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Deadleg Stress Corrosion Cracking Risks in SS Piping Systems in Refining and Renewable Units

Although the problem of chloride stress corrosion cracking (SCC) of austenitic stainless steel drain lines in hydroprocessing units has been well known for many years, new questions on these deadlegs are arising with the renewable units handling biofuel feeds. Some potential issues are in the hydrodeoxygenation (HDO) units and certain pretreatment units, wherever these units have high pressure SS piping. Many of the hydroprocessing unit case histories of leaks and cracks occurred shortly after startups from turnarounds and were attributed to water not being drained before startup. In contrast, some of the renewable units may have a risk of water condensing in deadlegs even during normal operation. The hydroprocessing unit case histories have been compiled to help to define the conditions, such as main line operating temperature and pressure which contribute to SCC in the deadlegs. The process chemistry, especially water content, oxygen and pH differences between the refining and renewable units are reviewed, and material recommendations are given for drain lines and other deadlegs in each type of unit.
Product Number: 51324-20816-SG
Author: Cathleen Shargay; Garry Jacobs; Shahab Soltaninia
Publication Date: 2024
$40.00
$40.00
$40.00
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Quantifying Effect of Hydrogen and Sulfur in Mitigating Free Fatty Acid Corrosion in Renewable Diesel Applications

Product Number: 51324-20864-SG
Author: Sridhar Srinivasan; Winston Robbins; Gerrit Buchheim
Publication Date: 2024
$40.00
Production of Renewable Diesel (RD) and Sustainable Aviation Fuels (SAF) from bio / natural oils has seen significant investment in recent years, stemming from worldwide government mandated need to reduce fossil fuel CO2 emissions. New investments have occurred in retrofitting / adapting existing refinery hydroprocessing infrastructure to process natural oils or coprocess natural oils blended with crudes to produce RD and SAF. This stems from the fact that natural oils have the hydrocarbon (HC) structures to fit within the mid-distillate fuel product such as diesel and aviation fuel as well as that these processes are optimized for removal of unwanted Sulfur and Oxygen removal. In Corrosion/2023, the authors introduced a molecular mechanistic model to quantify FFA corrosion as a function of temperature and FFA concentration. This model exploited the similarity of FFA to carboxylic acids, akin to naphthenic acids found in conventional refinery crude unit process streams, especially in case of unsaturated FFA. A key aspect of modeling corrosion for FFA is the inhibitive role of hydrogen in the presence of Iron sulfide species. While natural oils do not contain sulfur compounds, presence of reactive sulfur species such as thiols and sulfides in coprocessing applications provides an easy pathway to provide for the formation of a potentially protective nano barrier layer of FeS. Further, the presence of FeS acts as a catalyst towards dissociation of molecular H2 to atomic H and subsequent reduction of FFA through atomic hydrogen. A threshold H2 partial pressure is required to ensure hydrogen reduction of FFA is kinetically dominant when compared to acid corrosion of Fe. Residence time of acid is another key parameter that will impact propensity for corrosion and / or H2 inhibition and is considered in the development of the prediction model. A framework incorporating the effects of H2 partial pressure, residence time and reactive S concentration is proposed for assessing FFA corrosion for various commonly utilized natural oils in renewable applications.