Within the downstream oil, gas and petrochemical storage industry, storage terminals are increasingly turning to 3D laser scanning for the purpose of obtaining accurate tank data.
This innovative technological advancement assists in the efficient day-to-day running of storage facilities; including engineering, maintenance and expansion. Traditionally, equipment that has been used when gathering tank shell data requires contact with the shell plates in order to measure the thickness. Temporary access platforms can therefore be required, in some cases, otherwise contact instruments can be limited to movement between natural obstructions, such as tank nozzles, stairways and stiffening rings. The resulting data collected may therefore be limited to only a few hundred data points, with some of the inaccessible areas of tank shell missed entirely. In worst case scenarios, the inaccuracy or absence of data can result in costly incidents where tank integrity is lost.
In comparison to these traditional methods, a laser scanner can collect several million data points, providing detailed information about the tank and the surrounding area without the need to be in contact with the tank. Laser scanning can be used to accurately map entire facilities as well as provide bund volume calculations and modelling of all local pipework and their supporting structures. This technique helps to minimise human error and leaves the client with a much higher resolution, detailed report that can be exported as electronic files that are compatible with the clients’ design software, such as 2D computer aided design (CAD) files.
During the calibration of a storage tank, the traditional method would involve taking reference from a strapping table to calculate tank volume. A global positioning system (GPS) workstation would also be used for the purpose of finding the centre point of the tank. Following this, the distance from the centre point to the tank wall would be manually calculated using a tape measure. Typically, in one working day, approximately 160 different points would be measured from the centre to the internal wall. In comparison, a laser scanner collects millions of reference data points within minutes, saving considerable time for plant personnel and money for the asset owner. By comparing either an existing internal scan, or the original fabrication drawings, with the external scans, the deadwood volume inside the tank can be accounted for – providing in-service tank strapping tables.
Figure 1. Buried tank showing inside deviations of shell plate internally.
The scanning process
Following the scanning of the tanks, the files are registered and imported into Advanced 3D Laser Solutions' (ALS) analysis software. Data that is not associated with the tank analysis, including stairs, pipework and manways, are then removed from the file. The analysis process is able to rationalise overlaps in scan data while it simultaneously creates a deviation map. Selected radial cuts and later segmental cuts prepare the file for reporting radial and vertical alignment. Further analysis performed on the tank skirt is then processed in order to prepare a tank settlement report. Finally, the captured data on surrounding bunds is processed to calculate the overall bund volumes.
Individual 3D laser scans can be combined to produce a ‘point cloud’ file, giving the client a clear view of shell verticality, shell plate radial deflection, tank settlement and bottom edge differential settlement. Consequently, as well as providing cut-through views of the tank from both the X and Y axis, 3D laser scanning eliminates the need for ‘dumpy level’ and ‘total station’ methods. Furthermore, a bottom edge differential settlement allows scanning from within the tank, determining localised movement of the tank floor plate. Internal structural data, including floating roof drainage lines, etc., can also be scanned and presented separately to clients.
Figure 2. Overview of typical tank terminal scan.
A leading storage terminal based in the UK has implemented 3D laser scanning. It has helped to save the operators time previously spent on draughting plant layouts and piping and instrumentation diagrams/drawings (P&IDs). It has also eliminated the time involved in the logistics of getting to and from the process plant and conducting comprehensive surveys. The technology provides quick reference whilst discussing issues that need to be addressed within the plant, generally eliminating the need to visit the location in question. Other additional benefits of the technology that have yet to be exploited at the terminal include training and presentations. However, a representative at the terminal mentioned that 3D laser scanning does not always totally negate the need to physically visit the plant.
The potential for 3D video fly-throughs – or drones – to be used as a commercial tool was further highlighted by the terminal’s commercial team, who complimented the technology’s effectiveness as a visual aid during technical presentations to clients and in training programmes for personnel.
Over the last 18 months, ALS provided 3D laser scanning services to terminals and industrial facilities across the UK, including several recent projects for terminals and refineries. There has also been a growing appreciation of the benefits that 3D laser scanning technology can bring to the oil products sector, particularly with regards to applications for pipework modelling and storage tank analysis. ALS’ ability to prepare an inexpensive and detailed ‘in-service’ health check on customers’ tanks enables a company to make an informed decision on where they should be concentrating their inspection budget on localised material thickness analysis. The rate at which tank 3D laser scanning can be achieved ensures that the study can be completed before any influencing factors are allowed to change, such as temperature or tank contents. The final reports are versatile in terms of how they can be utilised by a company, including assisting in company compliance with industry and government standards and regulations.
Figure 3. Typical shell plate displacement on Y axis.
In an ongoing project for a major UK oil refinery, ALS is providing its 3D laser scanning service in support of the client’s inspection programme for API 653, and its control of major accident hazards (COMAH) legislation compliance. The company has been commissioned to scan 120 storage tanks, assessing tank settlement, tank shell verticality at selected points (determined by Engineering Equipment and Materials Users Association [EEMUA] guidelines), shell plate radial deflection and tank settlement. Scan files will also be used to calculate bund volumes.
Figure 4. Detailed areas of shell plate bulge and indentation.
ALS is now able to assess the differential settlements between the tank and its connected piping where additional bending moments and loads, which were not considered in the original design, are imparted. This is achieved by performing several annular plate scans at a close distance. It also requires the company conducting the scan to employ the use of pipework modelling techniques on local lines. The resulting modelled pipework is offered for structural analysis, this is in order to decide where additional support or, indeed, expansion joints or bellows are necessary. This means that, cumulatively, the team is now able to scan approximately 96% of the average storage tank.
Figure 5. Plan view of detailed shell plates.
Laser scanning is now proven to be a trusted source of data collection within the oil and gas industry. With the high accuracy of data available, ALS has noticed a large shift in client expectations and a strong demand for its services as a cost effective solution for collecting analytical data from the site. With the auxiliary services such as tank calibration available, the saving on cost is further increased in comparison to traditional methods of analysing tank terminal assets.
Written by Colin Pittman, Advanced 3D Laser Solutions Ltd, UK.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/07032017/laser-spectacular/