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Cathodic Protection Close Interval Surveys

Field Manual

Prepared by R.L. Pawson
Table of Contents

1.0 INTRODUCTION 3
2.0 STANDARD FIELD PRACTICES 3
2.01 Reference Electrodes 4
2.02 Structure to Soil Potentials 6
2.03 Rectifier Interruption 10
2.04 Dataloggers 14
2.05 Pipe Location 15
2.06 Auxiliary Equipment 16
2.07 Close Interval Survey Data 17
2.08 TestStation Data 18
2.09 Stationary Datalogger 20
2.10 Datalogs 23
2.11 Miscellaneous Testing 24
2.12 Daily Progress Logs 24
3.0 SPECIAL PIPING SYSTEMS 25
3.01 Well Piping 25
3.02 Bare Piping 28

Copyright:

The informational content, presentation, graphics and text are the property of Cybex Corp. and may not be changed or altered in whole or in part. The Field Manual may be copiedfor personnel use only.

Disclaimer:

The content of this document is for informational purposes only and no liability is expressed or implied as to the suitability to any survey project.

1.0 INTRODUCTION

Cathodic Protection systems are an electrical means of mitigating corrosion on buried and submerged metallic structures (primarily steel).

This Field Manual describes many aspects ofthe equipment and testing required when undertaking a Close Interval Potential survey (C.I.S.) on natural gas and oil piping systems to verify the Cathodic Protection system effectiveness.

Testing of pipeline Cathodic Protection systems is required by law in many countries and is an important means of maintaining pipeline integrity.

One of the most common methods of testing these systems isthe annual test station survey. This requires the measurement and recording of pipe to soil potentials at designated test stations each year. While this is very useful information, particularly for well-coated pipelines, the test station data only represents the potentials on less than 1% of the pipeline surface. The test station data does not provide any information on the pipe to soilpotentials at a distance from the test station.

On bare or poorly coated pipelines, the test station data may not represent potentials more than a few meters from the test station.

Consequently, it has become a standard practice to undertake “close interval potential surveys” (C.I.S.) on pipelines, every few years, in order to provide the data for assessing the effectiveness of the CathodicProtection system over the full length of the pipeline. The C.I.S. measures and records the pipe to soil potential on a regular spacing of between 1 and 3 meters (spacing depending on client requirements, field conditions and pipeline physical properties).

Prior to the introduction of computerized dataloggers, undertaking the C.I.S. was very difficult due to the volumes of data that needed to berecorded and plotted. The availability of computerized dataloggers for Cathodic Protection system monitoring enabled the development of the C.I.S. into a viable means of assessing system effectiveness.

Project planning, cooperation of the client and contractor, a high level of technical expertise, fieldcraft and dedicated equipment are required to benefit from this type of survey. The C.I.S. willgenerate large volumes of data, and it is essential that this data be technically correct and its management and reporting efficient.

2.0 STANDARD FIELD PRACTICES

In order to properly undertake the close interval survey, the survey crew needs to be educated and trained in the all aspects of the work. This section will discuss many of the factors that will affect the quality of the fielddata.

2.01 Reference Electrodes

The standard reference electrode used for land based C.I.S. is the Copper/Copper Sulfate electrode. This is shown in Figure 1. This reference electrode is practical and can be used in a variety of field applications and soil conditions due to its relative stability.

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Figure 1

As pipe to soil and structure to soil potentials are...
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