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Recent Results
Determine the Requirements for Existing Systems to Transport Ethanol Without Cracking
Pipeline companies have a keen interest in assessing the feasibility of transporting fuel grade ethanol (FGE) and ethanol blends in existing pipelines. Previous field experience and laboratory research, funded by PRCI and API, has shown that steel can suffer stress corrosion cracking (SCC) when exposed to FGE in the presence of oxygen. Though cracking was prevalent under some conditions, variability in cracking susceptibility of steel was noted with different ethanol chemistries. Additionally, the effects of residence time of FGE or its blends on SCC (i.e. crack initiation time and growth rate) had not yet been determined. Finally, the effects of ethanol on other materials used in the pipelines, such as elastomeric seals and internal coatings, needed to be evaluated. Thus, the major objectives of the program are to: 1) Develop data necessary to make engineering assessments of the feasibility of transporting FGE and FGE blends in existing pipelines. The transportation may be in a dedicated pipeline or in a batching mode, 2) Identify ethanol blends that can be transported in existing pipelines without significant modification of the system and operations (Case 1), blends that require significant modifications (Case 2), and blends that cannot be transported in existing pipelines, but could be moved in specially designed systems (Case 3); and, 3) characterize the time to initiation of SCC in a range of potent ethanol environments and identify safe operating and or batching practices that prevent the initiation and growth of SCC.
A program consisting of two phases was performed to address these objectives.
Phase 1: In the first phase, screening tests were conducted to identify ethanol blends that are unlikely to cause internal SCC. A literature survey and laboratory testing also was performed to evaluate static and dynamic elastomeric seals.
Phase 2: In the second phase, crack growth tests under static and cyclic loads were conducted in ethanols/blends that caused cracking in SSR tests to identify safe operating and or batching practices that prevent the initiation and growth of SCC.
Key Results
Pipelines made of common line pipe steels (e.g., Grade B and X-42 to X-60) are likely to be susceptible to ethanol SCC and any differences in susceptibility are probably not significant from an integrity perspective. While differences in susceptibility were noted for some weld types, in general, the base metal, heat affected zone, and weld metal were all susceptible to SCC in Synthetic Fuel Grade Ethanol (SFGE). For sharp cracks, SCC initiation times are short once the line pipe steel is exposed to FGE or FGE blends capable of promoting SCC. The only blends that can be safely transported in existing pipelines without significant modification of the system or operations (Case 1) are those containing less than 15% (by volume) ethanol. All other blends require significant modifications of the system or operations (Case 2), or specially designed systems being studied in the SCC-4-5 project. Batching does not appear to be a viable method for SCC mitigation.