Session: CS-01-02: Structural Integrity of Pressure Components

Paper Number: 84770

84770 - Design of Ellipsoidal Heads and Torispherical Heads in Pressure Vessels and Review of Restrictions in Material Strength Imposed in Asme Sec. Viii Div. 1 – a Comparative Study of Various Codes of Construction. 

Pressure Vessels are made with various types of end closures. Commonly used end closures are ellipsoidal dished ends, torispherical dished end and hemispherical dished ends. For design of these end closures the rules provided in ASME Sec. VIII Div. 1 and ASME Sec. VIII Div. 2 differ significantly and a similar phenomenon could be observed when a review is done against popular international Codes for pressure vessel design like PD 5500, EN 13445. The difference in the design methodology is due to the design approach used in developing the equations in these Codes of Construction.

ASME Sec. VIII Div.1 in Para UG-32(d) and in Appendix 1-4 for design of all torispherical heads subject to internal pressure states that the maximum allowable stress used to calculate the required thickness cannot exceed 20 ksi (138 MPa) at room temperature irrespective of the strength of the material. This restriction is further reduced in proportion at elevated temperatures.  This requirement was added to ASME Sec. VIII Div.1 to prevent the possibility of buckling of the heads as the thickness is reduced due to the selection of materials with higher allowable stresses. Similar kind of a restriction in the allowable stress is imposed for design of ellipsoidal heads when the factor K (shape factor in the design of ellipsoidal head) exceeds 1.0 in ASME Sec. VIII Div. 1.

If we refer other Codes like ASME Sec. VIII Div.2 and PD 5500 and EN 13445, one can observe that the restriction of allowable stress in the design of ellipsoidal and torispherical heads are not imposed when high strength materials are selected for the construction of dished ends.

The work reported in this paper is an attempt to review the design methodology adopted for design of ellipsoidal dished ends with factor K exceeding 1.0 and all torispherical heads according to ASME Sec. VIII Div. 1 with ASME Sec. VIII Div. 2, PD 5500 and EN 13445 and to evaluate whether the restriction in the allowable stress imposed by ASME Sec. VIII Div. 1 are really required.

Presenting Author: Shyam Gopalakrishnan Lloyd's Register Marine & Inspection Services India LLP

Presenting Author Biography: Currently working in Lloyd’s Register Marine & Inspection Services India LLP as Senior Specialist for Inspection Services with total 16 years of experience in construction of heavy equipment’s used in Oil & Gas/ Fertiliser and Petrochemical Industries like columns/ Reactors/ Pressure Vessels, Heat Exchangers, Boilers, Piping and Piping Components.

Authors:

Shyam Gopalakrishnan Lloyd's Register Marine & Inspection Services India LLP
Ameya Mathkar Lloyd's Register Marine & Inspection Services India LLP
Sujay Pathre Lloyd's Register Marine & Inspection Services India LLP