ASME Code Section VIII Pressure vessel design Leonard D. Tijing PhD Candidate

Factor A

Factor A

Factor B : Fig. CS-2 For most common materials

Fig. NFA-1 Aluminum alloy 3003

Internal pressure formulas

Heads

Allowable stress for carbon and low alloy steel (S)

External pressure: Sphere and hemispherical head Procedure: 1) Assume t. 2) Calculate A, A=0.125/(Ro/t) 3) Get value of B. If A falls to the left, use Pa=0.0625E/(Ro/t)2 4) Calculate Pa=B/(Ro/t)

External pressure: Ellipsoidal head Procedure: Same with sphere procedure. Use Ro=0.9Do

External pressure: Torispherical head Procedure: Same procedure. Use Ro(maximum)=Do

Example: Internal pressure Design data: P = 100 psi S = SA 515-70 plate at 650oF E = 0.85 (spot-examined for shell and semispherical head) E = 1.0 (seamless head) R = 48 in D = 96 in t = required wall thickness CA = 0.125

Internal pressure: Cylindrical shell 1) Determine the required thickness of a shell. 2) Determine the MAWP, P for the design thickness used when the vessel is in new condition.

Internal pressure: Sphere and hemispherical head 1) Determine the required thickness of a hemispherical head. 2) Determine the MAWP, P for the head design thickness used when it is in new condition.

Internal pressure: Ellipsoidal head 1) Determine the required thickness of a seamless ellipsoidal head. 2) Determine the MAWP, P for the seamless head design thickness used when it is in corroded condition.

Example 1: External pressure Design information: P = full vacuum T = 500oF Shell and head material = SA-285 Gr. B, S=27 ksi CA = 0.0625 in. Question: Is 7/16 in thickness acceptable?

External pressure: Solution procedure 1)Calculate unstiffened design length, L and Do of the shell 2) Determine ratios L/Do and Do/t 3) Determine value of A using figure 4) Get value of B from graph. If A is to the left of the graph, calculate Pa=2AE/[3(Do/t)] 5) If there is B, use Pa=4B/[3(Do/t)] 6) Compare Pa with design external pressure. If Pa is greater, thickness is acceptable

Example 2: External pressure with stiffeners P = 15 psig Do = 96 in L = 48 ft Heads 2:1 ellipsoidal Material of shell SA-285 C plate T = 500oF E = see chart t = ?

Example: External pressure  Vessel with stiffeners 1)Calculate unstiffened design length, L and Do of the shell 2) Determine ratios L/Do and Do/t 3) Determine value of A using figure 4) Get value of B from graph. If A is to the left of the graph, calculate Pa=2AE/[3(Do/t)] 5) If there is B, use Pa=4B/[3(Do/t)] 6) Compare Pa with design external pressure. If Pa is greater, thickness is acceptable

Thickness range (inches) (1/16 inches step) 0.1875 0.25 0.3125 0.375 0.4375 0.5 0.5625 0.625 0.6875 0.75 0.8125 0.875 0.9375 1.0 …6.0