(B.1) The value of P to be used in the formulas in para. 104 shall be not less than the lowest set pressure of any safety valve on the boiler drum.
(B.2) The allowable stress value for the piping materials shall not exceed that permitted for the temperature of saturated steam at the maximum allowable working pressure of the boiler.
(B.3) All pipe shall be steel except as permitted below. Galvanized steel pipe and fittings shall not be used for blowdown piping. When the value of P does not exceed 100 psig [690 kPa (gage)], nonferrous pipe may be used and the fittings may be bronze, cast iron, malleable iron, ductile iron, or steel.
CAUTION: Nonferrous alloys and austenitic stainless steels may be sensitive to stress corrosion cracking in certain aqueous environments.
When the value of P exceeds 100 psig [690 kPa (gage)], the fittings shall be steel and the thickness of pipe and fittings shall not be less than that of Schedule 80 pipe.
(B.4) The size of blowdown piping shall be not less than the size of the connection on the boiler, and shall be in accordance with the rules contained in the ASME Boiler and Pressure Vessel Code, Section I, PG-59.3, PMB-12, and PEB-12.
(C) The blowoff and blowdown piping beyond the required valves described in (A) and (B) above are classified as nonboiler external piping. The requirements are given in para. 122.2.
122.1.5 Boiler Drains
(A) Complete drainage of the boiler and attached piping shall be provided to the extent necessary to ensure proper operation of the steam supply system. The pipe, fittings, and valves of any drain line shall not be smaller than the drain connection.
(B) If the drain lines are intended to be used both as drains and as blowoffs, then two valves are required and all conditions of paras. 122.1.4, 122.1.7(C), and 122.2 shall be met.
(C) Miniature boilers constructed in accordance with the rules contained in the ASME Boiler and Pressure Vessel Code, Section I, Parts PMB and PEB may use a single valve where drain lines are intended to be used for both blowoff and periodic automatic or manual flushing prior to startup. The single valve shall be designed for blowoff service but need not have locking capability.
(D) When a drain is intended for use only when the boiler is not under pressure (pressurizing the boiler for rapid drainage is an exception), a single shutoff valve is acceptable under the following conditions: either the valve shall be a type that can be locked in the closed position or a suitable flanged and bolted connection that accepts a blank insert shall be located on the downstream side of the valve. When a single valve is used, it need not be designed for blowoff service. Single valves on miniature boilers constructed in accordance with the rules contained in the ASME Boiler and Pressure Vessel Code, Section I, Parts PMB and PEB do not require locking capability.
(E) Drain piping from the drain connection, including the required valve(s) or the blanked flange connection, shall be designed for the temperature and pressure of the drain connection. The remaining piping shall be designed for the expected maximum temperature and pressure. Static head and possible choked flow conditions shall be considered. In no case shall the design pressure and temperature be less than 100 psig [690 kPa (gage)] and 220°F (105°C), respectively.
122.1.6 Boiler External Piping –Miscellaneous Systems
(A) Materials, design, fabrication, examination, and erection of piping for miscellaneous accessories, such as water level indicators, water columns, gage cocks, and pressure gages, shall be in accordance with the applicable sections of this Code.
(B) The value of P to be used in the formulas in para. 104 shall be not less than the maximum allowable working pressure of the boiler except as provided by para. 122.1.1(B).
(C) Valve requirements for water level indicators or water columns, special gage glass and gage cock requirements, minimum line sizes, and special piping configurations required specifically for cleaning, access, or reliability shall be in accordance with PG-60 of Section I of the ASME Boiler and Pressure Vessel Code.
122.1.7 Valves and Fittings. The minimum pressure and temperature rating for all valves and fittings in steam, feedwater, blowoff, and miscellaneous piping shall be equal to the pressure and temperature specified for the connected piping on the side that has the higher pressure, except that in no case shall the pressure be less than 100 psig [690 kPa (gage)], and for pressures not exceeding 100 psig [690 kPa (gage)] in feedwater and blowoff service, the valves and fittings shall be equal at least to the requirements of the ASME standards for Class 125 cast iron or bronze, or Class 150 steel or bronze.
(A) Steam Stop Valves. Each boiler discharge outlet, except safety valve or safety relief valve connections, or reheater inlet and outlet connections, shall be fitted with a stop valve located at an accessible point in the steam-delivery line and as near to the boiler nozzle as is convenient and practicable.
