Materials Performance

DEC 2018

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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50 DECEMBER 2018 W W W.MATERIALSPERFORMANCE.COM CM CORROSION MANAGEMENT U This article presents the effect of the deposition of sand and actual eld sludge on the corrosion mechanism of API 5L X60 carbon steel in sour envi- ronments. Underdeposit corrosion of X60 was studied underneath the sand- or eld-collected sludge deposits in a simulated sour environment by means of a coupled multi-electrode array sys- tem and weight-loss coupons. The results showed that when actual eld sludge was deposited on the X60, sig- nicant general and localized corro- sion rates were observed. However, in the sand deposit test, the general and localized corrosion rates were found to be very low, even lower than the no-deposit test. Underdeposit corrosion (UDC) in oil and gas pipelines is a treacherous attack that initiates at a break in the protective corro- sion product layer (e.g., iron sulfide [FeS]) o r u n d e r n e a t h s l u d g e d e p o s i t s . T h e p i p e l i n e s l u d g e d e p o s i t i s u s u a l l y comprised of sand, asphaltenes, FeS, iron carbonate (FeCO 3 ), barium sulfate (BaSO 4 ), and other debris saturated with brine that frequently contains high concentrations of chlori de ion and di ssolved aci d gases (carbon dioxide [CO 2 ] and hydrogen sulfide [H 2 S]). The corrosiveness of the system can be further exacerbated by bacterial growth and the co-deposition of wax or paraffin materials onto the surface deposits. These have frequently been cited as responsible for high corrosion rates and loss of contain- ment during operations. 1-4 It is reported in the literature 5-6 that the UDC causes localized corrosion, formation of pits, and mega-attacks. A theory was pos- tulated 7 that localized corrosion under deposits is the result of galvanic corrosion between steel and sludge deposits. The exact mechanism of this phenomenon is dependent upon the local operating condi- tions, as well as thickness and type of the deposits. UDC can be a major corrosion failure experienced by oil and gas companies. Because of the seriousness of UDC and the consequences resulting from this type of corrosion , it has become the focus of researchers' attention to develop laboratory methods to monitor localized UDC and develop corrosion inhibitors for its mitiga- tion. 8-10 In a recent review 11 of UDC mecha- nisms, testing, and mitigation in the oil and gas industry, six testing laboratory methods were compared to identify the most reliable testing methods for studying corrosion activities under deposits in different envi- ronments. The purpose of this work is to study the corrosion activities of UDC under d i f f e re n t t y p e s o f d e p o s i t s i n s o u r environments. Experimental Procedure Test Materials and Environment Weight-loss measurements and electro- chemical corrosion tests were conducted on API 5L X60 carbon steel (CS). Coupon discs were machined from X60 pipe to a diameter Sour Environment Underdeposit Corrosion Behavior of a Carbon Steel NAYEF M. ALANAZI AND A.M. EL-SHERIK, Research & Development Center, Saudi Aramco, Dhahran, Saudi Arabia

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