Australian Firm Validates Pressure Vessel Design

ALGOR FEA HELPS AUSTRALIAN FIRM VALIDATE PRESSURE VESSEL DESIGN

When Centurion Industries, Limited, was faced with proving the adequacy of a pressure vessel design that fell outside the standards specified by the Australian Unfired Pressure Vessel Code, engineers turned to Algor to help validate their design decision. Linear stress analysis results verified the structural integrity of the vessel, an 80,000 liter capacity tank designed to service the chlorination plant in a major titanium oxide processing center.

Centurion Industries, out of Welshpool, Western Australia, is a heavy engineering firm that specializes in the fabrication of pressure vessels for mining, petrochemical, and offshore industries. Terry Passanisi, a design engineer with Centurion, used finite element analysis to avoid conducting expensive prototype testing and experimental analyses that were the only other alternatives Centurion had for proving the validity of the vessel.

Terry Passanisi, design engineer with Centurion Industries, Limited.

"The model I created consists of a pipe attached to a semi-ellipsoidal dished head," states Passanisi. "The head is part of a pressure vessel subjected to internal pressure and external point loads.

"In design," Passanisi continues, "the pipe connects to the head in a location that is outside standard design rules as specified by the Australian Unfired Pressure Vessel Code AS 1210, Clause 3.18.5.1. The code states that 'Openings in dished ends shall be located so that the outside of any attachment, or the edge of any additional reinforcement, lies entirely within a circle, the center of which coincides with the center of the end and the diameter of which is equal to 80% of the outside diameter of the dished end.'

"Since the pipe in this model did not satisfy the above requirement and since the code does not deal with the analysis of such a situation, an alternative approach was needed to prove the design was satisfactory."

The pressure vessel model Passanisi created had 1410 Plate/Shell elements and 1250 nodes. He processed the model on an NEC 386 AT, 16 MHz with 1 MB RAM and an 80 MB hard disk.

"Static stress analysis results showed the stress values were satisfactory and confirmed the acceptability of the design," says Passanisi. "I found the Algor package easy to use and very intuitive. Features such as JetView made it simple to check the model before and after the analysis."

This pressure vessel design fell outside the standards specified by the Australian Unfired Pressure Vessel Code forcing Passanisi to turn to Algor FEA.
Zoomed in view.

Using Algor Over and Over

Passanisi has been using Algor to perform a number of different types of analyses. Another model he analyzed recently involved the interaction of external support pads with a pressure vessel wall.

"The pads connect a structure to the vessel to vertically support it," Passanisi explains. "Design checks were required to verify that point loads applied to vessel nozzles when combined with the vessel's self-weight did not result in stresses outside the design limit.

"The support pads are fixed to the vessel with continuous fillet welds around the periphery of the pad. Available design rules gave only approximate indications of the stress levels at the pad/wall interface. Algor FEA was used to help verify the approximate manual calculations."

Fifty-two Gap elements and 2924 Plate/Shell elements comprise this pressure vessel model. Analysis results revealed stress levels within acceptable limits.
Zoomed-in view of interface between support pads and vessel walls.

To model the interaction of the pad and wall, Passanisi placed 52 Gap elements adjacent to the pad supports. Only half of the overall model had to be constructed due to the structural symmetry. Along with the 52 Gap elements, the half model contained 2924 Plate/Shell elements and 2887 nodes.

FEACOM Technologies PTY LTD, Algor's Australian representative, ran the analysis on a Fujitech 386, 25 MHz with 4 MB RAM and a 340 MB hard disk.

"Results showed that the stress levels on the vessel walls were within acceptable limits. Manual calculations indicated stress levels of 210 MPA while Algor analysis gave a peak von Mises surface stress of 235 MPA," Passanisi remarks.