§ 14-12-52. Power boilers—Existing installations.

A.

Application of section. This section shall apply to existing power boiler installations.

B.

Maximum allowable working pressure for standard boilers. The maximum allowable working pressure for standard boilers shall be determined in accordance with the applicable provision of the edition of the A.S.M.E. Code under which they were constructed and stamped.

C.

Maximum allowable working pressure for nonstandard boilers. The maximum allowable working pressure on the shell of a nonstandard boiler or drum shall be determined by the strength of the weakest section of the structure computed from the thickness of the plate, the tensile strength of the plate, the efficiency of the longitudinal joint or tube ligaments, the inside diameter of the outside course and the factor of safety allowable by these rules.

TS × t × E	=	Maximum allowable working pressure in lb. per sq. in. gauge
R × FS

 

R × FS

Where

  TS = Ultimate tensile strength of shell plates, lb. per sq. in.

  t = Minimum thickness of shell plate, in weakest course, in inch.

  E = Efficiency of longitudinal joint.

  For riveted construction, E shall be determined by rules given in paragraph P-181 of A.S.M.E. Boiler Construction Code for Power Boilers. For fusion welded construction, E shall be determined by rules in paragraph P-102 of A.S.M.E. Boiler Construction Code for Power Boilers.

  For tube ligaments, E shall be determined by rules in paragraphs P 192 and P 193 of A.S.M.E. Boiler Construction Code for Power Boilers. For seamless construction, E shall be considered 100 percent.

  R = One-half the inside diameter of the weakest course of shell or drum in inches.

  FS = Factor of safety permitted.

1.

Tensile strength. When the tensile strength of steel or wrought iron shell plates is not known, it shall be taken as 55,000 pounds per square inch for steel and 45,000 pounds per square inch for wrought iron.

2.

Crushing strength of mild steel. The resistance to crushing of mild steel shall be taken at 95,000 pounds per square inch of cross sectional area.

3.

Strength of rivets in shear. When computing the ultimate strength of rivets in shear, the following values in pounds per square inch of the cross sectional area of the rivet shank shall be used:

Iron rivets in single shear	38,000
Iron rivets in double shear	76,000
Steel rivets in single shear	44,000
Steel rivets in double shear	88,000

 

When the diameter of the rivet holes in the longitudinal joints of a boiler is not known, the diameter and cross sectional area of rivets, after driving may be selected from the following table or ascertained by cutting out one rivet in the body of the joint:

_____

Sizes of Rivets Based on Plate Thickness

Thickness of plate	¼″	9/32 ″	5/16 ″	11/32 ″	3/8 ″	13/32 ″
Diameter of rivet after driving	11/16 ″	11/16 ″	¾″	¾″	13/16 ″	13/16 ″
Thickness of plate	7/16 ″	15/32 ″	½″	9/16 ″	5/8 ″
Diameter of rivet after driving	15/16 ″	15/16 ″	15/16 ″	1 1/16 ″	1 1/16 ″

 

4.

Factors of safety. The following factors of safety shall be increased by the inspector if the condition and safety of the boilers demand it.

a.

The lowest factor of safety permissible on existing installations shall be 4.5 excepting for horizontal return tubular boilers having continuous lap seams more than 12 feet in length where the factor of safety shall be eight, and when this latter type of boiler is removed from its existing setting, it shall not be reinstalled for pressures in excess of 15 pounds per square inch gauge.

b.

Reinstated or secondhand boilers shall have a minimum factor of safety of six when the longitudinal seams are of lap riveted construction and a minimum factor of safety of five when the longitudinal seams are of butt and double strap construction.

5.

Age limit of fire tube boilers. The age limit of a horizontal return tubular, flue or cylindrical boiler having a longitudinal lap joint and operating at a pressure in excess of 50 pounds per square inch gauge shall be 30 years. A reasonable time for replacement shall be given at the discretion of the director not to exceed one year.

6.

Welded boilers. Boilers having either longitudinal or circumferential seams of fusion welded construction shall have been constructed and stamped in accordance with the rules and regulations of the A.S.M.E. Boiler Construction Code or shall have the standard stamping of another state that has adopted a standard of construction equivalent to the standards of the A.S.M.E. Boiler Construction Code.

7.

Pressure on old boilers. In no case shall maximum working pressure of an old boiler be increased to a greater pressure than would be allowed for a new boiler of same construction.

8.

Cast iron headers and mud drums. The maximum allowable working pressure on a water tube boiler, the tubes of which are secured to cast iron or malleable iron headers or which have cast iron mud drums, shall not exceed 160 pounds per square inch gauge.

