STUDY OF CORROSION RATE OF LOW AND MEDIUM CARBON STEEL PRESSURE VESSEL IN NIGERIA OIL AND GAS INDUSTRY USING ULTRASONIC TESTING (UT)

Abstract

This investigative study was conducted on two on-stream test separators that are in similar service, hence exposed to similar damage mechanisms. The test separators were constructed of low and medium carbon steel BS 1501-224-490BLT50 and SA 516 Gr 70 materials respectively. The methods used for the evaluation was Manual Contact Ultrasonic Testing. For medium and low carbon steel test separator, thirteen and twelve years respectively of thinning and diminution of the wall thickness data was collected to establish their corrosion rates (both short and long term) and their remaining life. Low and medium carbon steel test separators corrosion rates were evaluated by using UT. From the results obtained, the short-term corrosion rate for both low and medium carbon steel test separators was noted to be higher than the long-term corrosion rate. The estimated corrosion rates of the inspected vessels are in excess of what is 0.125mm/year prescribed by API 510 code. These high corrosion rates can be attributed to the aggressive working conditions of the vessels. The results of the study show that the remaining life of the test separators can be safely and accurately predicted with the short-term corrosion rate.