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How New Gasoline Formulas Can Affect Petroleum Equipment

Over the years, petroleum equipment manufacturers have worked hard to ensure that their products remain compatible with new gasoline formulas. Gene Mittermaier, PE, looks at some incompatibility problems of the past and tells what the industry has done to avoid these problems in the future.



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Author: Mittermaier Armin E. , PE
What´s been done to solve the problems?

Stainless Steel Shells Corroded Through in Two Weeks of Use in Gasoline

Nylon Hose Destroyed by Gasoline Vapors

More than 100 Submersible Pumps Locked Up at One Time in a Major City

Suction Pumps Locked Up with Solid Rust in One Week.

These headlines and the stories that follow are not the result of a diabolical terrorist plot. Rather, problems occurred when old equipment met new automotive fuels. And small wonder since more fuel changes have been made in the last 25 years than at any time in the preceding 90 years. Changes include the removal of lead and the addition of ethanol, methanol, MTBE, ETBE and TAME.

During these 25 years, Reid vapor pressures have dropped from a high of 14 psi to the current levels of between seven and eight psi. These changes have resulted in some well-publicized but fairly isolated failures in retail fuel handling equipment.

Let’s review these equipment failures by starting at the bottom of the underground storage tank with electronic monitoring systems; then we’ll move up through submersible pumps, and out through the retail dispenser, hose and nozzle.

Underground fuel monitoring systems
Electronic fuel monitoring systems (tank gauge probes), are relatively new on the scene, having exploded in numbers over the last 10 years. The most common materials used for electronic tank gauges in fuel contact areas are:

• aluminum for electrical conduit
• epoxy to encapsulate capacitance elements
• glass in capacitance and buoyancy type probes
• nitrophyl in magnetostrictive floats
• nylon for electrical insulation
• PVC jacketed cable for wiring at the top of the probe
• stainless steel, type 316, in magnetostrictive shells
• fluorocarbon, (ASTM FKM) for “O” rings

Type 316 Stainless Steel is one of the most corrosion-resistant materials that a manufacturer can use to handle fuels. According to the National Association of Corrosion Engineers (NACE), it is the best stainless steel for gasoline. However, under what were very unusual circumstances, the following incident occurred.

Two years ago, electrolysis corrosion failure of in-tank level gauges was reported in one tenth of one percent of the probes sold by a large manufacturer. These probes used a nylon bushing to prevent electrical contact of the bottom of the probe with the steel tank. The type 316 stainless steel case of the probe was plated away and deposited onto the bottom of the steel tank; this caused a corrosion failure of the probe. Corrosion failure of the type 316 stainless steel shell occurred in as little as two to three weeks.

Opinions differ as to what may have happened. One thought is that the electrolysis failure occurred before the nylon inserts were added. If the tank bottoms had chlorinated water, the chloride might have corroded the stainless steel.

Another very possible culprit, however, could be the oxygenated fuel additives, which are slightly conductive polar compounds. Their use in gasoline may have permitted an electrical current flow from the steel shell around the nylon bushing and into the case of the tank level gauge. Therefore, the electrical current and the conductivity of the fuel additives would have created a “bath” similar to a plating solution. Not just chemistry, but electro-chemical forces may well have been at work here.

New probes have the stainless steel coated with nylon to a height of eight inches to prevent a recurrence of this problem.

In another situation, a company found its probes began to register incorrectly when placed in a tank with a relatively high level of water into which a gasoline/alcohol (ethanol) blend was introduced. The water was absorbed by the alcohol and created a third product, thus causing the floats to register incorrectly. The solution was to evacuate the tank completely, and then to fill it with the ethanol blend.

Submersible pumps

The first submersible pumps introduced in 1956 used die cast aluminum impellers to pump the product. In the mid ‘60s molded acetal (Delrin or Celcon trade names) impellers were introduced. By 1980, nearly all submersible pumps used impellers of this molded acetal engineering plastic, which had improved flow rates and had no apparent problems.

