A refinery fire occurred in March 2024 as a result of an occurrence, which prompted a thorough failure review to determine the root cause. Within four hours, the fire that started in the P-6A Pump area and moved to the E-4 heat exchanger was contained, seriously disrupting operations but leaving no casualties.
The Challenge: After a thorough investigation, TechCorr’s team of engineers determined that the fire was started by a ½” nipple to bushing connection failure on the P-6A pump discharge line. The forensic investigation emphasized how important non-destructive testing (NDT) and advanced metallurgical analysis were to identifying the fundamental problems that led to the incident.
TechCorr’s professional experts identified the main failure as the result of a fatigue crack in the ½” union nipple to bushing connection. A detailed fractography revealed a smooth, flat crack initiation point with typical ratchet signs suggestive of fatigue. The threaded part of the nipple was penetrated by these fatigue cracks, leading to an abrupt overload-related ductile failure. The crack started above the thread groove at the apex of the nipple and continued until the nipple completely failed. This finding was corroborated by high-magnification testing that revealed surface oxidation damage, which was likely exacerbated by improper maintenance and environmental exposure.
A failure tree analysis was instrumental in systematically evaluating potential causes, ranging from material integrity and maintenance practices to mechanical design and operational stresses. The investigation ruled out theories such overload impact and corrosion, emphasizing vibration- and fatigue-induced stresses as the main causes. A crucial element in the fracture initiation process was found to be the presence of martensite, a hard and brittle phase created during the nipple threading process, according to the metallographic analysis. Conditions were ideal for failure because of the brittleness of the martensite layer and high-cycle, low-load bending fatigue caused by the vibrations of the pump.
Finite Element Analysis (FEA) simulations further substantiated these findings by modeling the stress distribution within the nipple-bushing assembly. According to the FEA, the threaded grooves had the highest stress concentrations, which corresponded with the failure sites that were seen. The models showed that bending fatigue was largely caused by the threaded branch connection’s cantilevered design, which supported a load of 8.5 pounds. The proposed installation of a reinforcing bracket served to alleviate this problem by distributing the loads more evenly, so lowering the stress on the crucial threaded connection and averting further failures.
The nipple material complied with ASTM A29/A29M-20 criteria for grade 1026 carbon steel, according to a chemical composition analysis, ruling out the possibility of material flaws as a contributory issue. Hardness tests, however, indicated that the nipple’s surface hardness surpassed usual values because of cold deformation during threading, which further supported the brittleness and fatigue susceptibility of the material.
TechCorr’s thorough failure analysis highlights how sophisticated nondestructive testing (NDT) methods and metallurgical investigations should be integrated into asset management. The team produced actionable insights that not only addressed the immediate breakdown but also gave long-term solutions to improve the dependability and safety of key infrastructure by painstakingly tracking the incident up to its origins and verifying discoveries through simulations. This case study highlights the critical role that strong design principles and proactive maintenance play in averting catastrophic failures and guaranteeing operational continuity.
