If you are already saying to yourself, “I’m not going to read this because I always ground everything,” YOU, FRIEND, are the person we want to reach before you kill someone. Read the title again. Sparks FROM jet fuel. We are not talking about static charges on pipes, trucks, or any object. We are talking about electrostatic charges IN fuel.

Volumes and heaps of deep technical papers have been written on this subject but this article is a pioneering effort toward the non-technical. Have you ever noticed that the greater the number of scientific words that are written on a subject, the less the problem is really understood? That is the situation with static charges in jet fuel.

We like to describe how electrostatic charges build up in fuel by explaining that it is caused by rubbing molecules together. In other words, it is caused by friction — friction between molecules. The more vigorous the rubbing, the greater the charge becomes. The scientists call this “charge separations”. In other words, when the “pluses” separate from the “minuses” you have charge separation. This is when charge separation occurs. Also, the charge becomes bigger and bigger as more of the molecules in a given volume are agitated. If the charges move to the wall of the pipe or tank, they are immediately grounded and can cause no hazard; the whole problem is that the charges cannot easily move through some fuels to a “ground”: these are called “low conductivity” fuels. POSSIBLY YOURS!

There is one item of equipment that is clearly the champion of all static charge generators — a filter. The agitation created by splash loading or by pumps, piping, valves, and meters causes a charge to develop, but the filter is the place where the most “molecule separation” occurs — and the finer the filter, the greater the charge – and the higher the rate of flow through the filter, the greater the charge. If a filter salesman tries to tell you that his filters do not cause any static, throw him out. However, recent studies have demonstrated that Teflon coated separator elements generate lower charge levels than paper separators. It seems logical that there is less friction and charge separation caused by a 74 micrometer screen separator than by a tortuous flow path in a 5 micrometer paper.

Now we should return to the reader in the first paragraph who threatened not to read this issue because he “grounds everything.” Obviously, if his fuel always has a high conductivity, the charges will move to grounded metal components. But if he has a fuel with a low conductivity, the charges take a period of time to move to ground. If this “charged” fuel is dispensed into a tank, a spark may jump from the surface of the fuel to a grounded object but tests have proven that the most dangerous situation occurs when there is an unbonded object in the vapor space — it acts like a capacitor – it stores up charges – then ZAP. Need we explain what happens if the right amount of fuel vapor is in the path of the spark?

What to Do

A “rule of thumb” that most technical people seem to accept is to keep the fuel in piping or a pressure vessel for 30 seconds after filtering before dispensing it into an open tank. This period is called “system relaxation time.” The theory is that even if the fuel has low conductivity the positive and negative charges will have canceled one another out or have migrated to a grounded surface in that time. Some companies advocate the use of “anti-static” additives to avoid the need for relaxation time. However, the word “anti-static” is a very bad term. It should be called a conductivity improver.

So now if you do not use the additive, all you have to do is take a look at your filter installation to see if you have 30 seconds relaxation time! We wish we had a little gauge to sell to measure this for you but lacking one, we have worked out a sneaky, non-scientific method using simple arithmetic.

If you like real formulas, use this one:

C = 0.0408 x (L₁D₁² + L₂D₂² + L₃D₃² + etc.)

Where C is capacity in gallons, (as in Step 2) L is pipe section length, and D is pipe section diameter. The constant is 0.034 if using Imperial gallons. It is 0.5067 for liter calculations.

Finale:

If you found from your calculations that you did not have enough system relaxation time, we cheerfully offer two alternatives:

1. Reduce flow rate
2. Have the system redesigned

¡¡Sucedió DE NUEVO!! ¿Porqué es que la gente no lee nuestras instrucciones de instalación antes de instalar nuestros kits para muestreo? El propósito de una sonda de muestreo y algunas partes de acero inoxidable algo costosas con una conexión rápida es para asegurar que una prueba con membrana filtro se correrá en el combustible cuando este fluye por toda la tubería. Las compañías petroleras, aerolíneas, los militares y los contratistas para abastecimiento saben por experiencia que Ud. no puede correr una prueba significativa en combustible que está estancado en la conexión de un ramal. ¿Porqué es que algunos recurren a un contratista sin experiencia en combustibles de aviación que instala una sonda para prueba de manera que se verificará al combustible en una TRAMPA DE SUCIEDAD?

