Sec. 09.12.01.26. Pressure Vessel — Existing Installation

A. The maximum allowable working pressure for a standard pressure vessel:

(1) Shall be determined in accordance with the ASME Code under which it was constructed and stamped; and

(2) May not exceed the pressure shown on the manufacturer's name plate stamp and data report.

B. Nonstandard Pressure Vessel-Maximum Allowable Working Pressure.

(1) The maximum allowable working pressure on the shell of a nonstandard pressure vessel shall be determined by the strength of the weakest course computed by multiplying TS by t and E and dividing the product by R multiplied by FS:

(TS x t x E)/(R x FS) = maximum allowable working pressure, PSIG, where:

(a) TS = ultimate tensile strength of the shell plate, PSI, which, if unknown, shall be 55,000 PSI for steel, for temperatures not exceeding 700°F;

(b) t = minimum thickness of the shell plate of the weakest course, in inches;

(c) E = efficiency of the longitudinal joint, which is, for:

(i) Riveted joints, the calculated riveted efficiency, and

(ii) Fusion-welded and brazed joints:

Single lap weld ... 40 percent

Double lap weld ... 60 percent

Single butt weld ... 60 percent

Double butt weld ... 75 percent

Forge weld ... 70 percent

Brazed steel ... 80 percent

(d) R = radius of the weakest course of the shell, in inches, using the:

(i) Inside radius, if the thickness is 10 percent or less of the radius, and

(ii) Outside radius, if the thickness is greater than 10 percent of the radius;

(e) FS = factor of safety required by this regulation.

(2) The maximum allowable working pressure for a cylindrical nonstandard pressure vessel subjected to external or collapsing pressure shall be determined by the ASME Code, Section VIII, paragraphs UG-28 and UG-29.

(3) Factor of Safety.

(a) For an existing installation, the minimum factor of safety shall be at least four.

(b) When necessary to ensure safe operation, the inspector may increase the factor of safety based on the:

(i) Condition of the vessel; and

(ii) Specific service to which it is subject.

(4) The maximum allowable working pressure for formed heads under pressure shall be determined by the:

(a) Appropriate formulas from the ASME Code, Section VIII, Division 1, Paragraphs UG-32, UG-33, and UG-35; and

(b) Tensile strength and factors of safety set out in this regulation.

C. If the inspector determines, because of conditions disclosed during an inspection, that the interior or exterior lining, covering, or brickwork should be removed to expose parts of the vessel not normally visible, the owner shall remove the material to permit:

(1) Proper inspection; and

(2) Drilling any part of the vessel where necessary to ascertain thickness.

D. Safety Appliances.

(1) To ensure safe operation, a pressure vessel shall have:

(a) Safety and relief valves; and

(b) Indicating and controlling devices.

(2) Safety appliances shall be constructed, located, and installed so that they cannot readily be rendered inoperative.

(3) The relief capacity of a safety valve shall be sufficient to prevent pressure in the vessel from rising more than 10 percent above the maximum allowable working pressure, with static head pressure factored into the calculation.

(4) Safety valve discharge shall be carried to a safe place.

E. Repairs and replacements of fittings and appliances shall comply with the requirements for new installations.