Appendix D

FOREWORD

The general philosophy underlying this Power Piping Code is to parallel those provisions of Section I, Power Boilers, of the ASME Boiler and Pressure Vessel Code, as they can be applied to power piping systems. The Allowable Stress Values for power piping are generally consistent with those assigned for power boilers. This Code is more conservative than some other piping codes, reflecting the need for long service life and maximum reliability in power plant installations.

The Power Piping Code as currently written does not differentiate between the design, fabrication, and erection requirements for critical and noncritical piping systems, except for certain stress calculations and mandatory nondestructive tests of welds for heavy wall, high temperature applications. The problem involved is to try to reach agreement on how to evaluate criticality, and to avoid the inference that noncritical systems do not require competence in design, fabrication, and erection. Some day such levels of quality may be definable, so that the need for the many different piping codes will be overcome.

There are many instances where the Code serves to warn a designer, fabricator, or erector against possible pitfalls; but the Code is not a handbook, and cannot substitute for education, experience, and sound engineering judgment.

Nonmandatory Appendices are included in the Code. Each contains information on a specific subject, and is maintained current with the Code. Although written in mandatory language, these Appendices are offered for application at the user's discretion.

The Code never intentionally puts a ceiling limit on conservatism. A designer is free to specify more rigid requirements as he feels they may be justified. Conversely, a designer who is capable of a more rigorous analysis than is specified in the Code may justify a less conservative design, and still satisfy the basic intent of the Code.

The Power Piping Committee strives to keep abreast of the current technological improvements in new materials, fabrication practices, and testing techniques; and endeavors to keep the Code updated to permit the use of acceptable new developments.

The ASME B31 Code for Pressure Piping consists of a number of individually published Sections, each an American National Standard, under the direction of ASME Committee B31, Code for Pressure Piping.

Rules for each Section have been developed considering the need for application of specific requirements for various types of pressure piping. Applications considered for each Code Section include:

B31.1 Power Piping: piping typically found in electric power generating stations, in industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems;

B31.3 Process Piping: piping typically found in petroleum refineries, chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants, and related processing plants and terminals;

B31.4 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids: piping transporting products which are predominately liquid between plants and terminals and within terminals, pumping, regulating, and metering stations;

B31.5 Refrigeration Piping: piping for refrigerants and secondary coolants;

B31.8 Gas Transportation and Distribution Piping Systems: piping transporting products which are predominately gas between sources and terminals, including compressor, regulating, and metering stations; and gas gathering pipelines;

B31.9 Building Services Piping: piping typically found in industrial, institutional, commercial, and public buildings, and in multi-unit residences, which does not require the range of sizes, pressures, and temperatures covered in B31.1;

B31.11 Slurry Transportation Piping Systems: piping transporting aqueous slurries between plants and terminals and within terminals, pumping, and regulating stations.

B31.12 Hydrogen Piping and Pipelines: piping in gaseous and liquid hydrogen service, and pipelines in gaseous hydrogen service.

This is the B31.1 Power Piping Code Section. Hereafter, in this Introduction and in the text of this Code Section B31.1, where the word Code is used without specific identification, it means this Code Section.

It is the owner's responsibility to select the Code Section which most nearly applies to a proposed piping installation. Factors to be considered by the owner include: limitations of the Code Section; jurisdictional requirements; and the applicability of other codes and standards. All applicable requirements of the selected Code Section shall be met. For some installations, more than one Code Section may apply to different parts of the installation. The owner is also responsible for imposing requirements supplementary to those of the selected Code Section, if necessary, to assure safe piping for the proposed installation.

Certain piping within a facility may be subject to other codes and standards, including but not limited to:

ASME Boiler and Pressure Vessel Code, Section III: nuclear power piping;

ANSI Z223.1 National Fuel Gas Code: piping for fuel gas from the point of delivery to the connection of each fuel utilization device;

NFPA Fire Protection Standards: fire protection systems using water, carbon dioxide, halon, foam, dry chemical, and wet chemicals;

NFPA 99 Health Care Facilities: medical and laboratory gas systems;

NFPA 8503 Standard for Pulverized Fuel Systems: piping for pulverized coal from the coal mills to the burners;

Building and plumbing codes, as applicable, for potable hot and cold water, and for sewer and drain systems.

The Code sets forth engineering requirements deemed necessary for safe design and construction of pressure piping. While safety is the basic consideration, this factor alone will not necessarily govern the final specifications for any piping system. The designer is cautioned that the Code is not a design handbook; it does not do away with the need for the designer or for competent engineering judgment.

To the greatest possible extent, Code requirements for design are stated in terms of basic design principles and formulas. These are supplemented as necessary with specific requirements to assure uniform application of principles and to guide selection and application of piping elements. The Code prohibits designs and practices known to be unsafe and contains warnings where caution, but not prohibition, is warranted.

The specific design requirements of the Code usually revolve around a simplified engineering approach to a subject. It is intended that a designer capable of applying more complete and rigorous analysis to special or unusual problems shall have latitude in the development of such designs and the evaluation of complex or combined stresses. In such cases the designer is responsible for demonstrating the validity of his approach.

