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Fig. 17. Simplified schematic showing attachment of a coupling to flexible plastic piping.

Figure 17 Simplified schematic showing attachment of a coupling to flexible plastic piping.

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The level of dissolved water also has a pronounced effect. The results in Fig. 2 show the effect of water concentration in addition to ethanol level. In this figure, the electrical conductivity (listed as S in Fig. 2 and 1/Q in Fig. 1) is plotted for blends containing 5, 10, 15, 20, 30 and 40% ethanol by volume. As the level of ethanol increases, the conductivity curves for each blend increase as well, and for each set of curves the conductivity also increases with the level of dissolved water. In fact, the water solubility limit increases the conductivity by an order of magnitude when going from E10 to E15. In addition, water itsel! is a solvent for NaCl and acids, which can lead to even higher rates of corrosion.
The level of dissolved water also has a pronounced effect. The results in Fig. 2 show the effect of water concentration in addition to ethanol level. In this figure, the electrical conductivity (listed as S in Fig. 2 and 1/Q in Fig. 1) is plotted for blends containing 5, 10, 15, 20, 30 and 40% ethanol by volume. As the level of ethanol increases, the conductivity curves for each blend increase as well, and for each set of curves the conductivity also increases with the level of dissolved water. In fact, the water solubility limit increases the conductivity by an order of magnitude when going from E10 to E15. In addition, water itsel! is a solvent for NaCl and acids, which can lead to even higher rates of corrosion.
A simplified representation of solubility as a function of ethanol concentration in gasoline is shown in Fig. 3. The wide shaded horizontal band in the chart represents the range of solubility parameters, expressed as total Hansen Solubility Parameter (HSP) for many dispenser polymers, especially elastomers. Epoxies, such as those used as the matrix materials for underground storage tanks, have a total HSP value around 24(MPa)””, which is noticeably higher than the HSP for polymers. The implication for UST resins is that the solubility of the epoxy in the fuel will be highest for gasoline containing around 80% ethanol.
A simplified representation of solubility as a function of ethanol concentration in gasoline is shown in Fig. 3. The wide shaded horizontal band in the chart represents the range of solubility parameters, expressed as total Hansen Solubility Parameter (HSP) for many dispenser polymers, especially elastomers. Epoxies, such as those used as the matrix materials for underground storage tanks, have a total HSP value around 24(MPa)””, which is noticeably higher than the HSP for polymers. The implication for UST resins is that the solubility of the epoxy in the fuel will be highest for gasoline containing around 80% ethanol.
Fig. 3. Total Hansen Solubility Parameter as a function of ethanol concentration. The lowe blue horizontal band represents the solubility range of many UST system elastomer and plastics. The upper blue band is representative of FRP resins. the elastomer structure, which can result in swelling and softening of elastomers. Another negative feature associated with permeation is that soluble components, especially plasticizers added to impart flexibility and durability in the elastomer, may be leached out, thereby affecting the mechanical properties of the compounded elastomer component and degrading the ability of the component to perform its intended function.
Fig. 3. Total Hansen Solubility Parameter as a function of ethanol concentration. The lowe blue horizontal band represents the solubility range of many UST system elastomer and plastics. The upper blue band is representative of FRP resins. the elastomer structure, which can result in swelling and softening of elastomers. Another negative feature associated with permeation is that soluble components, especially plasticizers added to impart flexibility and durability in the elastomer, may be leached out, thereby affecting the mechanical properties of the compounded elastomer component and degrading the ability of the component to perform its intended function.
Table 1. List of materials evaluated in intermediate ethanol blends compatibility study. (Materials identified as being used in UST systems are highlighted.) Of the all the test fuels investigated (Fuel C, CE10a, CE17a, CE25a, CE50a and CE85a), only the metal and elastomeric materials were subjected to each fuel type. The plastics were originally exposed to Fuel C and CE25a (and later to CE50a and CE85a) and the sealants were evaluated only in Fuel C, CE10a and CE25a. Ata later point in this study, ORNL received sections of fiberglass USTs removed from use. Three UST sections were cut into test specimens and added to the final exposure runs of Fuel C, CE50a, and CE85a.
