46 CFR 56.50-40: -40 Blowoff piping (replaces 122.1.4).

(a)(1) The owner or operator of a vessel must follow the requirements for blowoff piping in this section instead of the requirements in 122.1.4 of ASME B31.1 (incorporated by reference; see § 56.01-2).

(2) Where blowoff valves are connected to a common discharge from two or more boilers, a nonreturn valve must be provided in the line from each boiler to prevent accidental blowback in the event the boiler blowoff valve is left open.

(b) Blowoff must be designed for not less than 125 percent of the maximum allowable working pressure of the boiler, or the maximum allowable working pressure of the boiler plus 225 psig, whichever is less. The value of allowable stress for design purposes must be selected as described in § 56.07-10(e) at a temperature not below that of saturated steam at the maximum allowable working pressure of the boiler.

(c) Boiler blowoff piping which discharges above the lightest loadline of a vessel must be arranged so that the discharge is deflected downward.

(d) Globe valves must not be used for blowoff service.