How Are Strapping Tables Used For Storage Tanks?
At Storage Tank Surveys, we are experts in providing a wide range of storage tank solutions. This includes the creation of strapping tables as an effective method of measuring the volume of liquid within a storage tank.
This article will define what strapping tables are, the history of the method and how exactly they are used within storage tank surveying. It will also explain why they are used, the importance of them and how advanced LIDAR technology is applied to storage tanks.
What Are Strapping Tables?
Strapping tables are extremely important tools used for measuring the volumes within storage tanks and are frequently used within a variety of industries. The table itself provides a way of converting a depth measurement (known as dipping, when a tape measure is lowered into the liquid inside a tank). The depth of liquid measured is cross referenced in the strapping table to find the volume of liquid in the tank for that depth.
The process is also known as tank calibration and the tables can also be called tank calibration tables.
This article will investigate the storage tank surveying method to create strapping tables and the history of the surveying technique. It will also discuss the importance of them within the storage tank industry, and how laser scanning technology is now a new and much better tank calibration method for storage tank volumes.
The History of Strapping Tables
Tank strapping is a particular procedure used to measure the substances within the storage tanks. The measurements that are collected as data are then analysed using strapping tables to determine the volume of the tank, otherwise known as tank calibration or tank gauging.
The name ‘strapping tables’ is derived from the original method that was used to measure the volume of liquid at important level intervals, using a steel tape wrapped around the storage tank (like a strap), at different levels up the outside of the tank wall, in order to calibrate the tank.
Though this traditional tank strapping method provided the necessary data, the methods were very time-consuming with access needed to different heights up the tank wall, with the measuring tape being prone to errors, and the fact that there is loss in accuracy due to the interpolation needed between measurement locations.
In more recent times measurements have been taken using a ‘total station’ method. This is a tripod mounted instrument, which uses a single laser to take single measurements around the tank wall. The standards require a minimum number of measurements at different heights and different spacings depending on the size of the tank. This may be between 60 and 100 points.
Now an even better method has arrived using laser scanners which can record up to a million points per second. See below for more information on this new method, to measure the tanks and create strapping tables.
When Is Tank Strapping Used?
Tank strapping is used wherever a large amount of liquid is stored within a tank, with storage tanks found within the below industries / locations:
- Oil Refineries
- Petrochemical Industry
- Distribution Terminals
- Pipeline Terminals
- Fuel Depots
- Air Fuelling Storage
- Chemical Storage
Why Is Tank Strapping Used for Storage Tanks?
Tank strapping is an important method of verifying the accuracy of the volume of contents of a storage tank. The tank strapping tables are used to compute and record the volumes of liquids inside a tank in order to obtain reliable measurements. It is vital to have high accuracy, because of the high values of most liquids in the oil and gas industry. Small percentage errors can make a big difference in determining the value of a liquid in the tank.
There has been a great advancement of storage tank measurement technology, the strapping table procedure is being performed now through laser scanning technology methods. Also known as LiDAR (which stands for Light Detection and Ranging). The data capturing procedure is significantly faster than the steel tape method, removing any deficiencies by being able to capture millions of points of data, within the same time that it takes to capture just ten points with a total station.
Instead of measuring a limited number of pre-defined points, the whole surface of the storage tank can be surveyed and analysed. The method can also be applied to any shape of tank. The industry standards define a tank strapping method that is only of use on cylindrical tanks.
There are many different purposes to tank strapping, with volumetric data, computed from strapping tables, used for:
- Oil movement and operations
- Inventory Control
- Custody Transfer
- Loss control and mass balance
- Volume Reconciliation
- Overfill Prevention
- Leak Detection
Oil Movement and Operations
It is vital that we know what is going on inside the tank, which is why monitoring any oil shifts is extremely important. By using reliable and the latest up-to-date data, we can ensure that the levels of oil are safely met, by being alerted if there are any high levels of oil within the tank, which could be potentially dangerous
Inventory Control
Storage tanks store a wide range of valuable resources, which is why they must be supervised closely and carefully. Assessments are frequently carried out to provide inventory reports that can also be used for financial purposes. Net volumes and mass can also be calculated with the data capturing system, providing in-depth information for the analysed storage tanks.
Custody Transfer
The data extracted from tank strapping is also beneficial for when large volumes of liquids are bought and sold, with the data making it quicker and easier for the invoicing and taxing of stored and transferred liquids.
Loss Control and Mass Balance
The refinery loss creates huge financial losses, which is why these must be minimised as much as possible. To reduce the amount of refinery loss, a high degree of accuracy is crucial when conducting inventory measurements, heightening the importance of accurate tank strapping.
Volume Reconciliation
Managing a tank’s transactions and comparing reconciliation tank transfers to physical inventory is essential for storage tanks, with any errors flagged, noted and fixed.
How Is LiDAR Technology Applied To Storage Tanks For Other Uses?
In addition to the creation of high accuracy strapping tables, once the data has been collected it can be used for many other applications.
For example, laser scanning allows us to monitor the entire tank shell for deformation which is great advance on previous methods which used a limited number of discrete points, providing surveyors and our clients with more detailed sets of data.
3D laser scanning can also be used for tank calibration, as well as the creation of accurate filling tables. This is through placing the 3D scanner inside a tank which is out-of-service, capturing the tank’s interior.
Overfill Prevention
This is self-explanatory, with the tanks overfilling resulting in detrimental consequences that can ultimately have catastrophic effects. Overfilling a tank can result in a spill or in fires, with the damages costing many millions of pounds.
These overfilling spills occur when the tank operators are not aware of what is happening in the tank, often derived from undetected faults that have arisen within the tank. The laser scanning process contributes to prevention work by recording the height of overflow alarms, plus the actual physical height of any likely overflow point. This data can be included in modern fluid level measurement equipment setups.
Additional Analyses
Our experienced surveying team at Storage Tank Surveys have worked in a variety of locations carrying out important strapping table work, using laser scanning methods to also provide the following services:
- Difference Maps which compare millions of points between scans to highlight areas where change has occurred, and to monitor changes over time.
- Radial Displacement plots for each degree around the storage tank and at different heights to show ‘out of roundness’ or ovality.
- Verticality Analysis.
- Tilt and Subsidence Analysis
- Peaking and Banding Analysis
Construction monitoring We can laser scan and image a site during construction works and provide records of the surveyed areas for monitoring progress and provide ‘as-built surveys of structures after completion of the work.
IFR installation (internal floating roof) – By determining the exact roundness of a tank, this ensures that the roof fabrication or seal selections match the existing structure. Alternatively, the information can be used to identify areas to be corrected for roundness and to verify repairs before fabrication.
Expert UK & International Storage Tank Surveys
With survey projects carried out in over 60 countries, we are experts in providing specialised storage tank surveying services worldwide. We work together with our clients to provide bespoke services that are tailored to the needs of their project, utilising the latest technology to provide the most accurate results.
Contact us on 01392 362161 or at info@merrettsurvey.com and speak to one of our expert storage tank surveyors for a free, no-obligation quote. We look forward to working with you soon.
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