[Code of Federal Regulations]
[Title 46, Volume 2]
[Revised as of October 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 46CFR54.15-15]

[Page 159]
 
                           TITLE 46--SHIPPING
 
   CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED)
 
PART 54_PRESSURE VESSELS--Table of Contents
 
                  Subpart 54.15_Pressure-Relief Devices
 
Sec. 54.15-15  Relief devices for unfired steam boilers, evaporators, and 
heat exchangers (modifies UG-126).

    (a) An approved safety valve set to relieve at a pressure not 
exceeding the ``maximum allowable working pressure'' of the shell shall 
be fitted to all unfired steam boilers and evaporators except for 
evaporators of the atmospheric type designed for vapor discharge direct 
to a distiller with no shutoff valve in the discharge line. The 
distiller connected to atmospheric evaporators shall be fitted with a 
vent to prevent a buildup in pressure. In no case shall the vent be less 
than 1\1/2\ inches in diameter. Evaporators operating between 
atmospheric pressure and 15 p.s.i.g., may use a rupture disc as an 
alternative to the safety valve.
    (b) Safety valves for use on pressure vessels in which steam or 
pressure is generated shall comply with the requirements of Sec. 54.15-
10. Rupture discs used in lieu of these safety valves, as provided for 
in paragraph (a) of this section, shall comply with the requirements of 
Sec. 54.15-13.
    (c) The relieving capacity of evaporator safety valves required by 
paragraph (a) of this section shall be at least equal to the capacity of 
the orifice fitted in the steam supply to the evaporator. The orifice 
capacity shall be determined in accordance with the formula in paragraph 
(c) (1) or (2) of this section as appropriate:
    (1) Where the set pressure of the evaporator shell safety valve is 
58 percent or less than the setting of the safety valve in the steam 
supply:
W=51.45AP
    (2) Where the set pressure of the evaporator shell safety valve 
exceeds 58 percent of the setting of the safety valve on the steam 
supply:

W=105.3A[radic] P1(P-P1)

where:

W=The required orifice capacity, in pounds per hour.
A=Cross-sectional area of rounded entrance orifice, in square inches. 
The orifice shall be installed near the steam inlet or the coils or 
tubes and where no orifice is employed the area used in the formula 
shall be that of the inlet connection or manifold.
P=Set pressure of steam supply safety valve, in pounds per square inch, 
absolute.
P1=Set pressure of evaporator shell safety valve, in pounds 
per square inch, absolute.

    (d) The relieving capacity of safety valves on unfired steam boilers 
shall not be less than the maximum generating capacity of the unfired 
steam boiler as certified by the manufacturer.
    (e) On new installations and where the orifice size of an existing 
unfired steam boiler or evaporator is increased, an accumulation test 
shall be made by closing all steam outlet connections except the safety 
valves for a period of five minutes. When conducting the accumulation 
test, the water shall be at the normal operating level and the steam 
pressure shall be at the normal operating pressure, and while under this 
test the pressure shall not rise more than 6 percent above the safety 
valve setting.
    (f) A heat exchanger with liquid in the shell and the heating medium 
in the tubes or coils, shall be fitted with a liquid relief valve 
meeting the requirement of Sec. 54.15-5.
    (g)(1) A heat exchanger with steam in the shell and liquid in the 
tubes or coils at a pressure exceeding that in the shell, shall have a 
liquid relief valve fitted to protect the shell against excess pressure.
    (2) The discharge capacity of such relief valves shall be calculated 
on the basis of the discharge from one tube using the difference in 
pressures between that in the shell and that in the tubes and shall be 
not less than that determined by the following formula:

Q=29.81KD 2[radic] P1-P2

where:

Q=Required relief valve discharge capacity, in gallons per minute, based 
on relief valve set pressure.
P1=Pressure in the tube or coils, in pounds per square inch.
P2=Set pressure of the shell relief valve, in pounds per 
square inch.
D=Internal diameter of the largest tube or coil, in inches.
K=Coefficient of discharge=0.62.

[CGFR 68-82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 72-206R, 38 
FR 17226, June 29, 1973]

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