This Code Section includes the following:

(a) references to acceptable material specifications and component standards, including dimensional requirements and pressure-temperature ratings

(b) requirements for design of components and assemblies, including pipe supports

(c) requirements and data for evaluation and limitation of stresses, reactions, and movements associated with pressure, temperature changes, and other forces

(d) guidance and limitations on the selection and application of materials, components, and joining methods

(e) requirements for the fabrication, assembly, and erection of piping

(f) requirements for examination, inspection, and testing of piping

(g) requirements for operation and maintenance of piping systems

It is intended that this Edition of Code Section B31.1 and any subsequent Addenda not be retroactive. Unless agreement is specifically made between contracting parties to use another issue, or the regulatory body having jurisdiction imposes the use of another issue, the latest Edition and Addenda issued at least 6 months prior to the original contract date for the first phase of activity covering a piping system or systems shall be the governing document for all design, materials, fabrication, erection, examination, and testing for the piping until the completion of the work and initial operation.

Users of this Code are cautioned against making use of revisions without assurance that they are acceptable to the proper authorities in the jurisdiction where the piping is to be installed.

Code users will note that clauses in the Code are not necessarily numbered consecutively. Such discontinuities result from following a common outline, insofar as practicable, for all Code Sections. In this way, corresponding material is correspondingly numbered in most Code Sections, thus facilitating reference by those who have occasion to use more than one Section.

The Code is under the direction of ASME Committee B31, Code for Pressure Piping, which is organized and operates under procedures of The American Society of Mechanical Engineers which have been accredited by the American National Standards Institute. The Committee is a continuing one, and keeps all Code Sections current with new developments in materials, construction, and industrial practice. Addenda are issued periodically. New editions are published at intervals of two to five years.

When no Section of the ASME Code for Pressure Piping, specifically covers a piping system, at his discretion the user may select any Section determined to be generally applicable. However, it is cautioned that supplementary requirements to the Section chosen may be necessary to provide for a safe piping system for the intended application. Technical limitations of the various Sections, legal requirements, and possible applicability of other codes or standards are some of the factors to be considered by the user in determining the applicability of any Section of this Code.

The Committee has established an orderly procedure to consider requests for interpretation and revision of Code requirements. To receive consideration, inquiries must be in writing and must give full particulars (see Mandatory Appendix H covering preparation of technical inquiries). The Committee will not respond to inquiries requesting assignment of a Code Section to a piping installation.

The approved reply to an inquiry will be sent directly to the inquirer. In addition, the question and reply will be published as part of an Interpretation Supplement issued to the applicable Code Section.

A Case is the prescribed form of reply to an inquiry when study indicates that the Code wording needs clarification or when the reply modifies existing requirements of the Code or grants permission to use new materials or alternative constructions. The Case will be published as part of a Case Supplement issued to the applicable Code Section.

The ASME B31 Standards Committee took action to eliminate Code Case expiration dates effective September 21, 2007. This means that all Code Cases in effect as of this date will remain available for use until annulled by the ASME B31 Standards Committee.

Materials are listed in the Stress Tables only when sufficient usage in piping within the scope of the Code has been shown. Materials may be covered by a Case. Requests for listing shall include evidence of satisfactory usage and specific data to permit establishment of allowable stresses, maximum and minimum temperature limits, and other restrictions. Additional criteria can be found in the guidelines for addition of new materials in the ASME Boiler and Pressure Vessel Code, Section II and Section VIII, Division 1, Appendix B. (To develop usage and gain experience, unlisted materials may be used in accordance with para. 123.1.)

Requests for interpretation and suggestions for revision should be addressed to the Secretary, ASME B31 Committee, Three Park Avenue, New York, NY 10016-5990.

100 GENERAL

This Power Piping Code is one of several Sections of the American Society of Mechanical Engineers Code for Pressure Piping, B31. This Section is published as a separate document for convenience.

Standards and specifications specifically incorporated by reference into this Code are shown in Table 126.1. It is not considered practical to refer to a dated edition of each of the standards and specifications in this Code. Instead, the dated edition references are included in an Addenda and will be revised yearly.

100.1 Scope

Rules for this Code Section have been developed considering the needs for applications which include piping typically found in electric power generating stations, in industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems.

100.1.1 This Code prescribes requirements for the design, materials, fabrication, erection, test, inspection, operation, and maintenance of piping systems.

Piping as used in this Code includes pipe, flanges, bolting, gaskets, valves, relief devices, fittings, and the pressure containing portions of other piping components, whether manufactured in accordance with Standards listed in Table 126.1 or specially designed. It also includes hangers and supports and other equipment items necessary to prevent overstressing the pressure containing components.

Rules governing piping for miscellaneous appurtenances, such as water columns, remote water level indicators, pressure gages, gage glasses, etc., are included within the scope of this Code, but the requirements for boiler appurtenances shall be in accordance with Section I of the ASME Boiler and Pressure Vessel Code, PG-60.

The users of this Code are advised that in some areas legislation may establish governmental jurisdiction over the subject matter covered by this Code. However, any such legal requirement shall not relieve the owner of his inspection responsibilities specified in para. 136.1.

100.1.2 Power piping systems as covered by this Code apply to all piping and their component parts except as excluded in para. 100.1.3. They include but are not limited to steam, water, oil, gas, and air services.

(A) This Code covers boiler external piping as defined below for power boilers and high temperature, high pressure water boilers in which: steam or vapor is generated at a pressure of more than 15 psig [100 kPa (gage)]; and high temperature water is generated at pressures exceeding 160 psig [1 103 kPa (gage)] and/or temperatures exceeding 250 ° F (120 ° C).

Boiler external piping shall be considered as that piping which begins where the boiler proper terminates at

(1) the first circumferential joint for welding end connections; or

(2) the face of the first flange in bolted flanged connections; or

(3) the first threaded joint in that type of connection; and which extends up to and including the valve or valves required by para. 122.1.

