Current through Register Vol. 18, September 20, 2024
(1) Design of
tanks:
(a) Tanks may be designed for any
storage pressure desired as determined by economical design of the refrigerated
system.
(b) Tanks with a design
pressure exceeding 15 psig shall be constructed in accordance with ARM
4.12.704 in addition the materials
shall comply with ARM 4.12.704.
(c)
Tanks with a design pressure of 15 psig and less shall be constructed in
accordance with the general requirements of American Petroleum Institute
Standard 620 or API Standard 12-C with the following modifications:
(i) The liquid specific gravity used for
design shall be at least as high as the maximum specific gravity at minimum
storage temperature of the ammonia being stored.
(ii) The joint efficiency shall not exceed
0.85 unless inspection requirements exceed those of API Standard 12-C. A joint
efficiency of 1.00 may be used provided all shell weld junctions are
radiographed in addition to the spot radiographic requirements of API Standard
12-C. Full penetration double butt weld shall be used for girth
joints.
(iii) The design of shells
other than vertical cylindrical tanks for all pressure up to 15 psig inclusive
shall use design stresses no higher than the stress values given for pressures
from 0.5 to 5 psig inclusive in the first edition of API Standard
620.
(d) Refrigerated
storage tanks shall be hydrostatically tested to the highest level possible
without the shell membrane stress during the test exceeding 30 percent of the
specified minimum yield strength of the shell material. When this limitation
precludes completely filling the tank, the remaining welded joints shall be
tested using penetrant test methods specified in API Standard 12-C.
(e) Ferritic steels for tank shells and
bottoms shall be selected for the design temperature. This application may be
based on impact test requirements or equivalent criteria (See Table
B).
(f) When austenitic steels or
non-ferrous materials are used the code shall be used as a guide for
temperature requirements.
(g)
Materials for nozzles, attached flanges, structural members which are in
tension, and other such critical elements shall be selected for the design
temperature. This selection may be based on impact test requirements or
equivalent criteria (See Table B).
(2) Installation of storage tank:
(a) Tanks shall be supported on a
non-combustible foundation designed to accommodate the type of tank being
used.
(b) Secure anchorage or
adequate pier height shall be provided against tank flotation wherever high
flood water might occur.
(3) Tank valves and accessories, fill pipes
and discharge pipes:
(a) Shutoff valves shall
be:
(i) provided for all connections, except
those with a No. 54 drill size restriction, plugs, safety valves, thermometer
wells; and
(ii) located as close to
the tank as practicable.
(b) When operating conditions make it
advisable, a check valve shall be installed on the fill connection and a
remotely operated shutoff valve on other connections located below the maximum
liquid level.
(4) Safety
devices:
(a) Safety relief valves shall be
set to start-to-discharge at a pressure not in excess of the design pressure of
the tank and shall have a total relieving capacity sufficient to prevent a
maximum pressure in a container of more than 120 percent of the design
pressure.
(b) The size of relief
valves shall be determined by the largest volume requirement of the following:
(i) possible refrigeration system upset, such
as:
(A) cooling water failure,
(C) instrument air or instrument
failure,
(D) mechanical failure of
any equipment, or
(E) excessive
pumping rates.
(ii) the
American National Standards Institute's Fire Safety Provisions (Section
4.5.2.2).
(c) All safety
devices shall comply with the following;
(i)
The discharge from safety relief valve shall be vented away from the tank at
any desired angle above the horizon using a vent stack designed for weather
protection. The size of discharge lines from safety relief valves shall not be
smaller than the nominal size of the relief valve outlet connections.
Provisions shall be made for draining condensation which may
accumulate.
(ii) Discharge lines
from two or more safety relief devices located on the same unit may be run into
a common discharge header, provided the cross-sectional area of such header is
at least equal to the sum of the cross-sectional area of the individual
discharge lines and that the settings of the safety relief valves are the
same.
(5)
Protection of tank accessories and grounding: Refrigerated storage tanks shall
comply with the provisions of ARM
4.12.719(9).
