(a) Piping. The definitions contained in 100.2 of ASME B31.1 (incorporated by reference; see § 56.01-2) apply, as well as the following:

(1) The word piping within the meaning of the regulations in this subchapter refers to fabricated pipes or tubes with flanges and fittings attached, for use in the conveyance of vapors, gases or liquids, regardless of whether the diameter is measured on the inside or the outside.

(2) [Reserved]

(b) Nominal diameter. The term nominal diameter or diameter as used in this part, means the commercial diameter of the piping, i.e., pipe size.

(c) Schedule. The word Schedule when used in this part generally relates to the wall thickness of piping, and refers to specific values as given in ASME B36.10M and B36.19M (both incorporated by reference; see § 56.01-2).

(d) Fittings and appurtenances. The word fitting and the phrase fittings and appurtenances within the meaning of the regulations in this subchapter refer to pressure containing piping system components other than valves and pipe. This includes piping system components whose function is to join branches of the system (such as tees, wyes, elbows, unions, bushings, etc.) which are referred to as pipe joining fittings, as well as components which operate on the fluid contained in the system (such as traps, drains, strainers, separators, filters, meters, etc.), which are referred to as “fluid conditioner” fittings. Thermometer wells and other similar fittings which form part of the pressure barrier of any system are included under this heading. Expansion joints, slip joints, rotary joints, quick disconnect couplings, etc., are referred to as special purpose fittings, and may be subject to such special design and testing requirements as prescribed by the Commandant. Refer to subpart 56.15 for design requirements for fittings.

(e) Nonstandard fittings. “Nonstandard fitting” means a component of a piping system which is not fabricated under an adopted industry standard.

(f) Vital systems. (1) Vital systems are those systems that are vital to a vessel's survivability and safety. For the purpose of this subchapter, the following are vital systems:

(i) Systems for fill, transfer, and service of fuel oil;

(ii) Fire-main systems;

(iii) Fixed gaseous fire-extinguishing systems;

(iv) Bilge systems;

(v) Ballast systems;

(vi) Steering systems and steering-control systems;

(vii) Propulsion systems and their necessary auxiliaries and control systems;

(viii) Ship's service and emergency electrical-generation systems and their auxiliaries vital to the vessel's survivability and safety;

(ix) Any other marine-engineering system identified by the cognizant OCMI as crucial to the survival of the vessel or to the protection of the personnel aboard.

(2) For the purpose of this subchapter, a system not identified by paragraph (1) of this definition is a non-vital system.

(a) Maximum allowable working pressure. (1) The maximum allowable working pressure of a piping system must not be greater than the internal design pressure defined in 104.1.2 of ASME B31.1 (incorporated by reference; see § 56.01-2).

(2) Where the maximum allowable working pressure of a system component, such as a valve or a fitting, is less than that computed for the pipe or tubing, the system pressure must be limited to the lowest of the component maximum allowable working pressures.

(b) Relief valves. (Modifies 101.2.)

(1) Every system, which may be exposed to pressures higher than the system's maximum allowable working pressure, must be safeguarded by appropriate relief devices. Relief valves are required at pump discharges except for centrifugal pumps so designed and applied that a pressure in excess of the maximum allowable working pressure for the system cannot be developed.

(2) The relief valve setting must not exceed the maximum allowable working pressure of the system. Its relieving capacity must be sufficient to prevent the pressure from rising more than 20 percent above the system maximum allowable working pressure. The rated relieving capacity of safety and relief valves used in the protection of piping systems only must be based on actual flow test data and the capacity must be certified by the manufacturer at 120 percent of the set pressure of the valve.

(3) Relief valves must be certified as required in part 50 of this subchapter for valves, and must also meet the requirements of § 54.15-10 of this subchapter.

(c) Ship motion dynamic effects. (Replaces 101.5.3.) Piping system designs must account for the effects of ship motion and flexure, including weight, yaw, sway, roll, pitch, heave, and vibration.

(d) Ratings for pressure and temperature. (Modifies 102.2.) The material in 102.2 of ASME B31.1 applies, with the following exceptions:

(1) The details of components not having specific ratings as described in 102.2.2 of ASME B31.1 must be furnished to the Marine Safety Center for approval.

(2) Boiler blowoff piping must be designed in accordance with § 56.50-40.

(e) Pressure design. (Modifies 102.3, 104.1.2, and 104.4.)

(1) Materials for use in piping must be selected as described in § 56.60-1(a). Tabulated values of allowable stress for these materials must be measured as indicated in 102.3.1 of ASME B31.1.

(2) Allowable stress values, as found in the ASME BPVC, which are restricted in application by footnote or are italicized must not be used. Where multiple stresses are listed for a material, the lowest value of the listing must be used unless otherwise approved by the Commandant. In all cases, the temperature is understood to be the actual temperature of the component.

(3) Where the operator desires to use a material not listed, permission must be obtained from the Commandant. Requirements for testing found in subpart 56.97 may affect design and should be considered. Special design limitations may be found for specific systems. Refer to subpart 56.50 for specific requirements.

(f) Intersections. (Modifies 104.3.) The material in 104.3 of ASME B31.1 is applicable with the following additions:

(1) Reinforcement calculations where applicable shall be submitted.

(2) Wherever possible the longitudinal joint of a welded pipe should not be pierced.