Una vez visité una zona de almacenamiento de un aeropuerto donde encontré exactamente la situación descrita arriba. Una aerolínea había especificado nuestro Kit No. 1 (Ver Figura 1). Todas las partes fueron ensambladas correctamente pero la sonda estaba retirada por lo menos a 6″ de la corriente que fluía porque había sido colocada en una “T” de un ramal de 8″ sin uso. Habían gastado sobre $600.00 USD por lo menos en un ocasión al reemplazar los elementos del filtro separador porque las partículas de suciedad en la membrana filtro indujeron al personal operador a creer que algo estaba mal. ¡Y por favor no argumente que ellos no circularon apropiadamente antes de correr la prueba! En tal situación, Ud. tendría que circular cientos de galones antes de que el combustible en una conexión de un ramal se volviera representativo de la corriente principal.

El propósito real de nuestra sonda de prueba es para asegurar que la prueba con membrana filtro se corre en el tipo de combustible que está circulando por la tubería. La sonda (Ver Figura 2) penetrará por cualquier buje reductor así como por el cople soldado a la tubería.

FIGURA 1

FIGURA 2

En el arreglo mostrado en la Figura 1, el combustible que llega a la membrana nunca está en contacto con acero al carbón desde el momento que deja la corriente principal. El recorrido total del flujo hasta la membrana es acero inoxidable liso y el diámetro es pequeño de manera que se puede obtener una buena velocidad durante la circulación para eliminar cualesquier residuo o partícula atrapados.
¿Recuerda Ud. la discusión acerca de velocidad en el GamGram No. 4, “Anatomía de una Tubería para Turbo Combustible”? ¿No es aún más importante poder limpiar una conexión para muestreo? Esto es porqué hemos propugnado por 35 años que la manguera para lavado se use antes de correr la prueba con membrana filtro. Cada vez que se ha embarcado un MiniMonitor Kit ha sido equipado con una de manera que la velocidad de lavado será más de 10 pies por segundo en vez de aproximadamente 0.9 pie por segundo que la válvula para lavado del pequeño MiniMonitor (o la que fabrica Millipore Corp.) permite a 50 psi. Vea Model GTP-1110 en el Boletín No. 8.

HAGA ESTO

Inspeccione sus conexiones para muestreo y conteste las preguntas siguientes:

• ¿Está ubicado el acceso de manera que pueda Ud. muestrear la corriente principal?
• ¿Es el acceso de la tubería lo suficientemente pequeño de manera que realmente pueda limpiarlo con el chorro? Si no, una sonda resolverá el problema.
• ¿Hay una colección de bujes reductores de acero al carbón, codos o coples antes de que el combustible pueda alcanzar esa bella conexión rápida de acero inoxidable? Si así es, ¿usaría también una vieja y herrumbrosa conexión rápida? ¡Ciertamente no! Utilice uno de nuestros Kits para muestreo.
• PIENSE – ¿Ha corrido alguna vez pruebas con membrana filtro en el lado corriente arriba de su filtro separador de manera que pueda comparar resultados con la prueba corriente abajo? ¿No sería esta la manera lógica de satisfacerse a si mismo en cuanto a que los elementos son actualmente capaces de remover contaminantes?

Esto nos pone en una de nuestras filosofías favoritas. ¿Puede Ud. sentirse seguro solamente porque no encontró suciedad o agua corriente abajo de un filtro separador? ¡Ud. no se sentirá seguro! ¡Ud. puede tener combustible limpio, seco pasando por él! ¿Que seguridad tiene de que el filtro está actualmente en buena condición? Yo, por mi mismo, me sentiría mucho más feliz cuando se encuentra poca agua y suciedad en la entrada si las pruebas corriente abajo muestran que el filtro removió la contaminación. Cuando termino una prueba, me gusta poder palmear la tapa del filtro y decir, “Viejo amigo, estás haciendo tu trabajo.”

It happened AGAIN!!! Why is it that people don’t read our installation instructions before they install our sampling kits? The purpose of a sampling probe and some expensive stainless steel parts with a quick disconnect is to insure that a filter membrane test will be run on fuel as it flows through the pipe. The oil companies, airlines, the military and fueling contractors know from experience that you cannot run a meaningful test on fuel that is stagnated in a branch connection. Why is it that someone hires a contractor with no aviation fuel experience who installs a sampling probe so it will test the fuel in a DIRT TRAP?

