FAILURE ANALYSIS OF NATURAL GAS FUEL SUPPLY TUBES IN POWER PLANT COMBUSTION SYSTEMS

Abstract

Failures in natural gas fuel supply systems are often linked to the combined effects of material degradation, operational factors, and improper installation practices. In this study, the primary cause was identified as an installation error at the tube bend, leading to condensation-induced corrosion. Rapid temperature and pressure fluctuations during shutdowns created ideal conditions for moisture accumulation, particularly at the bend, which accelerated corrosion. The failure mechanisms involved stress corrosion cracking (SCC), sulfide stress cracking (SSC), hydrogen embrittlement (HE), and localised pitting corrosion. The presence of hydrogen sulfide (H₂S) and trace amounts of chlorides in the natural gas further intensified the degradation. The methodology included visual inspection, chemical composition analysis, stereomicroscopy, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). These analyses identified the extent of condensation-induced corrosion and the failure points. Results confirmed that the tube bend geometry contributed to moisture retention, exacerbating the corrosion process. Although AISI 304 stainless steel is suitable for general applications, it performs poorly in environments with moisture and condensation, as these promote passive film breakdown. Rapid temperature and pressure drops during shutdowns enhanced moisture condensation and corrosion under the influence of corrosive gases. The discussion highlights the need to redesign the tube bend geometry, adopt corrosion-resistant materials such as AISI 316L or AISI 321 stainless steel, and implement stress-relief and inspection techniques. Addressing the installation error, material selection, and operational practices will help prevent future failures and ensure long-term performance.