When building a new production or disposal tank battery, energy companies will install either fiberglass or steel tanks. Currently there is a myth that lightning strikes fiberglass tanks more often than steel tanks. The truth is that lightning strikes fiberglass and steel tanks equally. This article explains simple and inexpensive ways to make fiberglass tanks less susceptible to static and nearby lightning than steel tanks while still maintaining their advantage in corrosion.
Lightning usually strikes grounded objects near the base of the thundercloud. Tanks made of different materials have no lightning strike attachment advantage over each other. It is very important to understand that most tanks are not lost to direct lightning strikes. Rather, they are more commonly lost to secondary effect arcing that ignites flammable gases. Steel and Fiberglass Combo Mat are different materials that need to be protected in different ways. There are three areas of concern detailed below that make unprotected fiberglass tanks more susceptible to static and nearby lightning than unprotected steel tanks.
The first concern is arcing from secondary lightning effects which can simply be remedied by bonding across the top of a tank battery. A steel tank is inherently bonded to the catwalk, thief hatch and metallic plumbing attachments. A fiberglass tank instead electrically isolates these metal bodies across the top of the tank. To start with, the lid and the flange of every thief hatch on both steel and fiberglass tanks need to be bonded with a UL listed bonding strap. Fiberglass tanks additionally will need a need a UL listed tank top conductor system bonding between the catwalk, thief hatch, and any metallic inlets. Once tank top bonding and grounding is complete, a fiberglass tank will equal a steel tank in this regard.
The second concern is found inside the tank when charges accumulate in the fluid and vapors which for simplicity we will call static. Static can form inside a tank through normal operations which create friction such as transfer or pumping. Secondary effects of nearby lightning strikes can also introduce charges. When the static charges inside of a tank build to the point of recombining into an arc, the tank will likely be lost. Unlined steel tanks have the advantage of being able to relax accumulating static charge faster than fiberglass tanks. Fiberglass and epoxy lined steel tanks have insulating properties and, therefore, need assistance in draining static charge accumulation.