I once visited an airport fuel farm where I found the exact situation described above. An airline had specified our Kit No. 1 (See Figure 1). All of the parts were assembled correctly but the probe was at least 6” away from the flow stream because it had been located in an unused branch of an 8” pipe tee. Over $600.00 had been spent on at least one occasion to replace the elements in the filter separator because the dirt particles on the filter membrane led the operating personnel to believe that something was wrong. And please don’t argue that they must not have flushed properly before running the test! In such a situation, you might have to flush hundreds of gallons before the fuel in a branch connection becomes representative of the main flow stream.

The real purpose of our sampling probe is to make sure that the filter membrane test is run on the kind of fuel that is going through the pipe. The probe (See Figure 2) should penetrate through any reducing bushings as well as the coupling that is welded to the pipe.

FIGURE 1

FIGURE 2

In the pictured arrangement of Figure 1, the fuel that reaches the membrane never is in contact with carbon steel from the moment it leaves the flow stream. The entire flow path to the membrane is smooth stainless steel and the diameter is small so that a good velocity can be attained during flushing to carry away any residue or trapped particles.

Do you recall the discussion about velocity in GamGram No. 4, “Anatomy of a Jet Fuel Pipe”? Isn’t it even more important to be able to flush a sampling connection? This is why we have been advocating for 35 years that a flushing hose be used before running the filter membrane test. Every MiniMonitor Kit that has ever been shipped has been equipped with one so that the flushing velocity will be more than 10 feet per second instead of about 0.9 feet per second that the little MiniMonitor flushing valve (or the one made by Millipore Corp.) permits at 50 psi. See Model GTP-1110 in Bulletin No. 8.

DO THIS

Inspect your sampling connections and answer these questions:

• Is the fitting located so you can sample the main flow stream?
• Is the fitting on the pipe small enough so that you can really flush it clean? If not, a probe will solve the problem.
• Is there a collection of carbon steel reducing bushings, elbows or couplings before the fuel can reach that beautiful stainless steel quick disconnect? If so, would you use a rusty old quick disconnect also? Certainly not! Use one of our Sampling Kits.
• THINK – Do you ever run filter membrane tests on the upstream side of your filter separator so that you can compare results from the downstream test? Wouldn’t this be the logical way to satisfy yourself that the elements are actually capable of removing contaminants?

This puts us into one of our favorite philosophies. Can you feel safe just because you found no dirt or water downstream of a filter separator? You should not feel safe! You could have clean, dry fuel going into it! What assurance do you have that the filter is actually in good condition? I, for one, feel much happier when a little dirt and water is known to be in the inlet if the downstream tests show that the filter removed the contamination. When I finish a test, I like to be able to pat a filter on its dome and say, “You’re doing your job, old friend.”

If I had a dollar for every time that a customer has told me, “There is no water in my filter separator sump,” I would be very wealthy. I would be almost as wealthy if I had a dollar for every time I found water in a sump that had just been given its “daily drain.”

Why is it that one man can find no water but another man can? Obviously, it’s all in the way you do it.

The difficulty is that the area where the sump drain is located is usually flat. Water collects on the flat surface but it tends to lie in a “heap” until something happens to break the interface. Watch how water acts in a nearly flat-bottomed wash basin. Water lies on the surface for long periods of time when the water valve is turned off. If you touch it with your finger, at the edge of the drain hole, it suddenly begins to flow into the drain. (We strongly recommend doing this experiment in private, away from those who may not understand scientific studies).

Most filter sump draining seems to be done by cracking open the drain valve and collecting a pint or two. This does not disturb the layer of water enough to break its surface tension and so the water stays on the flat deck.

If you really want to do a proper job, you must get some velocity down the drain hole and the best way to do this is to turn on the pump to get pressure. Then open the drain valve as far as possible (without giving yourself a kerosene bath) and collect a couple of gallons in a white bucket.

I’ll never forget how I learned this trick. One of the real old-timers in jet fuel met me at an airport where a severe surfactant problem had been found. I sumped the filter separator in the conventional way and got a nice clear bucket of fuel. After a few very critical remarks, he used the method described above and collected a sickening bunch of slime, water and crud with the fuel. (I wonder if T.C. remembers this episode?)

A doctor can see inside the human body only by looking in your eyes. He uses a bright light and a special glass. Doctors learn many things about your general health this way. The best method we have to learn about the “health” of fuels is to study the water sump.

This is why we should try to interpret what we see. So much can be learned but only rarely does anyone really look.

