Current through Register Vol. 39, No. 6, September 16, 2024
(a) For the purpose of this Rule, the
following definitions shall apply:
(1)
"Condensate" means hydrocarbon liquid separated from natural gas that condenses
due to changes in the temperature or pressure and remains liquid at standard
conditions.
(2) "Crude oil" means a
naturally occurring mixture consisting of hydrocarbons or sulfur, nitrogen or
oxygen derivatives of hydrocarbons or mixtures thereof that is a liquid in the
reservoir at standard conditions.
(3) "Custody transfer" means the transfer of
produced crude oil or condensate, after processing or treating in the producing
operations, from storage tanks or automatic transfer facilities to pipelines or
any other forms of transportation.
(4) "External floating roof" means a storage
vessel cover in an open top tank consisting of a double deck or pontoon single
deck that rests upon and is supported by the petroleum liquid being contained
and is equipped with a closure seal or seals to close the space between the
roof edge and tank shell.
(5)
"Internal floating roof" means a cover or roof in a fixed roof tank that rests
upon or is floated upon the petroleum liquid being contained, and is equipped
with a closure seal or seals to close the space between the roof edge and tank
shell.
(6) "Liquid-mounted seal"
means a primary seal mounted so the bottom of the seal covers the liquid
surface between the tank shell and the floating roof.
(7) "Petroleum liquids" means crude oil,
condensate, and any finished or intermediate products manufactured or extracted
in a petroleum refinery.
(8)
"Vapor-mounted seal" means a primary seal mounted so there is an annular vapor
space underneath the seal. The annular vapor space is bounded by the bottom of
the primary seal, the tank shell, the liquid surface, and the floating
roof.
(b) This Rule
applies to all external floating roof tanks with capacities greater than 950
barrels containing petroleum liquids whose true vapor pressure exceed 1.52
pounds per square inch absolute.
(c) This Rule does not apply to petroleum
liquid storage vessels:
(1) that have external
floating roofs that have capacities less than 10,000 barrels and that are used
to store produced crude oil and condensate prior to custody transfer;
(2) that have external floating roofs and
that store waxy, heavy-pour crudes;
(3) that have external floating roofs, and
that contain a petroleum liquid with a true vapor pressure less than 4.0 pounds
per square inch absolute; and:
(A) the tanks
are of welded construction; and
(B)
the primary seal is a metallic-type shoe seal, a liquid-mounted foam seal, a
liquid-mounted filled type seal, or any other closure device of demonstrated
equivalence; or
(4) that
have fixed roofs with or without internal floating roofs.
(d) With the exceptions stated in Paragraph
(c) of this Rule, an external floating roof tank subject to this Rule shall not
be used unless:
(1) The tank has:
(A) a continuous secondary seal extending
from the floating roof to the tank wall, known as a rim-mounted secondary
seal;
(B) a metallic-type shoe
primary seal and a secondary seal from the top of the shoe seal to the tank
wall, known as a shoe-mounted secondary seal; or
(C) a closure or other control device
demonstrated to have an efficiency equal to or greater than that required under
Part (A) or (B) of this Subparagraph;
(2) The seal closure devices meet the
following requirements:
(A) There shall be no
visible holes, tears, or other openings in the seal or seal fabric;
(B) The seal shall be intact and uniformly in
place around the circumference of the floating roof between the floating roof
and the tank wall; and
(C) For
vapor mounted primary seals, any gaps exceeding 0.125 inch in width between the
secondary seal and the tank wall shall not exceed 1.0 square inch per foot of
tank diameter;
(3) All
openings in the external floating roof, except for automatic bleeder vents, rim
space vents, and leg sleeves, are:
(A)
provided with a projection below the liquid surface; and
(B) equipped with covers, seals, or lids that
remain in a closed position at all times except when in actual use;
(4) Automatic bleeder vents are
closed at all times except when the roof is floated off or landed on the roof
leg supports;
(5) Rim vents are set
to open only when the roof is being floated off the roof leg supports or at the
manufacturer's recommended setting;
(6) Any emergency roof drains are provided
with slotted membrane fabric covers or equivalent covers that cover at least 90
percent of the area at the opening;
(7) Planned routine visual inspections to
verify the conditions of the seal are conducted once per month;
(8) For tanks equipped with a vapor-mounted
primary seal, the secondary seal gap measurements are made annually in
accordance with Paragraph (e) of this Rule; and
(9) Records are maintained pursuant to
15A NCAC
02D .0903, including:
(A) reports of the results of inspections
conducted under Subparagraphs (7) and (8) of this Paragraph;
(B) a record of the average monthly storage
temperature and the true vapor pressures or Reid vapor pressures of the
petroleum liquids stored; and
(C)
records of the throughput quantities and types of petroleum liquids for each
storage vessel.
(e) The secondary seal gap area shall be
determined by measuring the length and width of the gaps around the entire
circumference of the secondary seal. Only gaps equal to or greater than 0.125
inch shall be used in computing the gap area. The area of the gaps shall be
accumulated to determine compliance with Part (d)(2)(C) of this Rule.
(f) The owner or operator of a petroleum
liquid storage vessel with an external floating roof that is not equipped with
a secondary seal or approved alternative and contains a petroleum liquid with a
true vapor pressure greater than 1.0 pound per square inch shall maintain
records of the average monthly storage temperature, the type of liquid,
throughput quantities, and the maximum true vapor pressure for all petroleum
liquids with a true vapor pressure greater than 1.0 pound per square
inch.
Authority
G.S.
143-215.3(a)(1);
143-215.107(a)(5);
Eff. July 1, 1980;
Amended Eff. June 1, 2004; July 1, 1994; March
1, 1991; December 1, 1989; January 1, 1985;
Readopted Eff. November
1, 2020.
