Operational experiences with cathodic protection fo statoil's main onshore pipelines: a description fo the online moitoring systems

摘要

Statiol is operating an increasing number of offshore and onshore pipelines in the North Sea area and elsewere. Cathodic protection is a significant part of the corrosion management for these lines and we have collected a significant amount of experience with respect to design and operation of the systems. This paper deals with our ocmprehensive program for the onshore cathodic protection systems and the various challenges in different countries with respect to technical matters, such as operating conditions and different terrain.Generally, the systems are based on automatically controlled rectifier systems with a wide range of current drainage and very comprehensive monitoring of potentials and current flowing. THe use of coupons, polarisation cells and buried reference cells are essential, as well as the use of intersive measurements along the rute. The use of online monitoring of selected test posts and all rectifier units is ocnsidered essential for remote areas and in a situaton where man power is getting more expensive. THis alos reduces the down time of the rectifiers significantly. The routine measurements and controls will be briefly described. The technical challenges have been connected to very variable resistivities, very low pH marches, AC and DC stray currentsand telluric currents. The durability of above surface equipment such as test posts is also of significance in areas of rough weather conditions. Statoil find it iportant to adapt the local conditions to the service and maintenance philosophy for each onshore pipeline. The frequency fo the various inspection methods, such as oridnary test post inspection, close interaval measurements, soil resistivity and pH-value, is strongly dependent on local area conditions. Govnemental requirements must be consideredas the minima. However, AC/DC interference, geomagnetic induced currents, sour soil conditions, etc., are all factors that can cause risk to pipeline integrity and they have to the included when an inspection programme is planned.