The terminal points themselves are considered part of the boiler external piping. The terminal points and piping external to power boilers are illustrated by Figs. 100.1.2(A), l00.1.2(B), and l00.1.2(C).

Piping between the terminal points and the valve or valves required by para. 122.1 shall be provided with Data Reports, inspection, and stamping as required by Section I of the ASME Boiler and Pressure Vessel Code. All welding and brazing of this piping shall be performed by manufacturers or contractors authorized to use the appropriate symbol shown in Figs. PG-105.1 through PG-105.3 of Section I of the ASME Boiler and Pressure Vessel Code. The installation of boiler external piping by mechanical means may be performed by an organization not holding a Code symbol stamp. However, the holder of a valid S, A, or PP Certificate of Authorization shall be responsible for the documentation and hydrostatic test, regardless of the method of assembly. The quality control system requirements of Section I of the ASME Boiler and Pressure Vessel Code shall apply. These requirements are shown in Appendix J of this Code.

The valve or valves required by para. 122.1 are part of the boiler external piping, but do not require ASME Boiler and Pressure Vessel Code, Section I inspection and stamping except for safety, safety relief, and relief valves; see para. 107.8.2. Refer to PG-11.

Pipe connections meeting all other requirements of this Code but not exceeding NPS ½ may be welded to pipe or boiler headers without inspection and stamping required by Section I of the ASME Boiler and Pressure Vessel Code.

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(B) Nonboiler external piping includes all the piping covered by this Code except for that portion defined above as boiler external piping.

100.1.3 This Code does not apply to the following:

(A) economizers, heaters, pressure vessels, and components covered by Sections of the ASME Boiler and Pressure Vessel Code

(B) building heating and distribution steam and condensate piping designed for 15 psig [100 kPa (gage)] or less, or hot water heating systems designed for 30 psig [200 kPa (gage)] or less

(C) piping for hydraulic or pneumatic tools and their components downstream of the first block or stop valve off the system distribution header

(D) piping for marine or other installations under Federal control

(E) towers, building frames, tanks, mechanical equipment, instruments, and foundations

104.1.3 Straight Pipe Under External Pressure. For determining wall thickness and stiffening requirements for straight pipe under external pressure, the procedures outlined in UG-28, UG-29, and UG-30 of Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code shall be followed.

104.2 Curved Segments of Pipe

1 04.2.1 Pipe Bends. Pipe bends shall be subject to the following limitations:

(A) The minimum wall thickness shall meet the requirements of para. 102.4.5 and the fabrication requirements of para. 129.

(B) Limits on flattening and buckling at bends may be specified by design, depending upon the service, the material, and the stress level involved. Where limits on flattening and buckling are not specified by design, the requirements of para. 129.1 shall be met.

104.2.2 Elbows. Elbows manufactured in accordance with the standards listed in Table 126.1 are suitable for use at the pressure-temperature ratings specified by such standards, subject to the requirements of para. 106.

104.3 Intersections

104.3.1 Branch Connections

(A) This paragraph gives rules governing the design of branch connections to sustain internal and external pressure in cases where the axes of the branch and the run intersect, and the angle between the axes of the branch and of the run is between 45 deg and 90 deg, inclusive.

Branch connections in which the smaller angle between the axes of the branch and the run is less than 45 deg or branch connections where the axes of the branch and the run do not intersect impose special design and fabrication problems. The rules given herein may be used as a guide, but sufficient additional strength must be provided to assure safe service. Such branch connections shall be designed to meet the requirement of para. 104.7.

(B) Branch connections in piping may be made from materials listed in Appendix A by the use of the following:

(B.1) fittings, such as tees, laterals, and crosses made in accordance with the applicable standards listed in Table 126.1 where the attachment of the branch pipe to the fitting is by butt welding, socket welding, brazing, soldering, threading, or by a flanged connection.

(B.2) weld outlet fittings, such as cast or forged nozzles, couplings and adaptors, or similar items where the attachment of the branch pipe to the fitting is by butt welding, socket welding, threading, or by a flanged connection. Such weld outlet fittings are attached to the run by welding similar to that shown in Fig. 127.4.8 (E) or Fig. 127.4.8 (F), as applicable. MSS SP-97 may be used for design and manufacturing standards for integrally reinforced forged branch outlet fittings. Couplings are restricted to a maximum of NPS 3.

(B.3) extruded outlets at right angles to the run pipe, in accordance with (G) below, where the attachment of the branch pipe is by butt welding.

(B.4) piping directly attached to the run pipe by welding in accordance with para. 127.4.8 or by socket welding or threading as stipulated below:

(B.4.1) socket welded right angle branch connections may be made by attaching the branch pipe directly to the run pipe provided.

(B.4.1.1) the nominal size of the branch does not exceed NPS 2 or one-fourth of the nominal size of the run, whichever is smaller.

(B.4.1.2) the depth of the socket measured at its minimum depth in the run pipe is at least equal to that shown in ASME B16.11. If the run pipe wall does not have sufficient thickness to provide the proper depth of socket, an alternate type of construction shall be used.

(B.4.1.3) the clearance between the bottom of the socket and the end of the inserted branch pipe is in accordance with Fig. 127.4.4(C).

(B.4.1.4) the size of the fillet weld is not less than 1.09 times the nominal wall thickness of the branch pipe.

(B.4.2) threaded right angle branch connections may be made by attaching the branch pipe directly to the run provided

(B.4.2.1) the nominal size of the branch does not exceed NPS 2 or one-fourth of the nominal size of the run, whichever is smaller.

