Study of Corrosion Rate of Low and Medium Carbon Steel Pressure Vessel in Nigeria Oil and Gas Industry Using Ultrasonic Testing (UT) and Phase Array Ultrasonic Testing (PAUT) Method

Abstract

This investigation was conducted on two on-stream test separators that
were exposed to similar damage mechanisms. The test separators were
constructed with low and medium carbon steel BS 1501-224-490BLT50
and SA 516 Gr 70 materials respectively. Thirteen and twelve years
respectively of thinning and diminution of the test separators wall
thickness data was collected to establish their corrosion rates (both short
and long term) and their remaining life using manual contact ultrasonic
test. Low and medium carbon steel test separators corrosion rates were
evaluated using UT and PAUT. From the results obtained, the short-term
corrosion rate for both low and medium carbon steel test separators was
observed to be higher than the long-term corrosion rate. The estimated
corrosion rates of the inspected vessels are in excess of 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 showed that the remaining life of the test separators can be
safely and accurately predicted with the short-term corrosion rate.