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Putting this knowledge into action allows operators to engage in better planning for prevention of corrosion fatigue, with a more diligent approach saving them time and meeting health and safety regulations

Pipelines more effectively. This approach also saves costs, improves safety and reli- ability and enhances the life of the riser by ensuring that risks to its integrity are mitigated insofar as possible.

Dr. Peter Barnes is a senior engineer at

Intertek Production and Integrity

Flexible riser schematic. Source: Intertek.

Assurance, part of the steel wire within the tensile armor. approximately twice as many Fe2+ ions in the company’s

We tested the corrosion fatigue of high- the solution for the seawater environment Exploration and strength steel wire in four different solu- than for the deionized water environment, Production business. tions. The purpose of this was to com- which would correspond with a lower cor- He has 13 years’ experience in the water, pare the effects of chloride and iron ion rosion rate. nuclear and oil and gas industries concentration on the corrosion fatigue The pH of solution of the two iron- working with clients on asset integrity behavior of the high-strength steel wire, saturated environments showed a reason- management, corrosion fatigue, design, which allowed us to simulate the dif- ably stable pH throughout the fatigue test construction and water treatment ferent failure modes. The four solutions period of 6.2. The pH for the seawater projects, among many others. Barnes has tested were modi? ed (5%NaCl) ASTM and deionized water environments a PhD in corrosion fatigue from the

D1141 synthetic seawater, iron supersatu- without iron saturation were lower, University of Manchester.

rated modi? ed (5%NaCl) ASTM D1141 with values on average of 5.4 and 5.1, synthetic seawater, deionized water and respectively. *Reproduced with permission from iron supersaturated deionized water Using a materials and corrosion sci- NACE International, Houston. All

These tests explored the effects of the ence approach to study the corrosion rights reserved. Presented at NACE different environments on the corrosion fatigue of high-strength steel wire in CORROSION 2015 in Dallas, Texas, USA, fatigue behavior in terms of levels of iron various environments aids understanding 2015. Co-author Tom McLaughlin, Senior (Fe2+) and sul? de (S2-) ions in solution of ? exible riser performance thresholds Engineer at Intertek Production and and pH. The fracture surfaces that con- for industry suppliers and operators. Integrity Assurance. sidered iron saturation and

Post-fatigue sample from the seawater environment seawater.

Photos from Intertek.

without iron saturation dem- onstrated signs of corrosion

SEM surface scale on the fracture surface and image showing a barrier exhibited a ductile type fail- between the formation ure. The fracture surface of of iron sul? de and iron the tensile armor tested in carbonate. a deionized water environ- ment without iron satura- tion exhibited a brittle type failure.

Iron saturation reduced the effects of hydrogen sul- fide corrosion through the reaction of Fe2+ ions with the S2- ions, which produced

SEM surface scale image an iron sulfide precipitate. showing iron sul? de

This reduced the sul? de in precipitates. the solution to zero after one and two days’ expo- sure for the seawater and deionized water environ- ments, respectively. The iron ion saturation ultimately leads to the lowering of the

FPSO in service. Photo courtesy of Intertek.

corrosion rate. There are

August 2015 | OE oedigital.com 48 046_OE0815_Pipelines1_Intertek.indd 48 7/21/15 9:50 PM