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An extra dimension can save a lot of time. At least that was the experience of Friede Goldman Offshore, an engineering company that serves the oil industry. The company says it cut 25 percent off the time to develop a deepwater drilling rig by switching from a 2-D to 3-D CAD system. The company saved approximately 1,000 man-hours designing the rig's equipment and piping.

Friede Goldman Offshore is building two deepwater semi-submersible drilling vessels, Bingo 9000-1 and Bingo 9000-2, for Ocean Rig, a Norwegian customer. Each rig is capable of drilling to depths of 10,000 feet.

The piping design group at Friede Goldman Offshore was charged with developing the piping for the drill floor, the engine room, the purifier room, passageways, and some of the crew accommodation areas.

It also designed the mud pump room and mud pit, which play a critical role in the rig's ability to drill in deep water. A rig's drill string is hollow to permit the circulation of drilling fluid, or mud, which cools the bit, lubricates the drill string, and keeps the hole free of cuttings.

Mud, pumped down the drill string, passes through jets in the bit and returns to the surface through an annular space between the drill string and the casing. Then, it is conditioned by passing through a mud-gas separator, over a shale shaker, then through a sand trap tank. After that come the degasser, desander, and desilter. Finally, the mud returns to the active pits before it is pumped down the drill string again.

On previous projects, Friede Goldman Offshore's design team relied on two-dimensional drawings to route pipes. Designers found that working in 2-D made it difficult to detect interferences.

Once the design was done, it was necessary to produce from scratch all of the spools, or isometric drawings, and other drawings needed for fabrication. A typical project required thousands of spools.

The desire to speed up this phase of the process led Friede Goldman Offshore to consider the 3-D design method, which can generate drawings automatically.

Friede Goldman Offshore purchased seven seats of the AutoPLANT 97 piping design module from Rebis of Walnut Creek, Calif. It also bought one seat of Rebis's equipment design module and two of the intelligent piping and instrumentation diagram, or P&ID, module.

The company runs the software on Pentium II 350-MHz and 300-MHz PCs equipped with 128 to 384 megabytes of RAM.

Engineers began the Bingo-9000 project by creating an overall layout of the systems they would be designing. The next step was placing the equipment, mostly from a library of parametrically defined components that can be altered with the specifications of the actual equipment.

Designers found that they could route a pipe in three dimensions. It was faster than trying to imagine elevations on a 2-D drawing and let designers see the impact of their efforts without flipping through a series of 2-D drawings.

Because the routing went faster, designers could try several options in order to get the best routes possible.

When the design was done, Friede Goldman Offshore used a module called Explorer/ID to evaluate the 3D models for interferences. Those that were found were fixed on the model.

The next step was creating the two dimensional drawings needed to document the project. Thirteen drawings were required and each was produced in about half the time that would have been required if it had been generated from scratch. On a previous project, for example, creating the detailed drill floor took 400 man-hours. On this project, it took 200. The user selected the view of the model that he wanted, added some dimensions and call-outs, and had the software generate the drawing.

The production of spools is where Friede Goldman Offshore saved the most time on the Bingo-9000 project. For each of the 13 drawings, there were 200 line numbers. Each line number required four spools, for a total of 10,400. Friede Goldman Offshore used Personal Isogen, the automatic isometric generation program that comes with AutoPLANT 97, to create the spools.

The company also saved time in the production of the bill of materials for the project. The system administrator had entered the piping specifications into a database, so the model of each pipe included that information. The computer kept track of the materials used in the model, and when the time came, the company could print out the list.

The Bingo-9000 rigs are approaching completion. So far, very little field rework has been needed because problems such as interferences were detected in the modeling stage and solved before fabrication.

Jim Dyche is a senior piping designer at Friede Goldman Offshore in Pascagoula, Miss.
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Author:Dyche, Jim
Publication:Mechanical Engineering-CIME
Date:Aug 1, 2000
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