(6) Tanks of such size as to require field
fabrication shall, when moved and reinstalled, be reconstructed and reinspected
in complete accordance with the code under which they were constructed. The
tanks shall be subjected to a pressure retest, and if re-rating is necessary,
it shall be done in accordance with the applicable code procedures.
(7) Precaution shall be taken to avoid any
damage by trucks, tractors or other vehicles.
(8) Refrigerated load and equipment:
(a) The total refrigeration load shall be
computed as the sum of the following:
(i)
Load imposed by heat flow into the tank caused by the temperature differential
between design ambient temperature and storage temperature.
(ii) Load imposed by heat flow into the tank
caused by maximum sun radiation.
(iii) Maximum load imposed by filling the
tank with anhydrous ammonia warmer than the design storage
temperature.
(b) More
than one storage tank may be handled by the same refrigeration
system.
(c) Compressors:
(i) A minimum of two compressors shall be
provided either of which is of sufficient size to handle the loads listed in
ARM 4.12.722(8) (a) (i)
(ii). Where more than two compressors are
provided, minimum standby equipment equal to the largest normally operating
equipment shall be installed.
(ii)
Compressors shall be sized to operate with a suction pressure at least 10
percent below the minimum setting of the safety valves) on the storage tank and
shall withstand a suction pressure at least equal to 120 percent of the design
pressure of the tank. Discharge pressure will be governed by condensing
conditions.
(d)
Compressor drives:
(i) Each compressor shall
have its individual driving unit.
(ii) Any standard drive consistent with good
design may be used.
(iii) An
emergency source of power of sufficient capacity to handle the loads in ARM
4.12.722(8) (a) (i)
(ii) shall be provided, unless facilities are
provided to safely dispose of vented vapors while the refrigeration system is
not operating.
(e)
Automatic control equipment:
(i) The
refrigeration system shall be arranged with suitable controls to govern the
compressor operation in accordance with the load as evidenced by pressure in
the tank or tanks.
(ii) Any
emergency alarm system shall be installed to function in the event the pressure
in the tank or tanks rises to the maximum allowable operating
pressure.
(iii) An emergency alarm
and shutoff shall be located in the condenser system to respond to excess
discharge pressure caused by failure of the cooling medium.
(iv) All automatic controls shall be
installed in a manner to preclude operation of alternate compressors unless the
controls will function with the alternate compressors.
(f) Separators:
(i) An entrainment separator of a size
capable of holding any liquid material entering the line during the transfer
operation shall be installed in the compressor suction line. The separator
shall be equipped with a drain and gauging device.
(ii) An oil separator of a size capable of
holding any liquid material entering the line during the transfer operation
shall be installed in the compressor discharge line. It shall be designed for
at least 250 psig and shall be equipped with a gauging device and drain
valve.
(g) Condensers:
The condenser system may be cooled by air or water or both. The condenser shall
be designed for at least 250 psig. Provision shall be made for purging
non-condensibles either manually or automatically.
(h) Receiver and liquid drain: A receiver
shall be provided which is equipped with an automatic float valve to discharge
the liquid anhydrous ammonia to storage or with a high pressure liquid drain
trap of a capacity capable of holding any liquid material entering the line.
The receiver shall be designed for at least 250 psig operating pressure and be
equipped with the necessary connections, safety valves, and gauging
device.
(i) Insulation:
(i) Where insulation is required, insulation
thickness shall be determined by good design.
(ii) Insulation of refrigerated tanks and
pipelines shall be waterproofed. The insulating material shall be fire
retardant. The weatherproofing shall be fire resistant.
(j) Piping: All piping shall be well
supported and provision shall be made for expansion and contraction. All
refrigeration system piping shall conform to Section 5 of the American
Standards Association's "Code for Pressure Piping" (B 31.1) as it applies to
anhydrous ammonia.
(k) Safety
equipment: All refrigerated storage plants shall have on hand the minimum
safety equipment required under ARM
4.12.711(2).
Sec.
80-10-503,
MCA; IMP, Sec.
80-10-503,
MCA;