Is a crack the end of life?

Many structures and components are used longer than their design life, or operate in conditions different from what was originally expected. As consequence, defects like cracks can be present and potentially grow.

During the life of a structure, cracks can be observed by regular inspection, with sometime intervals of several months of years. The question arising for any operation and maintenance manager is to know if the structure or component is still safe or needs to be repaired immediately.

While for rotating equipment the practice is to detect defects as early as possible to plan the maintenance accordingly, for quasi-static structures submitted to fluctuating loads like bridges, cranes, beams, pressure vessels etc… the inspection interval is generally long and the decision of taking the structure out of operation for repair can have tremendous costs.

Predict in-use behaviour via finite element modelling

To answer to these questions, OCAS is using a specific program for the estimation of the safety of a component based on BS 7910. This software is able to give a fast assessment if the size of the defect and the loads are known, for static and dynamic (fatigue) cases. For complex geometries, it is possible to perform fracture mechanics estimates by the finite element method.

With this approach, it is possible to pre-define the acceptable size of defects  in a structure from known loads. Operation and maintenance managers then have the possibility to decide if immediate repair is needed or can be delayed until planned maintenance.