The Measures Of Corrosion Prevention For The Mothballcd Sea-pipelines

The sea pipe is the most common offshore oil and gas pipeline, which is usually mothballed before the formal operation or during the overhaul of the oil tanker. Solving the corrosion problem of the sea pipe during the mothballing is very important for the safe operation of the pipelines.Because the corrosion problem exists in a lot of oil fields, the research methods and technology that ef Tectively inhibit the corrosion of oil pipe attract extensive concern in recent years, and great progress has already been made. Among the achievements, adding corrosion inhibitor to slow down the corrosion of oil pipe is considered as a most economical and effective method. In this thesis, electrochemical test method and corrosion test pieces are used to study the effect of three kinds of corrosion inhibitor, respectively in the fresh water, the seawater and a mixture of nitrogen gas and production water. The suitable type and dosage of corrosion inhibitor for different mothballing media are determined. The main conclusions are as follows:(1) When the corrosion media is fresh water, corrosion inhibitor B is the most suitable. When the filling dosage of inhibitor B is 30 ppm, the rate of corrosion inhibition meets the requirement of SY/T 6301-1997 standards and no local corrosion appears for X52 sea pipe material.(2) When the corrosion media is simulated seawater, corrosion inhibitor A is the most suitable. When the dosage of inhibitor A is 40 ppm, the rate of corrosion inhibition meets the requirement of SY/T 6301-1997 standards, and no local corrosion appears for X52 sea pipe material.(3) When the corrosion media is the mixture of nitrogen gas and production water, corrosion inhibitor A is the most suitable. When the dosage of inhibitor A is 40 ppm, the rate of corrosion inhibition meets the requirement of SY/T 6301-1997 standards, and no local corrosion appears for X52 sea pipe material.(4) In the real seawater, the corrosion rates of X52 sea pipe are very close when the dosage of inhibitor A is 40 ppm, 75 ppm, 150 ppm and 200 ppm. While at the dosage of 200 ppm, local corrosion are found in the surface of X52 sea pipe.