API STD 2000:2014 pdf download
API STD 2000:2014 pdf download.Venting Atmospheric and Low-pressure Storage Tanks.
a) larger or additional open vents as limited by 3.4.1.3.
b) larger or add Wonal PV valves,
c) a gauge hatch that permits the cover to lift under abnormal internal pressure,
d) a manhole cover that lifts when exposed to abnormal internal pressure,
e) weak (frangible) roof-to-shell attachment (see 3.3.3.2),
f) a rupture-disk device,
g) other forms of construction that can be proven to be comparable for the purposes of pressure relief.
3.5 Considerations for Tanks with Potentially Flammable Atmospheres
3.5.1 General
Depending on the process, operating conditions, and/or relieving conditions, the vapor space in the tank can be flammable. Ignition of the vapor space while within the flammable region likely leads to tank roof damage and/or loss of containment. Ignition sources include, but are not limited to, static discharge inside the tank due to splash filling or improper level gauging, pyrophonc materials on the inside surfaces of the tank, external hot work on the tank, tank or tank fittings above the auto-ignition temperature due to external fire exposure, or flame propagation through a tank opening or vent caused by a lightning strike or external fire. Consider the potential for a flammable atmosphere inside the tank and determine whether safeguards are adequate.
If explosion/deflagration venting is necessary, see 3.2.5.15.
3.5.2 Design Options for Explosion Prevention
If the tank’s vapor space can be within the flammable range, the user shall determine what safeguards are required to prevent internal deflagration. The following are typical safeguards.
a) Different Tank Selection—A different type of tank design can reduce or eliminate the formation of a flammable atmosphere.
EXAMPLES Floating-roof tank or a tank rated for full vacuum.
b) Inert-gas Blanketing—An effective means of reducing the likelihood of a flammable atmosphere inside a tank, when engineered and maintained properly. Note that inerting can introduce an asphyxiation risk and in sour services can promote the formation of pyrophoric deposits.
C) Flame Arrester—The use of this in an open vent line or on the inlet to the pressurelvacuum valve is an effective method to reduce the risk of flame transmission. The user is cautioned that a sustained fire on the outlet of the flame arrester not designed for endurance burning or on other parts of the tank/fittings may result in temperatures high enough to ignite internal flammable vapors. The use of high temperature alarms on flame arresters can provide warning of flame contact. In addition the use of a flame arrester within the tank’s relief path introduces the risk of tank damage from overpressure or vacuum due to plugging if the arrester is not maintained properly. The use of a flame an-ester increases the pressure drop of the venting system. The manufacturer(s) should be consulted for assessing the magnitude of these effects. More information on flame arresters can be found in ISO 16852 , NFPA 69h16i, TRbF 20tm, FM 6061 , and USCG 33 CFR 154’.
For the proper selection of a flame arrester, the piping configuration, operating pressure and temperature, oxygen concentration, compatibility of flame arrester material, and explosive gas group (IlA, 118, etc.) should be considered, For selection of the correct flame arrester, the manufacturer should be consulted.
3.5.4 Flame Propagation Through Pressure/Vacuum Valves
Testing has demonstrated that a flame can propagate through a pressure/vacuum valve and into the vapor space of the tank. Tests have shown that ignition of a PV valve’s relief stream (possibly due to a lighting strike) can result in a flashback to the PV valve with enough overpressure to lift the vacuum pallet, allowing the flame to enter the tank’s vapor space. Other tests show that, under low-flow conditions, a flame can propagate though the pressure side of the PV; see Reference [23].
Flashbacks through PV valves are rare in the petroleum industry. The following are some factors that may explain this.
