ANALYSIS OF A POLYESTER ROPE, FIBER ENCASED PRODUCT
FOR OILFIELD IN-TANK STATIC CONTROL
Lightning Master has long been the industry innovator and leader in static control, particularly for in-tank applications. One of our products is the in-tank static drain (ITSD) system for the oil and gas industry. This system controls and equalizes the accumulation of static charge within a tank, thereby reducing the likelihood of an ignition-causing arc.
An appliance designed to control static within a tank requires two properties: the ability to dissipate static charge and the ability to conduct current.
1. During normal operations, fluid movement can create a static charge in the droplets suspended in the vapor space above the stored product. The in-tank appliance must be able to dissipate that charge.
2. During a direct or nearby lightning strike, the appliance must be able to carry sufficient current to equalize the potential between the charge on both the stored product and in the vapor space above it and the charge on the electrically bonded mass of the tank.
We can find no basis in science for the claim that the rope-type product does either. We specifically raise the following points:
A. Point discharge is the principle used to control static charge. This phenomenon facilitates the transfer of charge from the stored medium to the tank. Point discharge relies upon the presence of small radius electrodes to perform this function. The electric field intensity (dissipation) is based upon the radius of these electrodes. We could find no evidence of electrodes or their equivalent in the rope. When placed in an electrostatic field, we could find no evidence of an ability to dissipate static charge. We found no evidence of corona discharge, but did observe arcing (a potential ignition source) between the strands of the weave of the fiber. Point discharge from dedicated, small radius electrodes works even if a correctly designed product is encased in a layer of gunk from the stored product. The presence of gunk on the rope product will compromise any dissipation capacity. Please reference the white papers on our web site for further discussion at https://www.lightningmaster.com/White-Papers/Streamer-Delaying-Technology.
B. Neither the woven carbon fiber casing nor the poly rope is an acceptable conductor. When used in the marine application, carbon fiber spars (masts, spinnaker poles, etc.) require a dedicated lightning protection conductor. Please reference NFPA 780,10.2.2.4 re use of carbon fiber composite masts as conductors. We tested the appliance to determine resistance and conductivity. The measured resistance of the Lightning Master® ITSD is .02 Ω/15 feet, a length typically used in tanks. The measured resistance of the rope is 9Ω/15 feet. During a direct or nearby lightning strike, the appliance must be able to conduct sufficient current to equalize the bound, or perhaps more accurately entrained, charge on the stored product and in the vapor space to the charge of the mass of the tank. In a steel tank, this mass consists of the tank structure. In a fiberglass or otherwise non-conductive tank, this mass consists of the various masses of inductance (valves, hatches, piping, gauges, etc.). In addition, the high resistance of the rope product may allow arcing between both the rope and the tank and between the loosely woven fibers, presenting two potential sources of ignition.
C. We are unaware of any other scientific basis to claim that the carbon rope performs the function purported in an in-tank application. The LES sales literature studiously avoids any discussion or even mention of the technological basis for their design. We have yet to see any technical material explaining how or why it supposedly works. The sales literature we have seen provides no reference to testing or even theory as a basis for their performance claims, and their technical explanation in their literature actually references that of an air terminal, a different type of product.
D. The rope product is encased in a woven fabric. This fabric will tend to wick hydrocarbons from the stored product through capillary action. This could become flammable. A correctly designed metal appliance will not wick, and, by its nature, is non-flammable. We have also noted a lack of robustness in the woven material with fraying of the fabric after shipping and routine handling.
Lightning Master has been preeminent in this field for more than twenty-five years. We are conversant with advances in this technology, yet are unaware of any basis in fact or science for the claims surrounding this product.
Anyone specifying, buying or using this type of system should have an understanding of the technology upon which it is based. That understanding is outlined above. Also, please feel free to call us to discuss any concerns you may have.