Cal. Code Regs. tit. 8, § 511
(a) Every vessel used in anhydrous ammonia service shall be fitted with 1 or more safety relief valves in direct communication with the vapor space. These safety relief valves shall be of the spring-loaded type suitable for anhydrous ammonia service. The discharge from safety relief valves shall be full size and be directed away from the vessel, and shall discharge upward and unobstructed to the open air.
All relief-valve discharge openings shall have suitable loose-fitting rain caps that will allow free discharge of the vapor and prevent entrance of water. Provision shall be made for draining condensate which may accumulate in the discharge pipe.
The safety relief valves for anhydrous ammonia service shall be set to start to discharge with relation to the allowable working pressure of the vessel as follows:
Pressure vessels constructed in accordance with:
Minimum
Maximum
Code paragraphs U-68 and U-69
110%
125%
Code paragraphs U-200, through 1974 edition
100%
110%
API-ASME Code
100%
110%
DOT Cylinders
As required by DOT Regulations
(b) Except for code paragraphs U-68 and U-69 tanks, the discharge capacity of safety relief valves for anhydrous ammonia tanks shall be sufficient to prevent pressure in the tank from exceeding 120 percent of the allowable working pressure of the tank. ASME code paragraphs U-68 and U-69 tanks shall have safety valve capacity sufficient to prevent pressure in the tank from exceeding 135 percent of the allowable working pressure of the tank. All safety relief valves required by this Order shall be ASME rated and stamped. The minimum required rate of discharge of safety relief valves for anhydrous ammonia tanks shall be in accordance with the following table:
(1) Cylindrical container with hemispherical heads.
Area = overall length in feet times outside diameter in feet times 3.1416
(2) Cylindrical containers with other than hemispherical heads.
Area = (overall length in feet plus 0.3 outside diameter in feet) times outside diameter in feet times 3.1416
(3) Spherical container.
Area = outside diameter in feet squared times 3.1416
Flow rate--CFM Air = cubic feet per minute of air required at standard conditions, 60 degrees Fahrenheit and atmospheric pressure (14.7 psia).
The rate of discharge may be interpolated for intermediate values of surface area. For containers with total outside surface area greater than 2,500 square feet, the required flow rate can be calculated using the formula: Flow Rate CFM Air = 22.11A0.82, where A = outside surface area of the container in square feet.
The minimum required rate of discharge of safety relief valves for anhydrous ammonia DOT cylinders shall be in accordance with the regulations of the Bureau of Explosives.
Surface area sq. ft.
Flow rate CFM air
Surface area sq. ft.
Flow rate CFM air
Surface area sq. ft.
Flow rate CFM air
20 or less
258
185
1,600
900
5,850
25
310
190
1,640
950
6,120
30
360
195
1,670
1,000
6,380
35
408
200
1,710
1,050
6,640
40
455
210
1,780
1,100
6,900
45
501
220
1,850
1,150
7,160
50
547
230
1,920
1,200
7,410
55
591
240
1,980
1,250
7,660
60
635
250
2,050
1,300
7,910
65
678
260
2,120
1,350
8,160
70
720
270
2,180
1,400
8,410
75
762
280
2,250
1,450
8,650
80
804
290
2,320
1,500
8,900
85
845
300
2,380
1,550
9,140
90
885
310
2,450
1,600
9,380
95
925
320
2,510
1,650
9,620
100
965
330
2,570
1,700
9,860
105
1,010
340
2,640
1,750
10,090
110
1,050
350
2,700
1,800
10,330
115
1,090
360
2,760
1,850
10,560
120
1,120
370
2,830
1,900
10,800
125
1,160
380
2,890
1,950
11,030
130
1,200
390
2,950
2,000
11,260
135
1,240
400
3,010
2,050
11,490
140
1,280
450
3,320
2,100
11,720
145
1,310
500
3,620
2,150
11,950
150
1,350
550
3,910
2,200
12,180
155
1,390
600
4,200
2,250
12,400
160
1,420
650
4,480
2,300
12,630
165
1,460
700
4,760
2,350
12,850
170
1,500
750
5,040
2,400
13,080
175
1,530
800
5,300
2,450
13,300
180
1,570
850
5,590
2,500
13,520
Surface area = total outside surface area of container in square feet. When the surface area is not stamped on the nameplate or when the marking is not legible, the area can be calculated by using one of the following formulas:
(d) Shutoff valves shall not be installed between the safety relief valve and tank, except that a shutoff valve may be used where the arrangement of this valve is such as always to provide full required capacity flow through sufficient relief valves to properly protect the tank. [This exception is intended to permit 3-way valves, mechanically interconnected valves, etc., to be installed between the tank and safety valve where the installation and arrangement will always permit the required number of valves to be in communication with the tank to provide the relief capacity required by (b) above.]
The flow capacity of the relief valve shall not be restricted by any connection to it on either the upstream or downstream side.
(e) Each safety relief valve used on anhydrous ammonia tanks shall be plainly marked with the following information:
1. Amendment filed 12-8-72 as procedural and organizational; effective upon filing (Register 72, No. 50).
2. Amendment of subsections (a) and (d) filed 3-28-75; effective thirtieth day thereafter (Register 75, No. 13).