Table 1. List of materials evaluated in intermediate ethanol blends compatibility study. (Materials identified as being used in UST systems are highlighted.) Of the all the test fuels investigated (Fuel C, CE10a, CE17a, CE25a, CE50a and CE85a), only the metal and elastomeric materials were subjected to each fuel type. The plastics were originally exposed to Fuel C and CE25a (and later to CE50a and CE85a) and the sealants were evaluated only in Fuel C, CE10a and CE25a. Ata later point in this study, ORNL received sections of fiberglass USTs removed from use. Three UST sections were cut into test specimens and added to the final exposure runs of Fuel C, CE50a, and CE85a.
Table 2. Breakdown of piping materials.°”” A large percentage of leaks occur in the piping system between the tank and the dispenser.'’ These leaks typically occur at joints and connections where the stresses are highest. Contributors to stress include movement and forces exerted on piping from environmental factors which can be caused by changes in ground-water level and settling changes in the soil. Even a small change in the position of a UST will result in stress on the piping, especially at joints.’® The level of stress will be higher for rigidly designed systems as opposed to flexible systems which can reduce stress through bending and relaxation. Outside of environmental contributions to stress, there are inherent changes caused by the piping materials’ response to the fuel chemistry. As stated earlier, ethanol will raise the solubility parameter of the fuel so that the resulting potential for degradation of plastics is increased. Increased solubility will likely cause a increase in the volume of the plastic. This volume increase will place the component pipe under additional elongation and stress. Expansion of piping caused by solubility (even at low levels of approximately 2%) may be high enough to lead to failure based on life cycle studies of polymeric piping materials.
Table 2. Breakdown of piping materials.°”” A large percentage of leaks occur in the piping system between the tank and the dispenser.'’ These leaks typically occur at joints and connections where the stresses are highest. Contributors to stress include movement and forces exerted on piping from environmental factors which can be caused by changes in ground-water level and settling changes in the soil. Even a small change in the position of a UST will result in stress on the piping, especially at joints.’® The level of stress will be higher for rigidly designed systems as opposed to flexible systems which can reduce stress through bending and relaxation. Outside of environmental contributions to stress, there are inherent changes caused by the piping materials’ response to the fuel chemistry. As stated earlier, ethanol will raise the solubility parameter of the fuel so that the resulting potential for degradation of plastics is increased. Increased solubility will likely cause a increase in the volume of the plastic. This volume increase will place the component pipe under additional elongation and stress. Expansion of piping caused by solubility (even at low levels of approximately 2%) may be high enough to lead to failure based on life cycle studies of polymeric piping materials.
Table 3. Flexible piping materials according to manufacturer.
Table 3. Flexible piping materials according to manufacturer.
One manufacturer used PET as the inner barrier layer. However, most materials are either nylon or PV DF. In reality the actual arrangement and location material arrangement for flexible piping is somewhat complex. A cutaway diagram showing the material arrangement for one commercially- available flexible pipe is shown in Fig. 4. In all flexible piping systems, there is an inner permeation barrier layer composed of a plastic material that has low solubility (i.e., high resistance) to petroleum fuels and alcohols.
One manufacturer used PET as the inner barrier layer. However, most materials are either nylon or PV DF. In reality the actual arrangement and location material arrangement for flexible piping is somewhat complex. A cutaway diagram showing the material arrangement for one commercially- available flexible pipe is shown in Fig. 4. In all flexible piping systems, there is an inner permeation barrier layer composed of a plastic material that has low solubility (i.e., high resistance) to petroleum fuels and alcohols.
Fig. 5. Volume swell results for representative barrier materials used in underground piping. The ORNL materials compatibility study evaluated the response of selected plastic materials to Fuel C and CE25a only. Test fuels representing 10 and 15 percent aggressive ethanol were not exposed to plastics. Volume swell and hardness results are shown in Figs. 5 through 7 for common nylon grades, PET, PVDF, and HDPE exposed to Fuel C and CE25a.