(A.1) Boiler stop valves shall provide bidirectional shutoff at design conditions. The valve or valves shall meet the requirements of para. 107. Valves with resilient (nonmetallic) seats shall not be used where the boiler maximum allowable working pressure exceeds 150 psig (1 035 kPa) or where the system design temperature exceeds 366°F (186°C). Valves of the outside screw and yoke, rising stem style are preferred. Valves other than those of the outside screw and yoke, rising stem style shall meet the following additional requirements.
(A.1.A) Each valve shall be equipped with a position indicator to visually indicate from a distance whether the valve is open or closed.
(A.1.B) Quarter turn valves shall be equipped with a slow operating mechanism to minimize dynamic loadings on the boiler and attached piping. Either a quick-opening manual quarter-turn valve or an automatic solenoid valve may be used on miniature boilers constructed in accordance with the rules contained in the ASME Boiler and Pressure Vessel Code, Section I, Parts PMB and PEB. Manual quarter-turn valves shall be provided with a handle or other position indicator to indicate from a distance whether the valve is open or closed.
(A.2) In the case of a single boiler and prime mover installation, the stop valve required herein may be omitted provided the prime mover throttle valve is equipped with an indicator to show whether it is opened or closed, and it is designed to withstand the required boiler hydrostatic test.
(A.3) When two or more boilers are connected to a common header, or when a single boiler is connected to a header having another steam source, the connection from each boiler having a manhole opening shall be fitted with two stop valves having an ample free-blow drain between them. The preferred arrangement consists of one stop-check valve (located closest to the boiler) and one valve of the style and design described in (A.1) above. Alternatively, both valves may be of the style and design described in (A.1) above.
When a second stop valve is required, it shall have a pressure rating at least equal to that required for the expected steam pressure and temperature at the valve, or a pressure rating at least equal to 85% of the lowest set pressure of any safety valve on the boiler drum at the expected temperature of the steam at the valve, whichever is greater.
(A.4) All valves and fittings on steam lines shall have a pressure rating of at least 100 psig [690 kPa (gage)] in accordance with the applicable ASME standard.
(B) Feedwater Valves
(B.1) The feedwater piping for all boilers, except for high temperature water boilers complying with the requirements of (B.8) below, and for forced flow steam generators with no fixed steam and water line complying with the requirements of (B.9) below, shall be provided with a check valve and a stop valve or cock between the check valve and the boiler. The stop valve or cock shall comply with the requirements of (C.5) below.
(B.2) The relative locations of the check and stop (or cock) valves, as required in (B.1) above, may be reversed on a single boiler-turbine unit installation.
(B.3) If a boiler is equipped with a duplicate feed arrangement, each such arrangement shall be equipped as required by these rules.
(B.4) When the supply line to a boiler is divided into branch feed connections and all such connections are equipped with stop and check valves, the stop and check valves in the common source may be omitted.
(B.5) When two or more boilers are fed from a common source, there shall also be a globe or regulating valve in the branch to each boiler located between the check valve and the source of supply. A typical arrangement is shown in Fig. 100.1.2(B).
(B.6) A combination stop and check valve in which there is only one seat and disk, and in which a valve stem is provided to close the valve, shall be considered only as a stop valve, and a check valve shall be installed as otherwise provided.
(B.7) Where an economizer or other feedwater heating device is connected directly to the boiler without intervening valves, the feed valves and check valves required shall be placed on the inlet of the economizer or feedwater heating device.
(B.8) The recirculating return line for a high temperature water boiler shall be provided with the same stop valve, or valves, required by (B.1) and (B.3) above. The use of a check valve in the recirculating return line is optional. A check valve shall not be a substitute for a stop valve.
(B.9) The feedwater boiler external piping for a forced flow steam generator with no fixed steam and water line may terminate up to and including the stop valve(s) and omitting the check valve(s) provided that a check valve having a pressure rating no less than the boiler inlet design pressure is installed at the discharge of each boiler feed pump or elsewhere in the feedline between the feed pump and the stop valve(s).
(B.10) Wherever globe valves are used within BEP feedwater piping for either isolation or regulation, the inlet shall be under the disk of the valve.
(C) Blowoff Valves
(C.1) Ordinary globe valves as shown in Fig. 122.1.7(C) sketch (a), and other types of valves that have dams or pockets where sediment can collect, shall not be used on blowoff connections.
(C.2) Y-type globe valves as shown in Fig. 122.1.7(C) sketch (b) or angle valves may be used in vertical pipes, or they may be used in horizontal runs of piping provided they are so constructed or installed that the lowest edge of the opening through the seat is at least 25% of the inside diameter below the centerline of the valve.
(C.3) The blowoff valve or valves, the pipe between them, and the boiler connection shall be of the same size except that a larger pipe for the return of condensate may be used.
