1、Stress Corrosion Cracking of Carbon Steel in Fuel-Grade Ethanol: Review, Experience Survey, Field Monitoring, and Laboratory TestingAPI TECHNICAL REPORT 939-DSECOND EDITION, MAY 2007ADDENDUM 1, OCTOBER 2013Stress Corrosion Cracking of Carbon Steel in Fuel-Grade Ethanol: Review, Experience Survey, Fi
2、eld Monitoring,and Laboratory TestingDownstream SegmentAPI TECHNICAL REPORT 939-DSECOND EDITION, MAY 2007Prepared under contract for API by:Honeywell Process Systems (Parts I and II) Southwest Research Institute(Part III)Dr. Russell D. Kane Dr. Narasi SridharDr. David Eden Dr. Julio MaldonadoAnand V
3、enkatesh Elizabeth Trillo, Ph.D.CC Technologies Laboratories, Inc. (Part IV)Michael P.H. Brongers, P.E.Dr. Arun K. AgarwalDr. John A. BeaversADDENDUM 1, OCTOBER 2013Prepared under contract for API by:iCorrosion LLC (Part V) Southwest Research Institute(Parts VI and IX)Dr. Russell D. Kane Dr. Elizabe
4、th TrilloHoneywell Process Solutions (Parts VII and VIII)Dr. Anand VenkateshMark YunovichSpecial NotesAPI publications necessarily address problems of a general nature. With respect to particular circumstances, local,state, and federal laws and regulations should be reviewed.Neither API nor any of A
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12、7, 2013 American Petroleum InstituteForewordStress corrosion cracking (SCC) of steel in contact with fuel ethanol has been observed, for the most part, in userterminals, specifically storage tanks and loading/unloading racks prior to blending fuel ethanol with gasoline toproduce gasoline grade E10.
13、SCC has not been observed in storage tanks used by ethanol producers or inequipment after blending ethanol with fuel. These observations prompted API and the Renewable Fuels Association(RFA) to fund a multi-year research effort to examine the factors that could lead to SCC of steel in fuel ethanol a
14、nd togain greater understanding of the extent of SCC in field equipment. The original research program was conductedconcurrently by Southwest Research Institute(SwRI), CC Technologies, Honeywell Process Systems andiCorrosion LLC. Separate reports of the results from these studies were provided in Pa
15、rts I - IV of API TechnicalReport 939-D 2nd Edition, dated May 2007.Since that time further API-funded fuel ethanol research, field surveying and other activities have continued by theaforementioned organizations and the results of these tasks are found in Parts V - VIII of this addendum to the APIT
16、echnical Report 939-D. It includes new findings that corroborate many of the conclusions found in the previous939-D report. These new findings also provide new insights into other possible locations for SCC failures in fieldoperations handling ethanol including ethanol-carrying pipelines and the SCC
17、 potential of exposure to other ethanol-gasoline blends with ethanol contents greater than E10 up to E85. Other factors examined are the influence ofethanol sources, the impact of post weld heat treatment, use of potential and dissolved oxygen monitoring foridentification of conditions likely to sup
18、port SCC, and the effects of deaeration and inhibitors specifically designed toreduce susceptibility to SCC. Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for themanufacture, sale, or use of any method, apparatus, or product covered b
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22、of up to two years may be added to this review cycle. Status of the publication can be ascertained from theAPI Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is publishedannually by API, 1220 L Street, NW, Washington, DC 20005.Suggested revisions are invi
23、ted and should be submitted to the Standards Department, API, 1220 L Street, NW,Washington, DC 20005, standardsapi.org.iiiExecutive SummaryThe effect of various impurities in fuel ethanol on stress corrosion cracking of steel was studied with the goals of: (i)determining if the existing fuel ethanol
24、 specification needs to be modified to mitigate SCC, (ii) recommendingmodifications in operating practice to mitigate SCC, and (iii) identifying monitoring methods and quality controlpractices. The current ASTM D4806 fuel ethanol specification places maximum limits on the concentration of water (1vo
25、lume percent), total acidity expressed as acetic acid (56 mg/l), chloride (32 mg/lin 2009 decreased to 8 mg/l),methanol (0.5 volume percent), and denaturant (4.76 volume percent), and specifies a range for pHe (6.5 to 9.0). Thestudy, funded jointly by API and Renewable Fuels Association (RFA), found
26、 that: SCC of steel can occur in fuel ethanol meeting the ASTM D4806 specification. Within the specification limits, none of the constituents in ethanol appear to have an adverse effect on SCC.Acetic acid and pHe over a wide range have no effect on SCC susceptibility. Chloride and methanol appear to
27、increase SCC susceptibility, but are not essential for SCC. Water within the range of water contents studied doesnot affect SCC susceptibility of steel. However, complete removal of water was not attempted, therefore, it canonly be speculated that completely anhydrous ethanol would not cause SCC. Th
28、e inhibitor Octel DCI-11 lowersthe corrosion rate of steel in ethanol, but has no effect on SCC. Therefore, narrowing the current fuel ethanolspecification does not appear to be a viable solution to mitigate SCC. In addition to water, which was present in all the samples studied, the most statistica
29、lly important factor thatcaused SCC in fuel ethanol appears to be dissolved oxygen. When dissolved oxygen was minimized throughnitrogen purging, no SCC occurred in the presence of all other species at their maximum levels. When oxygen, inthe proportion present in ambient air, was purged into ethanol
