PG-58.3.7 The miscellaneous piping shall include the piping for such items as drains, vents, surface-blow-off, steam and water piping for water columns, gage glasses and pressure gages, and the recirculation return line for a high-temperature water boiler. When a drain is not intended for blowoff purposes (when the boiler is under pressure) a single valve is acceptable, otherwise two valves in series are required except as permitted by PG-58.3.6.
PG-58.3.8 Welded piping in PG-58.3.1, PG-58.3.2, PG-58.3.3, PG-58.3.4, PG-58.3.5, PG-58.3.6, and PG-58.3.7 is also subject to the requirements of PG-104 for proper Code certification.
PG-59 APPLICATION REQUIREMENTS FOR THE BOILER PROPER
PG-59.1 Common to Steam, Feedwater, Blowoff, and Drain Systems
PG-59.1.1 Outlets of a boiler to which piping is to be attached for any purpose, and which piping comes within the Code requirements, shall meet the requirements of PG-39 and shall be:
PG-59.1.1.1 A tapped opening.
PG-59.1.1.2 Bolted flanged joints including those of the Van Stone type.
PG-59.1.1.3 Welding ends of the butt or socket welding type.
PG-59.1.1.4 Piping within the boiler proper may be expanded into grooved holes, seal welded if desired. Blowoff piping of firetube boilers shall be attached by threading into a tapped opening with a threaded fitting or valve at the other end if exposed to products of combustion, or by PG-59.1.1.1 or PG-59.1.1.2 if not so exposed (see PFT-49).
PG-59.1.2 Steam Mains. Provisions shall be made for the expansion and contraction of steam mains connected to boilers, by providing substantial anchorage at suitable points, so that there shall be no undue strain transmitted to the boiler. Steam reservoirs shall be used on steam mains when heavy pulsations of the steam currents cause vibration of the boiler shell plates.
PG-59.1.3 Figure PG-59.1 illustrates a typical form of connection for use on boiler shells for passing through piping such as feed, surface blowoff connections, etc., and which permits the pipes' being threaded in solid from both sides in addition to the reinforcing of the opening of the shell. The pipes shall be attached as provided in PG-59.1.1. In these and other types of boilers where both internal and external pipes making a continuous passage are employed, the boiler bushing or its equivalent shall be used.
PG-59.2 Requirements for Feedwater Connections. The feedwater shall be introduced into a boiler in such a manner that the water will not be discharged directly against surfaces exposed to gases of high temperature or to direct radiation from the fire. For pressures of 400 psi (3 MPa) or over, the feedwater inlet through the drum shall be fitted with shields, sleeves, or other suitable means to reduce the effects of temperature differentials in the shell or head. Feedwater, other than condensate returns as provided for in PG-59.3.6, shall not be introduced through the blowoff.
PG-59.3 Requirements for Blowoffs
PG-59.3.1 A blowoff as required herein is defined as a pipe connection provided with valves located in the external piping through which the water in the boiler may be blown out under pressure, excepting drains such as are used on water columns, gage glasses, or piping to feedwater regulators, etc., used for the purpose of determining the operating condition of such equipment. Piping connections used primarily for continuous operation, such as deconcentrators on continuous blowdown systems, are not classed as blowoffs but the pipe connections and all fittings up to and including the first shutoff valve shall be equal at least to the pressure requirements for the lowest set pressure of any safety valve on the boiler drum and with the corresponding saturated-steam temperature.
PG-59.3.2 A surface blowoff connection shall not exceed NPS 2 ½ (DN 65), and the internal pipe and the terminal connection for the external pipe, when used, shall form a continuous passage, but with clearance between their ends and arranged so that the removal of either will not disturb the other. A properly designed steel bushing, similar to or the equivalent of those shown in Fig. PG-59.1, or a flanged connection shall be used.
PG-59.3.3 Each boiler except forced-flow steam generators with no fixed steam and waterline and high-temperature water boilers shall have a bottom blowoff outlet in direct connection with the lowest water space practicable for external piping conforming to PG-58.3.6.
PG-59.3.4 All waterwalls and water screens that do not drain back into the boiler, and all integral economizers, shall be equipped with outlet connections for a blowoff or drain line and conform to the requirements of PG-58.3.6 or PG-58.3.7.
PG-59.3.5 Except as permitted for miniature boilers in Part PMB, the minimum size of blowoff connections shall be NPS 1 (DN 25), and the maximum size shall be NPS 2 ½ (DN 65), except that for boilers with 100 ft2 (9.3 m2) of heating surface or less, the minimum size of blowoff connections may be NPS ¾ (DN 20).