(B.4.2.2) the minimum thread engagement is: 6 full threads for NPS ½ and NPS ¾ branches; 7 for NPS 1, NPS 1 ¼ , and NPS 1 ½ branches; and 8 for NPS 2 branches. If the run pipe wall does not have sufficient thickness to provide the proper depth for thread engagement, an alternative type of construction shall be used.

(C) Branch Connections Not Requiring Reinforcement. A pipe having a branch connection is weakened by the opening that must be made in it. Unless the wall thickness of the branch and/or run pipe is sufficiently in excess of that required to sustain the pressure, it is necessary to provide additional material in order to meet the reinforcement requirements of (D) and (E) below. However, there are certain branch connections for which supporting calculations are not required. These are as follows:

(C.1) branch connections made by the use of a fitting (tee, lateral, cross, or branch weld-on fitting), manufactured in accordance with a standard listed in Table 126.1, and used within the limits of pressure-temperature ratings specified in that standard.

(C.2) branch connections made by welding a coupling or half coupling directly to the run pipe in accordance with Fig. 127.4.8(E), provided the nominal diameter of the branch does not exceed NPS 2 or one-fourth the nominal diameter of the run, whichever is less. The minimum wall thickness of the coupling anywhere in the reinforcement zone (if threads are in the zone, wall thickness is measured from the root of the thread to the minimum O.D.) shall not be less than that of the unthreaded branch pipe. In no case shall the thickness of the coupling be less than extra heavy or Class 3000 rating.

Small branch connections NPS 2 or smaller as shown in Fig. 127.4.8(F) may be used, provided t w is not less than the thickness of schedule 160 pipe of the branch size.

(C.3) integrally reinforced fittings welded directly to the run pipe when the reinforcements provided by the fitting and the deposited weld metal meets the requirements of (D) below.

(C.4) integrally reinforced extruded outlets in the run pipe. The reinforcement requirements shall be in accordance with (G) below.

(D) Branch Connections Subject to Internal Pressure Requiring Reinforcement

(D.1) Reinforcement is required when it is not provided inherently in the components of the branch connection. This paragraph gives rules covering the design of branch connections to sustain internal pressure in cases where the angle between the axes of the branch and of the run is between 45 deg and 90 deg. Subparagraph (E) below gives rules governing the design of connections to sustain external pressure.

(D.2) Figure 104.3.1(D) illustrates the notations used in the pressure-temperature design conditions of branch connections. These notations are as follows:

b = subscript referring to branch

D o = outside diameter of pipe, in. (mm)

d 1 = inside centerline longitudinal dimension of the finished branch opening in the run of the pipe, in. (mm)

= [ D ob -2( T b -A )]/sin á

d 2 = "half width" of reinforcing zone, in. (mm)

= the greater of d 1 or (T b - A) + (T h - A) + d 1 /2 but in no case more than D oh , in. (mm)

h = subscript referring to run or header

L 4 = altitude of reinforcement zone outside of run, in. (mm)

= 2.5 (T b - A) + t r or 2.5 (T h - A), whichever is smaller

t r = thickness of attached reinforcing pad, in Example A, in. (mm); or height of the largest 60 deg right triangle supported by the run and branch outside diameter projected surfaces and lying completely within the area of integral reinforcement, in Example B, in. (mm)

T b , T h = actual (by measurement), or minimum wall thickness of the branch or header pipe, in. (mm), permissible under purchase specification

t mb , t mh = required minimum wall thickness, in. (mm), of the branch or header pipe as determined by use of eq. (3) or (3A) in para. 104.1.2(A)

a = angle between axes of branch and run, deg

(D.2.1) If the run pipe contains a longitudinal seam which is not intersected by the branch, the stress value of seamless pipe of comparable grade may be used to determine the value of t mh for the purpose of reinforcement calculations only. If the branch intersects a longitudinal weld in the run, or if the branch contains a weld, the weld joint efficiency for either or both shall enter the calculations. If the branch and run both contain longitudinal welds, care shall be taken to ensure that the two welds do not intersect each other.

(D.2.2) The required reinforcement area in square inches (square millimeters) for branch connections shall be the quantity

A 7 = A 6 (2 - sin a ) = (t mh - A)d 1 (2 - sin a )

For right angle connections the required reinforcement becomes

A 7 = A 6 = (t mh – A)d 1

The required reinforcement must be within the limits of the reinforcement zone as defined in (D.2.4) below.

(D.2.3) The reinforcement required by (D.2) shall be that provided by any combination of areas A 1 , A 2 , A 3 , A 4 , and A 5 , as defined below and illustrated in Fig. 104.3.1(D) where

A 1 = area provided by excess pipe wall in the run
= (2 d 2 – d 1 )( T h - t mh )

A 2 = area, in. 2 (mm 2 ), provided by excess pipe wall in the branch for a distance L 4 above the run

= 2 L 4 ( T b - t mb )/sin a

A 3 = area provided by deposited weld metal beyond the outside diameter of the run and branch, and for fillet weld attachments of rings, pads, and saddles

A 4 = area provided by a reinforcing ring, pad, or integral reinforcement. The value of A 4 may be taken in the same manner in which excess header metal is considered, provided the weld completely fuses the branch pipe, run pipe, and ring or pad, or integral reinforcement. For welding branch connections refer to para. 127.4.8.

