Section 0800-03-03-.10 - EXISTING POWER BOILERS(1) Age Limits. (a) There shall be an age limit of thirty (30) years for any nonstandard existing power boiler, except for the following: 1. Any such boiler not having a lap-riveted longitudinal joint may be continued in operation for so long as no distress or leakage develops during a pressure test with water temperature between 60° to 120° F, of no more than ninety percent (90%) of the set pressure of the lowest setting pressure relief device on the boiler, held for a period of at least thirty (30) minutes.2. Any such boiler having lap-riveted longitudinal joints and operating at a pressure in excess of 50 psig shall have an age limit of twenty (20) years. When removed from an existing setting, this type of boiler shall not be reinstated for a pressure in excess of 15 psig.3. "Historic power boilers" as defined in T.C.A. § 68-122-104(c)(1) and Rule 0800-03- 03-.01(18).(b) The age limit for a standard existing power boiler shall be dependent upon the results of a thorough internal and external inspection and, where required by the inspector, a pressure test with water temperature between 60° to 120° F, of no more than ninety percent (90%) of the set pressure of the lowest setting pressure relief device on the boiler, held for a period of at least thirty (30) minutes.(2) Maximum Allowable Working Pressure for Standard Boilers. The maximum allowable working pressure for standard boilers shall be determined in accordance with the applicable provisions of the edition of the ASME Code under which they were constructed.(3) Maximum Allowable Working Pressure for Nonstandard Boilers. (a) The maximum allowable working pressure of a nonstandard boiler shall be determined in accordance with ASME Code, Section I, PG-27. Click to view Image
(b) Tensile Strength. When the tensile strength of steel or wrought iron shell plates is not known, it shall be taken as 55,000 psi for steel and 45,000 psi for wrought iron.(c) Crushing Strength of Mild Steel. The resistance to crushing of mild steel shall be taken as 95,000 psi.(d) 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: | PSI |
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 Table 1, or as ascertained by cutting out one (1) rivet in the body of the joint.
Table 1
Sizes of Rivets Based on Plate Thickness
Thickness of plate-in. | 1/4 | 9/32 | 5/16 | 11/32 | 3/8 | 13/32 |
Diameter of rivet after driving-in. | 11/16 | 11/16 | _ | _ | 13/16 | 13/16 |
Thickness of plate-in. | 7/16 | 15/32 | 1/2 | 9/16 | 5/8 | |
Diameter of rivet after driving-in. | 15/16 | 15/16 | 15/16 | 1-1/16 | 1-1/6 | |
(4) 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 be 160 psig.(5) Pressure on Cast Iron Boilers. The maximum allowable working pressure for any cast iron boiler, except hot water boilers, shall be 15 psig.(6) Safety Valves. See ASME Section I, PG-67 (a) The use of weighted-lever safety valves, or safety valves having either the seat or disk of cast iron, is prohibited.(b) Each boiler shall have at least one (1) ASME/NB stamped safety valve; and if it has more than five hundred (500) square feet of water-heating surface, or an electric power input of more than 500 kwh, it shall have two (2) or more safety valves.(c) 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.(d) No valve of any description shall be placed between the safety valve and the boiler, or on the escape pipe, if used. When an escape pipe is used, it shall be at least the full size of the safety valve discharge and fitted with an open drain to prevent water lodging in the upper part of the safety valve or in the escape pipe. When an elbow is placed on a safety valve escape pipe, it shall be located close to the safety valve outlet; or the escape pipe shall be anchored and supported securely. All safety valves discharged shall be so located or piped as to be carried clear from walkways or platforms.(e) 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 by the boiler without allowing the pressure to rise to more than six percent (6%) above the highest pressure to which any valve is set, and in no case to more than six percent (6%) above the maximum allowable working pressure.(f) One (1) 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 (3%) above the maximum allowable working pressure, but the range of setting of all the safety valves on a boiler shall not exceed ten percent (10%) of the highest pressure to which any valve is set.(g) When two (2) or more boilers operating at different pressures and safety valves settings are interconnected, the lower pressure boilers or interconnected piping shall be equipped with safety valves of sufficient capacity to prevent overpressure, considering the maximum generating capacity of all boilers.(h) Where the boiler is supplied with feedwater directly from water mains without the use of feeding apparatus (not to include return traps), no safety valve shall be set at a pressure greater than ninety four percent (94%) of the lowest pressure obtained in the supply main feeding the boiler.(i) The relieving capacity of the safety valves on any boiler shall be checked by one (1) of the three (3) following methods; and, if such capacity is found to be insufficient, additional valves shall be provided: 1. By making an accumulation test, which consists 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 rise of pressure in excess of six percent (6%) of the maximum allowable working pressure. This method should not be used on a boiler with a superheater or reheater;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 value of this fuel, these computations shall be made as outlined in the Appendix of the ASME Code, Section I; or3. By measuring the maximum amount of feedwater that can be evaporated.