13. ethanolscc
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Ethanol Stress Corrosion Cracking
Presented by: Mark Baker, P.E.
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http://images.google.com/imgres?imgurl=http://www.thewhiskystore.de/experte/images/etohh2o_6.jpg&imgrefurl=http://www.thewhiskystore.de/experts/alcohol.htm&h=337&w=400&sz=5&hl=en&start=14&tbnid=1tivTt-GU6P2sM:&tbnh=101&tbnw=120&prev=/images%3Fq%3Dethanol%2Bmolecule%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG -
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Increasing Domestic Use of EthanolRenewable Fuels Standard
Could change completely due to finding an enzyme that will break downcellulose like starches and sugars for fermentation possibilities.
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What Is SCC? Rapid cracking of steels through transgrannular
or intergrannular corrosion Duration of hours or months, but much shorter
than typical corrosion; ethanol appears to occur
in periods ranging from months to several years SCC not new (amine, carbonate, chloride), but
new for ethanol. Closest relative is methanol
SCC First known case in 1995 at Chevrons Willbridge
Terminal (2 tanks completely destroyed)
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Figure 16CC in Steel Tank Bottom Showing Highly Branched, Intergranular
Cracks at 100Source: API 939D
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API 939D Current Results SCC in fuel grade ethanol is not just a West Coast
problem limited to a few users that deal with foreign
sources of ethanol. End users should not consider fuel grade ethanol a
commodity. Fuel ethanol varies widely in composition.
SCC in fuel grade ethanol does not take years todevelop. Based on preliminary laboratory studies, the factorsthat increase corrosivity of fuel ethanol appear to be
increased water content and decreased pHe. Based on preliminary laboratory studies, SCC hasbeen produced in a sample of fuel ethanol that apparently
does not contain denaturants or inhibitors
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API 939D Results SCC in fuel grade ethanol has been reproduced
in laboratory tests in fuel ethanol samplesobtained from the field.
Some evidence has been generated based on
laboratory results, which indicates that materialfrom the near weld region in the base metal mayhave a greater susceptibility to SCC than base
metal. The economic impact of SCC in fuel grade
ethanol service in end user facilities has beenwell over $1 million in direct costs in the last fewyears.
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Slow Strain Rate Testing forScreening Ethanol SCC
Machining of SSR
Tension Specimen
Ethanol SCC inSSR Specimen
Slow strain rate
Testing machine
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SCC Crack Growth Testsin MTS Machine
Load frame &crosshead
Environment Cell& fracture fixtures
Hydraulic
Actuator &control
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Schematic of CT Specimen usedfor SCC Crack Growth Testing
Can be used for wedge loading or for testing in MTS orSlow Strain Rate (rising load) loading
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SCC on CT specimen followingtesting in fuel ethanol
SCC Crack growthin Fuel Ethanol
Mixed mode SCCIntergranular/TransgranularCT Specimen after testing in fuel ethanol
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Further Results
API 939D research continues
New factors have been found
Some factors eliminated or roles clarified
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Further Results
Primarily occurs for middle to end producer
No known cases for the producer
Occurs near weld HAZ
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Further Results
Factors found to be:Dissolved O2Secondary Coupling to rusted steel
Secondary Stress levels
Transportation Introduces O2Loading and unloading
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API 939D Revision Recommendations
Tank cleanliness is critical Wet MT needed to find cracks
Use ethanol fuel compatible coatings Leak detection for tank bottoms
Leak detection for piping systems
Minimize O2 exposure
No current analytical procedure
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API 939EGuidelines for Identification, Repair,and Mitigation of Cracking of Steel
Equipment in Fuel Ethanol Service
API RECOMMENDED PRACTICE 939-EFIRST EDITION, XXXXX
Laundry list of best practices such as:
PWHT
Coating
It is up to companies to do a risk assessment and to evaluate the
choices available to them using a ration method such as decisionanalysis.
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