30、, SCC occurred in the absence of all other species.Thus, SCC of steel in fuel ethanol can be mitigated by strictly limiting access to oxygen. Galvanic contact with pre-corroded steel appeared to exacerbate SCC. However, the present study indicatedthat galvanic coupling to rusted steel is not essenti
31、al in causing SCC. SCC can be either intergranular or transgranular. SCC appeared to be intergranular in low-chloride ethanol (bothlaboratory and field samples), whereas in high chloride or methanol-containing ethanol it was transgranular. These observations may signify that a narrow range of potent
32、ial is necessary for SCC to occur. The steelexposed to the user ethanol with access to air attained corrosion potential within the SCC-prone regime. On theother hand, in the one sample of producer ethanol from RFA, the steel exhibited a much higher corrosionpotential that may have placed it outside
33、the cracking potential regime. Since only one sample each of producerand user ethanol was studied, the variability in the corrosion potential of steel in ethanol obtained from the fieldcannot be quantified at this time. Further testing is needed to validate these conclusions. Corrosion potential is
34、a simple method to monitor the potential for SCC of steel exposed to ethanol. In all caseswhere SCC was observed, the corrosion potential was above about 0V with respect to Ag/AgCl EtOH referenceelectrode. When the potential was below this value, no SCC occurred regardless of the concentrations of v
35、ariousspecies in ethanol. Statistical analysis indicated that oxygen was the most significant factor that increased thecorrosion potential. The rust present on iron also increased the corrosion potential, but at a statistically lowersignificance level. Presence of methanol increased the corrosion po
36、tential, whereas acetic acid and chloridedecreased the corrosion potential. But these effects were at a statistically lower significance level than that ofoxygen. The cyclic potentiodynamic polarization curve may be another indicator of the susceptibility of steel to SCC in aparticular ethanol. In S
37、CC-prone environments, significant hysteresis was observed. However, further tests areneeded before this can be used as a quality control tool.ivRecommendations1) The effect of certain impurity levels beyond those specified in ASTM D4806 needs to be examined. It is wellknown that a small concentrati
38、on of water is sufficient to prevent SCC in anhydrous ammonia. Although thepresent study found that water up to 1 volume percent had no influence on SCC in ethanol, it is not knownwhether additional water would mitigate SCC. Further investigation of the effect of water beyond the ASTM limiton SCC sh
39、ould be undertaken, provided such water additions are acceptable commercially.2) A method to monitor the dissolved oxygen level in ethanol should be developed and tested in the field.Corrosion potential can be used as a measure of oxygen content, assuming no other oxidants are present in theethanol.
40、 The Ag/AgCl/EtOH reference electrode is quite suitable for measuring the corrosion potential, butneeds to be ruggedized for field use.3) Additional samples of user and producer ethanol should be acquired and the variability in the corrosion potentialof steel in these ethanol samples should be measu
41、red. Furthermore, the cyclic potentiodynamic polarizationbehavior of steel in these ethanol samples should be determined.4) Since slightly anodic potentials and rust appears to exacerbate SCC, mitigation methods may include gritblasting steel surfaces on new tanks prior to filling with ethanol, mini
42、mizing exposure of steel to air/moisture, orcathodic protection using sacrificial anodes/coatings. Impressed current systems will not be effective because ofthe low conductivity of ethanol. The galvanic protection of steel bottoms needs to be demonstrated throughlaboratory tests.5) Although the stud
43、y of the effect of stress level on SCC was not a goal of this project, it is well known that athreshold stress or stress intensity factor exists for SCC of steel. Fracture mechanics type testing (using variableloading to simulate loading/unloading of tanks) may help establish threshold stress intens
44、ity factor and crackgrowth parameters for evaluating the risk of tank failure. Slow strain rate tests provide rapid means to determineSCC, but do not provide the appropriate parameters for estimating risk of SCC from known defects.v939-D ContentsPagePart I Literature Review and Phase I Experience Su
45、rvey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Part II Phase II Experience Survey and Corrosion Field Monitoring. . . . . . . . . . . . . . . . . . . . . . 49Part III Identification and Mitigation of Factors Causing SCC in Fuel-Grade Ethanol . . . . . . . . 115Part IV Causes of SC
46、C and the Influence of Contaminants in Fuel-Grade Ethanol. . . . . . . . . . 151Part V Ethanol SCC Field Survey Update and Review of Recently Published Literature. . . . . 175Part VI SCC of Carbon Steel in Fuel Ethanol Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . 207Part VII Fr
47、acture Evaluation of Notched SSR (N-SSR) Specimens . . . . . . . . . . . . . . . . . . . . . . 233Part VIII Ethanol SCC Research on PWHT Effects and Threshold Stress Determination. . . . . . 253Part IX Ethanol SCC StudiesComposition, Round Robin, and Statistical Matrix SSR Testing. . 301viiPart ILit
48、erature Review and Phase IExperience SurveyPageI.1 Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1I.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2I.2.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2I.2.2 Technical Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2I.2.3 Technical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
