Appendix B

INTRODUCTION

The rules of this Section of the Code cover minimum construction requirements for the design, fabrication, installation, and inspection of steam heating, hot water heating, hot water supply boilers that are directly fired with oil, gas, electricity, coal, or other solid or liquid fuels, and for operation at or below the pressure and temperature limits set forth in this document. Similar rules for potable water heaters are also included.

For Section IV application, the boiler proper or other vessels terminate at the supply and return connections to the system or the supply and feedwater connections of a hot water supply boiler. These connections may be any of the following:

(a) the first circumferential joint for welding end connections

(b) the face of the first flange in bolted flanged connections

(c) the first threaded joint in that type of connection

Included within the scope of the boiler are pressure-retaining covers for inspection openings, such as manhole covers, handhold covers, and plugs; and headers required to connect individual coils, tubes, or cast sections within a boiler.

The rules are divided into four major Parts: Part HG, applying to all materials of construction except as provided for in Part HLW; Part HF, applying to assemblies fabricated of wrought material, except as provided for in Part HLW; Part HC, applying to cast iron assemblies; Part HA, applying to boilers constructed of cast aluminum; and Part HLW, applying to potable water heaters. Part HF is further subdivided into Subpart HW, containing rules for welded construction, and Subpart HB, containing rules for brazed construction.

The Parts and Subparts of this Section are divided into Articles. Each Article is given a number and a title, as for example, Part HG, Article 3, Design. Articles are divided into paragraphs that are given a three-digit number, the first of which corresponds to the Article number. Thus, under Article 3 of Part HG, paragraph HG-307 will be found. Paragraphs are further subdivided into subparagraphs. Major subdivisions of paragraphs are designated by three- or four-digit numbers followed by a decimal point and a digit or digits. Where necessary, further subdivisions are represented by letters and then by numbers in parentheses. Minor subdivisions of the paragraphs are also represented by letters. A reference to one of these paragraphs in the text of the Section includes all of the applicable rules in that paragraph. Thus, reference to HG-307 includes all the rules in HG-307.1 through HG-307.4.

This Section does not contain rules to cover all possible details of design and construction. Where complete details are not given, it is intended that the manufacturer, subject to the acceptance of the Authorized Inspector, shall provide details of design and construction that will be as safe as otherwise required by these rules.

When the strength of any part cannot be computed with a satisfactory assurance of safety, these rules provide procedures for establishing its maximum allowable working pressure.

HG-100 SCOPE

(a) The rules of Part HG apply to steam heating boilers, hot water heating boilers, hot water supply boilers, and to appurtenances thereto. They shall be used in conjunction with the specific requirements in Part HF, Boilers of Wrought Materials, Part HC, Cast Iron Boilers, and Part HA, Cast Aluminum Boilers, whichever is applicable. The foreword provides the basis for these rules. Part HG is not intended to apply to potable water heaters except as provided for in Part HLW.

(b) This Part contains mandatory requirements, specific prohibitions, and nonmandatory guidance for materials, designs, fabrication, examination, inspection, testing, certification, and pressure relief.

(c) Laws or regulations issued by a municipality, state, provincial, federal, or other enforcement or regulatory body having jurisdiction at the location of an installation, establish the mandatory applicability of these rules, in whole or in part.

HG-101 SERVICE RESTRICTIONS

HG-101.1 Service Restrictions. The rules of this Section are restricted to the following services:

(a) steam boilers for operation at pressures not exceeding 15 psi (100 kPa)

(b) hot water heating boilers and hot water supply boilers for operating at pressures not exceeding 160 psi (1 100 kPa) and/or temperatures not exceeding 250 ° F (120 ° C), at or near the boiler outlet, except that when some of the wrought materials permitted by Part HF are used, a lower temperature is specified

HG-101.2 Services in Excess of Those Covered by This Section. For services exceeding the limits specified in HG-101.l, the rules of Section I shall apply.

HG-102 UNITS

Either U.S. Customary, SI, or any local customary units may be used to demonstrate compliance with all requirements of this edition (e.g., materials, design, fabrication, examination, inspection, testing, certification, and overpressure protection).

In general, it is expected that a single system of units shall be used for all aspects of design except where unfeasible or impractical. When components are manufactured at different locations where local customary units are different than those used for the general design, the local units may be used for the design and documentation of that component. Similarly, for proprietary components or those uniquely associated with a system of units different than that used for the general design, the alternate units may be used for the design and documentation of that component.

For any single equation, all variables shall be expressed in a single system of units. When separate equations are provided for U.S. Customary and SI units, those equations must be executed using variables in the units associated with the specific equation. Data expressed in other units shall be converted to U.S. Customary or SI units for use in these equations. The result obtained from execution of these equations may be converted to other units.

Production, measurement and test equipment, drawings, welding procedure specifications, welding procedure and performance qualifications, and other fabrication documents may be in U.S. Customary, SI, or local customary units in accordance with the fabricator's practice. When values shown in calculations and analysis, fabrication documents, or measurement and test equipment are in different units, any conversions necessary for verification of Code compliance and to ensure that dimensional consistency is maintained shall be in accordance with the following:

(a) Conversion factors shall be accurate to at least four significant figures.

(b) The results of conversions of units shall be expressed to a minimum of three significant figures.

Conversion of units, using the precision specified above shall be performed to assure that dimensional consistency is maintained. Conversion factors between U.S. Customary and SI units may be found in the Nonmandatory Appendix M, Guidance for the Use of U.S. Customary and SI Units in the ASME Boiler and Pressure Vessel Code. Whenever local customary units are used the Manufacturer shall provide the source of the conversion factors, which shall be subject to verification and acceptance by the Authorized Inspector.

Material that has been manufactured and certified to either the U.S. Customary or SI material specification (e.g., SA-516M) may be used regardless of the unit system used in design. Standard fittings (e.g., flanges, elbows, etc.) that have been certified to either U.S. Customary units or SI units may be used regardless of the unit system used in design.

All entries on a Manufacturer's Data Report and data for Code required nameplate marking shall be in units consistent with the fabrication drawings for the component using U.S. Customary, SI, or local customary units. It is acceptable to show alternate units parenthetically. Users of this Code are cautioned that the receiving Jurisdiction should be contacted to ensure the units are acceptable.

HG-200 GENERAL MATERIAL REQUIREMENTS

HG-200.1 Materials Subject to Pressure Stress. Material subject to stress due to pressure shall conform to one of the specifications given in Section II and shall be limited to those that are permitted in HF-200 for boilers of wrought materials and HC-200 for cast iron boilers.

HG-200.2 Internal Parts Subject to Deterioration. Materials shall not be used for internal parts that are liable to fail due to deterioration when subjected to saturated steam temperatures at or below the maximum allowable working pressure.

HG-200.3 Materials Not Found in Section II. Material not covered by specifications in Section II shall not be used unless authorization to use the material is granted by the Boiler and Pressure Vessel Committee on the basis of data submitted to the Committee in accordance with Appendix A.

HG-200.4 Materials Use Not Limited by Specification Title. The title or scope paragraph of a material specification in Section II with respect to product form or service shall not limit the use of a material, provided the material is suitable for the application and its use is permitted by the rules of this Section.

HG-200.5 Materials Use Not Limited by Method of Production. Materials covered by specifications in Section II are not restricted as to the method of production unless so stated in the Specification, and as long as the product complies with the requirements of the Specification.

HG-200.6 Materials With Thicknesses Exceeding Specification Limits. Materials having thicknesses outside of the limits given in the title or scope clause of a specification in Section II may be used in construction, provided they comply with the other requirements of the Specification and with all thickness requirements of this Code.

HG-200.7 Nonpressure Part Materials. Material for nonpressure parts, such as skirts, supports, baffles, lugs, clips, and extended heat-transfer surfaces, need not conform to the specifications for the material to which they are attached or to a material specification permitted in HF-200 or HC-200; but, if welded, they shall be of weldable quality. The allowable stress value shall not exceed 80% of the maximum allowable stress permitted for similar material in Tables HF-300.1 and HF-300.2. Satisfactory performance of a specimen in such service shall not make the material acceptable for use in pressure parts of a vessel.

HG-201 SPECIFIC MATERIAL REQUIREMENTS

Specific material requirements for assemblies constructed of wrought materials are given in Part HF, Article 2 and for assemblies constructed of cast iron in Part HC, Article 2.

HG-400 PRESSURE RELIEVING VALVE
REQUIREMENTS - See PDF for table

HG-400.1 Safety Valve Requirements for Steam
Boilers

(a) Each steam boiler shall have one or more officially rated safety valves that are identified with the V or HV Symbol of the spring pop type adjusted and sealed to discharge at a pressure not to exceed 15 psi (100 kPa).

