Welding monitoring apparatus and welding monitoring method

A welding monitoring method for monitoring welding of a V-convergence region in which a strip-shaped metal sheet is converged in a V-shape, when the metal sheet is cylindrically formed while being conveyed in a longitudinal direction, and both side edges of the metal sheet are heated and melted in a manner of being butted each other while being converged in the V-shape, such that an electric resistance welded steel pipe is manufactured, the method comprising:

• an image capturing step of capturing images from above a region including the V-convergence region in a plan view in time series;
• and
• a detecting step of extracting a welding point based on the images captured from above in time series and detecting the presence or absence and a position of irregular arcing at the welding point or on an upstream side of the welding point,
• wherein RGB images are used as the images, and
• wherein in the detecting step,
• at least one of a red image and a blue image is extracted from the RGB images,
• inverted binarization and labeling of the red image are performed with respect to the red image, and
• a high-luminance portion in the blue image is detected with respect to the blue image.