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Apr-2017

Laser scanning with dimensional control

Integrating traditional methodology with new scanning technologies to achieve higher order accuracies for critical interfaces and tie-in points

PETER FIELD
Warner Surveys
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Article Summary
For oil and gas companies operating in a volatile climate, careful planning and tight control over construction and maintenance programmes have never been so vital. The sheer immensity of most projects and the scale of investment involved places huge pressures on all parties from stakeholders and engineers to engineering procurement, construction & design (EPCD) contractors, with projects often scheduled for completion within extremely short timescales, working around the clock.

Errors or misinterpretation during design and fabrication can easily occur, leading to the need to rework not just minor parts but substantial plant items. A key contributor to project over-runs, reworking can account for up to 15% of total budget costs on new build developments and a significant proportion of the cost for scheduled maintenance and engineering works. These are costs that could be totally removed by anticipating issues ahead of time through closer collaboration and employing survey techniques up front.

A huge leap forward for surveying, laser scanning enabled the remote capture and dissemination of large amounts of data, where previously each data point had to be measured individually and, frequently, physically. The technology is now used extensively for the accurate mapping of large scale developments and complex sites, including heavily congested or inaccessible areas with complicated assets in the hostile environments such as those to be found in 
refineries and industrial plants (see Figure 1).

Collaborative working
Being able to call on a comprehensive database offers benefits for collaborative working, where many different influencers require input into the design process. The interoperability of modern 3D models created using a variety of software packages, central to the building information modelling (BIM) workflow approach just now emerging in construction, has been employed extensively by the oil and gas sector over many years. Providing a visual representation of plant structural and operational aspects, the digitisation of data in this way creates a central information resource that saves time and greatly reduces the risk of errors and need for reworking to ensure projects are delivered on time, on programme and on budget. Having a shared source of accurate data allows project engineers and contractors to maintain control over all aspects of the engineering and fabrication phases of oil construction projects, delivering improved returns through an integrated approach.

Early intervention pays dividends
It is often the case that survey services are first deployed on large projects at the point where fabricated elements built to original designs are brought to site to check. Reworking may be required where misalignment occurs, causing delays that could be avoided by surveying earlier in the process to approve the designs ahead of fabrication, allowing build issues to be detected and rectified before on-site construction commences.

Design errors or omissions can lead to inadequate project specification, with estimates of cost accuracy being underestimated in some cases. The early involvement of surveyors at ‘cold eyes review’ stage can help with assessing design concepts for constructability, providing access to site-experienced expert knowledge of the issues that can occur and potential workarounds to guide engineers and designers with less experience to this level of project complexity. Early screening and availability to survey data plus a fresh pair of eyes can offer new solutions to deliver cost savings and prevent project overruns, helping to secure an earlier return on investment.

Shutdowns and turnarounds – minimising your downtime
Shutdowns are an inevitable feature of refining and can represent a significant proportion of a plant’s yearly budget. Typically, these will be scheduled every 3-5 years, taking plants or part-sections offstream to undertake inspections required to comply with regulations and to carry out necessary repairs and maintenance. A percentage of these events will involve major plant replacement, with planned downtime periods offering the opportunity for scheduling in revamps and regeneration.

Whilst shutdowns are usually planned when production is at its lowest, and such maintenance is important in maintaining productive capacity, extensive planning and control are required, often several years beforehand as well as during execution. Turnaround time is dependent on the extent of the project and any problems that occur. Any derailment of timetables – for example where reworking is required, with much of the work difficult to scope in advance – could result in the loss of millions of dollars for every day of lost production and incur additional direct costs for labour and heavy equipment usage.

Key to the planning process is the availability of accurate legacy data for buildings and structures. The availability of a comprehensive database generated through laser scanning and the conversion of point cloud data into computer aided design (CAD) models provides a tool for asset management and a valuable guide for extensions and alterations, particularly in clash prevention, where pipes and new elements of plant must be integrated within already congested sites or structures.

However, existing legacy data could be up to 15 years old in some cases, increasing the chances of misalignment or poor fit where plant elements are fabricated working to original designs. For this reason, it is advisable to consider commissioning additional laser scanning surveys to help plan the shutdown properly. Lack of detail could otherwise leave asset owners and contractors having to deal with considerable variations in scope during the execution of projects. Completion of design work in the point cloud or model environment in advance provides the necessary assurance that the process will be clash free.

Unplanned shutdowns
Unplanned shutdowns can have a significant effect on facilities and their operators. In addition to the production losses incurred during shutdown, unplanned events place huge pressure on resources when operations are restored, with capacity needing to be restored quickly. Outages of this kind can also affect the wider economy, with the lack of availability of fuel supplies creating a knock-on effect on industry and deliveries.

Managing shutdowns and turnarounds successfully involves planning ahead to extend the period between shutdowns and eliminate unexpected downtime through preventative maintenance. Although survey companies including Warners will generally offer a rapid response service to cover emergencies, regular surveys to assess plant condition can avoid unexpected maintenance costs and business disruption, both of which may seriously impact on the bottom line.

Laser scanning or dimensional control?
The choice of survey type can sometimes be confusing for project teams, with laser scan surveys often requested when the required tolerances in fact necessitate dimensional control techniques with more traditional instrumentation.

So how do you decide what you need? These definitions may help:

Laser scanning is a rapid and reliable method for surveying often inaccessible, complex or congested areas.

Survey control is the essential, traditional survey activity providing the auditable accuracy to so many 
survey operations including laser scanning.
Dimensional control is the name given to high accuracy survey techniques used to achieve a good fit up between new, basic pieces of plant.
Critical interface surveying raises the bar for dimensional control and relates to high accuracy techniques and instrumentation used to achieve first time fit-ups between new and old complex (often dimensionally corrupted) pieces of plant or structures.

SWHU (single weld hook up): although basically with the same objective as critical interface surveying, this has become the term generally applied to very large projects with multiple modules requiring a first time fit with no additional spool connections (see Figure 2).
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