United States Department of Transportation
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Effect of Ethanol Blends and Batching Operations on SCC of Carbon Steel
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2011-02-08
[PDF-3.41 MB]
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Alternative Title:Effect of Ethanol Blends and Batching Operations on Stress Corrosion Cracking of Carbon Steel
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TRIS Online Accession Number:01640831
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Edition:Final Report
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Abstract:This is the draft final report of the project on blending and batching (WP#325) of the Consolidated Program on Development of Guidelines for Safe and Reliable Pipeline Transportation of Ethanol Blends. The other two aspects of the consolidated program, ethanol source effects (WP#323) and monitoring (WP#327) are reported separately. 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 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, had 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). 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. The project accomplished substantially all of these objectives. The following were some of the major conclusions of the program: (1) Although slow strain rate tests (SSRT) are considered to be conservative (i.e. if SCC is not observed in SSRT, it is unlikely to occur in the field, but SCC detected in SSRT does not necessarily mean SCC will occur in the field), the results of SSRT in terms of the effects of various factors on ethanol SCC were in agreement with the more realistic fracture mechanics based crack growth measurements. (2) No SCC was observed in aerated ethanol less than about 15 percent (by volume) blend (E-15), prepared with simulated FGE. These results were consistent between slow strain rate tests and the long-term crack growth tests performed under loading conditions that simulate pipeline operating conditions. (3) Significant SCC was observed with both simulated and one lot of corn-based FGE but the simulated FGE was a slightly more potent SCC agent. The increased chloride concentration in the simulated ethanol could be a significant factor in increasing the susceptibility to SCC. (4) Dissolved oxygen is necessary for causing SCC under natural exposure conditions. SCC can be prevented by removing dissolved oxygen. If dissolved oxygen cannot be removed, certain inhibitors may be effective in mitigating SCC.
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