(C.4) For all boilers [except electric steam boilers having a normal water content not exceeding 100 gal (380 L), traction-purpose, and portable steam boilers; see (C.11) and (C.12) below] with allowable working pressure in excess of 100 psig [690 kPa (gage)], each bottom blowoff pipe shall have two slow-opening valves, or one quick-opening valve or cock, at the boiler nozzle followed by a slow-opening valve. All valves shall comply with the requirements of (C.5) and (C.6) below.
(C.5) When the value of P required by para. 122.1.4(A.1) does not exceed 250 psig [1 725 kPa (gage)], the valves or cocks shall be bronze, cast iron, ductile iron, or steel. The valves or cocks, if of cast iron, shall not exceed NPS 2½ and shall meet the requirements of the applicable ASME standard for Class 250, as given in Table 126.1, and if of bronze, steel, or ductile iron construction, shall meet the requirements of the applicable standards as given in Table 126.1 or para. 124.6.
(C.6) When the value of P required by para. 122.1.4(A.1) is higher than 250 psig [1 725 kPa (gage)], the valves or cocks shall be of steel construction equal at least to the requirements of Class 300 of the applicable ASME standard listed in Table 126.1. The minimum pressure rating shall be equal to the value of P required by para. 122.1.4(A.1).
(C.7) If a blowoff cock is used, the plug shall be held in place by a guard or gland. The plug shall be distinctly marked in line with the passage.
(C.8) A slow-opening valve is a valve which requires at least five 360 deg turns of the operating mechanism to change from fully clo sed to fully opened.
(C.9) On a boiler having multiple blowoff pipes, a single master valve may be placed on the common blowoff pipe from the boiler, in which case only one valve on each individual blowoff is required. In such a case, either the master valve or the individual valves or cocks shall be of the slow-opening type.
(C.10) Two independent slow-opening valves, or a slow-opening valve and a quick-opening valve or cock, may be combined in one body and may be used provided the combined fitting is the equivalent of two independent slow-opening valves, or a slow-opening valve and a quick-opening valve or cock, and provided further that the failure of one to operate cannot affect the operation of the other.
(C.11) Only one blowoff valve, which shall be either a slow-opening or quick-opening blowoff valve or a cock, is required on traction and/or portable boilers.
(C.12) Only one blowoff valve, which shall be of a slow-opening type, is required for the blowoff piping for forced circulation and electric steam boilers having a normal water content not exceeding 100 gal (380 L). Electric boilers not exceeding a normal water content of 100 gal (380 L) and a maximum MAWP of 100 psig [690 kPa (gage)] may use a quick-opening manual or slow-opening automatic quarter-turn valve up to NPS 1. Electric boilers not exceeding a normal water content of 100 gal (380 L) but with a MAWP greater than 100 psig [690 kPa (gage)] shall only use either a slow-opening type manual or automatic valve, regardless of size.
(D) Safety Valves
(D.1) Safety valves, relief valves, and safety relief valves shall conform to the requirements of PG-67, PG-68, PG-69, PG-70, PG-71, PG-72, and PG-73 of Section I of the ASME Boiler and Pressure Vessel Code.
122.2 Blowoff and Blowdown Piping in Nonboiler External Piping
Blowoff and blowdown piping systems shall be, where possible, self-draining and without pockets. If unavoidable, valved drains at low points shall allow system draining prior to operation. In order to minimize pipeline shock during the operation of blowoff systems, 3D pipe bends (minimum) should be used in preference to elbows, and wye or lateral fittings should be used in preference to tee connections.
(A) From Boilers
(A.1) Blowoff piping, located between the valves described in para. 122.1.4(A) and the blowoff tank or other point where the pressure is reduced approximately to atmospheric pressure and cannot be increased by closing a downstream valve, shall be designed for the appropriate pressure in accordance with Table 122.2. The provisions of paras. 122.1.4(A.3) and 122.1.7 shall apply. The size of non-BEP blowoff header to the safe point of discharge shall not be smaller than the largest connected BEP blowoff terminal [see para. 122.1.4(A.4)].
(A.2) Blowdown piping, in which the pressure cannot be increased by closing a downstream valve, shall be designed for the appropriate pressure and temperature in accordance with Table 122.2. The provisions of para. 122.1.4(B.3) shall apply. The size of non-BEP blowdown piping between the shutoff valve described in para. 122.1.4(B) and the flow control valve shall not be smaller than the BEP boiler shutoff valve [see para. 122.1.4(B.4)] unless engineering calculations confirm that the design flow rate can be achieved with a smaller piping size without flashing the blowdown prior to the flow control valve.
