API RP 2003:1998 pdf download

API RP 2003:1998 pdf download.Protection Against lgnitions Arising Out of Static, Lightning, and Stray Currents.
Static electricity is generated by the movement of materials. Ii involves the separation or pulling apart of surfaces that are in intimate contact with each other. This is also referred to as frictional charging. When two bodies of dissimilar materials are in close physical contact with one another there is often a transfer of free electrons. If one or both of the materials are poor conductors, uneven charges can not quickly recombine. A sudden separation will leave the excess electrons on one of the bodies and a deficiency of electrons on the other. If the two bodies are then insulated from their surroundings, they will tend to accumulate equal and opposite charges. The body has’ing the excess electrons will be negatively charged and the one with an electron deficiency will be positively charged. The electrical potential difference between the charged bodies can easily reach several thousand volts.
Some common examples of separation or frictional generation of static electricity are:
a. Separation of liquid or gas from a hose, nozzle, faucet, or pouring spout.
b. The movement of liquids, gases or solid particles relative to other materials, such as occurs commonly in operations involving flow through pipes, mixing. pouring. pumping. filtering. agitating, or other types of fluids handling.
c. Turbulent contact of dissimilar fluids, such as water or gas flowing through a liquid hydrocarbon.
d. Air. gas, or vapors containing solid particles (e.g.. dust. rust. etc.) or droplets being discharged from a pipe or jet. Dis. charge of carbon dioxide extinguishers. sand blasting. steam lances, and pneumatic transportation of solids are examples.
e. Nonconductive drive hells and conveyor belts moving across or separating from rollers or pulleys.
4.1.2 Charge Accumulation
l-lectrostatic charges continually leak away from a charged body. This mechanism, di.ssipasion. starts as soon as a charge is generated and can continue after generation has stopped. Electrostatic charges accumulate when they are generated at a higher rate then they dissipate. The ability of a charge to dissipate from a liquid is a function of the following:
a. The conductivity of the product being handled.
b. The conductivity of the cornainer,
c. The ability of the container to bleed a charge to ground.
In a grounded conductive container, the ability of a liquid to dissipate a charge is governed by the liquid’s conductivity. The higher the conductivity, the faster the charge dissipates. Generally. liquids with conductivity greater than 50 pSfm do not accumulate static charges provided the material is handled in a grounded conductive container. Above 50 pS/rn, charges will dissipate as fast as they are generated. Table A-I lists conductivities of some typical liquids handled in petroleum operation.