Stress Corrosion Cracking of an Electrohydraulic Oil Pipe

Cracking of an oil inlet pipe in an electrohydraulic governing system was detected and analyzed to determine its failure mechanism. Microscopic analysis methods, such as the scanning electron microscopy and energy-dispersive X-ray spectrum, were applied to obtain the effective information. Visual and micro-examination showed that the pipe suffered a brittle cracking at the elbow part. Corrosion pits and branched cracks had formed in the outer surface of the pipe. The element of chlorine was detected both in the corrosion pits and the corrosion products inside the cracks. In addition, the cracks were found initiating from the bottom of the corrosion pit. Transgranular cracking feature was identified for the cracks. All the collected evidences suggested that the EH oil pipe fractured due to the combination of a chloride pitting corrosion and a stress corrosion cracking failure.