ABSTRACT

This article describes the results of the 5-year cathodic protection maintenance program for the underground and submerged structures on a Petrochemical Complex. It shows the protection coverage before the program started, the progress at the first year, the results after the program had been implemented, diagnostic and troubleshooting methodology, experiences in anode retrofitting, installation of new systems, and corrective actions for attaining efficient cathodic protection systems.

The main actions taken were pipe-to-soil potential surveys at six month intervals, impressed current and sacrificial anode current measurements, two-month rectifier monitoring and electric circuits inspection, troubleshooting, rehabilitation of systems out of operation, and a 5-year project for design and construction of new required systems.

The excellent results obtained permit the conclusion that only a conscious cathodic protection maintenance program can provide optimal performance of the CP systems and continuous safe and efficient operation of all the installations of the Complex have improved cost effectiveness for the company.

INTRODUCTION

One of the Complexes of the Petrochemical Company of Venezuela (PEQUIVEN) operates at the eastern coast of Maracaibo Lake in Venezuela. The Complex El Tablazo includes a great variety of plants such as Natural Gas Processing, Olefins, Ammonium, Urea, MVC, PVC, Chlorine, Caustic Soda and Facility Semites. In 1995 the total production of the Complex was 2.5 million tons of different products; including: Ethylene, Propylene, EDC,MVC,PVC, Polypropylene, Raw Materials for Plastics, Ammonium, Urea, Chlorine, Hydrochloric Acid, Sodium Hypochlorite and Caustic Soda.

Since the starting date of the different plants of the Complex, the structures submerged in Maracaibo Lake, the underground pipelines and the above ground storage tank bottoms have cathodic protection systems. These systems have been evaluated using potential measurements every two years. Before the annual cathodic protection maintenance program and the retrofitting of inoperating systems were implemented in 1991, only 54% of the total test locations attained a negative (cathodic) voltage of at least 850mV (Cu/CuSO4), with the protective current applied.

At present, the Complex has 55 impressed current systems with an installed capacity of 3000 amperes to protect underground piping, aboveground storage tanks bottoms, sheet piling; and sacrificial aluminum anodes for the steel piles of the solids and liquids handling docks and magnesium anodes for isolated pipeline crossings around the Complex.

The first step of the program, by early 1991, consisted of a field study and diagnostic tests of all the systems, evaluating the electrical characteristics of the rectifiers, measuring potentials of all the structures, and current measurements of impressed current anodes. Based on this evaluation, in a second phase, the detailed engineering of new systems along with the implementation of the predictive maintenance program were generated.

The third phase consisted of a program for: rehabilitation of deteriorated systems, the retrofitting of existing systems with proved deficiencies, and the installation of new systems to achieve adequate levels of cathodic protection in all the structures. After this phase, in 1995, the potential survey was made and the data showed an important improvement of protection coverage; over 95% of the 2500 test locations exceeded -850mV (CSE).

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