Pressure Vessel Design

This equipment-design topic applies the ASME code to size shells and heads. You compute the required thickness for internal pressure, add a corrosion allowance, select head geometry (hemispherical, torispherical, ellipsoidal), and check that the relief-device set pressure does not exceed the maximum allowable working pressure.

(cylindrical shell, ASME VIII Div 1, internal pressure)

(hemispherical head)

(thin-wall stresses)

Relation 1 —

(cylindrical shell, ASME VIII Div 1, internal pressure)

Write this relation with symbols exactly as in Bhattacharya Chemical Equipment Design — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

(hemispherical head)

Write this relation with symbols exactly as in Bhattacharya Chemical Equipment Design — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

(thin-wall stresses)

Write this relation with symbols exactly as in Bhattacharya Chemical Equipment Design — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

A thin cylindrical shell under internal pressure carries a hoop (circumferential) stress twice its longitudinal stress, so failure tends to run along a longitudinal line and the circumferential weld seam and its joint efficiency govern design. The code thickness formula divides pressure times radius by the allowable stress reduced by the joint efficiency, with a small pressure correction. Heads are sized separately: a hemispherical head needs only about half the shell thickness because its stress is biaxial and lower, which is why spherical shapes are efficient but costlier to fabricate. Corrosion allowance is added on top so the vessel still meets code at end of life.

State assumptions explicitly before using any relation for pressure vessel design — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In Process Equipment Design viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in Process Equipment Design papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to pressure vessel design.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Pressure Vessel Design appears in EPCM and fabrication. In Indian chemical curricula this topic is tested because it connects theory to mechanical design of vessels and columns.

GATE and semester exams often combine pressure vessel design with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use pressure vessel design?" — answer with a lab, mini-project, or plant visit example if possible.

Students use diameter instead of radius, forget the joint-efficiency factor E, and omit the corrosion allowance. Mixing up hoop and longitudinal stress (or using the head formula for the shell) is a frequent error, as is using gauge versus design pressure inconsistently.

Before attempting pressure vessel design problems, confirm you can:

1. Add a corrosion allowance to the calculated thickness
2. Hoop stress is twice the longitudinal stress in a cylinder
3. Relief-valve set pressure must be ≤ the MAWP

Revise the solved examples in Bhattacharya Chemical Equipment Design — Standard reference and one previous-year GATE or university paper for this unit.