Dimensional control surveying is a technique used to accurately measure three dimensional spaces to determine the area between points. This results in the creation of digitally mapped distances and angles. This process has been used for decades, but it wasn’t until 1988 that the process started to be used on offshore installations.
Piper Alpha Disaster
The event in 1988 that encouraged the use of dimensional control surveying on offshore fabrications, specifically on oil rigs, occurred on the Piper Alpha oil production platform in the North Sea, owned and operated by Occidental Petroleum. Production on the platform in 1976, and ended when the platform was destroyed on July 6, 1988 in an explosion, killing 167 people. The total cost of the loss was $3.4 billion, so it is clear that dimensional control surveying can save fabrication companies quite a bit of money in disaster diversion.
The disaster happened in this way: at noon, the pressure safety valve on one of the condensate pumps was removed for service, and replaced with a flat metal disk that was hand tightened. The note stating that the pump was not to be used was misplaced when the next shift of workers came in at 6 pm. The pumps on the firefighting system were also disabled, and in manual mode, which was standard operation for this platform whenever there were divers in the water, to prevent them from accidentally being sucked into the intakes used to gather ocean water for firefighting. By 9:45 pm, flammable ice began accumulating in the pipework, causing a blockage that resulted in the second pump being unable to restart. If the pump could not be put back online, the platform would lose power. The manager, having not found the paperwork indicating that the initial pump should not be turned on for any reason, turned the pump on, which resulted in a massive gas leak. This is what resulted in the massive and deadly explosion.
Dimensional control surveys reduce the need for “hot work.” Hot work is defined as any process that can cause ignition when there is flammable material present. Welding, soldering, brazing, and cutting are all examples of hot work. Hot work is what caused the disaster in 1988 that led to the process of dimensional control surveying being used in offshore fabrication, specifically on offshore oil rigs.
Dimensional control surveying is useful in industrial measurement, replacement pipework, laser scanning, fabrication surveys, alignment surveys, and topographical surveys. It can be more accurately described as the process of acquiring precise dimensional documentation referenced to an established benchmark. Surveyors can make three dimensional CAD models from these measurements.
The objective of dimensional control surveying is to help with the correct design, installation, and fit of components before construction. Benefits to be gained by using dimensional control surveying include accurate and efficient data collection of three-dimensional objects, ability to survey objects without removing them from the larger component, reduction of cost, improved safety, reduced wear and tear on equipment, accurate fittings of two or more components, assurance that design tolerances are achieved and that practices will meet the needs of the client, and reducing time in fabrication by ensure everything operates smoothly the first time.