As-built survey : laser scanning and 3D modelling of chemical plant

Context

Our client produces compounds required in the manufacture of polymers, a flourishing growth industry. It was planned to build a new plant to increase production capacity. However the installation of a new unit adjoining the old called for integration of the new design with as-built plans of the latter – which had never previously been produced …

The problem

For this project in which the new unit would bear directly on the old, it was necessary to ensure that the overall structure could withstand the extra loading of the additional plant. This included a check on wind bracing of the structure ; the existing structural framework required computational analysis before any such work could be planned. The whole steel framework was very dense, and crowded with equipment and pipework. Our survey would inevitably be hampered by multiple obstructions. The only possible choice of method was 3D laser scanning.

Project setting

• Height : 25 m ; length : 8 m ; width : 8 m
• Plant continuing in operation
• Annual production capacity : 40 000 tonnes
• 120 loops
• 310 items of equipment, flanges, valves and servo valves appareils, brides et vannes/servovannes
• Weight of structure 27.5 tonnes

Objectives

• To provide a base document on which to design a new, adjoining unit
• To provide an accurate 3D model divided into thematic layers

The requirement

• Knowledge of the as-built geometry
• Documents compatible with MicroStation
• All annotation to be done by the client, treating the geometry as the starting point

Constraints

• No existing as-built plans
• Network of pipes of small diameter (some < 1 inch)
• The unit is built on six levels, with very little clearance around it

Our responses

The six levels were scanned in two days on site. Back in the office, the modelling work took two weeks using Leica Cyclone software.

Laser scans were carried out around the unit at ground level and on each of the six levels. They were then georeferenced in the coordinate system of the whole works in order to integrate them into the client’s database of drawings and plans. The combined point cloud consisted of 20 million spatially referenced points.

Modelling takes place in several stages. The overall structure is given by the 3D model of the structural steel framework in which different types of profile (angles and sections such as HE, IPN, UPN, etc., with their dimensions including steel thickness and depth) are identified semi-automatically from the point cloud. The extraction of pipework data is also controlled by the workstation operator. Once the pipework itself has been been identified, the point cloud is automatically replaced by standardised cylinders and elbow shapes. It should be noted that accuracy checking between modelled components and the point cloud is carried out continuously (standard deviation for each object).

Valves, flanges, vents and other point features are identified in the point cloud and their positions are adjusted to fit the alignments of the linear components. The user of the model can both follow the entire length of a system of pipework and take account of future modifications.

The exchange format which we have chosen for this project is Cyclone Object Exchange (COE), which offers several advantages:

• Free plug-in for MicroStation or AutoCAD, downloadable from the Leica Geosystems website
• Robust format and simple configuration
• Moderate file sizes
• Two-way transfer between AutoCAD or MicroStation and Cyclone

Deliverables

3D model file in COE format for MicroStation, exact replica of the existing plant, classified by function and conforming to standard symbolisation (pipework, structural steel)