set between the cathode and the anode simulates the natural circuit resistance of the cathodic protection system (eg structure plus electrolyte). Cathode materials can be made of carbon steel,


stainless steel or any other material whereas and anode material can be made of zinc, aluminium indium or aluminium gallium alloys. By immersing a set of CPC sensors for each tested


material, (eg each sensor with a different resistance value and eventually equipped with different anode alloy), it is possible to build a so-called pseudo-polarization curve


corresponding to the stationary state and to determine the cathodic current demand for the conventional protection potential. These pseudo-polarisation curves are integrated to various softwares which calculate cathodic protection potential and current density distribution of cathodically protected structures. Forty-eight CPC sensors were deployed from 9 to 18


months, at 35m to 900m depth. All data were recovered successfully and the results of this research are now integrated in major oil companies’ general specifications for cathodic protection design. A new research is ongoing which is focused on


cathodic protection of stainless steel in deep sea environment. Three CPC sensor arrays will be immersed from 150m to 2200m depth. Two shallow sites are going to be monitored with array directly laid on seafloor. ●


Enter 28 or ✔ at www.engineerlive.com/iog


The French Corrosion Institute is based in Brest, France. www.institut-corrosion.fr.


Nke Instrumentation is based in Hennebont, France. www.nke-instrumentation.com


ROV uses six thrusters for better control and response


added a Saab Seaeye Cougar XT to its ROV fleet. Operations manager Robert Black said: “The


A


Cougar XT has an outstanding power to weight ratio that nothing can touch.” He also


recognises the need to compete on a world stage where the search for oil keeps going deeper and conditions are more difficult. “That is why we chose a 2000 metre-rated ROV that does what it says it can do.” Mr Black was particularly keen on a vehicle that


could manoeuvre into tight spots. The Cougar XT’s control and response comes from


its six thrusters: four of which are vectored horizontal thrusters and two vertical. Each thruster has velocity feedback for precise control in all directions and is interfaced to a fast-acting control system and solid- state gyro for enhanced azimuth stability.


fter winning a five year contract with Shell in Brunei, Singapore based Kreuz Subsea has


The Cougar XT configuration chosen by Kreuz


in conjunction with Oceanvision, Saab Seaeye’s Singapore-based distributor and Far East service hub, makes the ROV a versatile light work vehicle suitable for a wide range of operations.


It includes a


Tritech Super SeaKing Sonar; a Kongsberg high-definition low light camera and a colour zoom camera; a dual five function heavy duty manipulator; and a CP proximity probe and contact probe.


A tether management system is also supplied with


a stainless steel cage and 200 metres of tether, along with its own Seaeye mini wide-angle B&W camera. An A-frame launch and recovery system is included with 1600 metres of armoured umbilical. The whole system comes with its own purpose-


built 20 foot air-conditioned control and workshop container. ●


For more information, visit www.seaeye.com


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