9.

Pressure on cast iron boilers. The maximum allowable working pressure for any cast iron boiler, except hot water boilers, shall be 15 pounds per square inch gauge.

D.

Safety valves. The use of weighted-lever safety valves shall be prohibited and these valves shall be replaced by direct spring-loaded pop type valves that conform to the requirements of the A.S.M.E. Boiler Construction Code for Power Boilers.

Safety valves having either the seat or disc of cast iron shall not be used.

Each boiler shall have at least one safety valve and if it has more than 500 square feet of water heating surface, it shall have two or more safety valves.

The valve or valves shall be connected to the boiler, independent of any other steam connection and attached as close as possible to the boiler without unnecessary intervening pipe or fittings. Where alteration is required to conform to this requirement, owners or users shall be allowed one year in which to complete the work.

No valve of any description shall be placed between the safety valve and the boiler nor on the escape pipe (if used) between the safety valve and the atmosphere. When an escape pipe is used, it shall be full size and fitted with an open drain to prevent water lodging in the upper part of the safety valve or escape pipe. When an elbow is placed on a safety valve escape pipe, it shall be located close to the safety valve outlet of the escape pipe, shall be securely anchored and supported. All safety valve discharges shall be so located or piped as to be carried clear from walkways or platforms used to control the main stop valves or boilers or steam headers.

The safety valve capacity of each boiler shall be such that the safety valve or valves will discharge all the steam that can be generated in the boiler without allowing the pressure to rise more than six percent above the highest pressure to which any valve is set and in no case to more than six percent above the maximum allowable working pressure.

One or more safety valves on every boiler shall be set at or below the maximum allowable working pressure. The remaining valves may be set within a range of three percent above the maximum allowable working pressure, but the range of setting of all of the safety valves on a boiler shall not exceed ten percent of the highest pressure to which any valve is set.

When two or more boilers operating at different pressures and safety valve settings are interconnected, the lower pressure boilers or interconnected piping shall be equipped with safety valves of sufficient capacity to prevent over pressure considering the generating capacity of all boilers.

In those cases where the boiler is supplied with feed water directly from pressure mains without the use of feeding apparatus (not to include return traps), no safety valve shall be set at a pressure greater than 94 percent of the lowest pressure obtained in the supply main feeding the boiler.

The relieving capacity of the safety valves on any boiler may be checked by one of the three following methods and, if found to be insufficient, additional valves shall be provided:

1.

By making the accumulation test, which consist of shutting off all other steam-discharge outlets from the boiler and forcing the fires to the maximum. The safety valve capacity shall be sufficient to prevent a pressure in excess of six percent above the maximum allowable working pressure;

2.

By measuring the maximum amount of fuel that can be burned and computing the corresponding evaporative capacity (steam generating capacity) upon the basis of the heating valve of this fuel. These computations shall be made as outlined in the appendix of the A.S.M.E. Boiler Construction Code for Power Boilers;

3.

By determining the maximum evaporative capacity by measuring the feed water.

When either of the methods outlined in subsection (D)(2) or (3) of this section is employed, the sum of the safety valve capacities shall be equal to or greater than the maximum evaporative capacity (maximum steam generating capacity) of the boiler.

E.

Boiler feeding and feed piping. All boilers shall have a feed supply which will permit the boilers being fed at any time while under pressure.

A boiler having more than 500 square feet of water heating surface shall have at least two means of feeding, one of which shall be an approved feed pump, injector or inspirator. Where a source of feed directly from pressure mains is available at sufficient pressure to feed the boiler against a pressure six percent greater than the release pressure of the safety valve with the highest release setting, this may be considered one of the means.

The feed water shall be introduced into the boiler in such manner that it will not be discharged close to riveted joints of shell or furnace sheets or directly against surfaces exposed to gases at high temperature or direct radiation from the fire.

The feed piping to the boiler shall be provided with a check valve near the boiler and a valve or cock between the check valve and the boiler. When two or more boilers are fed from a common source, there shall also be a valve on the branch to each boiler between the check valve and source of supply. Whenever a globe valve is used on feed piping, the inlet shall be under the disc of the valve.

In all cases where returns are fed back to the boiler by gravity, there shall be a check valve and stop valve on each return line, the stop valve to be placed between the boiler and the check valve and both shall be located as close to the boiler as is practicable.

