Corrosion

ESI staff have conducted a number of research programs for the American Gas Association involving pipeline corrosion research, cathodic protection systems, dc and ac interference, ac impedance studies, and corrosion detection instrumentation. The results of these studies are available for use in consulting services by ESI. Research has been conducted in the following areas:

*PREDICTION OF POTENTIAL/CURRENT DISTRIBUTION ALONG A CATHODICALLY PROTECTED OFFSHORE PIPELINE

* EVALUATION OF WELL HEAD MEASUREMENTS TO ASSESS THE CATHODIC PROTECTION LEVELS OF WELL CASINGS

* CATHODIC PROTECTION OF OFFSHORE PIPELINES

* MEASUREMENT TECHNIQUES FOR OFFSHORE PIPELINES

* CORROSION OF THE ANNULUS OF STORAGE WELLS

* TECHNIQUE DEVELOPMENT FOR TRUE PIPE-TO-SOIL POTENTIAL MEASUREMENT

* PIPELINE COATING EFFECTS ON POWER LINE FAULT CURRENT COUPLING

ESI reviewed the cathodic protection system design for the Kern River Gas Transmission Pipeline. Calculations were then made to determine possible interference and corrosion inducing conditions for situations where the cathodic protection system ground beds were in close proximity to the power line towers. Interference current levels causing tower corrosion were evaluated.

TESTING OF POLARIZED POTENTIAL MEASUREMENT SYSTEM - A.G.A.

ESI developed a prototype manpack portable system for buried pipeline pipe to soil voltage measurements. The system is based upon a measurement concept that allows the measured voltages to be separated into two components, i.e. the pipe steel polarized potential and the soil IR drop. Since the corrosion protection level of buried steel is dependent upon the polarized potential, elimination of the IR drop component gives the pipeline operator an improved assessment of the corrosion protection status of his pipeline.

The approach utilizes a combination of externally impressed ac and dc surface potential measurements along the pipeline, which can be processed to yield the polarized pipe-to-soil potential. The attractiveness of the method is that cathodic protection current interruption, with the attendant long line circulating current problems, is not required.

TECHNIQUE DEVELOPMENT FOR PIPELINE POLARIZED POTENTIAL MEASUREMENTS - A.G.A., ARLINGTON, VA.

The objective of this research project was to investigate and evaluate available methods for determining the polarized potential of a buried pipeline. Its importance rests with the fact that pipe-to-soil potential measurements are the most commonly used means for assessing the level of cathodic protection on buried gas transmission pipelines. However, the measurements require correction for the soil IR drop in order to obtain the desired polarized potential. This research project provided an evaluation and ranking of existing and newly developed techniques for the measurement of the polarized potential.

PIPELINE COATING EFFECTS ON POWER LINE FAULT CURRENT COUPLING A.G.A., ARLINGTON, VA.

A pipeline that is in the proximity of a faulted power transmission line is subject to high levels of induced voltage. These voltages are of concern relative to personnel safety and coating and pipe damage. Hence, it is important to quantify possible coupled voltage levels so as to institute appropriate mitigative measures. The use of existing electromagnetic coupling computer programs as a predictive tool to determine coupling levels necessitates that the user supply as input the high-voltage AC characteristics of the pipeline coating. The resultant voltage and currents predicted by the computer program are a major function of the assumed coating properties. Typically, the industry has used DC coating resistivity measurements as the only coating characterization for use in high voltage AC coupling studies without an adequacy assessment.

The objective of this project was to develop an electrical circuit model representative of oil wells which includes the production and surface casings and the associated annular region. The purpose of the model was to provide an analytical structure for the identification and assessment of field measurements which could provide information as to the corrosion activity within the well annulus.

INVESTIGATE NEGATIVE DRAIN CURRENT REVERSALS IN SASKATCHEWAN TRANSCANADA PIPELINES, LTD, CALGARY, ALBERTA

TransCanada Pipelines has a six pipeline natural gas transmission system located in an east-west corridor traversing the Province of Saskatchewan. The pipelines are corrosion protected with an impressed current cathodic protection system. For a pipeline under cathodic protection, the expected direction of protection current flow on the negative drain lead is from the pipe to the rectifier negative terminal. This was the situation that existed when four pipelines were located on the right-of-way. However, after the addition of the fifth and sixth pipelines, and bonding them into the cathodic protection system, current reversals occurred in a number of negative drain leads. The objectives of the project were to determine the cause of the reversals, to evaluate the reduction in corrosion protection, if any, the reversals may cause, and to recommend remedial measures.

TANK FARM CORROSION STUDY - ULTRASYSTEMS ENGINEERS AND CONSTRUCTORS, INC., IRVINE, CA.

A recently constructed cogeneration project in Renssselaer, NY exports excess electric power into the Niagara Mohawk Power Corporation transmission system. To accomplish this, the construction of a 4.6 mile length 115 kV electric power transmission line was necessary. For a portion of the distance, the transmission line parallels several aboveground fuel oil storage tank farms containing both above and below ground piping.

The objectives of the project were to investigate the impact of the collocated transmission line on the tank farms' facilities, namely,

* The hazardous effects of voltage and current induction unto the facilities during both normal and fault operation of the transmission line,

*The change in the natural corrosion rate caused by the induced ac current density, and

*The need for modification of existing cathodic protection systems, and the possible addition of new systems.