A 5 = area provided by a saddle on right angle connections

= (O.D. of saddle - D ob ) t r

A6 = pressure design area expected at the end of service life

= ( t mh - A ) d 1

Portions of the reinforcement area may be composed of materials other than those of the run pipe, but if the allowable stress of these materials is less than that for the run pipe, the corresponding calculated reinforcement area provided by this material shall be reduced in the ratio of the allowable stress being applied to the reinforcement area. No additional credit shall be taken for materials having higher allowable stress values than the run pipe.

(D.2.4) Reinforcement Zone. The reinforcement zone is a parallelogram whose width shall extend a distance d 2 on each side of the centerline of the branch pipe, and whose altitude shall start at the inside surface of the run pipe and extend to a distance L 4 from the outside surface of the run pipe.

(D.2.5) Reinforcement of Multiple Openings. It is preferred that multiple branch openings be spaced so that their reinforcement zones do not overlap. If closer spacing is necessary, the following requirement shall be met. The two or more openings shall be reinforced in accordance with (D.2), with a combined reinforcement that has a strength equal to the combined strength of the reinforcement that would be required for the separate openings. No portion of the cross section shall be considered as applying to more than one opening, or be evaluated more than once in a combined area.

When more than two adjacent openings are to be provided with a combined reinforcement, the minimum distance between centers of any two of these openings should preferably be at least 1 ½ times their average diameter, and the area of reinforcement between them shall be at least equal to 50% of the total required for these two openings.

(D.2.6) Rings, Pads, and Saddles. Reinforcement provided in the form of rings, pads, or saddles shall not be appreciably narrower at the side than at the crotch.

A vent hole shall be provided at the ring, pad, or saddle to provide venting during welding and heat treatment. Refer to para. 127.4.8(E).

Rings, pads, or saddles may be made in more than one piece, provided the joints between pieces have full thickness welds, and each piece is provided with a vent hole.

(D.2.7) Other Designs. The adequacy of designs to which the reinforcement requirements of para. 104.3 cannot be applied shall be proven by burst or proof tests on scale models or on full size structures, or by calculations previously substantiated by successful service of similar design

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(E) Branch Connections Subject to External Pressure Requiring Reinforcement. The reinforcement area in square inches (square millimeters) required for branch connections subject to external pressure shall be

0.5 t mh d 1 (2 - sin a )

where t mh is the required header wall thickness determined for straight pipe under external pressure, using procedures outlined in UG-28, UG-29, UG-30, and UG-31 of Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code.

Procedures established heretofore for connections subject to internal pressure shall apply for connections subject to external pressure provided that D oh , D ob , and t r are reduced to compensate for external corrosion, if required by design conditions.

(F) Branch Connections Subject to External Forces and Moments. The requirements of the preceding paragraphs are intended to assure safe performance of a branch connection subjected only to pressure. However, when external forces and moments are applied to a branch connection by thermal expansion and contraction, by dead weight of piping, valves, and fittings, covering and contents, or by earth settlement, the branch connection shall be analyzed considering the stress intensification factors as specified in Appendix D. Use of ribs, gussets, and clamps designed in accordance with para. 104.3.4 is permissible to stiffen the branch connection, but their areas cannot be counted as contributing to the required reinforcement area of the branch connection.

(G) Extruded Outlets Integrally Reinforced

(G.1) The following definitions, modifications, notations, and requirements are specifically applicable to extruded outlets. The designer shall make proper wall thickness allowances in order that the required minimum reinforcement is assured over the design life of the system.

(G.2) Definition. An extruded outlet header is defined as a header in which the extruded lip at the outlet has an altitude above the surface of the run which is equal to or greater than the radius of curvature of the external contoured portion of the outlet; i.e., h o = r o . See nomenclature and Fig. 104.3.1(G).

(G.3) These rules apply only to cases where the axis of the outlet intersects and is perpendicular to the axis of the run. These rules do not apply to any nozzle in which additional nonintegral material is applied in the form of rings, pads, or saddles.

(G.4) The notation used herein is illustrated in Fig. 104.3.1(G). All dimensions are in inches (millimeters).

D = outside diameter of run

d = outside diameter of branch pipe

d b = corroded internal diameter of branch pipe

d c = corroded internal diameter of extruded outlet measured at the level of the outside surface of the run

d r = corroded internal diameter of run

h o = height of the extruded lip. This must be equal to or greater than r o , except as shown in (G.4.2) below.

L 8 = altitude of reinforcement zone

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T o = corroded finished thickness of extruded outlet measured at a height equal to r o above the outside surface of the run

t b - A = actual thickness of branch wall, not including corrosion allowance

t h - A = actual thickness of run wall, not including the corrosion allowance

t mb - A = required thickness of branch pipe according to wall thickness eq. (3) or (3A) in para. 104.1.2(A), but not including any thickness for corrosion

t mh - A = required thickness of the run according to eq. (3) or (3A) in para. 104.1.2(A), but not including any allowance for corrosion

r 1 = half width of reinforcement zone (equal to d c )

r o = radius of curvature of external contoured portion of outlet measured in the plane containing the axes of the run and branch. This is subject to the following limitations:

(G.4.1) Minimum Radius. This dimension shall not be less than 0.05 d except that on branch diameters larger than NPS 30, it need not exceed 1.50 in. (38 mm).

(G.4.2) Maximum Radius. For outlet pipe sizes 6 in. (150 mm) nominal and larger, this dimension shall not exceed 0.l0 d + 0.50 in. (0.l0 d + 12.7 mm). For outlet pipe sizes less than NPS 6, this dimension shall be not greater than 1.25 in. (32 mm).

