Failure analysis methodology is applied to the principal mechanisms by which boiler tubes fail during service. sThe failure analysis procedure, or methodology for evaluation, is provided in a step by step approach. Among the case histories discussed are: fatigue, erosion, short-term overheating, and hydrogen damage.
Two successive leakages were reported in the heat exchanger composed of 8 rows of finned tubes of the convection section of the condensate stripper re-boiler. A comprehensive study (Failure Analysis) has been conducted to reveal the form of failure. The failure was recognized as erosion and cavitation damage.
A major fire in a Reactor Effluent Air Cooler (REAC) of the Hydrocracker Unit (HCU). Visual inspection was made on the failed portion. Metallurgical investigation, macrostructural and microstructural analysis, Scanning Electron Microscopy, and Energy Dispersive x-ray Spectroscopy was conducted on the failed air cooler.
Recently, there have been several cracking failures of type HL carbon steel sucker rods with evidence of fatigue striation. In order to find out the reason for the fracture failure, the fracture morphology, material properties, loading and corrosion product of the failed type HL 35CrMoA sucker rod were analyzed, combined with the corrosion environment. The results show that the material properties of the failed 35CrMoA sucker rod meet the GB/T 26075-2010 standard requirements. Also the result of loading analysis shows that the loading is far from the fatigue limit stress. The type HL sucker rod’s yield strength is almost 1049 MPa and hardness is 35.2 HRC. In addition, the low in-situ pH and high H2S-CO2 partial pressure places the sucker rods in the Region 3 of sulfide stress corrosion cracking, which means the quenched and tempered sucker rod’s yield strength should not exceed 863 MPa and hardness should not exceed 30 HRC, according to the ISO 15156-2:2015 standard. It is concluded that the high hardness level of the type HL sucker rod led to sulfide stress corrosion cracking in the high H2S-CO2 partial pressure and low in-situ pH condition.
Although Microbiologically Influenced Corrosion (MIC) is a critical damage mechanism that had been researched for decades in different environments, yet diagnosing a specific industrial failure to be attributed to MIC can still be challenging. The challenge of accurately identifying an MIC failure is partially due to the similarity of the failure morphology with other damage mechanisms, e.g., pitting corrosion due to chloride. Furthermore, the variously proposed initiation and propagation mechanisms for different types of bacteria may illustrate to the failure analyst that the MIC mechanisms are not yet well established. The confusion of MIC failure identification could also be aggravated by the fact that the presence of bacteria in a system does not necessarily mean that MIC is the culprit. Therefore, this paper will shed some light on the overlapping areas between MIC and pitting corrosion, especially the morphology of the attack. Moreover, several steps will be highlighted and discussed on how to correctly identify if MIC is the culprit in a specific failure.