Materials Performance

MAY 2015

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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61 NACE INTERNATIONAL: VOL. 54, NO. 5 MATERIALS PERFORMANCE MAY 2015 tate on the 3Cr steel surface. Muraki 10-11 found that after the corrosion product layer formed, the corrosion rate of low- c h r o m i u m s t e e l w a s s i g n i f i c a n t l y decreased. Kermani 12 proposed that the protection of 3Cr steel comes from the for- mation of a Cr-rich FeCO 3 layer. According to Chen, et al., 13 Cr(OH) 3 improved the cat- ion sel e ctiv ity of c orro sion scal e and blo cked anions p en etratin g th e scal e. Therefore, the Cr-rich layer caused a lower corrosion rate of 3Cr steel than L245 steel, and the protection of the corrosion product scale on 3Cr steel mainly resulted from the Cr-rich layer rather than the FeCO 3 layer. Conclusions The corrosion rates of 3Cr and L245 steels at 10 and 30% water cut were much lower than the corrosion rates at 80% water cut. Below 30% water cut, both steels had similar corrosion resistance, while at 80% water cut, 3Cr steel had much better corro- sion resistance than L245 steel. The corrosion product scales on 3Cr steel were divided into two parts: an outer scale, consisting of FeCO 3 , and an inner scale, consisting of FeCO 3 , Cr(OH) 3 , and traces of CaCO 3 . Corrosion product scales on L245 steel were also divided into two layers, which all consisted of FeCO 3 and traces of CaCO 3 , with Ca content decreas- ing as the depth of scale increased. The Cr element caused a reduction of the corrosion rate at higher water cut by forming a Cr-rich layer. However, pitting corrosion formed on 3Cr steel and became more serious with the increasing water cut. References 1 K.D. Efird, "Oil Characteristics, Water/Oil Wetting and Flow Inf luence on the Metal Loss Corrosion—Part II: Chemistry, Wetabil- ity and Experimental Evaluation," CORRO- SION 2006, paper no. 06114 (Houston, TX: NACE International, 2006). 2 Chong Li, et al., "Experimental Study On Water Wetting and CO 2 Corrosion in Oil- Water Two-Phase Flow," CORROSION 2006, paper no. 06595 (Houston, TX: NACE, 2006). 3 C. De Waard, U. Lotz, "Prediction of CO 2 Cor- rosion of Carbon Steel ," CORROSION/93, paper no. 69 (Houston, TX: NACE, 1993). FIGURE 4 The surface morphologies of corrosion product scale on L245 steel with (a) 10%, (b) 30%, and (c) 80% water cut. FIGURE 5 The cross-section morphologies and compositions analysis (80% water cut) of corrosion product scale on L245 steel with (a) 10%, (b) 30%, and (c) 80% water cut. Continued on page 62 Effects of Crude Oil on the Corrosion Behavior of Pipeline Steel Under Wet CO 2 Conditions

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