(G.4.3) When the external contour contains more than one radius, the radius of any arc sector of approximately 45 deg shall meet the requirements of (G.4.1) and (G.4.2) above. When the external contour has a continuously varying radius, the radius of curvature at every point on the contour shall meet the requirements of (G.4.1) and (G.4.2) above.

(G.4.4) Machining other than grinding for weld cleanup shall not be employed in order to meet the above requirements.

(G.5) Required Area. The required area is defined as

A 7 = K (t mh - A) d c

where K shall be taken as follows.

For d/D greater than 0.60,

K = 1.00

For d/D greater than 0.15 and not exceeding 0.60,

K = 0.6 + 2/3 d/D

For d/D equal to or less than 0.15,

K = 0.70

The design must meet criteria that the reinforcement area defined in (G.6) below is not less than the required area.

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(G.6) Reinforcement Area. The reinforcement area shall be the sum of areas

A 1 + A 2 + A 4

as defined below.

(G.6.l) Area A l is the area lying within the reinforcement zone resulting from any excess thickness available in the run wall.

A 1 = d c (t n – t mh )

(G.6.2) Area A 2 is the area lying within the reinforcement zone resulting from any excess thickness available in the branch pipe wall.

A 2 = 2L 8 (t b – t mh )

(G.6.3) Area A 4 is the area lying within the reinforcement zone resulting from excess thickness available in the extruded outlet lip.

A 4 = 2r o [T o – (t b – A)]

(G.7) Reinforcement of Multiple Openings. It is preferred that multiple branch openings be spaced so that their reinforcement zones do not overlap. If closer spacing is necessary, the following requirements shall be met. The two or more openings shall be reinforced in accordance with (G) with a combined reinforcement that has a strength equal to the combined strength of the reinforcement that would be required for separate openings. No portion of the cross section shall be considered as applying to more than one opening, or be evaluated more than once in a combined area.

(G.8) In addition to the above, the manufacturer shall be responsible for establishing and marking on the section containing extruded outlets, the design pressure and temperature. The manufacturer's name or trademarks shall be marked on the section .

104.3.3 Miters. Miter joints, and the terminology related thereto, are described in Appendix D. A widely spaced miter with

- See PDF for diagram

shall be considered to be equivalent to a girth buttwelded joint, and the rules of this paragraph do not apply. Miter joints, and fabricated pipe bends consisting of segments of straight pipe welded together, with q equal to or greater than this calculated value may be used within the limitations described below.

(A) Pressure shall be limited to 10 psi (70 kPa) under the following conditions:

(A.1) The assembly includes a miter weld with q > 22.5 deg, or contains a segment which has a dimension

B < 6t n

(A.2) The thickness of each segment of the miter is not less than that determined in accordance with para. 104.1.

(A.3) The contained fluid is nonflammable, non-toxic, and incompressible, except for gaseous vents to atmosphere.

(A.4) The number of full pressure cycles is less than 7,000 during the expected lifetime of the piping system.

(A.5) Full penetration welds are used in joining miter segments.

(B) Pressure shall be limited to 100 psi (700 kPa) under the conditions defined in (A.2), (A.3), (A.4), and (A.5) above, in addition to the following:

(B.1) the angle q does not exceed 22.5 deg

(B.2) the assembly does not contain any segment which has a dimension

B < 6t n

(C) Miters to be used in other services or at design pressures above 100 psi (700 kPa) shall meet the requirements of para. 104.7.

(C.1) When justification under para. 104.7 is based on comparable service conditions, such conditions must be established as comparable with respect to cyclic as well as static loadings.

(C.2) When justification under para. 104.7 is based on an analysis, that analysis and substantiating tests shall consider the discontinuity stresses which exist at the juncture between segments; both for static (including brittle fracture) and cyclic internal pressure.

(C.3) The wall thickness, t s , of a segment of a miter shall not be less than specified in (C.3.1) or (C.3.2) below, depending on the spacing.

(C.3.1) For closely spaced miter bends (see Appendix D for definition)

- See PDF for diagram

(C.3.2) For widely spaced miters (see Appendix D for definition)

- See PDF for diagram

(The above equation requires an iterative or quadratic solution for t s . )

104.3.4 Attachments. External and internal attachments to piping shall be designed so as not to cause flattening of the pipe, excessive localized bending stresses, or harmful thermal gradients in the pipe wall. It is important that such attachments be designed to minimize stress concentrations in applications where the number of stress cycles, due either to pressure or thermal effect, is relatively large for the expected life of the equipment.

104.4 Closures

104.4.1 General. Closures for power piping systems shall meet the applicable requirements of this Code and shall comply with the requirements described in (A) or (B) below. Closures may be made

(A) by use of closure fittings, such as threaded or welded plugs, caps, or blind flanges, manufactured in accordance with standards listed in Table 126.1, and used within the specified pressure-temperature ratings, or

(B) in accordance with the rules contained in the ASME Boiler and Pressure Vessel Code, Section I, Power Boilers, PG-31, or Section VIII, Pressure Vessels, Division 1, UG-34 and UW-13, calculated from

t m = t + A

where

t = pressure design thickness, calculated for the given closure shape and direction of loading using appropriate equations and procedures in Section I or Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code.

The definition of A and the symbols used in determining t shall have the definitions shown herein, instead of those given in the ASME Boiler and Pressure Vessel Code.

Attachment of a welded flat permanent closure with only a single fillet weld is not permitted.

104.4.2 Openings in Closures . Openings in closures may be made by welding, extruding, or threading. Attachment to the closure shall be in accordance with the limitations provided for such connections in para. 104.3.1 for branch connections. If the size of the opening is greater than one-half of the inside diameter of the closure, the opening shall be designed as a reducer in accordance with para. 104.6.

