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

Paper Number: 61801

Start Time: Tuesday, July 13, 2021, 09:00 AM

61801 - Design Considerations for Half-Pipe Jackets Operating Under Vacuum Conditions 

Pressure Vessel is defined as an equipment having pressure differential between inside and outside. The pressure is accompanied with suitable temperature of the fluid. Based on the process requirement, the temperature within the pressure vessel is maintained. The temperature can be controlled by application of heat from direct or indirect source. Half-pipe jacket or limpet coil is one of the methods to maintain the temperature of fluid in the pressure vessel. The nonmandatory Appendix EE of ASME Sec VIII Div 1 and Para. 4.11.6 of Part 4 of ASME Sec VIII Div 2 provide the rules to design the half-pipe jackets constructed of size NPS 2, NPS 3 and NPS 4. Both ASME Sec VIII Div 1 and Div 2 stipulates rules for calculation of minimum thickness of half-pipe jacket and the maximum permissible pressure in the half-pipe jacket.

 Certain condition of applicability is provided in both ASME Sec VIII Div 1 and Div 2 to use the calculation procedure for design of half-pipe jackets.

1.       There is positive pressure inside the shell/head.

2.       There is positive pressure inside the half-pipe jacket. 

Under certain situations, the above conditions may partially be met. e.g. The equipment may be under full vacuum with positive pressure in half-pipe jacket. Also, possibility could exist that the equipment is having some positive pressure while the half-pipe jacket may be experiencing vacuum simultaneously. 

Such designs are not covered under the rules provided in nonmandatory appendix EE of ASME Sec VIII Div 1 as well as in Part 4 of ASME Sec VIII Div 2 and the users must demonstrate compliance by meeting U-2(g) for ASME Sec VIII Div 1 and by designing in accordance with Part 5 of ASME Sec VIII Div 2. For such design condition, elastic buckling and plastic deformation shall be evaluated for the entire equipment.

 Unlike ASME Sec VIII Div 1 and Div 2, other international Codes like PD5500 and EN 13445 in addition to providing the rules for evaluating half-pipe jacket or limpet coils also states that when the equipment is subject to vacuum, the half-pipe jacket may be considered to contribute as stiffeners.

 This paper is an attempt to find out the means to design the equipment with half-pipe jacket or limpet for which the conditions specified in ASME Sec VIII Div 1 and Div 2 are not satisfied.

Keywords: Cylindrical shell, Limpet, Half-pipe jacket, External pressure, Buckling, MAWP, MAEWP.

Presenting Author: Ameya Mathkar Lloyd’s Register Marine and Inspection services India LLP

Authors:

Ameya Mathkar Lloyd’s Register Marine and Inspection services India LLP
Shyam Gopalakrishnan Lloyd’s Register Marine and Inspection services India LLP
Sujay Pathre Lloyd’s Register Marine and Inspection services India LLP