Fitness for Service (FFS)- Level 3

In this project, a metal spherical pressure vessel was investigated for FFS level 3 based on API 679. For modeling and numerical simulation of the vessel under the effect of pitting corrosion, using modeling in Abaqus finite element software and according to the provided coordinates, for 11 different areas of the outer surface of the vessel, was simulated. In the simulation, the compressive load inside the tank and weight load were applied.

Critical area thickness data were received from the inspection company and Fitness for Service (FFS) assessments were performed at Level 3. The software results were consistent with the results extracted from levels 1 and 2 of the inspection. We calculated the minimum thickness in different areas of the vessel. As a result, with the performed analysis, the service status of the tank was determined and the company was informed.

Fitness for Service (FFS)

Critical point data collection. This figure shows the distribution of stress in these areas


Fitness for Service (FFS)

Sample of the main vessel examined



Safe predicted thicknesses for different vessel areas

Contact us if you are an inspection company and need level 3 FFS assessments.