PG-59.3.6 Condensate return connections of the same size or larger than the size herein specified may be used, and the blowoff may be connected to them. In such case the blowoff shall be so located that the connection may be completely drained.
PG-59.3.7 A bottom blowoff pipe when exposed to direct furnace heat shall be protected by firebrick or other heat resisting material that is so arranged that the pipe may be inspected.
PG-59.3.8 An opening in the boiler setting for a blowoff pipe shall be arranged to provide free expansion and contraction.
PG-59.4 Requirements for Drains
PG-59.4.1 Ample drain connections shall be provided where required to permit complete drainage of all piping, superheaters, waterwalls, water screens, integral economizers, high-temperature water boilers, and all other boiler components in which water may collect. Piping shall conform to the requirements of PG-58.3.6 or PG-58.3.7.
PG-59.4.1.1 Each superheater shall be equipped with at least one drain connection so located as to most effectively provide for the proper operation of the apparatus.
PG-59.4.1.2 Each high-temperature water boiler shall have a bottom drain connection of at least NPS 1 (DN 25) in direct connection with the lowest water space practical for external piping conforming to PG-58.3.7.
PG-59.5 Requirements for Valves and Fittings. The following requirements apply to the use of valves and fittings in the boiler proper.
PG-59.5.1 Steam Stop Valves
PG-59.5.1.1 If a shutoff valve is used between the boiler and its superheater, the safety valve capacity on the boiler shall comply with the requirements of PG-67.2 and PG-70, except as provided for in PG-59.5.1.2, no credit being taken for the safety valve on the superheater, and the superheater must be equipped with safety valve capacity as required by PG-68. A stop valve is not required at the inlet or the outlet of a reheater or separately fired superheater.
PG-59.5.1.2 When stop valves are installed in the water-steam flow path between any two sections of a forced–flow steam generator with no fixed steam and waterline, the safety valves shall satisfy the requirements of PG-67.4.4.
DESIGN AND APPLICATION
PG-60 REQUIREMENTS FOR MISCELLANEOUS PIPE, VALVES, AND FITTINGS
Piping referred to in this paragraph shall be designed in accordance with the applicable requirements of ASME B31.1.
PG-60.1 Water Level Indicators. All boilers having a fixed water level (steam and water interface) shall have at least one gage glass (a transparent device that permits visual determination of the water level). Boilers not having a fixed water level, such as forced-flow steam generators and high-temperature water boilers of the forced circulation type, are not required to have a gage glass. The lowest visible water level in a gage glass shall be at least 2 in. (50 mm) above the lowest permissible water level, as determined by the boiler Manufacturer. Electrode-type electric boilers are required to have only one gage glass, regardless of MAWP.
Gage glasses having multiple tubular sections shall have a minimum of 1 in. (25 mm) overlap of the sections in which the water level may be visible. Segmented gage glasses, such as ported or end-connected strip gages, shall be equipped to provide obvious visual discrimination between water and vapor in the individual sections.
PG-60.1.1 Boilers having a maximum allowable working pressure exceeding 400 psi (3 MPa) shall have two gage glasses. Instead of one of the two required gage glasses, two independent remote water level indicators (two discrete systems that continuously measure, transmit, and display water level) may be provided.
PG-60.1.1.1 When the water level in at least one gage glass is not readily visible to the operator in the area where control actions are initiated, either a fiber optic cable (with no electrical modification of the optical signal) or mirrors shall be provided to transfer the optical image of the water level to the control area. Alternatively, any combination of two of the following shall be provided:
(a) an independent remote water level indicator
(b) an independent continuous transmission and display of an image of the water level in a gage glass.
PG-60.1.1.2 When two independent remote water level indicators are in reliable operation (continuously indicating water level), the one required gage glass may be shut off, but shall be maintained in the serviceable condition.
PG-60.1.1.3 The display of a remote water level indicator shall have a clearly marked minimum water level reference at least 2 in. (50 mm) above the lowest permissible water level, as determined by the Manufacturer.
PG-60.1.6 Each gage glass shall be fitted with a drain cock or valve having an unrestricted drain opening of not less than ¼
in. (6 mm) diameter to facilitate cleaning. When the boiler MAWP exceeds 100 psi (700 kPa), the gage glass shall be furnished with a connection to install a valved drain to a point of safe discharge.