Fig. 5. Volume swell results for representative barrier materials used in underground piping. The ORNL materials compatibility study evaluated the response of selected plastic materials to Fuel C and CE25a only. Test fuels representing 10 and 15 percent aggressive ethanol were not exposed to plastics. Volume swell and hardness results are shown in Figs. 5 through 7 for common nylon grades, PET, PVDF, and HDPE exposed to Fuel C and CE25a.
Fig. 6. Absolute hardness results for representative barrier materials used in flexible piping.
Fig. 6. Absolute hardness results for representative barrier materials used in flexible piping.
Fig. 7. Point change in hardness (from baseline) for representative barrier materials used in flexible piping.
Fig. 7. Point change in hardness (from baseline) for representative barrier materials used in flexible piping.
Table 4. Volume swell results for representative barrier materials used in flexible underground piping Table 5. Measured and calculated results for PVDF and Nylon 6
Table 4. Volume swell results for representative barrier materials used in flexible underground piping Table 5. Measured and calculated results for PVDF and Nylon 6
The results in Table 5 show that the expected increase in volume swell when going from E10 to E15 is less than 1 percent for the primary barrier liner materials used in flexible piping. The low additional volume swell is not likely to create much stress in the piping since these materials are able to relax due to the flexible nature of the piping. Based on these results, we do not anticipate any noticeable potential for release associated with going from E10 to E15. However, if the piping is rigidly constrained somehow, then stress buildup may occur to cause bucking (or cracking) of the piping. Most of the changes in swell (and hardness) will occur from moving from E0 to E10.
The results in Table 5 show that the expected increase in volume swell when going from E10 to E15 is less than 1 percent for the primary barrier liner materials used in flexible piping. The low additional volume swell is not likely to create much stress in the piping since these materials are able to relax due to the flexible nature of the piping. Based on these results, we do not anticipate any noticeable potential for release associated with going from E10 to E15. However, if the piping is rigidly constrained somehow, then stress buildup may occur to cause bucking (or cracking) of the piping. Most of the changes in swell (and hardness) will occur from moving from E0 to E10.
Fig. 9. Volume swell results for UST resins following exposure to Fuel C and CE25a.
Fig. 9. Volume swell results for UST resins following exposure to Fuel C and CE25a.
Table 6. Measured and calculated results for UST resins Vipel F774 and Vipel F085 The change in hardness results for the UST resins are shown in Fig. 11. For each resin type, the hardnes: dropped slightly with exposure to Fuel C, but CE25a was shown to significantly lower hardness in the wetted condition. Vipel F701 and Vipel F764 exhibited greatest drop hardness (31 and 20 points, respectively) from the original condition. These values are considered high and since hardness is a measure of strength and elastic modulus, it is not surprising that these two specimens exhibited fracture following exposure to CE25a. Interestingly, Vipel F774 also experienced a relatively large decrease in hardness of around 15 points. The combination of reduced volume swell and lower change in hardness (relative to the F701 and F764 resins) were enough to prevent fracture of the F774 resin. The most advanced resin grade, Vipel F085 exhibited the least change in hardness of the resins tested.
Table 6. Measured and calculated results for UST resins Vipel F774 and Vipel F085 The change in hardness results for the UST resins are shown in Fig. 11. For each resin type, the hardnes: dropped slightly with exposure to Fuel C, but CE25a was shown to significantly lower hardness in the wetted condition. Vipel F701 and Vipel F764 exhibited greatest drop hardness (31 and 20 points, respectively) from the original condition. These values are considered high and since hardness is a measure of strength and elastic modulus, it is not surprising that these two specimens exhibited fracture following exposure to CE25a. Interestingly, Vipel F774 also experienced a relatively large decrease in hardness of around 15 points. The combination of reduced volume swell and lower change in hardness (relative to the F701 and F764 resins) were enough to prevent fracture of the F774 resin. The most advanced resin grade, Vipel F085 exhibited the least change in hardness of the resins tested.
Fig. 11. Point change in hardness for the UST resin samples following exposure to Fuel C and CE25a.
