Materials Performance

APR 2017

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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63 NACE INTERNATIONAL: VOL. 56, NO. 4 MATERIALS PERFORMANCE APRIL 2017 Optimizing Non-Corrosion Engineering-Based Costs As illustrated in Figure 3, non-CE-based corrosion costs are divided into four sub- categories that are associated with differ- ent integrity management measures. The cost optimization pertaining to each mea- sure is discussed individually. Inspection-Related Costs Inspection-related costs are best opti- mized if the inspection scope is fully risk- based. A conservative inspection scope can mean unnecessary inspection costs. Con- versely, a scope that is not risk-based and has fewer selected points (compared to a risk-based scope) may not detect high-risk or high-corrosion-rate areas. That means there is a greater likelihood of failure and the occurrence of post-failure corrosion costs. Corrosion Monitoring and Fluid Sampling Costs This situation is exactly the same as in- spection-related costs. A conservative ap- proach to corrosion monitoring and f luid sampling creates unnecessary costs. On the other hand, a less conservative approach increases the chance that higher corrosion rates are not detected, which can possibly lead to failures and their associated post- failure corrosion costs. based and non-CE-based integrity manage- ment measures and simultaneously opti- mize their pertinent costs, thereby opti- mizing the overall corrosion costs. Optimizing Corrosion Engineering-Based Costs CE-based costs are divided into the fol- lowing three subcategories: • Design costs (e.g., corrosion allow- ance) • Materials selection costs (e.g., me- tallic and non-metallic options) • Environmental control costs (e.g., corrosion inhibitor injection) The variables listed under each subcat- egory (Figure 2) determine the total cost associated with that subcategory and con- tribute to the overall CE-based cost. A very important point is highlighted here regarding the upstream hydrocarbon assets and their associated pipelines. The costs associated with these three CE-based subcategories are very much dependent on conducting proper well sampling and the accuracy of sample analyses during an as- set's design stage. Any erroneous conclu- sions regarding the corrosivity level of the produced fluids can have huge adverse re- percussions. Conclusions that fluid corro- sivity is greater than is actually the case can increase design-stage costs when imple- menting the following: • Specifying thicker corrosion allow- ances • Selecting corrosion-resistant alloys (CRAs), which are typically more ex- pensive than carbon steel • Including inner coatings or clad- dings instead of, or in addition to, corrosion inhibitor injection for in- ternal protection of equipment • Inje ctin g hi g h er -than-n e c e ssar y concentrations of various chemicals (e.g., corrosion inhibitors) Thus, opting for such overdesign op- tions, due to erroneous f luid sampling and/or compositional analysis, could have a huge adverse effect on the overall CE- based costs at the design stage. Some com- ponents of such overdesign options at the design stage (e.g., overdosed ch emical treatment) could also continue well into an asset's operation stage before (if at all) they are rectified. Furthermore, asset underdesign based on sampling/analyses errors may appear to have optimized corrosion costs at the de- sign stage; however, such assets can suffer from the following corrosion costs post- commissioning: • Increased CE-based costs such as material replacements or corrosion allowance upgrades along with in- jection of higher doses of chemicals to control or reduce an increasing number of corrosion failures due to an underdesign • Increased post-failure corrosion costs due to inadequate corrosion control measures that result in ear- lier and more frequent failures than expected in an asset's life The best way to optimize CE-based cor- rosion costs is to avoid both overdesigned and underdesigned corrosion control mea- sures, while requiring that f luid sampling and analyses are carried out in an accurate and meticulous manner. It is of paramount importance to re- member that CE-based cost optimization commences at the design stage and contin- ues throughout the operating stage. Any revisions, alterations, or variations in the incumbent corrosion measures during the operating stage will directly influence the overall CE-based corrosion costs. FIGURE 3 Corrosion cost subcategorization for non-CE-based integrity management measures. Corrosion Management and Cost Optimization

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