3-D software boosts offshore platform design capability - Unocal Thailand Ltd invests in new design system

World Oil, August, 1998 by Paul Anthony

Using manual drafting methods, Unocal Thailand was adding two or three new offshore drilling platforms each year to its natural gas fields in the Gulf of Thailand. By converting to the 3-D plant design system, AutoPLANT, from Rebis, Walnut Creek, California, the company increased this to 8 to 11 platforms annually, with only a slight increase in its design staff. The company's piping designers, who formerly needed 600 to 800 hr to prepare new platform drawings, now complete them in 80 to 160 hr, not including time spent on developing specification data and model base.

The new design system, which works on top of AutoCAD, improves productivity by using a 3-D model as a project foundation. From the model, piping designers now generate isometric drawings virtually automatically. Bills of materials are also generated quickly through the software's link to a textual database.

Platform expansion, demands on designers. With more than 60 offshore drilling platforms already in place in ! 994, Unocal Thailand planned a significant expansion of its natural gas production over the next five years. The company expected to build about 35 new platforms in that time.

Most of the platforms are of the same basic design; structures vary only slightly, depending on water depth. Most instrumentation and electrical equipment has been standardized. And most of the topside design work required to create a new platform involves piping, which is handled at Unocal by a department of four people.

The piping requirements for a new platform depend on its location in the field. At the field's edge, the platform will normally have a single 10-in. export line central to a processing facility or another wellhead platform. Platforms in other locations within the field may have entirely different piping configurations.

The exact configuration depends on the number of incoming and outgoing pipelines. The exact combination of incoming/outgoing pipelines is thus field/location dependent, but normally varies from a single export line to three or four incoming and one or two export lines.

For each platform, the design team creates two sets of piping drawings - one for bid, another for construction. A complete platform set contains more than 550 drawings. Using manual drawing methods, three platforms were built each year, with a typical set of 292 piping drawings taking 600 to 800 hr to prepare. The increased development program, however, required that 8 to 11 platforms per year be engineered, constructed and installed.

Office automation boosts production. To enable the piping design department to handle the planned increase in platform construction, the company began a major drawing office automation project, introducing the AutoCAD/AutoPLANT system in mid-1993. Unocal chose these software packages because the latter adds the specific, timesaving functions needed for plant design to the well-known CAD package, from Autodesk, Inc., Sausalito, California.

AutoPLANT's use of 3-D design and its link to a textual database was the key to improving the piping designers' productivity. Another major factor for going to CAD was the repetitive nature and similarities between wellhead platforms. The major components requiring development time of the specs and model are nearly identical for each platform. Thus, it was believed that CAD would be a very effective option.

The new system's 3-D capability makes a dramatic difference in productivity because, once a 3-D model is complete, drawings can be generated quickly from the model. Unocal requires three types of drawings for piping - plan, sections and isometric - which are used for pipe fabrication and assembly. In a typical bid package, there are 12 Process & Instrumentation Diagrams (P & IDs), eight plan drawings, seven sections and 200 - 250 isometrics. Isometrics are the most difficult to produce manually because the designer has to mentally add the third dimension.

The company is using the new system's P & ID module to draw all the sheets for each type of platform module. For each new platform design, they simply select the appropriate module sheets, then go into the software and change the title block. P & IDs describe the basic flow of natural gas through the platform and establish pipe sites and sizes of construction materials.

Plan and section drawings are produced in true 3-D format. Rather than simply entering elevation data on the drawing as before, the elevation becomes an integral part of the drawing so that it can be viewed from the front or any other angle to check clearances and fits, i.e., clashcheck. This is important because of the confined nature of off-shore work, with its compressed space and potential for interferences.

Significant time savings. The time required to develop the 3-D model was about the same as the time previously required to produce orthographic layouts. The significant time savings with the 3-D model approach was the isometrics. Since the new system's model already contains the third dimension, producing isometrics is done almost automatically by simply blocking off the symbols which are to be included.