Other openings in closures shall be reinforced in accordance with the requirements of reinforcement for a branch connection. The total cross-sectional area required for reinforcement in any plane passing through the center of the opening and normal to the surface of the closure shall not be less than the quantity of d 5 t, where

d 5 = diameter of the finished opening, in. (mm)

t = as defined in (B) above

121.8 Structural Attachments

121.8.1 Nonintegral Type

(A) Nonintegral attachments include clamps, slings, cradles, saddles, straps, and clevises.

(B) When clamps are used to support vertical lines, it is recommended that shear lugs be welded to the pipe to prevent slippage. The provisions of para. 12l.8.2(B) shall apply.

(C) In addition to the provision of (B) above, clamps to support vertical lines should be designed to support the total load on either arm in the event the load shifts due to pipe and/or hanger movement.

121.8.2 Integral Type

(A) Integral attachments include ears, shoes, lugs, cylindrical attachments, rings, and skirts which are fabricated so that the attachment is an integral part of the piping component. Integral attachments shall be used in conjunction with restraints or braces where multiaxial restraint in a single member is to be maintained. Consideration shall be given to the localized stresses induced into the piping component by the integral attachments. Where applicable, the conditions of para. 12l.8.1(C) are to apply.

(B) Integral lugs, plates, angle clips, etc., used as part of an assembly for the support or guiding of pipe may be welded directly to the pipe provided the materials are compatible for welding and the design is adequate for the temperature and load. The design of hanger lugs for attachment to piping for high temperature service shall be such as to provide for differential expansion between the pipe and the attached lug.

121.9 Loads and Supporting Structures

Considerations shall be given to the load carrying capacity of equipment and the supporting structure. This may necessitate closer spacing of hangers on lines with extremely high loads.

121.10 Requirements for Fabricating Pipe Supports

Pipe supports shall be fabricated in accordance with the requirements of para. 130.

122 DESIGN REQUIREMENTS PERTAINING TO SPECIFIC PIPING SYSTEMS

Except as specifically stated otherwise in this Part 6, all provisions of the Code apply fully to the piping systems described herein.

122.1 Boiler External Piping; in Accordance With Para. 100.1.2(A) -Steam, Feedwater, Blowoff, and Drain Piping

122.1.1 General. The minimum pressure and temperature and other special requirements to be used in the design for steam, feedwater, blowoff, and drain piping from the boiler to the valve or valves required by para. 122.1 shall be as specified in the following paragraphs. Design requirements for desuperheater spray piping connected to desuperheaters located in the boiler proper and in main steam piping are provided in para. 122.4.

(A) It is intended that the design pressure and temperature be selected sufficiently in excess of any expected operating conditions, not necessarily continuous, to permit satisfactory operation without operation of the overpressure protection devices. Also, since the operating temperatures of fired equipment can vary, the expected temperature at the connection to the fired equipment shall include the manufacturer's maximum temperature tolerance.

(B) In a forced flow steam generator with no fixed steam and water line, it is permissible to design the external piping, valves, and fittings attached to the pressure parts for different pressure levels along the path through the steam generator of water-steam flow. The values of design pressure and the design temperature to be used for the external piping, valves, and fittings shall be not less than that required for the expected maximum sustained operating pressure and temperature to which the abutted pressure part is subjected except when one or more of the overpressure protection devices covered by PG-67.4 of Section I of the ASME Boiler and Pressure Vessel Code is in operation. The steam piping shall comply with the requirements for the maximum sustained operating conditions as used in (A) above, or for the design throttle pressure plus 5%, whichever is greater.

(C) Provision shall be made for the expansion and contraction of piping connected to boilers to limit forces and moments transmitted to the boiler, 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.

(D) Piping connected to the outlet of a boiler for any purpose shall be attached by

(D.1) welding to a nozzle or socket welding fitting

(D.2) threading into a tapped opening with a threaded fitting or valve at the other end

(D.3) screwing each end into tapered flanges, fittings, or valves with or without rolling or peening

(D.4) bolted joints including those of the Van Stone type

(D.5) blowoff piping of firetube boilers shall be attached in accordance with (D.2) above if exposed to products of combustion or in accordance with (D.2), (D.3), or (D.4) above if not so exposed

(E) Nonferrous pipe or tubes shall not exceed NPS 3 in diameter.

(F) American National Standard slip-on flanges shall not exceed NPS 4. Attachment of slip-on flanges shall be by double fillet welds. The throats of the fillet welds shall not be less than 0.7 times the thickness of the part to which the flange is attached.

(G) Hub-type flanges shall not be cut from plate material.

(H) American National Standard socket welded flanges may be used in piping or boiler nozzles provided the dimensions do not exceed NPS 3 for Class 600 and lower and NPS 2 ½ in Class 1500.

122.1.2 Steam Piping

(A) The value of P to be used in the formulas in para. 104 shall be as follows:

(A.1) For steam piping connected to the steam drum or to the superheater inlet header up to the first stop valve in each connection, the value of P shall be not less than the lowest pressure at which any drum safety valve is set to blow, and the S value shall not exceed that permitted for the corresponding saturated steam temperature.

(A.2) For steam piping connected to the superheater outlet header up to the first stop valve in each connection, the design pressure, except as otherwise provided in (A.4) below shall be not less than the lowest pressure at which any safety valve on the superheater is set to blow, or not less than 85% of the lowest pressure at which any drum safety valve is set to blow, whichever is greater, and the S value for the material used shall not exceed that permitted for the expected steam temperature.

