The authors focused on blowholes caused by the anticorrosive paint for the groove. The parameters are the assembly method of the backing strip and the presence or absence of the mill scale on the surface where the backing strip and the base metal contact. As a result, many blowholes were generated depending on the assembly method of the backing strip without completely removing the mill scale. By the assembly method of the backing strip from the groove side, the blowholes were reduced to the same extent as the complete removal of the mill scale without removing the mill scale.