1. Water
   • Clear water: if it is clear, you are lucky. If it seems to have a brown film on it, this is probably a surfactant layer. If you touch it with a straw, you can often see clear water under it.
   • Dark Water: this is bad news! It generally means a severe surfactant problem but it can also indicate a problem at the refinery or it may be water from dirty fuels (heating oils and crude oil) that were previously handled in the same ship, barge or pipeline. Dark water can also indicate microorganism growth. There is no more certain indicator of trouble than dark water. Does it have a sulfur-like odor? More Bad News!
2. A white filmy thing seems to float around in the fuel, but you can’t collect it or gather it. This is a form of surfactant. Air bubbles that meet it as they rise toward the surface have difficulty penetrating this film but in a few minutes they break through. I have never known of anyone who has successfully analyzed this film because it simply cannot be collected.
3. Globs, slimes, jellies–microorganism growth. Remember, microorganisms cannot live in fuel. They live in water. If you eliminate water, you can have no growths.
4. Large dirt particles – either a coalescer element burst, was incorrectly installed or you didn’t clean the sump properly when the elements were last changed.

What action should be taken when unsatisfactory sump conditions are found? The first step is to insure that contamination does not progress farther in the supply system because every time that a surfactant contaminated fuel passes through a filter separator, its life is shortened and its performance may be degraded. The second step is to trace the source of the contamination and insure that corrective steps are taken. The third step is to clean all of the contaminated equipment and change filters as deemed necessary.

In conclusion, look diligently for water in fuel systems. If you find it, inspect it carefully and report all details.

Do you know what “half fast” engineering is? In handling jet fuel, this kind of engineering takes form when someone begins to think it is just like any other fuel — heavier than gasoline, lighter than fuel oil. He whips out a few calculations, looks at some pressure drop data in Cameron’s Hydraulic Data book, selects a pump that barely “squeaks” by and then compensates by going up 2 pipe sizes to make sure the pump will work. He justifies the larger pipe “for future plant expansion”. Oh Wow! What an engineer he is!

Here is a real-life story. An oil company terminal supplies fuel to a major airport using transport trailers. The loading rack at the terminal can handle 2 transports at a time, one loading arm on each side of an island. A 1200 gpm filter separator is located 100 ft. from the rack. About 70 ft. of the pipe is 8” and is underground — the last 30 ft. length is 12” and is aboveground, running the length of the rack island. The fuel is received into the terminal storage tanks from a common-carrier pipeline and is then prefiltered through clay before it enters a receiving filter separator. Over a period of time, the filter membranes were B 2 (by ASTM Test Method D-2276) out of the filter separator near the loading rack.

The customer at the airport receives the fuel through a filter separator. The “white bucket” test is performed on every trailer load before it is off-loaded.

Recently, the number of particles in the bucket increased to such an extent that the customer began refusing loads of fuel. The membrane tests remained entirely acceptable from a color standpoint. In checking back through the system, the particles were found to exist at the loading rack but not at the discharge end of the filter separator. The particles were mostly iron oxide — the size of coffee grounds.

The 12” pipe was opened under the rack. The upper 3/4 of the pipe surface was covered with rust particles, coffee ground size. The bottom 1/3 of the pipe was deep in wet slime, rust and dirt. We used shovels to dig it out!

Calculations show that the velocity in the 12” pipe at the 1200 gpm rated flow was only 3.4 feet per second. However, investigation revealed that the technical department had ordered a reduction of maximum flow rate to 550 gpm to insure adequate static charge relaxation time. This incredibly low flow resulted in a velocity of a “trickling” 1.6 feet per second. This was the cause of the dirt — a flow rate so low that the pipe was not being swept clean. Water condensed out of the fuel in the underground portion whenever the tank temperature was greater than ground temperature. It condensed out of the above-ground section every night that the temperature dropped. The water could not get out of the pipe. It couldn’t be drained out — it simply collected and caused rust and slime growth.

A prime lesson to be learned by this experience is that you should make fuel do its own housekeeping. Design and maintain flow velocities that will keep pipes swept clean and dry. We recommend at least 6 feet per second.

A good “rule of thumb” to remember is that jet fuel holds about as many parts per million of water as the temperature in degrees Fahrenheit. In other words, at 80°F there can be about 80 ppm of water dissolved in the fuel. If the temperature drops to 60°F in an underground pipe, there can be 20 ppm of free water to deal with.

