ASTM: Gasoline Today and Tomorrow – An Executive Report

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Octane Week | ASTM: Gasoline Today and Tomorrow - An Executive Report (from p3) Imran Hussami of Frontier Oil Corp. have developed silver methodologies based on modifications to D-130, most obviously, substituting a silver strip for the copper strip. Their separate processes have many similarities and critical differences. Both use 30 ml samples of gasoline that are heated to 50oC. Bainʼs test method specifies heating the sample for three hours while Hussamiʼs test method requires only two hours. At the end of the heating period in either method, the silver strip is removed and washed, and the color and tarnish level is ranked. Both Bain and Hussami have developed methods having procedures for testing with and without a pressure vessel. Method A uses a pressure vessel and method B involves the use of a vented test tube. Both have designed innovative devices for suspending a silver strip. “In the D-130 method, the copper strip was not suspended,” Bain said. “We had to study how to use the cable tie that was developed for suspending the silver strip, which is a little longer than the copper strip.” The underlying issue is one of incompatibility, she explained. “The metallurgy of certain fuel sensors is an issue when certain naturally occurring sulfur compounds in gasoline interact with silver. Automobile manufacturers are replacing silver sensors with a more robust metallurgy to remedy this problem,” she said. Bain reminded us that in 2000, Audi of America, Inc. voluntarily recalled 50,000 vehicles to replace the existing fuel sending units inside the fuel tank because they could cause the fuel gauge to read full while the fuel tank may not in fact be full or could be empty. Audi attributed interactions of certain reactive sulfur on contact points of any of the three fuel level sending units causing them to send an erroneous signal to the fuel gauge. Audi replaced the sending units with sturdier alloys. Suspension Devices Differ “Gasoline might not need the pressure vessel,” Bain told us. When using a pressure vessel (method A), the gasoline sample is placed in a clean and dry test tube. A prepared silver strip measuring 0.7 in. long, 0.5 inches wide and 0.1 inches thick is placed inside the assembly (see fi gure right, Silver Strip Suspension Assembly, Method A), which is then placed in the test tube. The sample tube and suspension assembly are then placed in the pressure vessel. After three hours, plus or minus five minutes in the bath, the pressure vessel is to be withdrawn and immersed for a few minutes in cool water. The technician is advised to open the pressure vessel carefully as contents may be under pressure. The strip is to be withdrawn from the suspension assembly with forceps and immersed in 2,2,4-trimethylpentane, dried with ashless filter paper or cotton ball and inspected for tarnishing or corrosion. A silver corrosion interlaboratory study conducted by Marathon indicated that Method A and Method B yield equivalent results. Method B is advantageous because labs can use the same bath used in copper corrosion testing of finished gasoline. Another advantage is that labs do not need pressure cylinder vessels for testing silver corrosion. When testing without pressure (method B), the technician is to secure the silver strip as with a cable tie lanyard (see fi gure above, Silver Strip Suspension Assembly, Procedure B). The cable should hold the strip securely at the four corners but it should not contact any of the other surfaces. The assembly is to be placed in a test tube, and the test tube in a water bath for three hours. The silver strip is cleaned and compared in the same way as in the previous procedure. Thinner Strip Tested “Frontierʼs Hussami has also developed a modified D 130 test method, but it employs thinner, longer, reusable silver strips. This method suggests that strips be discarded when their original shape becomes deformed or the surface shows pitting, scratches or corrosion that cannot be removed by the specified polishing procedure. Polishing of unused, fresh strips is done with a 400-grit scouring-pad, while used strips are first polished with a piece of 150-grit roll, followed by the 400-grit pad. “At 1.5 inches long, 0.5 inch wide and 0.021 inch thick, itʼs a fat-free silver strip,” Hussami quipped. This size has (continued on p5) 4 February 2007
Octane Week | ASTM: Gasoline Today and Tomorrow - An Executive Report (from p4) the advantage of providing a greater surface area, not only to facilitate the strip polishing process but also to allow greater exposure of the strip to the sample in the overall corrosion process. Hussami has designed and gotten fabricated a silver strip centering device that differs significantly from Bainʼs design by securely gripping only the top edge of the strip. The upper part of this same device functions as a test-tube stopper and sample vent (see fi gure, right). In Procedure A, with pressure vessel, 30 mL of sample is placed in a test tube and stoppered with a cork. Within one minute after completing its surface preparation, the solvent-washed/dipped silver strip is to be secured in the centering device, and placed into the test tube containing the gasoline sample. Test tube is placed in the pressure vessel which is then placed in the liquid or solid heating bath. After two hours, the pressure vessel is removed from the bath, immersed in cool water for a few minutes before opening to remove the test tube with forceps inserted into the vent holes of the centering device. Centering device is removed from the test tube, strip immersed completely in iso-octane, removed immediately, solvent allowed to dry off before inspection of strip for tarnishing or corrosion. Procedure B, without pressure vessel, uses a vented test tube containing the silver strip mounted in the centering device. Test tube is placed directly in the 50oC liquid or solid bath for two hours, removed from bath, allowed to cool slightly, before removal of centering device from the test tube, and continuation as outlined in Procedure A. Silver strips are to be rated as per the Classifications and Color Chart employed in the IP227 method. The Chart consists of five pictures of tarnished silver, ranked 0 to 4, in accordance with the severity of tarnish or corrosion. Strips rated 0 for no tarnish or 1 for slight tarnish indicate a passing sample. Any sample ranking between 2 and 4 indicates a corrosive gasoline. Hussami told us that part of the “experience gained from the success of the Rapid Copper Corrosion Test, using thin copper strips, is being applied to the development of this silver strip corrosion test method.” – Carol Cole Task Force Details Scope of Inter Laboratory Study This story appeared on November 28, 2005. The chairman of ASTMʼs Silver Corrosion Task Force prepared a broadcast message soliciting labs outside the group to participate in the ASTM Silver Corrosion in Gasoline Inter Laboratory Study (ILS) involving four methodologies. The Task Force expects participating labs to run 16 samples in duplicate. Task Force Chairman Kevin Bly hopes that labs would not pay to participate if ASTM provides the necessary funding. ASTM members meeting in Norfolk, Va. in December 2005 will get an update on the Task Forceʼs activities. The group has readied four methods for determining the silver corrosion capability of gasoline. Task Force member Scott Fenwick of Intertek Caleb Brett has concentrated on a silver corrosion method that utilizes the IP227 test and applies it to gasoline. IP227 is a copper corrosion test developed by the Institute of Petroleum, now the Energy Institute in the UK. Caleb Brett became involved when corrosive gasoline appeared in the U.S. Southeast in 2004, and since that time, Fenwick has become an advocate for the modified IP227 test method. “Rather than trying to create something, we went with an established method, and we didnʼt have to do much to modify it,” he told us. Gasoline was outside the scope of the original method, and there was concern gasolineʼs vapor pressure might have caused the glass to shatter. “Weʼve made modifications to apply it to gasoline, and we slightly increased the cooling water flow to ensure it wouldnʼt build up too much pressure. Weʼve run more than 1,000 samples, and nothing like that has happened,” Fenwick said. The modified IP-based method utilizes 250 mL of sample in a 350 mL capacity test tube of heat-resistant amber glass. A single ended condensed hollow tube, called a cold finger, is fitted through a glass stopper at the top of the test tube. Through the tube circulates cooling water. At the bottom (continued on p6) February 2007 5
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ASTM: Gasoline Today and Tomorrow – An Executive Report

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