CO2-SCC in Flexible Pipe Carbon Steel Armor Wires

Abstract

Carbon Dioxide-induced Stress Corrosion Cracking (CO2-SCC) is an environmentally assisted corrosion cracking phenomenon that has recently been identified as a new failure mode in flexible pipe armor wires. The phenomenon has been observed to take place notably in severe CO2 environments and is a cause of great concern to the flexible pipe industry. Since its detection, a diverse and extensive testing program has been established to develop an understanding of the phenomenon and define safe application limits for carbon steel wires to prevent the initiation of CO2-SCC. Several different testing methodologies have been explored and small-scale laboratory testing has played an instrumental role to this overall effort. This paper focuses on the results from three different small scale testing methodologies and the impact of different parameters such as CO2 fugacity, temperature and confinement that play a crucial role in the initiation of CO2-SCC. Furthermore, careful prominence has been given to the test set-up and methodology that has been rigorously developed over the last few years. With this developed protocol in place, CO2-SCC has been effectively reproduced on all wire grades in a small-scale testing environment. Results have also shown that for a CO2 fugacity greater than 15 bar and applied stress at 100% of the actual yield strength (AYS), all existing wire grades are susceptible to CO2-SCC thus creating significant limitations to flexible pipe design with respect to this new failure phenomenon.

A Coupled, Global/Local Finite Element Methodology to Evaluate the Fatigue Life of Flexible Risers Attached to Floating Platforms for Deepwater Offshore Oil Production

“…Moreover, the contact region with the seabed touchdown zone (TDZ) experiences high hydrostatic pressures associated with bending moments. Altogether, this scenario is highly favorable to fatigue failure that may be aggravated by stress corrosion cracking (SCC) [6]. Indeed, the performance of flexible risers in the offshore fatigue context is not a recent concern [7][8][9]; codes, standards, and a set of theoretical studies have been developed to establish the best practices for flexible risers analysis [3,10,11].…”

Effect of Dissolved CO2 on the Interaction of Stress and Corrosion for Pipeline Carbon Steels in Simulated Marine Environments

“…Several studies have been conducted in various corrosive environments (NS4 solution, saturated CO 2 medium, carbonate/bicarbonate solutions, mixture of CO 2 /O 2 , CO 2 /H 2 S medium, 3.5% NaCl solution, etc.) [5,[23][24][25][26] to understand the stress corrosion cracking behavior of pipeline carbon steels after failure. However, understanding the corrosion behavior with applied stress before the failure of pipeline steels in marine environments saturated with CO 2 has not yet been reported.…”

Corrosion of tensile wires covered with PA11 layers in simulated annulus environments at low CO2 pressure

“…Nevertheless, studies investigating the corrosion behavior of armor wires in simulated annulus environments usually consist of exposing the entire surface area of the test specimens to the test environment, without considering the influence of the antiwear layer covering the steel on the corrosion morphology. [2][3][4][5][6][7][8][9][10][11][12][13] The study described in this paper addressed the influence of oxygen on the corrosion of high-strength steel wires exposed to different simulated annulus environments containing CO 2 while covered with PA11 plates simulating the antiwear tapes. The wire specimens were tensioned by four-point bending to account for the tensile loads to which the wires are subjected during service.…”

“…Nevertheless, studies investigating the corrosion behavior of armor wires in simulated annulus environments usually consist of exposing the entire surface area of the test specimens to the test environment, without considering the influence of the antiwear layer covering the steel on the corrosion morphology. [ 2–13 ]…”