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PublisherNACE InternationalLanguageEnglish
Document ID 10369
Content TypeConference Paper
TitleRISK MODELS FOR MATERIALS SELECTION AND CORROSION INHIBITION IN OFFSHORE OIL/GAS RISERS AND NUCLEAR WASTE STORAGE TANKS
AuthorsDavion Hill, DNV Research and Innovation; Feng Gui, DNV Columbus
SourceCORROSION 2010, March 14 - 18, 2010 , San Antonio, TX
Copyright2010. NACE International
KeywordsRisk assessment, materials selection, integrity, offshore, oil, gas, nuclear waste
PreviewABSTRACTBuilding infrastructure for the production, transportation, and storage of hazardous materials is sometimes a risky venture because of environmental variables that conspire against the materials used to construct such infrastructure. Materials are selected early in the development stage, and decisions must be made to sacrifice capital costs for operational costs or vice versa. For example, an upstream producer may weigh the costs of using carbon steel with an inhibitor versus nickel-plated steel to determine the short- and long-term risks of either decision. Whether the enterprise is to build an offshore oil rig or contain and transport hazardous materials, the corrosion rate is a critical parameter in assessing risk. By assessing the corrosion rate and mechanisms of corrosion, prediction of the lifetime and financial performance of the system is possible. Corrosion is an event that corresponds to a consequence which will have varying degrees of severity, and assigning values to these consequences describes an overall risk picture of the endeavor. Therefore, corrosion rates can be directly correlated to lifetime or financial consequences of materials selection and corrosion inhibition. This paper examines case studies where laboratory and field data are used as inputs to refine a risk model. The methodology to create the risk picture and assign value to the consequence of corrosion in these systems is explained.

INTRODUCTION

In piping and storage systems, materials are selected based on a balance between durability and cost. Corrosion affects the integrity of the system and therefore affects the useful operating life of the system. However, prediction of the corrosion rate is only the first step in determining the lifetime of a piping system. The corrosion rate is rarely an absolute number, but is instead a range of values that can vary depending on chemical and material contributions that are dynamic and constantly changing. In order to predict the life of the pipe or storage system, both historical data and real-time data can be used to estimate the remaining useful life (RUL) of the system.

A low pressure water distribution system is a straight forward case, as the effects of corrosion are somewhat predictable. The cast iron will suffer some corrosion rate due to the corrosivity of the water, the level of oxygen in the water, and the thickness of the passive layer on the cast iron itself. Because of this uniform corrosion, most cast iron low pressure water systems can be designed with a large safety factor in the wall thickness which will tolerate corrosion and metal loss through the life of the system. If the corrosion rate were to be measured, however, a cast iron sensor probe in the same environment may measure the corrosion rate of the probe tip. This measurement could be accomplished via electrochemical means or it could be done via periodic weight loss inspection, but this corrosion rate could be used to help determine the longevity of the water pipe.
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