We all know that water collects in tanks because of “condensation”– water dropping out of solution. Why is it that so many of us seem to forget that the same thing happens in piping? Only more so! The temperature of fuel in pipes changes more (and far more rapidly) than in tanks because of low mass and large exposed surface area.

In a recently finished airport fuel system, we just learned that a mile long, underground 24 inch pipe will handle a maximum flow rate of 2400 gpm during the next 3 years until a hydrant system is built. That means a velocity of 1.7 feet per second! It is not a pipe – it is a mile long condenser! And there are no water draw-off sumps. This is the type of design that keeps the filter separator manufacturers in business. This one is going to be a “king sized engineered problem”.

QUICK CALCULATIONS

1. Multiply the pipe size by itself
2. Then divide that number into gallons per minute
3. Then multiply by 0.4

1. 6 times 6 equals 36
2. 360 divided by 36 is 10
3. 10 X 0.4 equals 4 feet per second

In GamGram No. 2, we explained how large dirt particles get into a filter separator sump without going through the coalescer. In this issue, we talk about very small particles that go through the coalescer.

How many times have you opened a filter separator and found a fine film of dirt all over the sump? In a horizontal vessel, the film may extend halfway up on the sides. In most cases, it comes off easily with a rag. The particles are far too small to see individual ones – they are really super-fine! Your filter membrane tests have been consistently acceptable and there have been no unusual situations, except an occasional bit of water — but the outlet fuel has been dry. Yet there is enough dirt on the walls of the filter tank to make thousands of bad membranes — and that dirt is downstream of the coalescer — and the coalescers are the filters. How can this happen?

The answer is dirty water. Dirt came through the coalescer in the water. The water drops settled and clung to surfaces of the vessel shell or the sump walls. Then these extremely fine particles of dirt settled inside of each water drop until they contacted and attached themselves to the epoxy lining in the filter tank. The water was either drained away or it may have dissolved back into the fuel. You say the coalescer was at fault because the dirt came through. Wrong — the coalescer did its job just fine. What really counts is whether or not the fuel was clean.

To appreciate what a fantastic device a coalescer element really is, you should visit a filter separator testing laboratory someday and watch a qualification test. They use a “test dirt” known as red iron oxide and the particles are scientifically graded as shown in the chart. Note that 47% is under ¼ micro-meters or less than 0.00001 inches (that is 1 one-hundred thousandth or 10 millionths of an inch)! Incredible!

A coalescer does not actually strain these small particles out of the fuel. Instead, small clusters of particles gather together; the clump is then retained in the coalescer. A test proceeds with a gradual increase in pressure drop because the dirt is beginning to plug up the passages. Now, suddenly, water is injected. The coalescers go to work but the sump water turns red! The fuel remains clean and dry!

What actually is happening is that when the water comes in contact with the dirt that is already in the coalescer, it wets it and causes the clumps to break down into particles again. Instead of being in an environment of fuel and fibers, the dirt enters the water because the dirt “likes” to be water-wetted instead of fuel-wetted. The result – submicronic dirt goes through the coalescer in the water. The fuel? It remains clean!!

What should you do if you find a dirt film in a filter vessel sump? First of all, if your membrane tests have been good, don’t be alarmed because it is not a hazard. However, you definitely should go back through your system to find out why you are getting water. Always clean a filter separator thoroughly when the elements are changed. Remove all of the dirt film. Sometimes it just won’t come off with water or fuel and this author believes that this indicates a microorganism situation. Why? Because water drops that remain intact for any length of time can begin to grow a colony of microorganisms. The debris from this growth is much harder to clean off than ordinary dirt.

The most important thing to do when cleaning a filter separator is to be absolutely certain that the cleaning compounds are completely removed. This is why we do not recommend using chlorine-based bleach. Such chemicals can be very corrosive when in contact with some metals such as aluminum. They also can attack some elastomers and may cause early failure of valve seals. Remember also that the man in a filter vessel will be breathing hazardous vapors from bleach because there is almost no air circulation

Industrial cleaners, such as trisodium phosphate, are very effective but you must scrub the surface with water after cleaning to be sure none is left in the filter. Observe proper handling of TSP per the MSDS from your supplier. Never use steam cleaners because they almost always are contaminated with soap, a powerful surfactant that must never be used in a filter separator.

Never use a power washer if it has ever been used with any soap or detergent.