Assessment of a Damaged Piping System Utilizing Laser Surface Scanning and Finite Element Analysis

The application of laser surface scanning technology in conjunction with finite element analysis to evaluate the fitness for service of a damaged section of piping is presented in this paper. The difference between the results obtained using a simplified dimensional model produced using hand measurements and the laser scan is also discussed. A section of NPS 18 (DN 450) diameter piping that carries vapors generated by a coke drum in an oil refinery delayed coking unit had been damaged in service from contact with a nearby structural steel member. The damaged area was deformed nearly 1.2 in. (30 mm) deep over an area measuring approximately 10 in. × 12 in. (250 mm × 300 mm) and included a pronounced crease along the line of contact with the steel. The piping was also slightly out of round outside of the area of gross distortion. Laser scanning was employed to obtain an accurate dimensional representation of the surface geometry and to develop a finite element analysis model. The decision to allow the piping system to continue to operate until the next scheduled outage was then based upon the operating stresses, maximum strain in the deformed area and fatigue life determined for the damaged section.