Research On Long-life Reference Electrode For General FPSO

Since the 1970 s,FPSO has been widely used in offshore oil and gas exploration.Compared with the FPSO constructed in the traditional way,the general FPSO is designed and constructed for a wide range of applications.It can be compatible with external turrets,internal turrets or multi-point mooring systems and riser systems.It can also be applied to a series of upper modules and the mooring system solution is highly adaptable,and its production cycle can be shortened by 6 to 12 months.The hull of FPSO has been operating in environments with salt spray,moisture and sea water for a long time,and is subjected to long-term electrochemical corrosion due to the action of the surrounding medium,and the structural corrosion is very serious.Corrosion generally reduces the mechanical properties of structural materials and shortens the service life.Because FPSO operates in sea areas far away from land for a long time,it is bulky and has complicated pipeline constraints with oil fields.It cannot enter the dock on a regular basis like ordinary ships.For maintenance,it is very necessary to take effective corrosion protection measures for FPSO.For the corrosion protection of FPSO,a combination of external coating and cathodic protection is usually used.The cathodic protection method is mainly divided into two methods: the sacrificial anode method and the impressed current method.Compared with the sacrificial anode method,the method of impressed current has better protection effect and is suitable for long-term use.This article mainly focuses on the method of impressed current,mainly the research of the reference electrode of the key component.The reference electrode is one of the main components in the universal FPSO impressed current cathodic protection system,and its performance is the key to determining whether the hull can be within the reasonable protection range of the impressed current cathodic protection system.This paper conducts research from the two aspects of the electrode body material and structure design of the reference electrode.Through investigation,the performance and applicability of various reference electrodes are compared,and Ag/Ag Cl reference electrode and reference electrode suitable for use in seawater environment are selected.The high-purity zinc reference electrode carried out the long-term stability test of potential,and further analyzed the long-life reference electrode suitable for the universal FPSO impressed current cathodic protection system.Study the packaging structure of the high-purity zinc reference electrode,check the structural strength of the designed and processed reference electrode,and carry out watertightness tests and insulation tests.The test results show that the watertight performance of the reference electrode and the insulation performance of the packaging material meet the specification requirements and engineering needs.In view of the possibility of accidental damage to the reference electrode,an underwater replacement tool for the reference electrode was designed and an underwater replacement plan for the reference electrode was developed.Simulate the installation state of the reference electrode on the FPSO,and carry out the underwater replacement test of the reference electrode in the laboratory.The test successfully verified the rationality of the underwater replaceable test scheme.After the replacement,the flange compartment was well sealed,and the designed underwater replacement structure of the reference electrode could meet the engineering requirements.Use boundary element software to simulate the corrosion protection state of FPSO underwater wet surface structure during the whole life cycle,select appropriate boundary conditions and polarization curves according to the specifications,and repeatedly optimize the installation number and location of auxiliary anodes based on the results of numerical simulations And the size of the output current,finally determine a set of reasonable auxiliary anode layout plan and reference electrode layout plan to ensure that the designed protection plan can reasonably and effectively protect the target FPSO’s full life cycle.Finally,in view of the situation that the reference electrode may suffer accidental damage,the underwater replaceable tooling of the reference electrode is designed and the underwater replacement scheme of the reference electrode is formulated.To simulate the installation state of reference electrode on FPSO,the underwater replacement test of reference electrode was carried out in the laboratory.The experiment successfully verifies the rationality of the underwater replaceable test scheme,the flange cabin is sealed well after the replacement,and the designed underwater replacement structure of the reference electrode can meet the engineering requirements.