Point of Beginning

Seamless Fit

February 5, 2013
Mustang used CADWorx, Intergraph’s plant design and modeling solution, to create intelligent 3D models from the laser scan data. Within CADWorx Plant, designers were able to lay out existing vessels, tanks and various other plant equipment using real-world coordinates.

Laser scanning provides the high level of detail needed for precise modeling of a natural gas processing plant expansion.

The Hess Tioga natural gas processing plant (TGP) in northwestern North Dakota is undergoing an expansion that will equip the facility to meet demand for processing the increased natural gas production coming from western North Dakota’s oil fields. Currently, the plant can process approximately 120 million cubic feet of natural gas daily. The plant expansion will more than double Hess’s processing capacity to 250 million cubic feet a day.

As-built data on the existing plant, built in the 1950s, is outdated and insufficient to help engineers design the expansion with adequate tie-ins from the new to the existing facility. To facilitate the expansion, Hess needed an as-built model of sections of the existing plant to support the design and engineering efforts. Already familiar with laser scanning and as-built data gathering from a previous expansion project for the Hess gas plant in Seminole, Texas, the project manager for the Hess Tioga project looked to Wood Group Mustang (Mustang), a global project management, engineering, procurement and construction management company headquartered in Houston, to provide as-built conditions in certain areas of the existing plant.

The plant expansion will be located adjacent to the existing plant and will facilitate ethane recovery, full fractionation and sales of natural gas liquids. The expansion includes the design and construction of a new “early flare” system for the existing plant that will allow the existing flare to be relocated to make room for the expansion. This new early flare system was installed and commissioned in August 2011. The expansion project to double processing capacity began in June 2010 and is scheduled for completion in 2013.

The initial scope of work on the Hess expansion project was for Mustang to scan various portions of the existing plant that were associated with the early flare system upgrade, and to provide data for the overall plant expansion front end engineering and design (FEED) study. No tie-ins had been identified when the laser scan/survey team performed their initial fieldwork in August 2009. “The existing plant sits on 80 acres of land,” explains David Stevens, a piping designer and laser scan coordinator within the Mustang Laser Scanning/Special Projects Group. “We had large areas to laser scan and survey, particularly since we did not know the exact locations of the final tie-ins. Then the new plant expansion added another 15 acres to the plant.”

Mustang used CADWorx, Intergraph’s plant design and modeling solution, to create intelligent 3D models from the laser scan data. Within CADWorx Plant, designers were able to lay out existing vessels, tanks and various other plant equipment using real-world coordinates.

Mustang would need both time-of-flight and phased-based technology to complete the scans on the large site.

Mustang began using laser scan technology on brownfield projects in 2005 with a Leica Geosystems HDS3000 time-of-flight scanner, ideal for the long-range scanning required for topographic surveys or as-built data gathering. In 2006, the firm purchased a Leica HDS6000 phased-base scanner to speed workflows. Phase-based scanners can gather over one million points per second as compared to time-of-flight, which typically collect up to 50,000 points per second. With the introduction of the ScanStation 2, the company upgraded its HDS3000 to get the extra speed associated with the time-of-flight system. Both time-of-flight and phase-based scanners are highly accurate.

Stevens says, “The combination of time-of-flight and phased-based scanning gave us the ease of making big jumps throughout the plant with limited need for conventional surveying. In fact, our survey efforts primarily focused on locking the laser scan data to the existing plant grid and ensuring that the data was level for design.”

Laser control was set up utilizing a Leica TS1200 total station. The scanning team registered the laser scan data to two different sets of control--the local plant grid and the plant’s state plane coordinates. The laser scan team gathered the initial scope of work area using 355 scan positions, 313 using the HDS6000 and 42 using the ScanStation 2. The data was delivered to the original engineering firm contracted to perform the initial FEED study and the design of the early flare system.

After the flare system had been designed and the associated tie-ins located, Mustang was awarded the detail design of the balance of the plant upgrades, including the development of the current as-built plant sections. This second effort required 278 laser scan positions. Mustang used the HDS6000 for 259 scan positions and the ScanStation 2 for another 19 scan positions.

Once the early flare system was installed, the laser scan team returned to the facility and did a complete as-built of the newly installed system with the HDS6000, adding another 131 scan positions. The scan team set 764 scan positions to gather all of the information needed for both design and engineering.

