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Oct-2014

Laser scanning for revamps

A review of benefits, best practices and emerging opportunities in laser-enabled revamp projects

GARY FARROW
AVEVA

Viewed : 3982


Article Summary

3D laser scanning has matured enough to have even become the subject of mainstream television programmes; young engineers joining the profession are no doubt astonished by their senior colleagues’ tales of trying to as-build a facility with little more than a measuring tape and a theodolite.

A recent example of how effective laser scanning can be was provided by Burgasnefte-project, a Bulgarian EPC company specialising in petrochemicals projects. Tackling a flaring system upgrade on a 30-year-old H-Oil processing facility, the company discovered wide divergence between the as-built plant and its original design documentation. Laser scanning was the obvious choice to resolve this discrepancy. By importing the scan data into Aveva Laser Modeller, designers were able to create an accurate 3D model of the facility which was then transferred into Aveva PDMS for modification work. A task which would otherwise have taken 700–900 man-hours required only 136, an 80% saving in time and effort that also achieved a higher level of design accuracy and created a valuable asset for future engineering work.

But such stories can create an impression that laser scanning solves all the old problems at a stroke. While the technology has certainly unlocked an unprecedented level of capability, like any other tool there are right and wrong ways to use it. Part of the Aveva group, LFM Software is a provider of software solutions for exploiting the rich data generated by today’s high-resolution scanners. As a result, we encounter a wide variety of user experiences, both good and bad, with laser scanning projects. In planning a major plant revamp project and considering scanning as a first step to capture its true as-operating condition, here are some simple best-practice tips to help achieve a successful outcome.

Plan the project
You should first define exactly what the objective is. This should take a broader perspective than just the immediate need to upgrade a particular module, which may actually be part of a longer-term programme to revamp the entire facility. Today, operators are commissioning pre-emptive scans of entire facilities as  baselines for their long-term revamp programmes. But there are other reasons for doing this. At the least, a contractor may consider scanning additional areas in readiness for future work; once the survey team is on site, the marginal cost of doing so can be relatively modest.

There is also the need to decide when to perform the survey. Laser scanning is rapid and non-intrusive and can usually be performed without interfering with normal plant operation. However, it may require entry into areas that are off-limits during operation, or the structure may be subject to vibration, so it may be desirable to perform the survey during 
a planned shutdown. Paradoxically however, during a shutdown may not necessarily be the best time as there will be frenetic activity to complete the maximum number of essential work orders in the minimum time and there may be people and equipment continually moving through the survey area. Either way, the scan itself is best managed as a work order so that proper risk assessment is carried out and clashes are avoided; you do not want to find a maintenance team busy dismantling the equipment that was planned for survey the same day. In some situations, such as on an offshore platform, it may also be necessary to consider weather windows.

Choose the service provider
Laser scanning has such a broad range of application that there are a great many service providers to choose from. At LFM, we operate a Certified Service Provider (CSP) programme to enable companies to shortlist suitable providers. The choice of scanner hardware is not critical; leading software applications can handle data from all popular scanners.

Choose the software
To state the obvious, you need the right kind of software to extract the value of a 3D survey; it is of little use if all that is available is 2D software for schematic design. Here there is a need to work with an EPC or internal engineering department to ensure that they can use a suitable 3D design solution. In the oil and gas industry, almost every EPC operates Aveva PDMS, which is one of the most capable solutions for this purpose. An alternative to Burgasnefte-proekt’s approach of using Aveva Laser Modeller would be to bring the laser scan data directly into Aveva PDMS to enable design and clash detection against the as-built condition. In appropriate circumstances this can be an even more efficient workflow (see Figure 2).

Plan the scan
A skilled service provider will know how to dispose scan locations to achieve an optimum survey, but it is helpful to understand key aspects of the procedure. Little preparation is required, but there is a need to ensure that the area is free of obstructions such as ladders, barrels, pallets and so on, and that personnel can be temporarily excluded. Scanning is not hazardous to health, but moving personnel can cause vibrations in the structure on which the scanner stands, degrading accuracy. They can also inadvertently block part of the scan; it is not unknown to find a scan including half a person.

The survey technician will select enough scan locations to cover the area to be surveyed, with sufficient overlap between adjoining scans to enable them to be registered or ‘stitched together’ to form a complete survey on a common coordinate system. Scans are also positioned to minimise shadowing, where an object is hidden by a foreground object from one scan viewpoint. Remember also that a plant is a three-dimensional object; it may be necessary to perform some scans at different heights.

Registration can be facilitated by fixing optical target markers at suitable locations. However, current technology usually does not require these as the registration algorithms are now sufficiently sophisticated to automatically align point clouds without them.

Create high-quality deliverables
The success of any engineering project depends heavily on the quality of the drawings and other deliverables required for its execution. This becomes even more important for revamps, because an operating plant will be a more hazardous working environment than a new one being constructed.

The Aveva /LFM solution facilitates high-quality deliverables. New design can be created in situ against the as-operating condition represented by the BubbleView or point cloud; where necessary, point clouds representing physical pipes and steelwork can be converted into intelligent 3D models, accurately aligned with their originals (see Figure 3). Intelligent clash detection between designed objects and scanned objects ensures that an individual clash is identified as such, not as thousands of clashes with separate scan data points. Once the new design has been created in the 3D solution, automated functions can be used to create fully detailed isometrics, fabrication drawings, bills of material and so on. The result is that the revamp design will fit accurately; our experience is that contractors using Aveva/LFM technology typically achieve consistently ‘right-first-time’ installation, with less than 1% design-related rework cost.


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