(7) Boiler Feeding. (a) Each boiler shall have a feed supply which will permit it to be fed at any time while under pressure.(b) A boiler having more than five hundred (500) square feet of water-heating surface shall have at least two (2) suitable means of feeding, one (1) of which shall be a feed pump. A source of feed at a pressure six percent (6%) greater than the set pressure of the safety valve with the highest setting may be considered one (1) of the means. Boilers fired by gaseous, liquid, or solid fuel in suspension may be equipped with a single means of feeding water, provided means are furnished for the shutoff of heat input prior to the water level reaching the lowest safe level.(c) The feedwater shall be introduced into the boiler in such a manner that it will not be discharged close to riveted joints of shell or furnace sheets, or directly against surfaces exposed to products of combustion, or to direct radiation from the fire.(d) 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 near the boiler. When two (2) 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 the source of supply. Whenever a globe valve is used on the feed piping, the inlet shall be under the disk of the valve.(e) When deaerating heaters are not employed, it is recommended that the temperature of the feedwater be not less than 120o F to avoid the possibility of setting up localized stress. Where deaerating heaters are employed, it is recommended that the minimum feedwater temperature be not less than 215o F so that dissolved gases may be thoroughly released.(8) Water Level Indicators. (a) No outlet connections (except for damper regulator, feedwater 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 there from) 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 (3/4) inch pipe size, with the discharge to be piped to a safe location.(b) Per ASME Code, Section I, gauge cocks are no longer required.(c) For all installations where the water gauge glass or glasses are more than thirty (30) feet above the boiler operating floor, remote water level indicating or recording gauges shall be installed at eye level.(9) Steam Gauges. (a) Each steam boiler shall have a steam gauge with dial range not less than one and one half (11/2) 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. Such siphon (or equivalent device) shall be so arranged that the gauge cannot be shutoff from the boiler, except by a cock with tee or lever handle placed in the pipe near the gauge. The handle of the cock shall be parallel to the pipe in which it is located when the cock is open.(b) When a steam gauge connection longer than eight (8) 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 of ample size, with provision for free blowing.(c) Each boiler shall be provided with a one half (1/2) 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.(10) Stop Valves. (a) Each steam outlet from a boiler (except safety valve and water column connections) shall be fitted with a stop valve located as close as practicable to the boiler.(b) 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.(c) When boilers provided with manholes are connected to a common steam main, the steam connection from each boiler shall be fitted with two (2) stop valves having ample free blow drain between them. The discharge of the drain shall be visible to the operator while manipulating the valves, and shall be piped clear of the boiler setting. The stop valves should consist of one (1) non-return valve (set next to the boiler) and a second valve of the outside-screw-and-yoke type.(11) Blowoff Connection. (a) The construction of the setting around each blowoff 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 blowoff piping.(b) When exposed to furnace heat, all blowoff piping shall be protected by fire brick or other heat-resistant material, so as constructed the piping may be inspected readily.(c) Each boiler shall have a blowoff pipe, fitted with a valve or cock in direct connection with the lowest water space. Cocks shall be of the gland or guard type, and suitable for the pressure allowed. The use of globe valves is prohibited. When the maximum allowable working pressure exceeds 100 psig, each blowoff pipe shall be provided with two (2) valves or a valve and cock.(d) When the maximum allowable working pressure exceeds 100 psig, blowoff piping shall be at least extra-heavy steel from the boiler to the valve or valves, and shall be run full-size without use of reducers or bushings. The piping shall not be galvanized.(e) All fittings between the boiler and blowoff valve shall be of steel. In case of renewal of blowoff pipe or fittings, they shall be installed in accordance with the rules for new installations. See Recommended Rules for National Board Boiler Blowoff Equipment.(12) Repairs and Renewals of Boiler Fittings and Appliances. Whenever fittings or appliances are repaired or replaced, the work shall comply with the rules governing new installations.(13) Conditions Not Covered by These Requirements. All cases not specifically covered by these requirements shall be treated as new installations, or may be referred to the Chief Inspector or Chief Inspector's Designee for instructions.Tenn. Comp. R. & Regs. 0800-03-03-.10
New rule filed June 16, 2016; effective 9/14/2016.Authority: T.C.A. §§ 68-122-102 and 68-122-104.