California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 1 - Unfired Pressure Vessel Safety Orders
Article 6 - Anhydrous Ammonia
Section 511 - Safety Relief Valves

Universal Citation: 8 CA Code of Regs 511

Current through Register 2024 Notice Reg. No. 38, September 20, 2024

(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:MinimumMaximum
Code paragraphs U-68 and U-69..........................110%125%
Code paragraphs U-200, through 1974 edition..........................100%110%
API-ASME Code..........................100%110%
DOT CylindersAs 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:

Surface area sq. ft.Flow rate CFM airSurface area sq. ft.Flow rate CFM airSurface area sq. ft.Flow rate CFM air
20 or less.......................... 258..........................1851,600.......................... 900 5,850
25.......................... 310 ..........................1901,640.......................... 950 6,120
30.......................... 360 ..........................1951,670..........................1,000 6,380
35.......................... 408 ..........................2001,710..........................1,050 6,640
40.......................... 455 ..........................2101,780..........................1,100 6,900
45.......................... 501 ..........................2201,850..........................1,150 7,160
50.......................... 547 ..........................2301,920..........................1,200 7,410
55.......................... 591 ..........................2401,980..........................1,250 7,660
60.......................... 635 ..........................2502,050..........................1,300 7,910
65.......................... 678 ..........................2602,120..........................1,350 8,160
70.......................... 720 ..........................2702,180..........................1,400 8,410
75.......................... 762 ..........................2802,250..........................1,450 8,650
80.......................... 804 ..........................2902,320..........................1,500 8,900
85.......................... 845 ..........................3002,380..........................1,550 9,140
90.......................... 885 ..........................3102,450..........................1,600 9,380
95.......................... 925 ..........................3202,510..........................1,650 9,620
100.......................... 965 ..........................3302,570..........................1,700 9,860
105..........................1,010 ..........................3402,640..........................1,75010,090
110..........................1,050 ..........................3502,700..........................1,80010,330
115..........................1,090 ..........................3602,760..........................1,85010,560
120..........................1,120 ..........................3702,830..........................1,90010,800
125..........................1,160 ..........................3802,890..........................1,95011,030
130..........................1,200 ..........................3902,950..........................2,00011,260
135..........................1,240 ..........................4003,010..........................2,05011,490
140..........................1,280 ..........................4503,320..........................2,10011,720
145..........................1,310 ..........................5003,620..........................2,15011,950
150..........................1,350 ..........................5503,910..........................2,20012,180
155..........................1,390 ..........................6004,200..........................2,25012,400
160..........................1,420 ..........................6504,480..........................2,30012,630
165..........................1,460 ..........................7004,760..........................2,35012,850
170..........................1,500 ..........................7505,040..........................2,40013,080
175..........................1,530 ..........................8005,300..........................2,45013,300
180..........................1,570 ..........................8505,590..........................2,50013,520

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:

(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.

(c) Safety relief valves shall be so designed and installed that the possibility of tampering will be minimized. If the pressure setting is external, the relief valves shall be provided with acceptable means for sealing the adjustment.

(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) With the letters "AA."

(2) The pressure in pounds per square inch gage (psig) at which the valve is set to start to discharge.

(3) The rate of discharge of the valve at its full open position in cubic feet per minute (cfm) of air.

(4) The manufacturer's name and catalog number.

(5) The symbol of the ASME Code.

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).

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