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API TR 939-D:2003 pdf download

API TR 939-D:2003 pdf download.Stress Corrosion Cracking of Carbon Steel in Fuel Grade Ethanol: Review and Survey.
Oxygen solubility is also a major departure point as well. Oxygen solubilily values in methanol and ethanol are similar; however, they arc both an order of magnitude higher than that of water. Therefore, the availability of oxygen for participation in the corrosion reaction is expected to be generally greater in ethanol and its solutions as well.
Another important aspect of ethanol with potential relevance to its corrosivity is its hygroscopic nature relative to other tiiels (see Table 3) using the Karl Fischer method j2j.
It shows a radical increase in water content of ethanol after thirty days exposed tO a humid environniem which is much greater than that observed for either gasoline or ElO (gasohol). Additional inknllatioli discussed later in this report indicates that water pick-up can txcur even in a controlled laboratory environment. Therefore, open exposure to the atmosphere during transportation or storage tends to increase water content and likely impacts corrosion reactions.
With the specilic concerns of this study for the corrosion behavior of steel, the comparison of the electrode potential of iron in water, methanol and ethanol with ionic impurities is perhaps the most useful. This reveals that the electrode potentials for iron decrease in the following order E° 1120> E° methanol > E° ethanol.j 11 This generally indicates that the oxidizing power of the medium is decreasing in the sante order. Therefore, it is expected that on first glance. the corrosivity would also decrease in the same order, thus making ethanolic solutions potentially less corrosive than either those ol methanol or water, But. corrosion studies conducted in many alcjl containing city ironments show that the relationship is a little more complex. Figure 2, shows corrosivity of iinc. iron and nickel in water and in alcohols versus their chain length (for C1 — Cg) Ill. The relationship displayed indicates that there is an increase in aggressivity going from water to methanol (C1). which then decreases with increasing carbon number. This relationship leaves ethanol with approximately the same general corrosivily as water. The reason for the increase in corrosivity going from water to methanol is generally considered to be the effect of the increased oxygen solubility in methanol. Since it has been shown that the oxygen soluhility of methanol and ethanol is similar (both higher than that of water), the decrease in corrosion rate from C1 — C is likely to he the result of the increased chain length and, in turn, its impact on molecular or ionic mobility in the media.
A major finding of this study was that there was very limited documented data on SCC of ethanol of steel obtained from the published literature. j3, 4] The first of the two references cited indicate that SCC of steel may he possible in ethanolic solutions as evidenced by examination of surface features of slow strain rate (SSR) test specimens exposed to ethanol with additions of LiCI and I-f 2S04. The cracking in ethanol appeared qualitatively to be less severe than found for methanol but no ductility loss data (elongation or reduction in area versus air properties) was presented. The cracking of steel in methanolic and cihanolic environments was compared to SCC of steel in liquid ammonia where susceptibility can be afkcted by minor impunties of water. The sccond reference describes the SSR testing of’ steel in ethanolic solutions with formic and acetic acids, and water at 60’C. Additions of 0.10% — 25% formic and 0.1% water in thanol did not produce SCC. However, steel bend specimens produced SCC in a solution of 0.01% acetic acid and 0.1% water that was less severe than found in methanolic solutions. Cracking was less than 0.01 mm in depth.
Despite the limited data on SCC of steel in ethanolic solutions. there was, in fact, substantial infonnation found on the general and pining corrosion behavior of steel in ethanol and ethanolic solutions that were relevant to the present concerns for corrosion of steel tanks and piping in fuel ethanol, Since SCCof steel likely involves corrosion to a certain degree and. in particular, the initiation of local anodic sites, it was felt that a this review should attempt to characterize corrosion in ethanolic solutions.


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