Using Dimensional Control to Mitigate Risk for Pre-Assembled Units/Piperacks Installation

Dimensional control surveys are used to facilitate the correct design, fabrication, and installation to ensure that pre-assembled units fit together prior to setting at their final locations. Validating the dimensional geometry can facilitate effective fabrication, construction, and installations. Minimizing site rework for resolving fit-up issues ensures successful project executions by avoiding additional project costs and schedule delay. Digital scanned survey activities using electronic laser and infrared total stations provide accurate, high quality dimensional data. For small and medium-sized pre-assembled unit projects, structural engineers often find noticeable deviations as compared to project’s specified tolerances, resulting in additional time spent on examining whether fit-up issues at those locations will truly require design modifications. This paper addresses some of the common concerns by structural engineers in order for them to more adequately interpret the collected dimensional control survey data. The paper also provides pre-assembled unit design suggestions, including connection designs that facilitate fit-up. These design considerations, when working with the dimensional control surveyors, can enhance interface compatibility at pre-installation and reduce the chances of potential fitting problems. A better understanding of the required survey checks will help structural engineers determine which out-of-tolerance data must be reviewed, and thus finding solutions in a timely manner, to mitigate costly delays and rework during the installation phase.