51316-7879-A Comparison of Mono- to Di- PE Ratio in Inhibitor Formulations in the Mitigation of UDC

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Product Number: 51316-7879-SG

ISBN: 7879 2016 CP

Author: Bruce Brown

Publication Date: 2016

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Mitigation of localized under deposit corrosion (UDC) in upstream oil and gas pipelines has been an important research topic for both industry and academia. This paper reviews the effect of varied ratios of mono- to di- nonyl-phenol phosphate esters (PEs) on the mitigation of UDC in sweet conditions which were tested using a set of specifically formulated inhibitors.Three mono- to di- PE ratios were tested at 200 ppm with and without 3.4% 2-mercaptoethanol (ME) and tested at 100 ppm without ME. UDC testing was conducted for 28 days in a CO2 saturated solution at 70°C and 1 bar total pressure using two 1.25-inch (3.18 cm) diameter API 5L X65 pipeline steel samples and 250 micron silica sand. Electrochemical data were collected on a daily basis and both samples were removed after 28 days. Analysis has shown that localized corrosion (pit penetration rate) increased for a non-sulfur containing nonyl-phenol PE as the amount of di-PEs became equivalent to the concentration of mono-PEs. The sample inhibited by 200 ppm of the 90:10 mono- to di- nonyl-phenol PE was observed to have possible initiation of localized corrosion (15 micron depth) while the sample inhibited by 200 ppm of the 50:50 mono- to di- nonyl phenol PE had definite localized corrosion (120 micron depth). This large increase in the penetration rate by the 50:50 mono- to di- nonyl phenol PE was much greater than a simple relationship to the decreasing concentration of mono-PEs. The nonyl phenol PE inhibitor with a 50:50 mono- to di-PE ratio at 100 ppm concentration failed to protect the surface of the sample under the individual sand grains. Even the base product inhibitor package with no PE provided better mitigation under these test conditions than the 50:50 mono- to di- nonyl phenol PE. But it was observed that the addition of ME provided a dramatic improvement in the mitigation of UDC for each mono- to di-PE ratio of the nonyl phenol PE tested.