(b) No safety valve for a steam boiler shall be smaller than NPS ½ (DN 15) or larger than NPS 4 (DN 100). The inlet opening shall have an inside diameter equal to, or greater than, the seat diameter.

(c) The minimum relieving capacity of valve or valves shall be governed by the capacity marking on the boiler called for in HG-530.

(d) The minimum valve capacity in pounds per hour shall be the greater of that determined by dividing the maximum Btu output at the boiler nozzle obtained by the firing of any fuel for which the unit is installed by 1,000, or shall be determined on the basis of the pounds (kg) of steam generated per hour per square foot (m 2 ) of boiler heating surface as given in Table HG-400.1. For cast iron boilers constructed to the requirements of Part HC, the minimum valve capacity shall be determined by the maximum output method. In many cases a greater relieving capacity of valves will have to be provided than the minimum specified by these rules. In every case, the requirement of HG-400.l(e) shall be met.

(e) The safety valve capacity for each steam boiler shall be such that with the fuel burning equipment installed, and operated at maximum capacity, the pressure cannot rise more than 5 psi (35 Kpa) above the maximum allowable working pressure.

(f) When operating conditions are changed, or additional boiler heating surface is installed, the valve capacity shall be increased, if necessary, to meet the new conditions and be in accordance with HG-400.l (e). The additional valves required, on account of changed conditions, may be installed on the outlet piping provided there is no intervening valve.

HG-400.2 Safety Relief Valve Requirements for Hot Water Boilers

(a) Each hot water heating or supply boiler shall have at least one officially rated safety relief valve, of the automatic reseating type, identified with the V or HV Symbol, and set to relieve at or below the maximum allowable working pressure of the boiler.

(b) Hot water heating or supply boilers limited to a water temperature not in excess of 210 ° F (99 ° C) may have, in lieu of the valve(s) specified in (a) above, one or more officially rated temperature and pressure safety relief valves of the automatic reseating type identified with the HV symbol, and set to relieve at or below the maximum allowable working pressure of the boiler.

(c) When more than one safety relief valve is used on either hot water heating or hot water supply boilers, the additional valves shall be officially rated and may have a set pressure within a range not to exceed 6 psi (40 kPa) above the maximum allowable working pressure of the boiler up to and including 60 psi (400 kPa), and 5% for those having a maximum allowable working pressure exceeding 60 psi (400 kPa).

(d) No safety relief valve shall be smaller than NPS ¾ (DN 20) nor larger than NPS 4 (DN 100) except that boilers having a heat input not greater than 15,000 Btu/hr (4.4 kW) may be equipped with a rated safety relief valve of NPS ½ (DN 15).

(e) The required steam relieving capacity, in pounds per hour (kg/h), of the pressure relieving device or devices on a boiler shall be the greater of that determined by dividing the maximum output in Btu at the boiler nozzle obtained by the firing of any fuel for which the unit is installed by 1,000, or shall be determined on the basis of pounds (kg) of steam generated per hour per square foot (m 2 ) of boiler heating surface as given in Table HG-400.1. For cast iron boilers constructed to the requirements of Part HC, the minimum valve capacity shall be determined by the maximum output method. In many cases a greater relieving capacity of valves will have to be provided than the minimum specified by these rules. In every case, the requirements of HG-400.2 (g) shall be met.

(f) When operating conditions are changed, or additional boiler heating surface is installed, the valve capacity shall be increased, if necessary, to meet the new conditions and shall be in accordance with HG-400,2(g). The additional valves required, on account of changed conditions, may be installed on the outlet piping provided there is no intervening valve.

(g) Safety relief valve capacity for each boiler with a single safety relief valve shall be such that, with the fuel burning equipment installed and operated at maximum capacity, the pressure cannot rise more than 10% above the maximum allowable working pressure. When more than one safety relief valve is used, the overpressure shall be limited to 10% above the set pressure of the highest set valve allowed by HG-400.2 (c).

HG-400.3 Safety and Safety Relief Valves for Tanks and Heat Exchangers

(a) Steam to Hot Water Supply. When a hot water supply is heated indirectly by steam in a coil or pipe within the service limitations set forth in HG-101, the pressure of the steam used shall not exceed the safe working pressure of the hot water tank, and a safety relief valve at least NPS 1 (DN 25), set to relieve at or below the maximum allowable working pressure of the tank, shall be applied on the tank.

(b) High Temperature Water to Water Heat Exchanger. 1 When high temperature water is circulated through the coils or tubes of a heat exchanger to warm water for space heating or hot water supply, within the service limitations set forth in HG-101, the heat exchanger shall be equipped with one or more officially rated safety relief valves that are identified with the V or HV Symbol, set to relieve at or below the maximum allowable working pressure of the heat exchanger, and of sufficient rated capacity to prevent the heat exchanger pressure from rising more than 10% above the maximum allowable working pressure of the vessel.

(c) High Temperature Water to Steam Heat Exchanger. 1 When high temperature water is circulated through the coils or tubes of a heat exchanger to generate low pressure steam, within the service limitations set forth in HG-101, the heat exchanger shall be equipped with one or more officially rated safety valves that are identified with the V or HV Symbol, set to relieve at a pressure not to exceed 15 psi (100 kPa), and of sufficient rated capacity to prevent the heat exchanger pressure from rising more than 5 psi (35 kPa) above the maximum allowable working pressure of the vessel. For heat exchangers requiring steam pressures greater than 15 psi (100 kPa), refer to Section I or Section VIII, Division 1. - See PDF for table

1 Suggested installation practices for the secondary side of heat exchangers.

HG-401 MINIMUM REQUIREMENTS FOR SAFETY AND SAFETY RELIEF VALVES

HG-401.1 Mechanical Requirements

(a) The inlet opening shall have an inside diameter approximately equal to, or greater than, the seat diameter. In no case shall the maximum opening through any part of the valve be less than ¼ in. (6 mm) in diameter or its equivalent area.

(b) Safety relief valves officially rated as to capacity shall have pop action when tested by steam.

(c) O-rings or other packing devices when used on the stems of safety relief valves shall be so arranged as not to affect their operation or capacity.

(d) The design shall incorporate guiding arrangements necessary to insure consistent operation and tightness. Excessive lengths of guiding surfaces should be avoided. Bottom guided designs are not permitted on safety relief valves.

(e) Safety valves shall have a controlled blowdown of 2 psi to 4 psi (15 kPa to 30 kPa) and this blowdown need not be adjustable.

(f) Safety valves shall be spring loaded. The spring shall be designed so that the full lift spring compression shall be no greater than 80% of the nominal solid deflection. The permanent set of the spring (defined as the difference between the free height and height measured 10 min after the spring has been compressed solid three additional times after presetting at room temperature) shall not exceed 0.5% of the free height.

(g) There shall be a lifting device and a mechanical connection between the lifting device and the disk capable of lifting the disk from the seat a distance of at least 1/16 in. (1.5 mm) with no pressure on the boiler.

(h) A body drain below seat level shall be provided by the Manufacturer for all safety valves and safety relief valves, except that the body drain may be omitted when the valve seat is above the bottom of the inside diameter of the discharge piping. For valves exceeding NPS 2 ½ (DN 65) the drain hole or holes shall be tapped not less than NPS 3/8 (DN 10). For valves NPS 2 ½ (DN 65) or smaller, the drain hole shall not be less than ¼ in. (6 mm) in diameter. Body drain connections shall not be plugged during or after field installation. In safety relief valves of the diaphragm type, the space above the diaphragm shall be vented to prevent a buildup of pressure above the diaphragm. Safety relief valves of the diaphragm type shall be so designed that failure or deterioration of the diaphragm material will not impair the ability of the valve to relieve at the rated capacity.

(i) In the design of the body of the valve consideration shall be given to minimizing the effects of water deposits.

(j) Valves shall be provided with wrenching surfaces to allow for normal installation without damaging operating parts.

(k) The set pressure tolerances, plus or minus, of safety valves shall not exceed 2 psi (15 kPa), and for safety relief valves shall not exceed 3 psi (20 kPa) for pressures up to and including 60 psig (400 kPa) and 5% for pressures above 60 psig (400 kPa).

(l) Safety valves shall be arranged so that they cannot be reset to relieve at a higher pressure than the maximum allowable working pressure of the boiler.

HG-401.2 Material Selection

(a) Cast iron seats and disks are not permitted.

(b) Adjacent sliding surfaces such as guides and disks shall both be of corrosion resistant material.

(c) Springs of corrosion resistant material or having a corrosion resistant coating are required.

(d) Material for seats and disks should be such as to provide a reasonable degree of resistance to steam cutting.