(A.3) For steam piping between the first stop valve and the second valve, when one is required by para. 122.1.7, the design pressure shall be not less than the expected maximum sustained operating pressure or 85% of the lowest pressure at which any drum safety valve is set to blow, whichever is greater, and the S value for the material used shall not exceed that permitted for the expected steam temperature.

(A.4) For boilers installed on the unit system (i.e., one boiler and one turbine or other prime mover) and provided with automatic combustion control equipment responsive to steam header pressure, the design pressure for the steam piping shall be not less than the design pressure at the throttle inlet plus 5%, or not less than 85% of the lowest pressure at which any drum safety valve is set to blow, or not less than the expected maximum sustained operating pressure at any point in the piping system, whichever is greater, and the S value for the material used shall not exceed that permitted for the expected steam temperature at the superheater outlet. For forced-flow steam generators with no fixed steam and water line, the design pressure shall also be no less than the expected maximum sustained operating pressure.

(A.5) The design pressure shall not be taken at less than 100 psig [700 kPa (gage)] for any condition of service or material.

122.1.3 Feedwater Piping

(A) The value of P to be used in the formulas in para. 104 shall be as follows:

(A.1) For piping from the boiler to and including the required stop valve and the check valve, the minimum value of P except as permitted in para. 122.1.3(A.4) shall exceed the maximum allowable working pressure of the boiler by either 25% or 225 psi (1 550 kPa), whichever is the lesser. For an installation with an integral economizer without valves between the boiler and economizer, this paragraph shall apply only to the piping from the economizer inlet header to and including the required stop valve and the check valve.

(A.2) For piping between the required check valve and the globe or regulating valve, when required by para. 122.1.7(B), and including any bypass piping up to the shutoff valves in the bypass, the value of P shall be not less than the pressure required to feed the boiler.

(A.3) The value of P in the formula shall not be taken at less than 100 psig [700 kPa (gage)] for any condition of service or material, and shall never be less than the pressure required to feed the boiler.

(A.4) In a forced flow steam generator with no fixed steam and water line, the value of P for feedwater piping from the boiler to and including the required stop valve may be in accordance with the requirements of para. 122.1.1(B).

(B) The S value used, except as permitted in (A.4) above, shall not exceed that permitted for the temperature of saturated steam at the maximum allowable working pressure of the boiler.

(C) The size of the feed piping between the boiler and the first required valve [para. 122.1.7(B)] or the branch feed connection [para. 122.1.7(B.4)] shall, as a minimum, be the same as the boiler connection.

122.1.4 Blowoff and Slowdown Piping. Blowoff and blowdown piping are defined as piping connected to a boiler and provided with valves or cocks through which the water in the boiler may be blown out under pressure. This definition is not intended to apply to (i) drain piping, and (ii) piping such as used on water columns, gage glasses, or feedwater regulators, etc., for the purpose of determining the operating condition of the equipment. Requirements for (i) and (ii) are described in paras. 122.1.5 and 122.1.6. Blowoff systems are operated intermittently to remove accumulated sediment from equipment and/or piping, or to lower boiler water level in a rapid manner. Blowdown systems are primarily operated continuously to control the concentrations of dissolved solids in the boiler water.

(A) Blowoff piping systems from water spaces of a boiler, up to and including the blowoff valves, shall be designed in accordance with (A.1) to (A.4) below. Two shutoff valves are required in the blowoff system; specific valve requirements and exceptions are given in para. 122.1.7(C).

(A.1) The value of P to be used in the formulas in para. 104 shall exceed the maximum allowable working pressure of the boiler by either 25% or 225 psi (1 550 kPa) whichever is less, but shall be not less than 100 psig [690 kPa (gage)].

(A.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.

(A.3) All pipe shall be steel except as permitted below. Galvanized steel pipe and fittings shall not be used for blowoff 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.

(A.4) The size of blowoff 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.

(B) The blowdown piping system from the boiler, to and including the shutoff valve, shall be designed in accordance with (B.1) through (B.4) below. Only one shutoff valve is required in the blowdown system.

(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.

- See PDF for diagram

(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 2 ½ 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. - See PDF for table

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.

(B) When discharging directly to the atmosphere, discharge shall not impinge on other piping or equipment and shall be directed away from platforms and other areas used by personnel.

(C) It is recommended that individual discharge lines be used, but if two or more reliefs are combined, the discharge piping shall be designed with sufficient flow area to prevent blowout of steam or other fluids. Sectional areas of a discharge pipe shall not be less than the full area of the valve outlets discharging thereinto and the discharge pipe shall be as short and straight as possible and so arranged as to avoid undue stresses on the valve or valves.

(D) Discharge lines from pressure-relieving safety devices within the scope of this Code shall be designed to facilitate drainage.

(E) When the umbrella or drip pan type of connection is used, the discharge piping shall be so designed as to prevent binding due to expansion movements.

(F) Drainage shall be provided to remove water collected above the safety valve seat.

(G) Carbon steel materials listed in Appendix A may be used for discharge piping which is subjected to temperatures above 800 ° F (427 ° C) only during operation of pressure relieving safety devices provided that

(G.1) the duration of pressure relieving safety device operation is self-limiting

(G.2) the piping discharges directly to atmosphere

(G.3) the allowable stresses for carbon steel materials at temperatures above 800 ° F (427 ° C) shall be taken from Section II, Part D, Table 1A for materials applicable to Section I and Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code.

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