§ 14-12-59. Unfired pressure vessels—Existing installations.

A.

Application of section. This section applies to existing unfired pressure vessel installations.

B.

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

C.

Maximum allowable working pressure for nonstandard unfired pressure vessels.

1.

For internal pressure. The maximum allowable working pressure on the shell of a nonstandard pressure vessel shall be determined by the strength of the weakest course computed from the thickness of the plate, the tensile strength of the plate, the efficiency of the longitudinal joint, the inside radius of the course and the factor of safety allowed by these rules.

  TS × T × E = Maximum allowable working pressure.

  R × FS = Pounds per square inch.

  TS = Ultimate tensile strength of shell plate pounds per square inch. When the tensile strength is not known it shall be taken as 55,000 pounds per square inch for temperatures not exceeding 700 degrees Fahrenheit.

  T = Minimum thickness of shell plate of weakest course, inches.

  E = Efficiency of longitudinal joint depending upon construction.

  Use valves as follows:

For Riveted Joints

  Calculated riveted efficiency.

For Fusion Welded Joints

Single lap weld	40%
Double lap weld	60%
Single butt weld	50%
Double butt weld	70%
Forge weld	70%
Brazed steel	80%
Brazed copper	90%

 

  R = Inside radius of weakest course of shell, inches, provided the thickness does not exceed ten percent of the radius. If the thickness is over ten percent of the radius, the outer radius shall be used.

  FS = Factor of safety allowed by these rules.

2.

For external pressure. The maximum allowable working pressure for cylindrical vessels subjected to external or collapsing pressure shall be determined by the rules in Paragraphs U-120 to U-138 inclusive of the A.S.M.E. Boiler and Unfired Pressure Vessel Construction Code, section 8.

D.

Factors of safety. The minimum factor of safety shall in no case be less than four for vessels up to and including 20 years of age and shall be not less than four and one-half where the age of the vessel is more than 20 years. These factors of safety may be increased when deemed necessary by the inspector to insure the operation of the vessel within safe limits. The condition of the vessel and the particular service it is being subjected to will be the determining factor.

E.

Inspection of inaccessible parts. Where, in the opinion of the inspector, as the result of conditions disclosed at an inspection, it is advisable to remove interior or exterior lining, covering or brick work to expose certain parts of the vessel not normally visible, the owner or user shall remove such material to permit proper inspection and the drilling of any part of the vessel where necessary to ascertain thickness.

F.

Safety appliances. Each unfired pressure vessel shall be protected by such safety and relief valves and indicating and controlling devices as will insure its safe operation. These valves and devices shall be so constructed, located and installed that they cannot readily be rendered inoperative. The relieving capacity of safety valves shall be such as to prevent a rise of pressure in the vessel of more than ten percent above the maximum allowable working pressure taking into account the effect of static head. Safety valve discharges shall be carried to a safe place.

G.

Rupture discs. Rupture discs or safety heads may be used for additional protection of unfired pressure vessels.

H.

Repairs and renewals of fittings and appliances. Whenever repairs are made to fittings and appliances or it becomes necessary to replace them, the work must comply with this chapter.

I.

Stamping of existing unfired pressure vessels. Each unfired pressure vessel 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.

(Code 1967, § 45-89; Code 1985, § 42-94)