(e) Material for valve bodies and bonnets or their corresponding metallic pressure containing parts shall be listed in Section II , except that in cases where a manufacturer desires to make use of materials other than those listed in Section II, he shall establish and maintain specifications requiring equivalent control of chemical and physical properties and quality.

(f) Synthetic disk inserts of O-ring or other types if used shall be compatible with the maximum design temperature established for the valve.

(g) No materials liable to fail due to deterioration or vulcanization when subjected to saturated steam temperature corresponding to capacity test pressure shall be used.

HG-401.3 Manufacture and Inspection

(a) A Manufacturer shall demonstrate to the satisfaction of an ASME designee that his manufacturing, production, and testing facilities and quality control procedures will insure close agreement between the performance of random production samples and the performance of those valves submitted for capacity certification.

(b) Manufacturing, inspection, and test operations including capacity are subject to inspections at any time by an ASME designee.

(c) A Manufacturer may be granted permission to apply, the HV Code Symbol to production pressure relief valves capacity certified in accordance with HG-402.3 provided the following tests are successfully completed. This permission shall expire on the sixth anniversary of the date it is initially granted. The permission may be extended for 6 year periods if the following tests are successfully repeated within the 6 month period before expiration.

(1) Two sample production pressure relief valves of a size and capacity within the capability of an ASME accepted laboratory shall be selected by an ASME designee.

(2) Operational and capacity tests shall be conducted in the presence of an ASME designee at an ASME accepted laboratory. The valve Manufacturer shall be notified of the time of the test and may have representatives present to witness the test.

(3) Should any valve fail to relieve at or above its certified capacity or should it fail to meet performance requirements of this Section, the test shall be repeated at the rate of two replacement valves, selected in accordance with HG-401.3(c)(1), for each valve that failed.

(4) Failure of any of the replacement valves to meet the capacity or the performance requirements of this Section shall be cause for revocation within 60 days of the authorization to use the Code Symbol on that particular type of valve. During this period, the Manufacturer shall demonstrate the cause of such deficiency and the action taken to guard against future occurrence, and the requirements of HG-401.3(c) above shall apply.

(d) Safety valves shall be sealed in a manner to prevent the valve from being taken apart without breaking the seal. Safety relief valves shall be set and sealed so that they cannot be reset without breaking the seal.

HG-401.4 Manufacturer's Testing

(a) Every safety valve shall be tested to demonstrate its popping point, blowdown, and tightness. Every safety relief valve shall be tested to demonstrate its opening point and tightness. Safety valves shall be tested on steam or air and safety relief valves on water, steam, or air. When the blowdown is nonadjustable, the blowdown test may be performed on a sampling basis.

(b) A Manufacturer shall have a well-established program for the application, calibration, and maintenance of test gages.

(c) Testing time on safety valves shall be sufficient, depending on size and design, to insure that test results are repeatable and representative of field performance.

(d) Test fixtures and test drums shall be of adequate size and capacity to assure representative pop action and accuracy of blowdown adjustment.

(e) A tightness test shall be conducted at maximum expected operating pressure, but not at a pressure exceeding the reseating pressure of the valve.

HG-401.5 Design Requirements. At the time of the submission of valves for capacity certification, or testing in accordance with this Section, the ASME Designee has the authority to review the design for conformity with the requirements of this Section, and to reject or require modification of designs that do not conform, prior to capacity testing.

HG-402 DISCHARGE CAPACITIES OF SAFETY AND SAFETY RELIEF VALVES

HG-402.1 Valve Markings. Each safety or safety-relief valve shall be plainly marked with the required data by the Manufacturer in such a way that the markings will not be obliterated in service. The markings shall be stamped, etched, impressed, or cast on the valve or on a nameplate, which shall be securely fastened to the valve.

(a) The markings shall include the following:

(1) the name or an acceptable abbreviation of the Manufacturer

(2) Manufacturer's design or type number

(3) NPS size _____ in. (DN) (the nominal pipe size of the valve inlet)

(4) set pressure _____ psi

(5) capacity _____ lb/hr (kg/hr), or capacity _____ Btu/hr in accordance with HG-402.7 (a)

(6) year built or, alternatively, a coding may be marked on the valves such that the valve Manufacturer can identify the year the valve was assembled and tested, and

(7) ASME Symbol as shown in Fig. HG-402

(b) Nameplates of safety or safety-relief valves may be marked solely in metric units under the following conditions:

(1) The pressure-relief device will be installed in a location where metric units are required or accepted by local authorities, if any.

(2) Metric units shall be those required by the user when not mandated by enforcement authorities.

(3) The Manufacturer's quality control system shall provide for the conversion from U.S. customary units to the metric units that will be marked on the nameplate.

HG-402.2 Authorization to Use ASME Stamp. Each safety valve to which the Code Symbol (Fig. HG-402) is to be applied shall be produced by a Manufacturer and/or Assembler who is in possession of a valid Certificate of Authorization. (See HG-540.) For all valves to be stamped with the HV Symbol, a Certified Individual (CI) shall provide oversight to ensure that the use of the "HV" Code symbol on a safety valve or safety relief valve is in accordance with this Section and that the use of the "HV" Code symbol is documented on a Certificate of Conformance Form, HV-1.

- See PDF for diagram

(a) Requirements for the Certified Individual (CI). The CI shall

(1) be an employee of the Manufacturer.

(2) be qualified and certified by the Manufacturer. Qualification shall include the following as a minimum:

(a) knowledge of the requirements of this Section for the application of the "HV" Code Symbol

(b) knowledge of the Manufacturer's quality program

(c) training commensurate with the scope, complexity, or special nature of the activities to which oversight is to be provided

(3) have a record, maintained and certified by the Manufacturer, containing objective evidence of the qualifications of the CI and the training program provided

(b) Duties of the Certified Individual (CI). The CI shall

(1) verify that each item to which the Code Symbol is applied meets all applicable requirements of this Section and has a current capacity certification for the "HV" symbol

(2) review documentation for each lot of items to be stamped, to verify, for the lot, that the requirements of this Section have been completed

(3) sign the Certificate of Conformance Form (HV-1) prior to release of control of the item

(c) Certificate of Conformance Form (HV-1 ) (see Appendix N)

(1) The Certificate of Conformance shall be filled out by the Manufacturer and signed by the Certified Individual. Multiple duplicate pressure relief devices may be recorded on a single entry provided the devices are identical and produced in the same lot.

(2) The Manufacturer's written quality control program shall include requirements for completion of Certificates of Conformance forms and retention by the Manufacturer for a minimum of 5 years.

HG-402.3 Determination of Capacity to Be Stamped on Valves. The Manufacturer of the valves that are to be stamped with the Code symbol shall submit valves for testing to a place where adequate equipment and personnel are available to conduct pressure and relieving-capacity tests which shall be made in the presence of and certified by an authorized observer. The place, personnel, and authorized observer shall be approved by the Boiler and Pressure Vessel Committee. The valves shall be tested in one of the following three methods.

(a) Coefficient Method. Tests shall be made to determine the lift, popping, and blowdown pressures, and the capacity of at least three valves each of three representative sizes (a total of nine valves). Each valve of a given size shall be set at a different pressure. However, safety valves for steam boilers shall have all nine valves set at 15 psig (100 kPa). A coefficient shall be established for each test as follows:

- See PDF for diagram

The average of the coefficients K D of the nine tests required shall be multiplied by 0.90, and this product shall be taken as the coefficient K of that design. The stamped capacity for all sizes and pressures shall not exceed the value determined from the following formulas:

For 45 deg seat,

(US. Customary Units)

W = 51.5 p DLP × 0.707K

(SI Units)

W = 5.25 p DLP × 0.707K

For flat seat,

(U.S. Customary Units)

W = 51.5 p DLPK

(SI Units)

W = 5.25 p DLPK

For nozzle,

(U.S. Customary Units)

W = 51.5APK

(SI Units)

W = 5.25APK

where

A = nozzle-throat area

D = seat diameter

K = coefficient of discharge for the design

L = lift

P = (1.10 × set pressure + 14.7) psia or (1.10 × set pressure + 0.101) MPa, for hot water applications or

= (5.0 psi + 15 psi set + 14.7) psia or (0.035 MPa + 0.100 MPa set + 0.101) MPa, for steam boilers

