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Optical and scanning electron microscopy examination and 180 degree U-bend test indicated that defect free seam welds could be obtained with this method .
 process characterization: Optical; process characterization: scanning electron microscopy; process characterization: U-bend test; concept or principle: defect; engineering feature: seam welds; material: be
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 process characterization: Optical; process characterization: scanning electron microscopy; process characterization: U-bend test; concept or principle: defect; engineering feature: seam welds; material: be