Each gage glass shall be equipped with a top and a bottom shutoff valve of such through-flow construction as to prevent stoppage by deposits of sediments. If the bottom valve is more than 7 ft (2 m) above the floor or platform from which it is operated, the operating mechanism shall indicate by its position whether the valve is open or closed. The pressure—temperature rating of valves, fittings, and piping shall be at least equal to the boiler MAWP and the corresponding saturated-steam temperature.
Straight-run globe valves shall not be used on such connections. Automatic shutoff valves, if permitted to be used, shall conform to the requirements given in A-18.
PG-60.2 Water Columns
PG-60.2.1 A water column shall be so mounted that it will be correctly positioned, relative to the normal water level under operating conditions.
PG-60.2.3 Each water column shall be furnished with a connection of at least NPS ¾ (DN 20) to install a valved drain to a safe point of discharge.
PG-60.2.4 The design and material of a water column shall comply with the requirements of PG-8.2, PG-8.3, and PG-42.
PG-60.3 Connections.
PG-60.3.1 Gage glasses that are required by PG-60.1 shall be connected directly to the shell or drum of the boiler or to an intervening water column. When two gage glasses are required, both may be connected to a single water column.
PG-60.3.2 The lower edge of the steam connection between a water column or gage glass in the boiler shall not be below the highest visible water level in the gage glass. There shall be no sag or offset in the piping that will permit the accumulation of water.
PG-60.3.3 The upper edge of the water connection between a water column or gage glass and the boiler shall not be above the lowest visible water level in the gage glass. No part of this pipe connection shall be above the point of connection at the water column.
PG-60.3.4 Connections from the boiler to the water column shall be at least NPS 1 (DN 25). Connections for gage glasses connected directly to the boiler or to an intervening water column shall be at least NPS ½ (DN 15). Connections from the boiler to the remote level indicator shall be at least NPS ¾
(DN 20) to and including the isolation valve and from there to the remote level indicator at least ½ in. (13 mm) O.D. tubing.
PG-60.3.5 When the boiler MAWP exceeds 400 psi (3 MPa), lower connections to drums for water columns and remote level indicators shall be provided with shields, sleeves, or other suitable means to reduce the effect of temperature differentials in the shells or heads.
PG-60.3.6 The steam and water connections to a water column or a gage glass shall be readily accessible for internal inspection and cleaning. Some acceptable methods of meeting this requirement are by providing a cross or fitting with a back outlet at each right-angle turn to permit inspection and cleaning in both directions, or by using pipe bends or fittings of a type that does not leave an internal shoulder or pocket in the pipe connection and with a radius of curvature that will permit the passage of a rotary cleaner. Screwed plug closures using threaded connections as allowed by PG-39.5.3 are acceptable means of access for this inspection and cleaning. When the boiler MAWP exceeds 400 psig (3 MPa), socket-welded plugs may be used for this purpose in lieu of screwed plugs. If the water connection to the water column has a rising bend or pocket that cannot be drained by means of the water-column drain, an additional drain shall be placed on this connection so that it may be blown off to clear any sediment from the pipe.
PG-60.3.7 Shutoff valves, if provided in the pipe connections between a boiler and a water column or between a boiler and the shutoff valves required for the gage glass (PG-60.1.6), shall be of such through-flow construction as to prevent stoppage by deposits of sediment and shall indicate whether they are in open or closed position of the operating mechanism.
Some examples of acceptable valves are:
(a) outside-screw-and-yoke type gate valve
(b) lever-lifting-type gate valve with permanently fastened lever
(c) stopcock with the plug held in place by a guard or gland
(d) ball valve
Such valves shall be locked or sealed open except under the following additional conditions:
(1) The boiler MAWP shall not exceed 250 psig (1.7 MPa).
(2) The boiler shall not be hand fired or fired with solid fuel not in suspension.
(3) Interlocks between the valve and the burner control system shall stop fuel supply and prevent firing whenever the valve between the drum and the water column is not in the fully open position.
(4) The minimum valve size shall be NPS 1 (DN 25).
PG-60.3.8 Except for control devices such as damper regulators and feedwater regulators, drains, steam pressure gages, or apparatus of such form as does not permit the escape of an appreciable amount of steam or water therefrom, no outlet connections shall be placed on the piping connecting a water column or gage glass to a boiler. No outlet connections shall be placed on the piping connecting a remote level indicator to the boiler or to a water column for any function other than water level indication.