Where deaerating heaters are not employed, it is recommended that the temperature of the feed water be not less than 120 degrees Fahrenheit to avoid the possibility of setting up localized stress. Where deaerating heaters are employed, it is recommended that the minimum feed water temperature be not less than 215 degrees Fahrenheit so that dissolved gases may be thoroughly released.

F.

Fusible plugs. Fire-actuated fusible plugs if used shall con form to the requirements of the A.S.M.E. Boiler Construction Code for Power Boilers.

G.

Water columns, gauge glasses and gauge cocks. No outlet connections (except for damper regulator, low water fuel cutout, drains, steam gauges or such apparatus that does not permit the escape of an appreciable amount of steam or water therefrom) shall be placed on the piping that connects the water column to the boiler. The water column shall be provided with a valved drain of at least three-fourths-inch pipe size, the drain to be piped to a safe location.

Each boiler shall have three or more gauge cocks, located within the range of the visible length of the water glass, except when such boiler has two water glasses with independent connections to the boiler, located on the same horizontal line and not less than two feet apart.

For all installations where the water gauge glass or glasses are more than 30 feet from the boiler operating floor, it is recommended that water level indicating or recording gauges be installed at eye height from the operating floor.

H.

Steam gauges. Each steam boiler shall have a steam gauge, with dial range not less than 1½ times the maximum allowable working pressure, connected to the steam space or to the steam connection to the water column. The steam gauge shall be connected to a siphon or equivalent device of sufficient capacity to keep the gauge tube filled with water and so arranged that the gauge cannot be shut off from the boiler except by a cock placed near the gauge 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.

When a steam gauge connection longer than eight feet becomes necessary, a shut-off valve may be used near the boiler provided the valve is of the outside screw and yoke type and is locked open. The line shall be ample size, with provision for free blowing.

Each boiler shall be provided with a one-quarter-inch nipple and globe valve connected to the steam space for the exclusive purpose of attaching a test gauge when the boiler is in service so that the accuracy of the boiler steam gauge may be ascertained.

I.

Stop valves. Each steam outlet from a boiler (except safety valve connections) shall be fitted with a stop valve located as close as practicable to the boiler.

When a stop valve is so located that water can accumulate, ample drains shall be provided. The drainage shall be piped to a safe location and shall not be discharged on the top of the boiler or its setting.

When boilers provided with manholes are connected to a common steam main, the steam connection from each boiler shall be fitted with two stop valves having an ample free flow drain between them. The discharge of this drain shall be visible to the operator while manipulating the valves and shall be piped clear of the boiler setting. The stop valves shall consist preferably of one automatic nonreturn valve (set next to the boiler) and a second valve to the outside-screw and yoke type.

J.

Blow-off piping. The construction of the setting around each blow-off pipe shall permit free expansion and contraction. Careful attention shall be given to the problem of sealing these setting openings without restricting the movement of the blow-off piping.

All blow-off piping, when exposed to furnace heat, shall be protected by fire brick or other heat resisting material so constructed that the piping may be readily inspected.

Each boiler shall have a blow-off pipe fitted with a valve or cock, in direct conflection with the lowest water space. Cocks shall be of the gland or guard type and suitable for the pressure allowed. The use of lobe valves shall not be permitted. When the maximum allowable working pressure exceeds 100 pounds per square inch gauge, each blow-off pipe shall be provided with two valves or a valve and cock, such valves and cocks to be not less than extra heavy type.

When the maximum allowable working pressure exceeds 100 pounds per square inch gauge, blow-off piping shall be not less than extra heavy from the boiler to the valve or valves and shall be run full size without use of reducers or bushings. The piping shall be wrought iron or steel and shall not be galvanized.

All fittings between the boiler and blow-off valve shall be steel. In case of renewal of blow-off pipe or fittings, they shall be installed in accordance with the rules and regulations for new installations.

K.

Repairs and renewals of boiler fittings and appliances. Whenever repairs are made to fittings or appliances or it becomes necessary to replace them, the work shall comply with the provisions of this chapter for new installations.

L.

Stamping of existing boilers. Each boiler shall be stamped with a serial number of the city followed by the letters "MFS," such letters and figures to be not less than 5/16 inch in height. The stamping shall not be concealed by lagging or paint and shall be exposed at all times.

M.

Suggested operating practices. It is recommended that the suggested rules of the A.S.M.E. Boiler Construction Code covering the care of power boilers and pressure vessels be used as a guide for proper and safe operating practices.

(Code 1967, § 45-82; Code 1985, § 42-87; Ord. No. 1427, § 1, 8-29-1972)