Stevens recalls, “With the right scheduling and the cooperation of the engineering, design and operations staff, we were able to perform the entire laser scan and survey work during the summer months of June through September.”

Then Mustang’s laser scanning scope of work grew again. “During one of our trips to the facility, the client asked us to laser scan an 80-acre section located across the highway from the gas plant, of which 35 acres is already utilized (by the electrical utility companies in the area),” Stevens says. This area was to be used for construction office trailers and parking, as a staging area for equipment, piping and construction supplies, and as a source of fill dirt for the expansion site. The scan data was used to create topographic maps as well as to locate power line clearances and other obstruction locations across the property.

Back in the office, the survey team post-processed and registered the scan data within Leica Cyclone software and created TruViews, which are placed in both the engineering and multiple discipline design folders for easy access to the whole team. “We utilize Leica Cyclone on 95 percent of our projects to post-process point cloud data,” says Stevens.

Using Cyclone Object Exchange (COE), the team exported the point cloud model to AutoCAD where designers launched CADWorx, Intergraph’s plant design and modeling solution, to create intelligent 3D models. Within CADWorx Plant, designers were able to lay out existing vessels, tanks and various other plant equipment using real-world coordinates. “The equipment was quickly and easily modeled in 3D using Leica CloudWorx for AutoCAD tools to represent the equipment shape for visual reference,” Stevens says. “(This helped) establish the overall plant site model, which would make it easier to review the new proposed project for those not familiar with the site.”

More detail could be applied in the event an existing vessel was to be tied into or used to fabricate an addition. For instance, the design engineer can determine a nozzle orientation using the point cloud and CloudWorx tools, and then model the nozzle in CADWorx. With that level of detail, the designer knows that the tie-in location to the vessel is accurate and will be called out on the subsequent isometric drawing. Along with equipment, existing buildings were modeled from the point cloud to help the designer find and mark the penetration coordinates for call-out on the isometric drawing.

Point clouds were used during model reviews to resolve potential problems before they occurred. Having immediate access to exact as-built conditions kept the project on track.

The post-processed laser scan data was originally handed over to the engineering firm selected to perform the front-end engineering and design (FEED) study of the overall plant expansion as well as the flare expansion. Once the FEED study was completed, Mustang was awarded the detail design of the project, which includes the development of isometric drawings from the 3D intelligent models.

The model for the FEED study was also created using CADWorx. The FEED study model was subsequently provided to Mustang to determine tie-in locations for the newly constructed flare relocation facilities. After relocation of the flare, Mustang went back to the plant to scan the new area and added this scan to the original point cloud model.

Tie-in locations to the new flare systems were then modeled to real-world coordinates of the point cloud for a seamless field fabrication fit. “The point cloud comparison was done by back modeling the point cloud tie-in locations using CloudWorx to determine the coordinate, and then modeling a flange and stub in pipe with CADWorx Plant,” says Stevens. “These components were then marked as ‘existing’ and placed on their own AutoCAD layer. Once the isometric was created, these components would display on the isometric as the original tie-in points.”

Conventional walk-down practices without laser scanning often involve multiple trips to the field to verify locations. Various obstacles frequently slow down the process, and numerous personnel are required. “With laser scanning, we were able to minimize occurrences in the field to just a handful, (which was) particularly important due to weather constraints in North Dakota,” says Stevens. The number of individuals entering the plant is also drastically reduced, he says, which is an important consideration given the emphasis on safety.

The project team used the point clouds in the office during model reviews to resolve potential problems before they occurred. Many questions were easily answered after overlaying a portion of the scan over the CADWorx model. For more detail, the TruView files provided photo-quality visualizations. Designers also had an immediate reference to exact as-built conditions, so there was no slowdown waiting for more detail from the field.

“Through scanning data, we were able to provide an enormous amount of data that would not have been available through a conventional survey effort,” Stevens says. “That same data provided benefits through construction with the creation of isometrics and the resolution of field issues, and will provide a solid foundation for lifecycle maintenance of the facility.”


For more information about Wood Group Mustang, visit www.mustangeng.com.

Hess Corp.’s website is www.hessenergy.com, and Leica Geosystems’ website is www.leica-geosystems.us.