The geomagnetic field fluctuations are accompanied by the geo-electric (telluric) field and telluric currents at the surface of the Earth and in the pipelines. These telluric currents disturb pipeline cathodic protection levels, creating pipe-to-soil potential (PSP) fluctuations with different amplitudes. Amplitudes of PSP fluctuations directly depend on the telluric activity in the area of the pipeline location.

To estimate the amplitudes of PSP variations due to telluric activity, pipeline circuit model based on Distributed Source Transmission Line Theory can be applied. The unknown and most important input into this model are values of driving ground electric fields i.e. telluric activity in the pipeline area.

Two parameters define telluric electric fields in the particular area, one is the geomagnetic field variations and other is the deep ground conductivity structure. The magnetotelluric theory was applied in order to calculate geo-electric telluric field variations in the pipeline area. For the Alaska area magnetic data from four Geomagnetic Observatories were used with one-dimensional Earth conductivity model for four different zones, obtained on the basis of the geological surveys in order to find the telluric electric field.

To properly evaluate effects of telluric activity on the scale of years, statistical study has been done. For the statistical analysis of telluric activity in pipeline area, we established two types of indices of telluric electric field: hourly maximum of the absolute value of the electric field and hourly standard deviation of the electric field. The developed hourly telluric indices were calculated for two different areas, low latitude (Ottawa) and area of interest. Statistical distribution of these indices was used to derive the different levels of telluric activity and their rate of occurrences (number of days in the year). The results of the study are universal and can be applied for different pipeline configurations to estimate effectiveness of the cathodic protection.

Subject
Pipe surfaces, Materials, Cathodic protection, Structures, Impedance, Pipelines, Inspection, Electrical resistivity, Surface layers, Telluric current, Corrosion protection, Surveys, Conductivity
Keywords:
Telluric currents, geomagnetic induction, cathodic protection
© 2012 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2012
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.