Acetal is a crystalline plastic based on formaldehyde polymerization technology. Acetal will swell only an infinitesimal amount when the amount of methanol mixed with gasoline is less than 10 percent. Also, acetal exhibits little swell in 100 percent methanol. Unfortunately, some types of acetal can swell about .2 percent in a mixture of 16 percent methanol to gasoline.

In the late ‘80s, in Johannesburg, South Africa, a mixture of 16 percent methanol and gasoline caused swollen acetal impellers in approximately 100 submersible pumps. The swollen impellers locked against the pumps stators; this caused the pumps to fail to rotate and deliver product. It was necessary to trim 0.05 of an inch off the radius of each impeller to place the pumps back in operation.

This is a case where the material needed to be tested in the same percentage of fuel mixtures that will be used in the field to determine if the mixture will provide a satisfactory performance. The most common materials used in submersible pumps in contact with the fuel are:

• Anodized Aluminum—Pump and motor shells, wiring conduit
• Buna N—“O” rings and lathe cut gaskets
• Cast iron—Flow manifolds and electrical enclosures
• Epoxy—Wiring seals
• Fluorocarbon—“O” rings and check valve seats

Failure of the following materials can cause equipment failure:

• Acetal plastic—Pump impellers and housings
• Black iron—Fuel piping in the tank
• Carbon—Motor pump thrust bearings w
• Stainless steel—Motor shells, motor/pump shafts

The Buna-N lathe cut gasket seals, which are used in submersible pump flow manifolds, were involved in an outbreak of fuel leaks. This occurred in the fall of the year when winter gasoline, with added oxygenates, replaced summer gasoline, which has low oxygenates. The failure occurred in Buna-N seals that had been in use for several years without oxygenates.

New Buna-N gaskets did not seem to experience this problem. There are approximately 870,000 submersible pumps in use at fueling sites across the United States and about 95 percent have Buna-N seals.

Fuel dispensers
Materials often found in contact with fuel for fuel dispensers can result in external leakage, should these materials fail. These materials are:

• Aluminum tubing—Fuel paths
• Black steel pipe—Riser pipes and ground joint unions
• Buna-N—“O” rings and lathe cut gaskets
• Cast iron—Meter bodies and fluid paths
• Copper—Air eliminator floats
• Copper tubing—Fuel paths
• Cork/Buna-N—Flat gaskets
• Die cast aluminum—Meter bodies and fluid paths
• Graphite rope—Suction pump shaft seals
• Fluorocarbon—“O” rings and lathe cut gaskets

Materials often found in contact with fuel for fuel dispensers can result in product malfunctions, should these materials fail. These materials are:

• Carbon—Bearings and meter valves
• Cast iron—Pumping units
• Leather—Meter piston cups
• Rulon—Meter piston cups and shaft seals
• Stainless steel—Meter and valve shafts
• Zinc plated stl. stampings—Meter pistons and valve parts

An example of severe product failure occurred in Brazil where a major automotive fuel is ethanol, mixed with seven percent water. Service stations in Brazil use many suction pumps with cast iron rotors running at very close tolerances in a cast iron housing.

To test if the cast iron units were compatible with this fuel, rotary pumping units were filled with 93 percent ethanol and seven percent water; then the units were opened every month to see if any rust occurred.

After testing for more than eight months with no appreciable rust found, several shipments of suction pump fuel dispensers were shipped from the plant, located 1,000 miles up the Amazon River, to Sao Paulo, more than 2,000 miles away. The pumps lasted less than one week in the Sao Paulo service stations before the cast iron pumping rotors were solidly rusted in place.

When checked, the fuel was 93 percent ethanol, seven percent water as tested in the United States. However, here was the problem: every day the pumps were run until they pumped the underground storage tanks dry. This brought oxygen laden air into the pumping units that were wet with the ethanol/water mixture, thus causing severe rusting in less than one week of service.

Certain materials in fuel dispensers need attention when new fuels are introduced. These materials include:

Unprotected aluminum tubing and diecastings. These are used to confine the fuel in 75 percent of all fuel dispensers. This aluminum can be eroded one thirty-second of an inch per year by pure methanol under certain conditions. The Metals Handbook indicates aluminum erosion can occur in dry alcohol at elevated temperatures. Some field experience indicates that certain types of aluminum erode at ambient temperatures in methanol when mixed with specific percentages of water.