W = weight of steam/hr

Note

The maximum and minimum coefficient determined by the tests of a valve design shall not vary more than ± 5% from the average. If one or more tests are outside the acceptable limits, one valve of the Manufacturer's choice shall be replaced with another valve of the same size and pressure setting or by a modification of the original valve. Following this test a new average coefficient shall be calculated, excluding the replaced valve test. If one or more tests are now outside the acceptable limits, as determined by the new average coefficient, a valve of the Manufacturer's choice must be replaced by two valves of the same size and pressure as the rejected valve. A new average coefficient, including the replacement valves, shall be calculated. If any valve, excluding the two replaced valves, now falls outside the acceptable limits, the tests shall be considered unsatisfactory. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Slope Method. If a Manufacturer wishes to apply the Code Symbol to a design of pressure relief valves, four valves of each combination of pipe and orifice size shall be tested. These four valves shall be set at pressures that cover the approximate range of pressures for which the valve will be used, or that cover the range available at the certified test facility that shall conduct the tests. The capacities shall be based on these four tests as follows: Microsoft Windows NT 6.1.7601 Service Pack 1 (1) The slope (W/P) of the actual measured capacity versus the flow pressure for each test point shall be calculated and averaged: Microsoft Windows NT 6.1.7601 Service Pack 1 - See PDF for diagram Microsoft Windows NT 6.1.7601 Service Pack 1 All values derived from the testing must fall within ± 5% of the average value: Microsoft Windows NT 6.1.7601 Service Pack 1 minimum slope = 0.95 × average slope Microsoft Windows NT 6.1.7601 Service Pack 1 maximum slope = 1.05 × average slope Microsoft Windows NT 6.1.7601 Service Pack 1 If the values derived from the testing do not fall between the minimum and maximum slope values, the Authorized Observer shall require that additional valves be tested at the rate of two for each valve beyond the maximum and minimum values with a limit of four additional valves. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) The relieving capacity to be stamped on the valve shall not exceed 90% of the average slope times the absolute accumulation pressure: Microsoft Windows NT 6.1.7601 Service Pack 1 rated slope = 0.90 × average slope Microsoft Windows NT 6.1.7601 Service Pack 1 stamped capacity = rated slope × (1.10 × set pressure + 14.7) psia or (1.10 × set pressure + 101) kPa for hot water applications Microsoft Windows NT 6.1.7601 Service Pack 1 (c) Three-Valve Method. If a Manufacturer wishes to apply the Code Symbol to steam safety valves or safety relief valves of one or more sizes of a design set at one pressure, he shall submit three valves of each size of each design set at one pressure for testing and the stamped capacity of each size shall not exceed 90% of the average capacity of the three valves tested. Microsoft Windows NT 6.1.7601 Service Pack 1 The discharge capacity as determined by the test of each valve tested shall not vary by more than ± 5% of the average capacity of the three valves tested. If one of the three valve tests falls outside of the limits, it may be replaced by two valves and a new average calculated based on all four valves, excluding the replaced valve. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-600 GENERAL Microsoft Windows NT 6.1.7601 Service Pack 1 All instruments, fittings, and controls described in this Article shall be installed prior to operation. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-601 FOR STEAM HEATING BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 HG-602 STEAM GAGES Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each steam boiler shall have a steam gage or a compound steam gage connected to its steam space or to its water column or to its steam connection. The gage or piping to the gage shall contain a siphon or equivalent device that will develop and maintain a water seal that will prevent steam from entering the gage tube. The piping shall be so arranged that the gage cannot be shut off from the boiler except by a cock placed in the pipe at the gage and provided with a tee- or lever-handle arranged to be parallel to the pipe in which it is located when the cock is open. The gage connection boiler tapping, external siphon, or piping to the boiler shall not be less than NPS ¼ (DN 8). Where steel or wrought iron pipe or tubing is used, the boiler connection and external siphon shall be not less than NPS ½ (DN 15). Ferrous and nonferrous tubing having inside diameters at least equal to that of standard pipe sizes listed above may be substituted for pipe. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The scale on the dial of a steam boiler gage shall be graduated to not less than 30 psi (200 kPa) nor more than 60 psi (414 kPa). The travel of the pointer from 0 psi to 30 psi (0 kPa to 200 kPa) pressure shall be at least 3 in. (75 mm). Microsoft Windows NT 6.1.7601 Service Pack 1 HG-603 WATER GAGE GLASSES Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each steam boiler shall have one or more water gage glasses attached to the water column or boiler by means of valved fittings not less than NPS ½ (DN 15), with the lower fitting provided with a drain valve of a type having an unrestricted drain opening not less than ¼ in. (6 mm) in diameter to facilitate cleaning. Gage glass replacement shall be possible with the boiler under pressure. Water glass fittings may be attached directly to a boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 Boilers having an internal vertical height of less than 10 in. (250 mm) may be equipped with a water level indicator of the Glass Bull's-Eye type provided the indicator is of sufficient size to show the water at both normal operating and low-water cutoff levels. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The lowest visible part of the water gage glass shall be at least 1 in. (25 mm) above the lowest permissible water level recommended by the boiler Manufacturer. With the boiler operating at this lowest permissible water level, there shall be no danger of overheating any part of the boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 Each boiler shall be provided at the time of the manufacture with a permanent marker indicating the lowest permissible water level. The marker shall be stamped, etched, or cast in metal; or it shall be a metallic plate attached by rivets, screws, or welding; or it shall consist of material with documented tests showing its suitability as a permanent marking for the application. This marker shall be visible at all times. Where the boiler is shipped with a jacket, this marker may be located on the jacket. Microsoft Windows NT 6.1.7601 Service Pack 1 Transparent material other than glass may be used for the water gage provided that the material will remain transparent and has proved suitable for the pressure, temperature, and corrosive conditions expected in service. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) In electric boilers of the submerged electrode type, the water gage glass shall be so located to indicate the water levels both at startup and under maximum steam load conditions as established by the manufacturer. Microsoft Windows NT 6.1.7601 Service Pack 1 (d) In electric boilers of the resistance element type, the lowest visible part of the water gage shall be located at least 1 in. (25 mm) above the lowest permissible water level specified by the Manufacturer. Each electric boiler of this type shall also be equipped with an automatic low-water cutoff on each boiler pressure vessel so located as to automatically cut off the power supply to the heating elements before the surface of the water falls below the visible part of the glass. Microsoft Windows NT 6.1.7601 Service Pack 1 (e) Tubular water glasses on electric boilers having a normal water content not exceeding 100 gal (300 l) shall be equipped with a protective shield. Microsoft Windows NT 6.1.7601 Service Pack 1 (f) A water level indicator using an indirect sensing method may be used in lieu of an operating water gauge glass; however, a water gauge glass must be installed and operable but may be shut off by valving. The water level indicator must be attached to a water column or directly to the boiler by means of valved fittings not less than NPS ½ (DN 15). The device shall be provided with a drain valve of a type having an unrestricted drain opening not less than ¼ in. (6 mm) in diameter to facilitate cleaning. Service and replacement of internal parts and/or housing shall be possible with the boiler under pressure. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-604 WATER COLUMN AND WATER LEVEL CONTROL PIPES Microsoft Windows NT 6.1.7601 Service Pack 1 (a) The minimum size of ferrous or nonferrous pipes connecting a water column to a steam boiler shall be NPS 1 (DN 25). No outlet connections, except for damper regulator, feedwater regulator, steam gages, or apparatus that does not permit the escape of any steam or water except for manually operated blowdowns, shall be attached to a water column or the piping connecting a water column to a boiler (see HG-705 for introduction of feedwater into a boiler). If the water column, gage glass, low-water fuel cutoff, or other water level control device is connected to the boiler by pipe and fittings, no shutoff valves of any type shall be placed in such pipe, and a cross or equivalent fitting to which a drain valve and piping may be attached shall be placed in the water piping connection at every right angle turn to facilitate cleaning. The water column drain pipe and valve shall be not less than NPS ¾ (DN 20). Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The steam connections to the water column of a horizontal firetube wrought boiler shall be taken from the top of the shell or the upper part of the head, and the water connection shall be taken from a point not above the center line of the shell. For a cast iron boiler, the steam connection to the water column shall be taken from the top of an end section or the top of the steam header, and the water connection shall be made on an end section not less than 6 in. (150 mm) below the bottom connection to the water gage glass. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-605 PRESSURE CONTROL Microsoft Windows NT 6.1.7601 Service Pack 1 Each automatically fired steam boiler shall be protected from overpressure by two pressure-operated controls. Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each individual automatically fired steam boiler shall have a safety limit control that will cut off the fuel supply to prevent steam pressure from exceeding the 15 psi (100 kPa) maximum allowable working pressure of the boiler. Each control shall be constructed to prevent a pressure setting above 15 psi (100 kPa). Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Each individual steam boiler shall have a control that will cut off the fuel supply when the pressure reaches an operating limit, which shall be less than the maximum allowable pressure. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) Shutoff valves of any type shall not be placed in the steam pressure connection between the boiler and the controls described in (a) and (b) above. These controls shall be protected with a siphon or equivalent means of maintaining a water seal that will prevent steam from entering the control. The control connection boiler tapping, external siphon, or piping to the boiler 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 NPS ½ (DN 15). The minimum size of an external siphon shall be NPS ¼ (DN 8) or 3/8 in. (10 mm) O.D. nonferrous tubing. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-606 AUTOMATIC LOW-WATER FUEL