PG-60.3.9 An acceptable arrangement is shown in Fig. PG-60.3.9
PG-60.4 Gage Cocks. Not required.
PG-60.5 Water Fronts. Each boiler fitted with a water jacketed boiler-furnace mouth protector, or similar appliance having valves on the pipes connecting them to the boiler shall have these valves locked or sealed open. Such valves, when used, shall be of the straightway type.
PG-60.6 Pressure Gages
PG-60.6.1 Each boiler shall have a pressure gage so located that it is easily readable. The pressure gage shall be installed so that it shall at all times indicate the pressure in the boiler. Each steam boiler shall have the pressure gage connected to the steam space or to the water column or its steam connection. A valve or cock shall be placed in the gage connection adjacent to the gage. An additional valve or cock may be located near the boiler providing it is locked or sealed in the open position. No other shutoff valves shall be located between the gage and the boiler. The pipe connection shall be of ample size and arranged so that it may be cleared by blowing out. For a steam boiler the gage or connection shall contain a syphon or equivalent device that will develop and maintain a water seal that will prevent steam from entering the gage tube. Pressure gage connections shall be suitable for the maximum allowable working pressure and temperature, but if the temperature exceeds 406°F (208
°C), brass or copper pipe or tubing shall not be used. The connections to the boiler, except the syphon, if used, shall not be less than NPS ¼ (DN 8) but where steel or wrought iron pipe or tubing is used, they shall not be less than ½ in. (13 mm) inside diameter. The minimum size of a syphon, if used, shall be ¼ in. (6 mm) inside diameter. The dial of the pressure gage shall be graduated to approximately double the pressure at which the safety valve is set, but in no case to less than 1 ½ times this pressure.
PG-60.6.2 Each forced-flow steam generator with no fixed steam and waterline shall be equipped with pressure gages or other pressure measuring devices located as follows:
PG-60.6.2.1 At the boiler or superheater outlet (following the last section which involves absorption of heat), and
PG-60.6.2.2 At the boiler or economizer inlet (preceding any section that involves absorption of heat), and
PG-60.6.2.3 Upstream of any shutoff valve that may be used between any two sections of the heat absorbing surface.
PG-60.6.3 Each boiler shall be provided with a valve connection at least NPS ¼ (DN 8) for the exclusive purpose of attaching a test gage when the boiler is in service, so that the accuracy of the boiler pressure gage can be ascertained.
PG-60.6.4 Each high-temperature water boiler shall have a temperature gage so located and connected that it shall be easily readable. The temperature gage shall be installed so that it at all times indicates the temperature in degrees Fahrenheit (Celsius) of the water in the boiler, at or near the outlet connection.
PG-61 FEEDWATER SUPPLY
PG-61.1 Except as provided for in PG-61.2 and PG-61.4, boilers having more than 500 ft2 (47 m2) of water-heating surface shall have at least two means of feeding water. Except as provided for in PG-61.3, PG-61.4, and PG-61.5, each source of feeding shall be capable of supplying water to the boiler at a pressure of 3% higher than the highest setting of any safety valve on the boiler. For boilers that are fired with solid fuel not in suspension, and for boilers whose setting or heat source can continue to supply sufficient heat to cause damage to the boiler if the feed supply is interrupted, one such means of feeding shall not be susceptible to the same interruption as the other, and each shall provide sufficient water to prevent damage to the boiler.
PG-61.2 Except as provided for in PG-61.1, a boiler fired by gaseous, liquid, or solid fuel in suspension, or heated by combustion turbine engine exhaust, may be equipped with a single means of feeding water, provided means are furnished for the shutting off of its heat input prior to the water level reaching the lowest permissible level established by PG-60.
PG-61.3 For boilers having a water-heating surface of not more than 100 ft2 (9.3 m2) the feed connection to the boiler shall not be smaller than NPS ½ (DN 15). For boilers having a water-heating surface more than 100 ft2 (9.3 m2) the feed connection to the boiler shall not be less than NPS ¾ (DN 20).
PG-61.4 High-temperature water boilers shall be provided with means of adding water to the boiler or system while under pressure.
PG-61.5 A forced-flow steam generator with no fixed steam and waterline shall be provided with a source of feeding capable of supplying water to the boiler at a pressure not less than the expected maximum sustained pressure at the boiler inlet, as determined by the boiler Manufacturer, corresponding to operation at maximum designed steaming capacity with maximum allowable working pressure at the superheater outlet.
OVERPRESSURE PROTECTION REQUIREMENTS
PG-67 BOILER
