Ametallurgical investigation was conducted to determine the cause of weld failures in condensate service piping at a hydrogen production facility.
The evaluation focused on several pipe components that had experienced multiple leaks during service. These components included reducers, elbows and tee-pipes, each exhibiting varying degrees of cracking, primarily at circumferential welds.
Visual and fracture analysis
Visual inspection revealed no external signs of cracking on the OD surfaces of most welds, except were leaks were observed. However, fracture examination uncovered multiple cracks, initiating at the root of the welds at the ID surface. The most severe cracking was found in welds connecting elbow pipes to tee-joints, where the fractures propagated through the weld face and into the adjoining pipe material.
To better understand the failure mechanisms, the cracked sections were cut to allow closer examination under magnification. Fracture surfaces were cleaned and analyzed using scanning electron microscopy, revealing features characteristic of fatigue failure, such as ratchet marks and beach lines. These indicators pointed to cyclic loading as the primary cause of crack initiation and propagation.
Material and microstructural evaluation
Chemical composition analysis confirmed that the materials used in the piping components met the specifications for their respective grades. The reducer was consistent with ASTM A234 WPBN, and the flange met ASTM A105N standards. No anomalies were found in the material composition that could have contributed to the observed failures.
Metallographic cross-sections of the fractured welds showed smooth fracture paths and additional microcracks originating from stress concentration points at the weld toes. The microstructure of the welds and base metals was consistent with duplex stainless steel, and no metallurgical defects were observed. Hardness testing across the welds, heat-affected zones and base metals revealed no significant localized hard zones that might have contributed to embrittlement or crack initiation.
Failure causes and mitigation
The investigation concluded that the weld failures were a result of cyclic fatigue due to vibration in the piping system and likely exacerbated by localized stress concentrations created by the weld profiles. The fatigue cracks initiated at the ID toe of the welds and propagated outward, eventually leading to through-wall leaks.
To mitigate future occurrences, it was recommended that the pipe support system be reviewed and monitored for vibration. Additionally, inspection protocols for similar piping systems, especially those in similar service, should be reassessed to account for the potential of fatigue-related failures.
WJE’s expertise allowed for a comprehensive evaluation of the piping failures, from initial inspection through advanced laboratory analysis. With decades of experience investigating complex failures across industries, WJE provides owners, operators and engineers with actionable insights to improve reliability and safety in critical systems.
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