API RP 2023:2001 pdf download

API RP 2023:2001 pdf download.Guide for Safe Storage and Handling of Heated Petroleum-Derived Asphalt Products and Crude-Oil Residua.
4.6 FIRE PREVENTION
Before there is the possibility of a storage tank fire there must be a flammable mixture in the tank. Some actions to help prevent fires and explosions by controlling the vapor space in heated storage tanks are:
a. Ventilating to remove vapors and keep vapor space in the lean” range (for tanks with low volatility materials stored at least 50°F below their open cup flash point).
b. Venting limited to a single vent that is properly sized [see
API 20001.
c. Preventing restriction caused by condensed, solidified deposits building up in the vent.
d. Keeping gauge hatches closed during normal operation.
e. Regulating the storage temperature to keep the evolved vapors outside the flammable range (either too lean or too rich—see Appendix D3).
f. Careful control if lines are blown with air(see 6.4).
g. Careful control if using air for mixing (see 7.3).
h. Inert blanketing the vapor space o reduce oxygen content.
i. Temporarily inciting the vapor space with flue gas or another suitable medium when tanks are emptied at rates substantially above normal.
Ignition of hydrocarbon vapors is possible when the oxygen level is about ll%(by volume) or greater. To maintain a safety margin, SOLAS calls for a maximum of 8% (by volume) oxygen in inert blanketed tanks on board crude oil tankers. This is achieved using systems supplying inert gas with a maximum of 5% oxygen. Inert gas is lighter (lower molecular weight) than hydrocarbonair mixtures. If blanketing is used, the potential time effect” of the inerting technique should be recognized. If the inert gas is introduced near the top there can be stratification in the tank, with the heavier air/fuel mixture near the surface of the stored hydrocarbon. Diffusion and thermal currents will eventually provide dilution of the original atmosphere. If an empty tank is being inert blanketed this stratification effect can be used to advantage by venting the tank of HC vapors from the bottom with inert gas introduced near the top. This will tend to displace (instead of dilute) the heavier hydrocarbon/air mixture. Potemial personnel exposure and environmental issues should be addressed. Tanks which have been inert blanketed may require special procedures when being removed from service (see 612) because inerting can cause a buildup of pyrophonc iron sulfide.
Precautions against exposure to sources of ignition should be emphasized and observed. If ignition occurs inside a tank there may be an internal explosion. The resulting overpressure may cause the tanks roof to flu I and separate from the shell.