Failure Analysis on Heat Exchanger Tube Bundle Exposed to Naphthenic Acid Corrosion

Naphthenic acid is a sort of organic acid which present in crude oil and cause severe corrosion in certain circumstances. This type of acid will lead to the corrosion phenomenon known as naphthenic acid corrosion (NAC). Damage mechanism by NAC attack can be analysed using Scanning Electron Microscope (SEM), Electron-dispersive X-ray (EDX) and X-ray Diffraction (XRD). These characterization methods aim to observe the morphology, element content, and crystal structure of the NAC. The objective of this research is to apply failure analysis (FA) on heat exchanger (HE) tube bundle made form stainless steel 410 (SS410). SEM reveals the inter-granular attack initiate to crack propagation. A particular result of interest is that nickel catalytically decomposes naphthenic acids at high temperatures (e.g. 270°C) via a catalytic mechanism. For XRD testing, the corrosion product have been known and the main causes that lead to the corrosion has been detected which there is a formation of chromium carbide continuously along the pipe tube. However there is also formation of iron sulphide and chromium sulphide obtained in the XRD analysis where both are the reaction element that can retard the formation of NAC. Material selection is the most crucial task to resists from corrosion attack especially in high temperature applications. The mechanism of resistance of these elements provides insight into the failure mode of 304 and 400 series stainless steel in NA service.