An experimental study on the internal corrosion of a subsea multiphase pipeline

Based on the actual operational parameters of a subsea multiphase pipeline,an experimental study on the internal corrosion of a subsea multiphase pipeline was conducted in a dynamic,hightemperature autoclave,which had a similar environment to an actual field environment,using the partial pressure of CO2(PCO2),velocity of the corrosion medium,temperature,corrosion time,and corrosion inhibitor as variables.The results show that CO2 resulted in severe localized corrosion and that the corrosion rate increased as the PCO2 and velocity increased;the corrosion rate first increased and then decreased with increasing temperature.The corrosion rate peaked at approximately 65
C and then decreased continuously afterwards;the corrosion rate decreased as the duration of the experimental period increased.Under the operational conditions of the selected subsea pipeline,localized corrosion caused by CO2 was still the primary corrosion risk.Several types of corrosion inhibitors could inhibit the occurrence of localized corrosion for a short time period;however,most corrosion inhibitors could not completely inhibit localized corrosion.

Effect of Chlorine Salt on Durability of Mineral Admixture Concrete under Different Conditions

Mineral admixture concrete is a renewable material.It requires less cement than ordinary concrete and is thus beneficial for economical use of resources and environmental protection.To examine the impact of chloride salt on the durability of mineral admixture concrete under various conditions,in this study,test blocks are divided into two major groups:in one group,the test block is eroded by chloride salt on the interior and by sulphate/magnesium salts on the exterior,and in the second group,the test block is eroded by external chloride/sulphate/magnesium salts.Clean water is considered the control group.Dry-wet alternation tests are carried out to investigate the mechanical properties,mass,macromorphology,and ion content of the concrete.Furthermore,a series of methods,such as XRD,FT-IR,SEM,and EDS,are adopted to examine the phase composition and micromorphology of the concrete.The results show that,for the concrete subjected to the corrosion of internal chloride salt and external sulphate/magnesium salts(0–20 cycles),its mechanical properties improve slowly at the initial stage,but at the final stage(80–120 cycles),it is subjected to more severe corrosion compared to those only eroded by a single corrosive ion,such as the chloride/sulfate/magnesium salts.For concretes subjected to external corrosion of chloride/sulphate/magnesium salts,the concrete durability enhances with the concentration increase of the chloride salt.Mg^(2+)and SO_(4)^(2-)could jointly result in destructive damage to the admixture concrete,main generating corrosion products of ettringite,gypsum,Mg(OH)2,thaumasite,and M-S-H.