원문은 API STANDARD 650("Welded Steel Tanks for Oil Storage") 10th edition('98.11)입니다.
부록은 Addendum 4('05.12)까지 추가되어 있습니다.
Appendix H가 추후에 추가되지 않았나 생각됩니다.
H.5.2.2.1의 내용입니다.
H.5.2.2.1
Peripheral circulation vents shall be located on the tank roof (unless otherwise specified by the purchaser)
and meet the requirements of H.5.3.3, so that they are above the seal of the internal floating roof when the tank
is full. The maximum spacing between vents shall be 10 m (32 ft), based on an arc measured at the tank shell, but there shall not be fewer than four equally spaced vents. The venting shall be distributed such that the sum of the open areas of the vents located within any 10 m (32 ft) interval is at least 0.2 m2 (2.0 ft2). The total net open area of these vents shall be greater than or equal to 0.06 m2/m (0.2 ft2/ft) of tank diameter. These vents shall be covered with a corrosion-resistant coarse-mesh screen [13 mm (1/2 in.) openings unless specified otherwise by the purchaser] and shall be provided with weather shields (the closed area of the screen must be deducted to determine the net open vent area).
(1) Internal Floating Roof Tank 형태의 표준은 API 650 Standard의 Appendix H에 정리되어 있는데 질문의 부분에 대해서는 2001년에 보완Update한 것으로 보이고 이후 2008년에 (겨울철 Screen 눈에 결빙문제가 발생하는 것이 발견되어 ) Mesh screen의 크기를 3/4'(20mm)로 키우는 것으로 수정한 것 같습니다.
