229 Neb. Admin. Code, ch. 27, § 003

Current through September 17, 2024

Section 229-27-003

Maximum Allowable Working Pressure for Nonstandard Pressure Vessels, except as provided in 004 of this chapter.

A. The maximum allowable working pressure 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 diameter of the course and the factor of safety set by these rules.

TStE / RFS = maximum allowable working pressure (MAWP), psig where:

TS = specified minimum tensile strength of shell plate material, psi. (When the tensile strength of carbon steel plate is not known, it may be taken as 55,000 psi for temperatures not exceeding 650 degrees Fahrenheit. For other materials use the lowest stress values for that material from ASME Section VIII.)

t = minimum thickness of shell plate of weakest course, inches.

E = efficiency of longitudinal joint depending upon construction. Use the following values: for riveted joints - calculated riveted efficiency; for fusion-welded and brazed joints:

single lap weld ......................................................	40%
double lap weld ....................................................	50%
single butt weld .....................................................	60%
double butt weld or forge weld ..............................	70%
brazed steel ..........................................................	80%

R = inside radius of weakest course of shell (inches) provided the thickness does not exceed 10 percent of the radius shall be used.

FS = factor of safety allowed by these rules.

B. The minimum factor of safety shall in no case be less than 5 for existing installations. The working pressure shall be decreased 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 to which it is subject will be the determining factors.

C. The maximum allowable working pressure permitted for formed heads under pressure shall be determined by using the appropriate formulas from ASME code, and the tensile strength and factors of safety given in 002 and 003(A) of this Chapter.

D. The maximum allowable working pressure for nonstandard pressure vessels subjected to external pressure shall be determined by the rules of the appropriate ASME code.

229 Neb. Admin. Code, ch. 27, § 003

Amended effective 8/7/2016.