CUTOFF AND/OR WATER FEEDING DEVICE Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each automatically fired steam or vapor-system boiler shall have an automatic low-water fuel cutoff so located as to automatically cut off the fuel supply before the surface of the water falls below the lowest visible part of the water gage glass. If a water feeding device is installed, it shall be so constructed that the water inlet valve cannot feed water into the boiler through the float chamber and so located as to supply requisite feedwater. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Such a fuel cutoff or water feeding device may be attached directly to a boiler. A fuel cutoff or water feeding device may also be installed in the tapped openings available for attaching a water glass direct to a boiler, provided the connections are made to the boiler with nonferrous tees or Y's not less than NPS ½ (DN 15) between the boiler and the water glass so that the water glass is attached directly and as close as possible to the boiler; the run of the tee or Y shall take the water glass fittings, and the side outlet or branch of the tee or Y shall take the fuel cutoff or water feeding device. The ends of all nipples shall be reamed to full-size diameter. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) Fuel cutoffs and water feeding devices embodying a separate chamber shall have a vertical drain pipe and a blowoff valve not less than NPS ¾ (DN 20), located at the lowest point in the water equalizing pipe connections so that the chamber and the equalizing pipe can be flushed and the device tested. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-607 MODULAR STEAM HEATING BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each module of a modular steam heating boiler shall Microsoft Windows NT 6.1.7601 Service Pack 1 be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (1) steam gage, see HG-602 Microsoft Windows NT 6.1.7601 Service Pack 1 (2) water gage glass, see HG-603 Microsoft Windows NT 6.1.7601 Service Pack 1 (3) a pressure control that will cut off the fuel supply when the pressure reaches an operating limit, which shall be less than the maximum allowable pressure Microsoft Windows NT 6.1.7601 Service Pack 1 (4) low water cutoff, see HG-606 Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The assembled modular steam boiler shall also be equipped with a safety limit control that will cut off the fuel supply to prevent steam pressure from exceeding the 15 psi (100 kPa) maximum allowable working pressure of the boiler. The control shall be constructed to prevent pressure setting above 15 psi (100 kPa). Microsoft Windows NT 6.1.7601 Service Pack 1 HG-610 FOR HOT WATER HEATING OR HOT WATER SUPPLY BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 HG-611 PRESSURE OR ALTITUDE GAGES Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each hot water heating or hot water supply boiler shall have a pressure or altitude gage connected to it or to its flow connection in such a manner that it cannot be shut off from the boiler except by a cock with tee or lever handle, placed on the pipe near the gage. The handle of the cock shall be parallel to the pipe in which it is located when the cock is open. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Mechanical Gages (Analog). The scale on the dial of the pressure or altitude gage shall be graduated to not less than 1 ½ nor more than 3 ½ times the pressure at which the safety relief valve is set. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) Electronic gages used in lieu of mechanical gages shall meet the following requirements: Microsoft Windows NT 6.1.7601 Service Pack 1 (1) Gage shall be powered from the boiler power supply and it shall have a display that remains on at all times. The gage shall have a backup power supply. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) The full scale range of the transducer must be a minimum of 1 ½ times the pressure at which the safety relief valve is set. It shall be accurate to within ± 2% of full scale. Microsoft Windows NT 6.1.7601 Service Pack 1 (3) The transducer shall have a media compatibility of both liquids and gases and be temperature compensated. Microsoft Windows NT 6.1.7601 Service Pack 1 (4) The gage shall have an operating temperature range of 32 ° F to 250 ° F (O ° C to 120 ° C) unless otherwise required by the application. Microsoft Windows NT 6.1.7601 Service Pack 1 (d) Piping or tubing for pressure- or altitude-gage connections shall be of nonferrous metal when smaller than NPS 1 (DN 25). Microsoft Windows NT 6.1.7601 Service Pack 1 HG-612 THERMOMETERS/TEMPERATURE
SENSORS Microsoft Windows NT 6.1.7601 Service Pack 1 Each hot water heating or hot water supply boiler shall have a thermometer or temperature sensor with display so located and connected that it shall be easily readable. The thermometer or sensor shall be so located that it shall at all times indicate the temperature of the water in the boiler at or near the outlet. Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Thermometer shall have a minimum full scale range of 5O ° F to 250 ° F (10 ° C to 120 ° C). Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Electronic temperature sensor used in lieu of a thermometer shall meet the following requirements: Microsoft Windows NT 6.1.7601 Service Pack 1 (1) The sensor shall be powered from the boiler power supply and it shall have a display that remains on at all times. The gage shall have a backup power supply. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) The full scale of the sensor and display must be a minimum of 250 ° F (120 ° C). It shall be accurate to within: ± 1 deg. Microsoft Windows NT 6.1.7601 Service Pack 1 (3) The sensor shall have a minimum operating temperature range of 32 ° F to 300 ° F (0 ° C to 150 ° C). Microsoft Windows NT 6.1.7601 Service Pack 1 (4) The display shall have an ambient operating temperature range of 32 ° F to 120 ° F (0 ° C to 50 ° C) unless otherwise required by the application. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-613 TEMPERATURE CONTROL Microsoft Windows NT 6.1.7601 Service Pack 1 Each automatically fired hot water heating or hot water supply boiler shall be protected from over-temperature by two temperature-operated controls. Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each individual automatically fired hot water heating or hot water supply boiler shall have a high temperature limit control that will cut off the fuel supply to prevent water temperature from exceeding its marked maximum water temperature at the boiler outlet. This control shall be constructed to prevent a temperature setting above the maximum. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Each individual hot water heating or hot water supply boiler shall have a control that will cut off the fuel supply when the system water temperature reaches a preset operating temperature, which shall be less than the maximum water temperature. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-614 LOW-WATER FUEL CUTOFF Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each automatically fired hot water boiler with heat input greater than 400,000 Btu/hr (117 kW) shall have an automatic low-water fuel cutoff that has been designed for hot water service, and it shall be so located as to automatically cut off the fuel supply when the surface of the water falls to the level established in (b) below (see Fig. HG-703.2). Microsoft Windows NT 6.1.7601 Service Pack 1 (b) As there is no normal waterline to be maintained in a hot water boiler, any location of the low-water fuel cutoff above the lowest safe permissible water level established by the boiler manufacturer is satisfactory. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) A coil-type boiler or a watertube boiler with heat input greater than 400,000 Btu/hr (117 kW) requiring forced circulation to prevent overheating of the coils or tubes shall have a flow-sensing device installed in lieu of the low-water fuel cutoff required in (a) above to automatically cut off the fuel supply when the circulating flow is interrupted. Microsoft Windows NT 6.1.7601 Service Pack 1 (d) A means shall be provided for testing the operation of the external low-water fuel cutoff without resorting to draining the entire system. Such means shall not render the device inoperable except as described as follows. If the means temporarily isolates the device from the boiler during this testing, it shall automatically return to its normal position. The connection may be so arranged that the device cannot be shut off from the boiler except by a cock placed at the device and provided with a tee or lever-handle arranged to be parallel to the pipe in which it is located when the cock is open. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-615 MODULAR HOT WATER HEATING
BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Each module of a modular hot water heating boiler shall be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (1) pressure/altitude gage, see HG-611 Microsoft Windows NT 6.1.7601 Service Pack 1 (2) thermometer, see HG-612 Microsoft Windows NT 6.1.7601 Service Pack 1 (3) temperature control that will cut off the fuel supply when the temperature reaches an operating limit, which shall be less than the maximum allowable temperature Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The assembled modular hot water heating boiler shall also be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (1) a safety limit control that will cut off the fuel supply to prevent the water temperature from exceeding the maximum allowable temperature at the boiler outlet. The control shall be constructed to prevent a temperature setting above the maximum. This control shall be located within 3 ft. (1.0 m) of the fitting connecting the last module to the heating supply piping. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) low water fuel cutoff, see HG-614. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-620 FOR ALL BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 HG-621 INSTRUMENTS, FITTINGS, AND
CONTROLS MOUNTED INSIDE BOILER JACKETS Microsoft Windows NT 6.1.7601 Service Pack 1 Any or all instruments, fittings, and controls required by these rules may be installed inside of boiler jackets provided the water gage on a steam boiler is accessible without the use of tools and provided the water gage and pressure gage on a steam boiler or the thermometer and pressure gage on a water boiler are visible through an opening or openings at all times. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-630 ELECTRIC WIRING Microsoft Windows NT 6.1.7601 Service Pack 1 HG-631 ELECTRICAL CODE COMPLIANCE Microsoft Windows NT 6.1.7601 Service Pack 1 All field wiring for controls, heat generating apparatus, and other appurtenances necessary for the operation of the boiler or boilers should be installed in accordance with the provisions of the National Electric Code and/or should comply with the applicable local electrical codes. All boilers supplied with factory mounted and wired controls, heat generating apparatus, and other appurtenances necessary for the operation of the boilers should be installed in accordance with the provisions of the nationally recognized standards such as listed in footnote 2 [17]of HG-640. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-632 TYPE CIRCUITRY TO BE USED Microsoft Windows NT 6.1.7601 Service Pack 1 Whether field or factory wired, the control circuitry shall be positively grounded and shall operate at 150 V or less. One of the two following systems may be employed to provide the control circuit. Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Two-Wire Nominal 120 V System With Separate Equipment Ground Conductor Microsoft Windows NT 6.1.7601 Service Pack 1 (1) This system shall consist of the line, neutral, and equipment ground conductors. The control panel frame and associated control circuitry metallic enclosures shall be electrically continuous and be bonded to the equipment ground conductor. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) The equipment ground conductor and the neutral conductor shall be bonded together at their origin in the electrical system as required by the NEC. 1 - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 1 See Appendix H. Microsoft Windows NT 6.1.7601 Service Pack 1 (3) The line side of the control circuit shall be provided with a time delay fuse sized as small as practicable. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Two-Wire Nominal 120 V System Obtained By Using an Isolation Transformer Microsoft Windows NT 6.1.7601 Service Pack 1 (1) The two-wire control circuit shall be obtained from the secondary side of an isolation transformer. One wire from the secondary of this transformer shall be electrically continuous and shall be bonded to a convenient cold water pipe. All metallic enclosures of control components shall be securely bonded to this ground control circuit wire. The primary side of the isolation transformer will normally be a two-wire source with a potential of 230 V or 208 V or 440 V. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) Both sides of the two-wire primary circuit shall be fused. The hot leg on the load side of the isolation transformer shall be fused as small as practicable and in no case fused above the rating of the isolation transformer. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-633 LIMIT CONTROLS Microsoft Windows NT 6.1.7601 Service Pack 1 Limit controls shall be wired on the hot or line side of the control circuit. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-634 SHUTDOWN SWITCHES AND CIRCUIT BREAKERS Microsoft Windows NT 6.1.7601 Service Pack 1 A manually operated remote heating plant shutdown switch or circuit breaker should be located just outside the boiler room door and marked for easy identification. Consideration should also be given to the type and location of the switch to safeguard against tampering. If the boiler room door is on the building exterior the switch should be located just inside the door. If there is more than one door to the boiler room, there should be a switch located at each door. Microsoft Windows NT 6.1.7601 Service Pack 1 (a) For atmospheric-gas burners, and oil burners where a fan is on a common shaft with the oil pump, the complete burner and controls should be shut off. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) For power burners with detached auxiliaries, only the fuel input supply to the firebox need be shut off. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-640 CONTROLS AND HEAT GENERATING APPARATUS Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Oil and gas-fired and electrically heated boilers should be equipped with suitable primary (flame safeguard) safety controls, safety limit switches, and burners or electric elements as required by a nationally recognized standard. 2 - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 2 Examples of these nationally recognized standards are: Microsoft Windows NT 6.1.7601 Service Pack 1 American National Standard/CSA Standard Z21.13lCSA 4.9 for Gas-Fired Low Pressure Steam and Hot Water Boilers. Microsoft Windows NT 6.1.7601 Service Pack 1 American National Standard/CSA Standard Z21.171CSA 2.7 for Domestic Gas Conversion Burners. Microsoft Windows NT 6.1.7601 Service Pack 1 Underwriters Laboratories, Inc., UL 296, Standards for Safety, Oil Burners. Microsoft Windows NT 6.1.7601 Service Pack 1 Underwriters Laboratories, Inc., UL 726, Standards for Safety, Oil Fired Boiler Assemblies. Microsoft Windows NT 6.1.7601 Service Pack 1 Underwriters Laboratories, Inc., UL 795, Standards for Safety, Commercial-Industrial Gas-Heating Equipment. Microsoft Windows NT 6.1.7601 Service Pack 1 Underwriters Laboratories, Inc., UL 834, Electric Heating, Water Supply and Power Boilers. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The symbol of the certifying organization 3 that has investigated such equipment as having complied with a nationally recognized standard shall be affixed to the equipment and shall be considered as evidence that the unit was manufactured in accordance with that standard. - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 3 A certifying organization is one that provides uniform testing, examination, and listing procedures under established, nationally recognized standards and that is acceptable to the authorities having jurisdiction. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-700 INSTALLATION REQUIREMENTS, ALL BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701 MOUNTING SAFETY AND SAFETY RELIEF VALVES Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.1 Permissible Mounting. Safety valves and safety relief valves shall be located in the top or side 1 of the boiler. They shall be connected directly to a tapped or flanged opening in the boiler, to a fitting connected to the boiler by a short nipple, to a Y-base, or to a valveless header connecting steam or water outlets on the same boiler. Coil or header type boilers shall have the safety valve or safety relief valve located on the steam or hot water outlet end. Safety valves and safety relief valves shall be installed with their spindles vertical. The opening or connection between the boiler and any safety valve or safety relief valve shall have at least the area of the valve inlet. - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 1 The top or side of the boiler shall mean the highest practicable part of the boiler proper but in no case shall the safety valve be located below the normal operating level and in no case shall the safety relief valve be located below the lowest permissible water level. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.2 Requirements for Common Connections for Two or More Valves Microsoft Windows NT 6.1.7601 Service Pack 1 (a) When a boiler is fitted with two or more safety valves on one connection, this connection shall have a cross-sectional area not less than the combined areas of inlet connections of all the safety valves with which it connects. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) When a Y-base is used, the inlet area shall be not less than the combined outlet areas. When the size of the boiler requires a safety valve or safety relief valve larger than 4 ½ in. (115 mm) in diameter, two or more valves having the required combined capacity shall be used. When two or more valves are used on a boiler, they may be single, directly attached, or mounted on a Y-base. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.3 Threaded Connections. A threaded connection may be used for attaching a valve. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.4 Prohibited Mountings. Safety and safety relief valves shall not be connected to an internal pipe in the boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.5 Use of Shutoff Valves Prohibited. No shutoff of any description shall be placed between the safety or safety relief valve and the boiler, or on discharge pipes between such valves and the atmosphere. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.6 Safety and Safety Relief Valve Discharge Piping Microsoft Windows NT 6.1.7601 Service Pack 1 (a) A discharge pipe shall be used. Its internal cross-sectional area shall be not less than the full area of the valve outlet or of the total of the valve outlets discharging thereinto and shall be as short and straight as possible and so arranged as to avoid undue stress on the valve or valves. A union may be installed in the discharge piping close to the valve outlet. When an elbow is placed on a safety or safety relief valve discharge pipe, it shall be located close to the valve outlet downstream of the union. