Design and Analysis of Vertical Vessels for Lifting in Fully Dressed Condition

Abstract

Depending on plant/site location, it may be advantageous to dress a vertical vessel, in horizontal position, prior to erection. Dressing refers to the installation of items attached to the vessel such as internals, insulation, piping, ladders, platforms, electrical cable trays, lighting, etc. The decision to dress a vessel may be due to safety, schedule or economic reasons. Dressing a vessel results in higher lifting loads. Vessel Codes address loadings to be considered when designing a vessel in its operating position and not necessarily for lifting. Since the Codes do not address erection loadings, engineering judgment must be used in their consideration and analysis in order to avoid overstressing the vessel. In some cases, erection loads govern the design thickness of the vessel. Lifting analysis in the context of this paper is the evaluation of stresses in the vessel when it is initially picked up from the horizontal position. This paper discusses the compressive stresses which usually govern in the lifting analysis of thin-walled vessels. Different methods used in literature and industry are presented in the paper. Some Owners/Users, engineering firms, and fabricators use the Factor B in ASME Section II, Part D, Subpart 3 as the limiting criterion for compressive stresses. In some cases, this criterion is too conservative. This paper presents the application of alternative buckling criteria for lifting analysis.