API RP 545:2009 pdf download
API RP 545:2009 pdf download.Recommended Practice for Lightning Protection of Aboveground Storage Tanks for Flammable or Combustible Liquids.
4.2.1.1.4 DurabilIty
The shunts and termanation connections shall be of sufficient flexility, cross-sectional area, and corrosion resistance to have a minimum servce life of 30 years
4.2.1.2 Bypass Conductors
4.2.1.2.1 General
Bypass conductors are used for conduction of the intermediate and long duration component of lightning-stroke current.
4.2.1.2.2 Number, Length and Electrical Resistance
The tank floating root shall be bonded to the tank shell by dwect electrical connection through an appropriate number of bypass conductors. Each conductor, rncluding connections, shall have a maximum end-to-end electflcal resistance oF 0.03 t. The bypass conductors shall be of the minimum length necessary to permit full movement of the floating roof. Bypass conductors should be evenly spaced not more than every 3.0 m (100 ft) around the lank circumference with a minimum of two.
4.2.1.2.3 DurabIlity
The bypass conductors and termination connections shall be positioned and of sufficient flexibility, cross-sectional area, and corrosion resistance to have a minimum service life of 30 years.
4.2.2 Parallel Conducting Paths (Seal Assembly from the Floating-roof Tank)
Any non4ully submerged conductive seal assembly components including springs, scissor assemblies, seal membranes, etc, shall be electrically insulated from the lank roof, The insulation level shall be rated 1 kV or greater NOTE This allows any bghtning discharge current from the floating roof to the tank shell to take the preferential path ttvough the shunts and bypass conductors.
4.2.3 Insulation of Gauge or Guide Poles
Any gauge or gtade pole components or assemblies that penetrate the tank floating roof shall be electrically Insulated from the lank floating roof. The insulation level shall be rated 1 kV or greater.
NOTE This allows any bghtning discharge current from the floating root to the Lank shell to take the preferential path through the shunts and bypass conductors
5 Metal Thickness
Minimum metal thicknesses for tanks are provided in API 650 and API 653.
Additional information is presented in EIIAPI 545-A. Verification o(lightnwig pmtection requfrements fox above ground hyckocathon storage tanks.
6 Inspection and Maintenance Requirements
All bonding and grounding appurtenances shall be maintained and inspected In accordance with API 653. Belowdeck inspections shall coincide with API 653 out-of-service inspections.
b) An airgap spark occurs in a location with a small gap between conducting items where the lightning creates a voltage large enough to cause electrical breakdown of the air or vapor/air mixture in the gap.
C) Air gap sparks with energy above 0.2 rnJ are sufficient to ignite product vapor/air mixtures if they are within the flammable mixture range. For mixtures that are not optimum, the energy requirement is hiiec, however, the energy In lightning Induced sparks Is likely to be many orders of magnitude higher.
A pooity contacting nm-seal shunt on an EFRT is an example of where sparks might occur under lightning conditions.
The small contact area and the presence of surface treatments or contaminants are conducive tospaking. If there Is a nonconducting layer on the shell or the shunt, the spark will initially be an air-gap spark to break down Ihe insulation, followed by current flow in a poorty contacting area resulting in thermal sparks,
A.2 Grounding
A2.1 Flat-bottom tanks resting on the ground need not be grounded by the use of external grounding rods for the
purpose of llghtnrng protection. Grounding for other purposes is not addressed by this document.
A.2.2 The occurrences of incendiary sparks, nm-seal fires, etc. are not dependent on tank grounding resistance or tank dimensions. This is because the tank will inevitably have ground conductivity through its massive steel structure in contact with the ground. There Will also be additional grounding through the many pipes and cables that connect to eadi tank. A tank is considered adequately grounded if the tank bottom is resting on the ground or foundation. This applies whether or not there is an etastomeflc liner in or under the tank bottom.
A.2.3 There is no known occurrence of lightning induced fires around the base of tanks. or underneath tanks, which are the only places where inadequate grounng of the tank would result in sparking or other sources of ignition. The Initial attachment process of a lightning stroke would be unaffected by tank ground resistance, since it will be sufficiently low to permit the lightning leader attachment process to occur, even if the resistance to ground of the tank were many tens of ohms. Lightning safety for tanks is not dependent on tank grounding.
A.2.4 Tank grounding associated with the power frequency supply should conform to local elecffical codes.