Fig. 11. Point change in hardness for the UST resin samples following exposure to Fuel C and CE25a.
Fig. 12. Photograph showing the Batch 1 specimens before and after exposure to Fuel C, CE50a, and CE85a. Three coupons from each UST were evaluated in Fuel C, CE50a and CE85a test fuels. (The UST sections were not included in the earlier CE10a, CE17a, or CE25a test fluids, since this activity was started after these studies were completed.) These coupons were exposed in the test fluids for 16 weeks at 60°C along with other plastic specimens.
Fig. 12. Photograph showing the Batch 1 specimens before and after exposure to Fuel C, CE50a, and CE85a. Three coupons from each UST were evaluated in Fuel C, CE50a and CE85a test fuels. (The UST sections were not included in the earlier CE10a, CE17a, or CE25a test fluids, since this activity was started after these studies were completed.) These coupons were exposed in the test fluids for 16 weeks at 60°C along with other plastic specimens.
Fig. 13. Photograph showing the Batch 2 specimens before and after exposure to Fuel C, CE50a, and CE85a.
Fig. 13. Photograph showing the Batch 2 specimens before and after exposure to Fuel C, CE50a, and CE85a.
Fig. 14. Photograph showing the Batch 3 specimens before and after exposure to Fuel C, CE50a, and CE85a.
Fig. 14. Photograph showing the Batch 3 specimens before and after exposure to Fuel C, CE50a, and CE85a.
Fig. 15. Volume swell and point change in hardness for elastomers exposed to Fuel C, CE10a, CE17a and CE25a.
Fig. 15. Volume swell and point change in hardness for elastomers exposed to Fuel C, CE10a, CE17a and CE25a.
Fig. 16. Percent mass change and point change in hardness for elastomers exposed to Fuel C, CE10a, CE17a and CE25a following dry-out.
Fig. 16. Percent mass change and point change in hardness for elastomers exposed to Fuel C, CE10a, CE17a and CE25a following dry-out.
The adhesive method involves adding an adhesive to glue a fitting or coupling to FRP. Because of its inherent weakness, this method is not used to join pipe sections, but is restricted to attaching fittings (such as flanges). Typically the outer surface of the pipe is sanded to allow better distribution of the sealant and to enable the adhesive to better grip the pipe surface and thereby form a strong mechanical bond. One application of this method is shown in Fig. 19. The adhesive maintains a seal between the fitting and the pipe end. At the fitting face, the adhesive will be exposed to fuel in the crevice region between the adjacent pipe ends. For some applications, the outer pipe walls are tapered at the ends to enable better fit between the pipe wall and fitting. The adhesives used for FRP systems contain a mix of inorganics (over 50%), such as clay, limestone, and silica and a mix of hydrocarbons. The inorganic fraction imparts strength, rigidity and is resistant to attack from aggressive fuel components (including alcohols). The remaining hydrocarbons consist primarily of acrylic polymers, resins and distillate products. Information pertaining to adhesive resistance to ethanol was lacking and we were not able to ascertain ethanol compatibility.
The adhesive method involves adding an adhesive to glue a fitting or coupling to FRP. Because of its inherent weakness, this method is not used to join pipe sections, but is restricted to attaching fittings (such as flanges). Typically the outer surface of the pipe is sanded to allow better distribution of the sealant and to enable the adhesive to better grip the pipe surface and thereby form a strong mechanical bond. One application of this method is shown in Fig. 19. The adhesive maintains a seal between the fitting and the pipe end. At the fitting face, the adhesive will be exposed to fuel in the crevice region between the adjacent pipe ends. For some applications, the outer pipe walls are tapered at the ends to enable better fit between the pipe wall and fitting. The adhesives used for FRP systems contain a mix of inorganics (over 50%), such as clay, limestone, and silica and a mix of hydrocarbons. The inorganic fraction imparts strength, rigidity and is resistant to attack from aggressive fuel components (including alcohols). The remaining hydrocarbons consist primarily of acrylic polymers, resins and distillate products. Information pertaining to adhesive resistance to ethanol was lacking and we were not able to ascertain ethanol compatibility.
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