LETS Global - Structural Integrity and Life Extension of FPSOs and Offshore Installations

LETS Global is an engineering and consulting company focused on extending the life of welded structures and components. We have developed our own technologies, processes and equipment based on ultrasonic technology.

LETS Global achieves results by applying a wide structural integrity concept which embraces FEA (finite element analysis) modelling, measuring of hot-spot stresses, as well as treatment by ultrasonic peening on high-stress areas.

Assessment of the structural integrity of welded structures

The integrity of welded structures and components is almost always governed by the performance of their welded joints. Welded joints are susceptible to cracks when subjected to fatigue loads. When cracks are discovered during non-destructive testing, factors such as applied and internal stresses and the material properties are relevant when considering the likelihood of failure of the weld or component.

LETS Global assists you in determining the acceptance level for detected flaws. Using fractures mechanics principles, we can determine allowable stress levels and whether weld repair / enhancement is needed. The aim is to rationally assess whether a given fabrication is adequate for its intended purpose, taking into account all the relevant factors.

Stress analysis techniques

Fatigue life extension and structural integrity assessments require information about the stress levels, both static and dynamic, in the vicinity of the critical regions. LETS Global has experience in a variety of techniques used to generate the necessary data, depending on the nature of the work and the required precision. These techniques range from good engineering judgments and simplified analytical solutions, to sophisticated numerical (mainly finite element analysis) and experimental (strain gauges, ultrasonic method and SPATE) stress measurement techniques.

A detailed finite element analysis (FEA) model of the area subjected to high hot-spot stresses is necessary to carry out the assessment. The detailed model is based on a global FEA model from where the concerned detail constraints are obtained. FEA models must also be correlated with in-situ stress measurements in order to be sure that these models can be trusted. In-situ stress measurements can be carried out through a number of techniques as strain gages, ultrasonic technique, etc.

Ultrasonic peening treatment of highly stressed areas of welded structures

LETS Global specializes in the application of ultrasonic peening treatment on customers’ installations even in areas of difficult access, and has designed and manufactured custom-built manual and robotic ultrasonic equipment for this purpose.

Ultrasonic peening treatment is a fatigue life improvement technique which consists of the application of ultrasonic and mechanical impulses to the highly stressed locations in the weld. As a result of these ultrasonic and mechanical impulses the welded metal is modified at the atomic and metallurgical level. The stress concentrations as well as the residual stress, both caused by the welding process, are relieved, and the general fatigue strength of the structure is increased.

Ultrasonic peening treatment is a fatigue life improvement technique which combines geometric modification and redistribution of residual stresses at the weld toe region during the same working operation. This post-weld treatment has proven to be cost effective and reliable when compared to burr grinding or hammer peening.

UP treatment, weld quality and QA and QC documentation reports

The weld quality represented in the tested welds and treated specimens in the laboratory often do not reflect the real weld quality in the structure. These facts make it compulsory to do a re-assessment of the life extension studies after LETS Global has been on the installation and treated the concerned areas. Only then can we guarantee the accuracy of our preliminary assessment.

Inspection of structures and components subjected to fatigue loads

LETS Global experts carry out inspections of structures and components subjected to fatigue loads and therefore susceptible to fatigue damage. Through inspections we at LETS Global can present recommendations about necessary maintenance work to achieve the desired service life of any component or structure.