Treated leather meter piston cups. These cups are six percent of all fuel dispensers.

Old Buna-N lathe cut gaskets and “O” rings. These are used in 90 percent of all dispensers in from six to 30 sealing points per dispenser.

Hoses
Materials in which failure may cause a fuel leak:

• Epichlorohydroin—Inner fuel containing walls
• Neoprene—External cover of the hose
• Nitrile—Inner fluid containing walls
• Nitrile/PVC—External cover of the hose
• Nylon—Used for hose components in contact with vapors
• Thermo Plastics—Used for hose components in contact with vapors

One example of product failure in hoses occurred in Wisconsin when the EPA-mandated reformulated gasoline fumes met up with Stage II vapor recovery. Reformulated fuel was used with fuel dispensers equipped with positive displacement vapor pumps in a Stage II Vapor Assist System. The very close tolerance vapor pumps installed in each dispenser were protected from damage by a very fine mesh screen on the inlet to the pumps.

The first sign of trouble was that the fine mesh screens in the vapor return line to the pumps were very quickly clogged with a white powder. This made the vapor recovery system totally ineffective.

The culprit was the nylon compound used to line the inside of the vapor recovery hose. This compound had an unneeded stabilizer for high temperature operation (more than 200ºF) and for UV protection. Unfortunately, that stabilizer is soluble in a chemical called MTBE. The answer to the problem was to use nylon in hoses without this unnecessary stabilizer, and the nylon used today does not contain it.

Nozzles and swivels
Nozzles and swivels have many materials in contact with the fuel. The following materials, should they fail, can cause external leaks:

• Buna-N valve poppets and seals
• Die cast aluminum swivel fuel carrying parts
• Fluorocarbon valve poppets and seals
• Sand cast aluminum fuel carrying parts
• Super Fluorocarbon valve poppets and seals
• Teflon swivel seals

Should these materials fail, a product malfunction can result:

• Buna-N—Valve Poppets
• Nickel plated—Seal and bearing surfaces
• Stainless steel—Operating shafts
• Fluorocarbon—Valve poppets

Error in splash bending in Oregon caused mixtures higher than 40 percent methanol in gasoline to be introduced into storage tanks. This caused Fluorocarbon (ASTM FKM) poppets of many nozzles to swell to the point that the nozzles could not shut off. Some Fluorocarbon compounds are good in methanol and some are not as good.

A noteworthy, but basically unrelated problem occurred when unleaded gasoline was introduced in 1971, causing a rash of swivel seal leaks. The leaks were particularly bad because many Volkswagen Beetles were on the road with the gas tank and fill pipe inside of the trunk. This permitted the dripping swivels to leak onto items in the trunk.

Changing the design of the swivel to new Fluorocarbon compounds has solved the problem.

Fuel compatibility
In the 1960s through the 1980s, there was one controlling factor in seal material selection—which material would most cost-effectively pass the UL test requirements. Because Fluorocarbon parts cost 10 times more than the Buna-N, Buna-N was the choice for seals almost 100 percent of the time.

The Buna-N of the past was not as chemically resistant as the Buna-N available today. In the 1960s through the ‘80s, at least once a year, a dispenser manufacturing line would be shut down because the incoming Buna-N swelled more than the allowable 25 percent in UL test fluids. Those test fluids were fairly simple compared to what is in the reformulated fuels sold today. And yet the industry is handling such fuels with fewer and fewer problems.

As a whole, the petroleum industry is to be congratulated on the scarcity of incidents of failures related to new fuel introductions. This is due, in large measure, to two factors: (1) the statistically viable field tests that oil companies have conducted before new fuels are introduced; and (2) the foresight and skill of manufacturers who design equipment, knowing full well that any combination of more than 300 compounds may some day appear in the fuel that their equipment is designed to handle.

Fuel compatibility today is a challenge that is being successfully met.

Armin E. Mittermaier, PE was a long time Tokheim engineer and was President of Data Action and Poly Concrete Forms, located in Fort Wayne, IN. He is deceased.

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