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The discharge from safety or safety relief valves shall be so arranged that there will be no danger of scalding attendants. The safety or safety relief valve discharge shall be piped away from the boiler to the point of discharge, and there shall be provisions made for properly draining the piping. The size and arrangement of discharge piping shall be independent of other discharge piping and shall be such that any pressure that may exist or develop will not reduce the relieving capacity of the relieving devices below that required to protect the boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-701.7 Temperature and Pressure Safety Relief Valves. Hot water heating or supply boilers limited to a water temperature of 210 ° F (99 ° C) may have one or more officially rated temperature and pressure safety relief valves installed. The requirements of HG-701.1 through HG-701.6 shall be met, except as follows: Microsoft Windows NT 6.1.7601 Service Pack 1 (a) A Y-type fitting shall not be used. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) If additional valves are used they shall be temperature and pressure safety relief valves. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) When the temperature and pressure safety relief valve is mounted directly on the boiler with no more than 4 in. (100 mm) maximum interconnecting piping, the valve may be installed in the horizontal position with the outlet pointed down. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-703 PIPING 2 - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 2 Guidance for the design of piping systems may be found in ASME B31.9, Building Services Piping. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-703.1 Provisions for Expansion and Contraction. Provisions shall be made for the expansion and contraction of steam and hot water mains connected to boilers by providing substantial anchorage at suitable points and by providing swing joints when boilers are installed in batteries, so there will be no undue strain transmitted to the boilers. See Figs. HG-703.1(a), HG-703.1(b), and HG-703.2 for typical schematic arrangements of piping incorporating strain absorbing joints for steam and hot water heating boilers. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-703.2 Return Pipe Connections Microsoft Windows NT 6.1.7601 Service Pack 1 (a) The return pipe connections of each boiler supplying a gravity return steam heating system shall be so arranged as to form a loop substantially as shown in Fig. HG-703.l(b) so that the water in each boiler cannot be forced out below the safe water level. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) For hand-fired boilers with a normal grate line, the recommended pipe sizes detailed as "A" in Fig. HG-703.1 are NPS 1 ½ (DN 40) for 4 ft 2 (0.37 m 2 ) or less firebox area at the normal grate line, NPS 2 ½ (DN 65) for areas more than 4 ft 2 (0.37 m 2 ) up to 14.9 ft 2 (1.4 m 2 ), and NPS 4 (DN 100) for 15 ft 2 (1.4 m 2 ) or more. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) For automatically fired boilers that do not have a normal grate line, the recommended pipe sizes detailed as "A" in Fig. HG-703.1 are NPS 1 ½ (DN 40) for boilers with minimum safety valve relieving capacity 250 lb/hr (113 kg/hr) or less, NPS 2 ½ (DN 65) for boilers with minimum safety valve relieving capacity from 251 lb/hr (114 kg/hr) to 2,000 lb/hr (900 kg/hr), inclusive, and NPS 4 (DN 100) for boilers with more than 2,000 lb/hr (900 kg/hr) minimum safety valve relieving capacity. Microsoft Windows NT 6.1.7601 Service Pack 1 (d) Provision shall be made for cleaning the interior of the return piping at or close to the boiler. Washout openings may be used for return pipe connections and the washout plug placed in a tee or a cross so that the plug is directly opposite and as close as possible to the opening in the boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 - See PDF for diagram - See PDF for diagram - See PDF for diagram Microsoft Windows NT 6.1.7601 Service Pack 1 HG-705 FEEDWATER AND MAKEUP WATER
CONNECTIONS Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Steam Boilers. Feedwater or water treatment shall be introduced into a boiler through the return piping system. Alternatively, feedwater or water treatment may be introduced through an independent connection. The water flow from the independent connection shall not discharge directly against parts of the boiler exposed to direct radiant heat from the fire. Feedwater or water treatment shall not be introduced through openings or connections provided for inspection or cleaning, safety valve, water column, water gage glass, or pressure gage. The feedwater pipe shall be provided with a check valve or a backflow preventer containing a check valve 3 near the boiler and a stop valve or cock between the check valve and the boiler or between the check valve and the return pipe system. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Hot Water Boilers. Makeup water may be introduced into a boiler through the piping system or through an independent connection. The water flow from the independent connection shall not discharge directly against parts of the boiler exposed to direct radiant heat from the fire. Makeup water shall not be introduced through openings or connections provided exclusively for inspection or cleaning, safety relief valve, pressure gage, or temperature gage. The makeup water pipe shall be provided with a check valve or a backflow preventer containing a check valve 3 near the boiler and a stop valve or cock between the check valve and the boiler or between the check valve and the piping system. - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 3 Plumbing codes may require the installation of a reduced pressure principle backflow preventer on a boiler when the makeup water source is from a potable water supply. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-707 OIL HEATERS Microsoft Windows NT 6.1.7601 Service Pack 1 (a) A heater for oil or other liquid harmful to boiler operation shall not be installed directly in the steam or water space within a boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Where an external type heater for such service is used, means shall be provided to prevent the introduction into the boiler of oil or other liquid harmful to boiler operation. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-708 STORAGE TANKS FOR HOT WATER
SUPPLY SYSTEMS Microsoft Windows NT 6.1.7601 Service Pack 1 If a system is to utilize a storage tank that exceeds the capacity exception of HLW-101.2 (c), the tank shall be constructed in accordance with the rules of Part HLW; Section VIII, Division 1; or Section X. For tanks constructed to Section X, the maximum allowable temperature marked on the tank shall equal or exceed the maximum water temperature marked on the boiler. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-709 PROVISIONS FOR THERMAL
EXPANSION IN HOT WATER SYSTEMS Microsoft Windows NT 6.1.7601 Service Pack 1 All hot water heating systems incorporating hot water tanks or fluid relief columns shall be so installed as to prevent freezing under normal operating conditions. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-709.1 Heating Systems With Open Expansion Tank. An indoor overflow from the upper portion of the expansion tank shall be provided in addition to an open vent, the indoor overflow to be carried within the building to a suitable plumbing fixture or the basement. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-709.2 Closed Heating Systems. An expansion tank shall be installed that will be consistent with the volume and capacity of the system. If the system is designed for a working pressure of 30 psi (200 kPa) or less, the tank shall be suitably designed for a minimum hydrostatic test pressure of 75 psi (520 kPa). Expansion tanks for systems designed to operate above 30 psi (200 kPa) shall be constructed in accordance with Section VIII, Division 1. Alternatively, a tank built to Section X requirements may be used if the pressure and temperature ratings of the tank are equal to or greater than the pressure and temperature ratings of the system. Provisions shall be made for draining the tank without emptying the system, except for prepressurized tanks. Microsoft Windows NT 6.1.7601 Service Pack 1 The minimum capacity of the closed type expansion tank may be determined from Table HG-709.2 or from the following formula where the necessary information is available: Microsoft Windows NT 6.1.7601 Service Pack 1 (U.S. Customary Units) Microsoft Windows NT 6.1.7601 Service Pack 1 V t = [(0.00041T - 0.0466)V s ]/[(P a /P f ) - (P a /P o )] Microsoft Windows NT 6.1.7601 Service Pack 1 (SI Units) Microsoft Windows NT 6.1.7601 Service Pack 1 V t = [(0.18155T – 8.236)V s ]/[(P a /P f ) - (P a /P o )] Microsoft Windows NT 6.1.7601 Service Pack 1 where Microsoft Windows NT 6.1.7601 Service Pack 1 P a = atmospheric pressure Microsoft Windows NT 6.1.7601 Service Pack 1 P f = fill pressure Microsoft Windows NT 6.1.7601 Service Pack 1 P o = maximum operating pressure Microsoft Windows NT 6.1.7601 Service Pack 1 T = average operating temperature Microsoft Windows NT 6.1.7601 Service Pack 1 V s = volume of system, not including tanks Microsoft Windows NT 6.1.7601 Service Pack 1 V t = minimum volume of tanks - See PDF for table - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 HG-709.3 Hot Water Supply Systems. If a system is equipped with a check valve or pressure reducing valve in the cold water inlet line, consideration should be given to the installation of an airtight expansion tank or other suitable air cushion. Otherwise, due to the thermal expansion of the water, the safety relief valve may lift periodically. If an expansion tank is provided, it shall be constructed in accordance with Section VIII, Division 1 or Section X. Except for prepressurized tanks, which should be installed on the cold water side, provisions shall be made for draining the tank without emptying the system. See Fig. HLW-809.1 for a typical acceptable installation. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-710 STOP VALVES Microsoft Windows NT 6.1.7601 Service Pack 1 HG-710.1 For Single Steam Boilers. When a stop valve is used in the supply pipe connection of a single steam boiler, there shall be one used in the return pipe connection. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-710.2 For Single Hot Water Heating Boilers Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Stop valves shall be located at an accessible point in the supply and return pipe connections as near the boiler nozzle as is convenient and practicable, of a single hot water heating boiler installation to permit draining the boiler without emptying the system. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) When the boiler is located above the system and can be drained without draining the system, stop valves may be eliminated. