Abstract
Aim: Development of a method to evaluate the current safety of overhead power line truss pylons, which have been in use for decades, and prediction of remaining lifespan for the continuous safe use of such structures.
Methodology: The degree of corrosive wear of pylon structural elements was analyzed from samples taken for laboratory testing from cross members of selected structures. Corroded structure rods were removed by etching and cross member section profiles were measured. Metallographic tests, identification of the chemical composition and durability measurements were performed on material samples. Securing bolts were also exposed to such tests. Pylons, with cross members weakened by corrosion, were subjected to an endurance evaluation with the aid of the author’s specialist computer programme, which is based on the finite element method. In all load bearing standard conditions, an analysis was performed on the load bearing capacity of pylon cross member rods exposed to consequences of their own weight, wind, icing and impact of overhead cable tension (where supported pylons are used).
Results: On average, corrosion pitting of angled flange surfaces achieved a depth of 0.29 mm. There was no corrosive processes found inside or at the granular boundary of steel. Analysis of the chemical composition indicates that pylons were constructed from steel, which can be exposed to welding, with increased corrosion resistance and strength grade of 10H. Durability tests revealed that the material meets the requirements specified for steel 10H. Examination of securing bolts did not reveal internal defects such as micro-cracks or corrosion and their durability is categorised within the range of 5.6-5.8. In some variations of load bearing capacity it was revealed that corroded rod cross members failed to fulfil safe endurance requirements. Resulting forecasts indicate a safe usage of pylons for the next 20 years, subject to the strengthening of some rod cross members, which were identified as unsafe.
Conclusions: The described method for determining the corrosive wear of tower elements and stress analysis of weakened structures, using the author’s specialized computer programme, enables the assessment of durability for the safe exploitation of overhead power lines. It is also possible to forecast remaining lifespan for the safe use of supporting structures. A periodic lifespan assessment should be performed, specifically for supporting corner pylons, because their failure will culminate in the failure of an entire section of the power line.
Keywords: durability, power line, pylon, corrosion, lifespan, finite element method
Type of article: case study