Large Pressure Vessel Lifting Analysis

Large Pressure Vessel Lifting Analysis
Analysis: 
ASME BPVC

When dealing with large pressure vessels lifting and transportation can be challenging.  ASME Section VIII code drives the design of the vessel but only includes details on operational loads.  Lifting and transportation is a critical aspect with structures of this size.  FEA analysis can help determine how the structure will behave.

When dealing with large pressure vessels lifting and transportation can be challenging.  ASME Section VIII code drives the design of the vessel but only includes details on operational loads.  Lifting and transportation is a critical aspect with structures of this size.  FEA analysis can help determine how the structure will behave.

In this analysis the pressure vessel was analyzed for lifting loads at various angles as the vessel is installed.  The main concern was the skirt, tailing lug and trunnions.  The mass of the vessel was a critical parameter.  To ensure proper mass was include the finite element model used beam elements to approximate the tube sheet.  This greatly improved the efficiency of the model.

Figure 1: The sheet surface geometry built from CAD drawings.

Figure 1: The sheet surface geometry built from CAD drawings.

Supplied with only CAD drawings the sheet surface of the midplanes was built as shown in Figure 1.  Once the geometry was modeled, 4-node plate elements were used to build the finite element model. 

Initially, the tailing lug was not adequate but after a couple design suggestions a final design was found.  This analysis helped the client better understand how the vessels act during installation.  Not only did they have confidence in this particular design, but they also gained valuable knowledge for future designs.

Figure 2: Plate element mesh.

Figure 2: Plate element mesh.

For the lifting analysis, it was necessary to create a FEA model of the complete vessel.  Loading was due to gravity and reacted through the saddles and skirt lifting lug.  All stresses had to meet the ASME Section VIII, Division 2 stress allowables for the specified material.

Figure 3: Beam elements for tube sheet

Figure 3: Beam elements for tube sheet

To account for the tube stiffness within the ASME pressure vessel, beam elements were used to model each heat exchanger tube and then tied into the top and bottom tube sheets.

Figure 4: ASME Section VIII, Divison 2 stress membrane plot

Figure 4: ASME Section VIII, Divison 2 stress membrane plot

ASME Section VIII, Division 2 membrane stress plot of the pressure vessel due to transportation loading.  The transportation loads are multiples of accleration with the vertical load at 1.2 g.

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