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-710.3 For Multiple Boiler Installations. A stop valve shall be used in each supply and return pipe connection of two or more boilers connected to a common system. See Figs. HG-703.1 and HG-703.2. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-710.4 Type of Stop Valve(s) Microsoft Windows NT 6.1.7601 Service Pack 1 (a) All valves or cocks shall conform with the applicable portions of HF-203 and may be ferrous or nonferrous. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) The minimum pressure rating of all valves or cocks shall be at least equal to the pressure stamped upon the boiler, and the temperature rating of such valves or cocks, including all internal components, shall be not less than 250 ° F (120 ° C). Microsoft Windows NT 6.1.7601 Service Pack 1 (c) Valves or cocks shall be flanged, threaded, or have ends suitable for welding or brazing. Microsoft Windows NT 6.1.7601 Service Pack 1 (d) All valves or cocks with stems or spindles shall have adjustable pressure type packing glands and, in addition, all plug type cocks shall be equipped with a guard or gland. The plug or other operating mechanism shall be distinctly marked in line with the passage to indicate whether it is opened or closed. Microsoft Windows NT 6.1.7601 Service Pack 1 (e) All valves or cocks shall have tight closure when under boiler hydrostatic test pressure. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-710.5 Identification of Stop Valves by Tags. When stop valves are used, they shall be properly designated substantially as follows by tags of metal or other durable material fastened to them: Microsoft Windows NT 6.1.7601 Service Pack 1 Supply Valve - Number ( ) Microsoft Windows NT 6.1.7601 Service Pack 1 Do Not Close Without Also Closing Return Valve -
Number ( ) Microsoft Windows NT 6.1.7601 Service Pack 1 Return Valve - Number ( ) Microsoft Windows NT 6.1.7601 Service Pack 1 Do Not Close Without Also Closing Supply Valve -
Number ( ) Microsoft Windows NT 6.1.7601 Service Pack 1 HG-715 BOTTOM BLOWOFF AND DRAIN VALVES Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Bottom Blowoff Valve. Each steam boiler shall have a bottom blowoff connection fitted with a valve or cock connected to the lowest water space practicable with a minimum size as shown in Table HG-715. The discharge piping shall be full size to the point of discharge. - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Boilers having a capacity of 25 gal (95 l) or less are exempt from the above requirements, except that they must have an NPS ¾ (DN 20) minimum drain valve. Microsoft Windows NT 6.1.7601 Service Pack 1 (c) Drain Valve. Each steam or hot water boiler shall have one or more drain connections, fitted with valves or cocks. These shall be connected at the lowest practicable point on the boiler, or to the lowest point on piping connected to the boiler, at the lowest practicable point on the boiler. The minimum size of the drain piping, valves, and cocks shall be NPS ¾ (DN 20). The discharge piping shall be full size to the point of discharge. When the blowoff connection is located at the lowest water containing space, a separate drain connection is not required. Microsoft Windows NT 6.1.7601 Service Pack 1 (d) Minimum Pressure Rating. The minimum pressure rating of valves and cocks used for blowoff or drain purposes shall be at least equal to the pressure stamped on the boiler but in no case less than 30 psi (200 kPa). The temperature rating of such valves and cocks shall not be less than 250 ° F (120 ° C). Microsoft Windows NT 6.1.7601 Service Pack 1 HG-716 MODULAR BOILERS Microsoft Windows NT 6.1.7601 Service Pack 1 (a) Individual Modules Microsoft Windows NT 6.1.7601 Service Pack 1 (1) The individual modules shall comply with all the requirements of Part HG, except as specified in HG-607, HG-615, and this paragraph. The individual modules shall be limited to a maximum input of 400,000 Btuh (gas), 3 gal/hr (1 l/hr) (oil), or 115 kW (electricity). Microsoft Windows NT 6.1.7601 Service Pack 1 (2) Each module of a steam heating boiler shall be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (a) safety valve, see HG-701 Microsoft Windows NT 6.1.7601 Service Pack 1 (b) blowoff valve, see HG-715 (a) Microsoft Windows NT 6.1.7601 Service Pack 1 (c) drain valve, see HG-715 (c) Microsoft Windows NT 6.1.7601 Service Pack 1 (3) Each module of a modular hot water heating boiler shall be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (a) safety relief valve, see HG-701 Microsoft Windows NT 6.1.7601 Service Pack 1 (b) drain valve, see HG-715 (c) Microsoft Windows NT 6.1.7601 Service Pack 1 (b) Assembled Modular Boilers Microsoft Windows NT 6.1.7601 Service Pack 1 (1) The individual modules shall be manifolded together at the job-site without any intervening valves. The header or manifold piping is field piping and is exempt from Article 2, Part HG, HF, HB, or HC. Microsoft Windows NT 6.1.7601 Service Pack 1 (2) The assembled modular steam heating boiler shall also be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (a) feedwater connection, see HG-705 (a) Microsoft Windows NT 6.1.7601 Service Pack 1 (b) return pipe connection, see HG-703.2 Microsoft Windows NT 6.1.7601 Service Pack 1 (3) The assembled modular hot water heating boiler shall also be equipped with Microsoft Windows NT 6.1.7601 Service Pack 1 (a) makeup water connection, see HG-705 (b) Microsoft Windows NT 6.1.7601 Service Pack 1 (b) provision for thermal expansion, see HG-709 Microsoft Windows NT 6.1.7601 Service Pack 1 (c) stop valves, see HG-710.2 Microsoft Windows NT 6.1.7601 Service Pack 1 HG-720 SETTING Microsoft Windows NT 6.1.7601 Service Pack 1 Boilers of wrought materials of the wet-bottom type having an external width of over 36 in. (900 mm) shall have not less than 12 in. (300 mm) between the bottom of the boiler and the floorline, with access for inspection. When the width is 36 in. (900 mm) or less, the distance between the bottom of the boiler and the floorline shall be not less than 6 in. (150 mm), except that, when any part of the wet bottom is not farther from an outer edge than 12 in. (300 mm), this distance shall be not less than 4 in. (100 mm). Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725 METHODS OF SUPPORT Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.1 Loadings Microsoft Windows NT 6.1.7601 Service Pack 1 (a) The design and attachment of lugs, hangers, saddles, and other supports shall take into account the stresses due to hydrostatic head in determining the minimum thicknesses required. Additional stresses imposed by effects other than working pressure or static head, which increase the average stress by more than 10% of the allowable working stress, shall also be taken into account. These effects include the weight of the component and its contents, and the method of support. Microsoft Windows NT 6.1.7601 Service Pack 1 (b) In applying the requirements of (a) above, localized stresses due to concentrated support loads, temperature changes, and restraint against dilation of the boiler due to pressure shall be provided for. Lugs, hangers, brackets, saddles, and pads shall conform satisfactorily to the shape of the shell or surface to which they are attached or are in contact. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.2 Boilers Over 72 in. (1 800 mm) in Diameter. A horizontal-return tubular boiler over 72 in. (1 800 mm) in diameter shall be supported from steel hangers by the outside-suspension type of setting, independent of the furnace wall. The hangers shall be so designed that the load is properly distributed. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.3 Boilers Over 54 in. (1 400 mm) up to 72 in. (1 800 mm) in Diameter. A horizontal-return tubular boiler over 54 in. (1 400 mm) and up to and including 72 in. (1 800 mm) in diameter shall be supported by the outside-suspension type of setting, or at four points by not less than eight steel brackets set in pairs, the brackets of each pair to be spaced not over 2 in. (50 mm) apart and the load to be equalized between them. [See Fig. HG-725(a).] Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.4 Boilers up to 54 in. (1 400 mm) in Diameter. A horizontal-return tubular boiler up to and including 54 in. (1 400 mm) in diameter shall be supported by the outside-suspension type of setting, or by not less than two steel brackets on each side. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.5 Supporting Members. If the boiler is supported by structural steel work, the steel supporting members shall be so located or insulated that the heat from the furnace can not impair their strength. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.6 Lugs or Hangers. Lugs, hangers, or brackets made of materials in accordance with the Code requirements may be attached by fusion welding provided they are attached by fillet welds along the entire periphery or contact edges. Figure HG-725(b) illustrates an acceptable design of hanger bracket with the additional requirement that the center pin be located at the vertical center line over the center of the welded contact surface. The bracket plates shall be spaced at least 2 ½ in. (64 mm) apart, but this dimension shall be increased if necessary to permit access for the welding operation. The stresses computed by dividing the total load on each lug, hanger, or bracket, by the minimum cross-sectional area of the weld shall not exceed 2800 psi (19 MPa). Where it is impractical to attach lugs, hangers, or brackets by welding, studs with not less than 10 threads/in. (approx. 4 threads/cm) may be used. In computing the shearing stresses, the root area at the bottom of the thread shall be used. The shearing and crushing stresses on studs shall not exceed 8% of the strength given in Table HF-300.1 for bolting materials. Microsoft Windows NT 6.1.7601 Service Pack 1 HG-725.7 Settings. Boilers of wrought materials of the wet-bottom type having an external width of over 36 in. (900 mm) shall be supported so as to have a minimum clearance of 12 in. (300 mm), between the bottom of the boiler and the floor, to facilitate inspection. When the width is 36 in. (900 mm) or less, the clearance between the bottom of the boiler and the floorline shall be not less than 6 in. (150 mm), except when any part of the wet bottom is not farther from the outer edge than 12 in. (300 mm). This clearance shall be not less than 4 in. (100 mm). Boiler insulation, saddles, or other supports shall be arranged so that inspection openings are readily accessible. Microsoft Windows NT 6.1.7601 Service Pack 1 - See PDF for diagram Microsoft Windows NT 6.1.7601 Service Pack 1