Metallurgical analysis of the collapse of a telecommunication tower: Service life versus capital costs tradeoffs

- The collapsed tower is a triangular lattice structure constructed with steel pipe.
- Defective welding caused cold cracks at the weldment.
- Low carbon steel used prone to corrosion inside due to differential aeration cells.
- Stress concentrated at the thinned spots of the pipe and joint as material degraded.
- Minimizing capital costs is the cause of failure of many engineering structures.

IntroductionDespite knowledge and expertise nowadays, minimizing capital costs may continue to be the remote cause of failure of many engineering structures. Failure analysis of a telecommunication tower, which collapsed during a thunderstorm recently in a public institution, was carried out in this work.MethodThe service history was obtained, and the design, fabrication and the material selection were scrutinized along with standard specification for such structure and microstructural examinations were done.Results and discussionThe material choice, joint design and weld fabrication allowed differential aeration cells and heat affected zone stress induced corrosion at the welded endplate joints on the structural members. External painting was of no use because while the structure was intact outside, the pipe had the option of corroding from inside due to differential aeration cells. Galvanizing also is sacrificial and consumed interior coating cannot be replaced in-situ. As materials degraded, stresses concentrated. Under wind current, the structure gave up where stress concentrated most. The tower came down after nine years of service, crushing nearby roof and walls. Comparison shows costs factor weighted heavily in the material selection and design, trading off service life.ConclusionRemote cause of failure - cost minimization. This reality features in many designs in today's world of ever tighter capital budgets. It appears an index of service life trade-offs for costs is now needed in designs.