(A.3) When the design pressure of Table 122.2 can be exceeded due to closing of a downstream valve, calculated pressure drop, or other means, the entire blowoff or blowdown piping system shall be designed in accordance with paras. 122.1.4(A) and 122.1.7 for blowoff and para. 122.1.4(B) for blowdown piping.
(A.4) Non-BEP blowdown piping downstream of the flow control valve shall not be smaller - and preferably will be larger - than the connection on the boiler [see para. 122.1.4(B.4)].
(B) From Pressure Vessels Other Than Boilers
(B.1) The design pressure and temperature of the blowoff piping from the pressure vessel to and including the blowoff valve(s) shall not be less than the vessel MAWP and corresponding design temperature.
122.3 Instrument, Control, and Sampling Piping
(A) The requirements of this Code, as supplemented by para. 122.3, shall apply to the design of instrument, control, and sampling piping for safe and proper operation of the piping itself.
(B) The term “Instrument Piping” shall apply to all valves, fittings, tubing, and piping used to connect instruments to main piping or to other instruments or apparatus or to measuring equipment as used within the classification of para. 100.1.
(C) The term “Control Piping” shall apply to all valves, fittings, tubing, and piping used to interconnect pneumatically or hydraulically operated control apparatus, also classified in accordance with para. 100.1, as well as to signal transmission systems used to interconnect instrument transmitters and receivers.
(D) The term “Sampling Piping” shall apply to all valves, fittings, tubing, and piping used for the collection of samples, such as steam, water, oil, gas, and chemicals.
(E) Paragraph 122.3 does not apply to tubing used in permanently closed systems, such as fluid-filled temperature responsive devices, or the temperature responsive devices themselves.
(F) Paragraph 122.3 does not apply to the devices, apparatus, measuring, sampling, signaling, transmitting, controlling, receiving, or collecting instruments to which the piping is connected.
122.3.1 Materials and Design. The materials utilized for valves, fittings, tubing, and piping shall meet the particular conditions of service and the requirements of the applicable specifications listed under general paras. 105, 106, 107, and 108 with allowable stresses in accordance with the Allowable Stress Tables in Appendix A.
The materials for pressure retention components used for piping specialties such as meters, traps, and strainers in flammable, combustible, or toxic fluid systems shall in addition conform to the requirements of paras. 122.7 and 122.8.
122.5 Pressure-Reducing Valves
122.5.1 General. Where pressure-reducing valves are used, one or more relief devices or safety valves shall be provided on the low pressure side of the system. Otherwise, the piping and equipment on the low pressure side of the system shall be designed to withstand the upstream design pressure. The relief or safety devices shall be located adjoining or as close as practicable to the reducing valve. The combined relieving capacity provided shall be such that the design pressure of the low pressure system will not be exceeded if the reducing valve fails open.
122.5.2 Bypass Valves. Hand controlled bypass valves having a capacity no greater than the reducing valve may be installed around pressure reducing valves if the downstream piping is protected by relief valves as required in para. 122.5.1 or if the design pressure of the downstream piping system and equipment is at least as high as the upstream pressure.
122.5.3 Design of Valves and Relief Devices. Pressure reducing and bypass valves, and relief devices, shall be designed for inlet pressure and temperature conditions. Safety and relief valves shall be in accordance with the requirements of para. 107.8 of this Code.
122.6 Pressure Relief Piping
Pressure relief piping within the scope of this Code shall be supported to sustain reaction forces, and shall conform to the requirements of paras. 122.6.1 and 122.6.2.
122.6.1 Piping to Pressure-Relieving Safety Devices
(A) There shall be no intervening stop valve(s) between piping being protected and the protective device(s).
(B) Diverter or changeover valves designed to allow servicing of redundant protective devices without system depressurization may be installed between the piping to be protected and the required protective devices under the following conditions:
(B.1) Diverter or changeover valves are prohibited on boiler external piping or reheat piping.
(B.2) One hundred percent (100%) of the required relieving capacity shall be continuously available any time the system is in service.
(B.3) Positive position indicators shall be provided on diverter or changeover valves.
(B.4) Positive locking mechanisms and seals shall be provided on diverter or changeover valves to preclude unauthorized or accidental operation.
(B.5) Diverter or changeover valves shall be designed for the most severe conditions of pressure, temperature, and loading to which they are exposed, and shall be in accordance with para. 107.
(B.6) Provision shall be made to safely bleed off the pressure between the isolated protective device and the diverter or changeover valve.
122.6.2 Discharge Piping From Pressure-Relieving Safety Devices
(A) There shall be no intervening stop valve between the protective device or devices and the point of discharge.
